Secondary battery

Abstract

A secondary battery includes: a positive electrode including a lithium-nickel composite oxide; a negative electrode including a lithium-titanium composite oxide; and an electrolyte including a dinitrile compound and a carboxylic acid ester. A ratio of a capacity per unit area of the positive electrode to a capacity per unit area of the negative electrode is 100% or more and 120% or less, and a ratio of a number of moles of the dinitrile compound to a number of moles of the carboxylic acid ester is 1% or more and 4% or less.

Description

Technical Field

[0001] This technology relates to a secondary battery. Background Technology

[0002] With the widespread use of mobile phones and other electronic devices, secondary batteries are being developed as small, lightweight power sources capable of achieving 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 improve low-temperature output characteristics, the operating voltage of the negative electrode is 1.2V or higher relative to the lithium potential, and the electrolyte contains carboxylic acid esters such as methyl acetate (see, for example, Patent Documents 1 and 2). To suppress the expansion of the secondary battery, the negative electrode contains spinel-type lithium titanate, and the electrolyte contains ethyl acetate (see, for example, Patent Document 3). To improve electrochemical characteristics over a wider temperature range, the negative electrode contains lithium titanate as the negative electrode active material, and the electrolyte contains an isocyanate compound (see, for example, Patent Document 4). To reduce gas generation during high-temperature use, the negative electrode contains titanium oxide, and the electrolyte contains a dinitrile compound (see, for example, Patent Document 5).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2010-205563

[0007] Patent Document 2: International Publication No. 2009 / 110490

[0008] Patent Document 3: Japanese Patent Application Publication No. 2013-229341

[0009] Patent Document 4: International Publication No. 2015 / 030190

[0010] Patent Document 5: International Publication No. 2015 / 033620 Summary of the Invention

[0011] Various studies have been conducted on improving the performance of secondary batteries, but not only is the energy density insufficient, but the expansion and charging characteristics are also inadequate, thus leaving room for improvement.

[0012] This technology was proposed in view of the above-mentioned problems, and its purpose is to provide a secondary battery that can achieve excellent expansion characteristics and excellent charging characteristics while ensuring energy density.

[0013] One embodiment of the present technology provides a secondary battery comprising: a positive electrode containing a lithium-nickel composite oxide; a negative electrode containing a lithium-titanium composite oxide; and an electrolyte containing a dinitrile compound and a carboxylic acid ester, wherein the ratio of the capacity of the positive electrode per unit area to the capacity of the negative electrode per unit area is 100% or more and 120% or less, and the ratio of the molar number of the dinitrile compound to the molar number of the carboxylic acid ester is 1% or more and 4% or less.

[0014] The term "lithium-nickel composite oxide" refers to oxides containing both lithium and nickel as constituent elements, while "lithium-titanium composite oxide" refers to oxides containing both lithium and titanium as constituent elements. It should be noted that detailed information about lithium-nickel composite oxides and lithium-titanium composite oxides will be provided later.

[0015] According to one embodiment of the present technology, the secondary battery comprises a positive electrode containing a lithium-nickel composite oxide, a negative electrode containing a lithium-titanium composite oxide, and an electrolyte containing a dinitrile compound and a carboxylic acid ester. Furthermore, the ratios related to the respective capacities of the positive and negative electrodes are within the aforementioned ranges, as are the ratios related to the respective molar numbers of the dinitrile compound and the carboxylic acid ester. Therefore, excellent expansion characteristics and excellent charging characteristics can be obtained while ensuring energy density.

[0016] It should be noted that the effects of this technology are not necessarily limited to those described herein, but can be any of the series of effects related to this technology described later. Attached Figure Description

[0017] Figure 1 This is a perspective view showing the structure of a secondary battery in one embodiment of the present technology.

[0018] Figure 2 It means Figure 1 The diagram shows a cross-sectional view of the structure of the battery element.

[0019] Figure 3 This is a three-dimensional view showing the structure of the secondary battery in Modified Example 1.

[0020] Figure 4 It means Figure 3 The diagram shows a cross-sectional view of the structure of the battery element.

[0021] Figure 5 This is a block diagram illustrating the structure of a secondary battery application example. Detailed Implementation

[0022] Hereinafter, one embodiment of the present technology will be described in detail with reference to the accompanying drawings. It should be noted that the description is presented in the following order.

[0023] 1. Secondary battery

[0024] 1-1. Structure

[0025] 1-2. Actions

[0026] 1-3. Manufacturing Method

[0027] 1-4. Functions and Effects

[0028] 2. Variations

[0029] 3. Uses of secondary batteries

[0030] <1. Secondary Battery>

[0031] First, a secondary battery according to one embodiment of this technology will be described.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] <1-1. Structure>

[0036] Figure 1 The three-dimensional structure of a secondary battery is shown. Figure 2 It shows Figure 1 The cross-sectional structure of the battery element 10 is shown. Additionally, Figure 1 The battery element 10 and the outer membrane 20 are shown in a state where they are separated from each other. Figure 2 Only a portion of battery element 10 is shown.

[0037] like Figure 1 As shown, the secondary battery includes a battery element 10, an outer film 20, a positive electrode lead 31, and a negative electrode lead 32. The secondary battery described here is a laminated film type secondary battery that uses a flexible (or supple) outer component (outer film 20) to house the battery element 10.

[0038] [Exterior film]

[0039] like Figure 1 As shown, the outer film 20 is a thin film component that can be folded in the direction of arrow R (single-dot dashed line). As described above, since the outer film 20 houses the battery element 10, it also houses the positive electrode 11, the negative electrode 12, and the electrolyte, which will be described later. A recessed portion 20U (so-called deep drawing portion) for accommodating the battery element 10 is provided on the outer film 20.

[0040] Specifically, the outer film 20 is a laminated film consisting of three layers: a welding layer, a metal layer, and a surface protective layer, layered sequentially from the inside. When the outer film 20 is folded, the outer peripheries of the opposing welding layers are bonded together (fused). Thus, the outer film 20 has a pouch-like structure capable of sealing the battery element 10 inside. The welding layer contains a polymer compound such as polypropylene. The metal layer contains a metallic material such as aluminum. The surface protective layer contains a polymer compound such as nylon.

[0041] Furthermore, the structure (number of layers) of the outer membrane 20 is not particularly limited; it can be one layer, two layers, or four or more layers. That is, the outer membrane 20 is not limited to a laminated membrane; it can also be a single-layer membrane.

[0042] A sealing membrane 21 is inserted between the outer membrane 20 and the positive electrode lead 31, and a sealing membrane 22 is inserted between the outer membrane 20 and the negative electrode lead 32. Sealing membranes 21 and 22 are components used to prevent external air from entering the interior of the outer membrane 20, and contain one or more polymeric compounds such as polyolefins, which have a sealing property relative to each of the positive electrode lead 31 and the negative electrode lead 32. The polyolefin is polyethylene, polypropylene, modified polyethylene, or modified polypropylene, etc. Alternatively, one or both of the sealing membranes 21 and 22 may be omitted.

[0043] [Battery Components]

[0044] like Figure 1 as well as Figure 2 As shown, the battery element 10 is housed inside the outer membrane 20 and includes a positive electrode 11, a negative electrode 12, a separator 13, and an electrolyte (not shown). The electrolyte is immersed in the positive electrode 11, the negative electrode 12, and the separator 13, respectively.

[0045] Here, since the battery element 10 is a structure (stacked electrode body) in which the positive electrode 11 and the negative electrode 12 are stacked with a separator 13 in between, the positive electrode 11 and the negative electrode 12 are placed opposite each other with a separator 13 in between.

[0046] Specifically, since the positive electrode 11 and the negative electrode 12 are alternately stacked with a separator 13 in between, the battery element 10 includes multiple positive electrodes 11, multiple negative electrodes 12, and multiple separators 13. The number of stacked positive electrodes 11, negative electrodes 12, and separators 13 is not particularly limited, and can therefore be set arbitrarily.

[0047] In this battery element 10, the capacity ratio of the positive electrode 11 to the negative electrode 12 is optimized. Specifically, the capacity per unit area of ​​the positive electrode 11 (mAh / cm²) is optimized. 2 The capacity per unit area of ​​negative electrode 12 (mAh / cm²) 2 The capacity ratio (R1) is 100% to 120%. This is because a high energy density can be obtained. This capacity ratio R1 is calculated by R1(%) = (capacity per unit area of ​​positive electrode 11 / capacity per unit area of ​​negative electrode 12) × 100.

[0048] To determine the capacity ratio R1, the capacity C1 of the positive electrode 11 and the capacity C2 of the negative electrode 12 are calculated using the steps described below, and then the capacity ratio R1 is calculated.

[0049] First, the positive electrode 11 and the negative electrode 12 are recovered by disassembling the secondary battery.

[0050] Next, a test secondary battery (coin type) was fabricated using positive electrode 11 as the test electrode and a lithium metal plate as the counter electrode. As described later, the positive electrode 11 contains lithium nickel composite oxide as the positive electrode active material.

[0051] Next, the capacity (mAh) of the positive electrode 11 was measured by charging and discharging the secondary battery used in the experiment. During charging, a constant current of 0.1C was applied until the voltage reached 4.3V, followed by constant voltage charging at that 4.3V until the total charging time reached 15 hours. During discharging, a constant current of 0.1C was applied until the voltage reached 2.5V. 0.1C is the current value required to fully discharge the battery's theoretical capacity within 10 hours.

[0052] Next, based on the area (cm²) of the positive electrode 11 2 ), calculate the capacity C1 (mAh / cm²) of the positive electrode per unit area 11. 2 The capacity C1 of the positive electrode 11 per unit area is calculated by C1 = capacity of positive electrode 11 / area of ​​positive electrode 11.

[0053] Next, a test secondary battery (coin type) was fabricated using negative electrode 12 as the test electrode and a lithium metal plate as the counter electrode. As described later, negative electrode 12 contains lithium titanium composite oxide as the negative electrode active material.

[0054] Next, the capacity (mAh) of the negative electrode 12 was measured by charging and discharging the secondary battery used in the experiment. During charging, a constant current of 0.1C was used to charge until the voltage reached 2.7V, and then a constant voltage of 2.7V was used to charge until the total charging time reached 15 hours. During discharging, a constant current of 0.1C was used to discharge until the battery voltage reached 1.0V.

[0055] Next, based on the area (cm²) of the negative electrode 12... 2 ), calculate the capacity C2 (mAh / cm²) of the negative electrode per unit area. 2 The capacity C2 of the negative electrode 12 per unit area is calculated by C2 = capacity of negative electrode 12 / area of ​​negative electrode 12.

[0056] Finally, based on the capacities C1 and C2, the capacity ratio R1 is calculated. As mentioned above, this capacity ratio R1 is calculated by R1 = (capacity C1 / capacity C2) × 100.

[0057] (positive electrode)

[0058] like Figure 2 As shown, the positive electrode 11 includes a positive current collector 11A having one opposite side and two positive active material layers 11B disposed on both sides of the positive current collector 11A. Alternatively, the positive active material layer 11B may be disposed on only one side of the positive current collector 11A.

[0059] The positive current collector 11A comprises one or more conductive materials, such as metals, aluminum, nickel, and stainless steel. The positive active material layer 11B comprises one or more positive active materials capable of lithium insertion and extraction, and may also include a positive binder and a positive conductive agent.

[0060] Here, as Figure 1 As shown, the positive current collector 11A includes a protrusion 11AT where no positive active material layer 11B is formed. Therefore, when the battery element 10 includes multiple positive electrodes 11 (multiple positive current collectors 11A), the battery element 10 includes multiple protrusions 11AT. The multiple protrusions 11AT are joined together to form a lead-like junction 11Z.

[0061] The positive electrode active material contains lithium-containing compounds, and more specifically, any one or more of lithium-nickel composite oxides. As mentioned above, "lithium-nickel composite oxide" is a general term for oxides containing lithium and nickel as constituent elements, and has a layered rock salt-type crystal structure. This is because a high energy density can be obtained.

[0062] The type (structure) of lithium-nickel composite oxides is any oxide containing lithium and nickel as constituent elements; there are no particular restrictions. Specifically, lithium-nickel composite oxides contain lithium, nickel, and other elements as constituent elements. The other elements are any one or more elements belonging to groups 2 to 15 of the long-period periodic table (excluding nickel).

[0063] More specifically, the lithium nickel composite oxide comprises any one or more of the compounds represented by the following formula (4).

[0064] Li x Ni (1-y) M4 y O2…(4)

[0065] (M4 is at least one element belonging to Groups 2 to 15 of the long-period periodic table (except for Ni). x and y satisfy 0.8 ≤ x ≤ 1.2 and 0 ≤ y < 1.0. In addition, the composition of lithium varies depending on the charge and discharge state, where x is the value for the fully discharged state.)

[0066] As shown in equation (4), the nickel content in the lithium-nickel composite oxide is determined by the content of other elements (M4). Furthermore, considering the range of possible values ​​for y, the lithium-nickel composite oxide can contain other elements (M4) as constituent elements, or it can not contain other elements (M4) as constituent elements. In this case, as long as the lithium-nickel composite oxide contains nickel as a constituent element, the nickel content in the lithium-nickel composite oxide is not particularly limited and can therefore be arbitrarily set.

[0067] In particular, the nickel content in the preferred lithium-nickel composite oxide is sufficiently high. More specifically, the molar ratio (molar proportion) R3, which is the ratio of the number of moles of nickel to the sum of the number of moles of nickel and the number of moles of other elements (M4), is preferably 80% or more. This molar proportion R3 is calculated by R3(%) = [number of moles of nickel / (number of moles of nickel + number of moles of other elements)] × 100.

[0068] That is, the lithium-nickel composite oxide preferably contains any one or more of the compounds represented by the following formula (5). This is because a higher energy density can be obtained.

[0069] Li x Ni (1-y) M5 y O2…(5)

[0070] (M5 is at least one element belonging to Groups 2 to 15 of the long-period periodic table (excluding Ni). x and y satisfy 0.8 ≤ x ≤ 1.2 and 0 ≤ y ≤ 0.2. In addition, the composition of lithium varies depending on the charge and discharge state, where x is the value for the fully discharged state.)

[0071] The steps to determine the molar ratio R3 are as follows.

[0072] First, accurately weigh X g of the sample (lithium-nickel composite oxide) for analysis, then place the sample into a beaker (capacity = 50 ml (50 cm)). 3 The precise weighing amount (Xg) of the sample can be set arbitrarily. Next, a stirring head is added to the beaker, and a full-volume pipette is used to add precision analytical hydrochloric acid (concentration = 0.01mol / ml) to the beaker. 3 Then use a stirrer to stir the contents of the beaker.

[0073] Next, extract all contents using a disposable syringe, and then filter the extract using a 0.2μm syringe filter. Then, collect 2.5ml (2.5cm) of the filtered material using a full-volume pipette. 3 Then use hydrochloric acid (concentration = 0.6 mol / L, dm³ = 0.6 mol / L). 3 Dilute the filtrate. Next, collect 1.0 ml (1.0 cm) of the filtrate using a full-volume pipette. 3 ), and put the filtered material into a volumetric flask (capacity = 25ml (= 25cm)). 3 Then use hydrochloric acid (concentration = 5.0 mol / L, dm³ = 5.0 mol / L). 3 Dilute the filtered material.

[0074] Next, elemental analysis of the filter material was performed using inductively coupled plasma (ICP) emission spectroscopy to measure the content (moles) of each constituent element, such as nickel.

[0075] Finally, the molar ratio R3 is calculated based on the number of moles of nickel and the number of moles of other elements (M4 or M5). As mentioned above, this molar ratio R3 is calculated by R3(%) = [number of moles of nickel / (number of moles of nickel + number of moles of other elements)] × 100.

[0076] Specific examples of lithium-nickel composite oxides are LiNiO2 and LiNi. 0.70 Co 0.30 O2, LiNi 0.80 Co 0.15 Al 0.05 O2, LiNi 0.82 Co 0.14 Al 0.04 O2, LiNi 0.50 Co 0.20 Mn0.30 O2, LiNi 0.80 Co 0.10 Al 0.05 Mn 0.05 O2, LiNi 0.80 Co 0.20 O2, LiNi 0.82 Co 0.18 O2, LiNi 0.85 Co 0.15 O2 and LiNi 0.90 Co 0.10 O2, etc. Among them, LiNi with a preferred molar ratio of R3 of 80% or higher is preferred. 0.80 Co 0.15 Al 0.05 O2, LiNi 0.80 Co 0.10 Al 0.05 Mn 0.05 O2, LiNi 0.80 Co 0.20 O2, LiNi 0.82 Co 0.18 O2, LiNi 0.85 Co 0.15 O2 and LiNi 0.90 Co 0.10 O2, etc.

[0077] It should be noted that the positive electrode active material only needs to contain the lithium-nickel composite oxide mentioned above, and may also contain any one or more of other positive electrode active materials (other lithium-containing compounds).

[0078] The types of other positive electrode active materials are not particularly limited; specifically, they include lithium transition metal compounds. "Lithium transition metal compounds" is a general term for compounds containing lithium and one or more transition metal elements as constituent elements, and may also contain one or more other elements. The types of other elements are not particularly limited, as long as they are elements other than transition metal elements; specifically, they are any one or more elements belonging to groups 2 to 15 of the long-period periodic table. Furthermore, the lithium transition metal compounds described here do not include the aforementioned lithium-nickel composite oxides.

[0079] The types of lithium transition metal compounds are not particularly limited, but specifically include oxides, phosphoric acid compounds, silicate compounds, and borate compounds. Specific examples of oxides are LiCoO2 and LiNi. 0.33 Co 0.33 Mn 0.33 O2, Li 1.2 Mn 0.52 Co 0.175 Ni0.1 O2, Li 1.15 (Mn 0.65 Ni 0.22 Co 0.13 O2 and LiMn2O4, etc. Specific examples of phosphoric acid compounds are LiFePO4, LiMnPO4, and LiFe 0.5 Mn 0.5 PO4 and LiFe 0.3 Mn 0.7 PO4, etc.

[0080] The positive electrode binder includes any one or more of synthetic rubbers and polymeric compounds. Synthetic rubbers include styrene-butadiene rubber, fluorinated rubbers, and ethylene propylene diene monomer (EPDM) rubber. Polymeric compounds include polyvinylidene fluoride (PVDF), polyimide, and carboxymethyl cellulose.

[0081] The positive electrode conductive agent includes any one or more conductive materials such as carbon materials, including graphite, carbon black, acetylene black, and Ketjen black. Alternatively, the conductive material can also be a metal or a polymer compound.

[0082] There is no particular limitation on the method for forming the positive electrode active material layer 11B. Specifically, it can be any one or more of the following methods: coating method, etc.

[0083] (negative electrode)

[0084] like Figure 2 As shown, the negative electrode 12 is positioned opposite the positive electrode 11 across a separator 13. The negative electrode 12 includes a negative current collector 12A with opposite sides and two negative active material layers 12B disposed on both sides of the negative current collector 12A. Alternatively, the negative active material layer 12B may be disposed on only one side of the negative current collector 12A.

[0085] The negative electrode current collector 12A comprises any one or more conductive materials, such as copper, aluminum, nickel, and stainless steel. The negative electrode active material layer 12B comprises any one or more negative electrode active materials capable of lithium insertion / extraction, and may also include a negative electrode binder and a negative electrode conductive agent. The details of the negative electrode binder and negative electrode conductive agent are the same as those of the positive electrode binder and positive electrode conductive agent.

[0086] Here, as Figure 1As shown, the negative electrode current collector 12A includes a protrusion 12AT where no negative electrode active material layer 12B is formed, and this protrusion 12AT is positioned not to overlap with the protrusion 11AT. Therefore, when the battery element 10 includes a plurality of negative electrodes 12 (a plurality of negative electrode current collectors 12A), the battery element 10 includes a plurality of protrusions 12AT. The plurality of protrusions 12AT are joined together to form a lead-like junction 12Z.

[0087] The negative electrode active material contains any one or more of lithium-titanium composite oxides. As mentioned above, "lithium-titanium composite oxide" is a general term for oxides containing lithium and titanium as constituent elements, and has a spinel-type crystal structure. This is because it can suppress the decomposition reaction of the electrolyte in the negative electrode 12, and therefore can also suppress the generation of gas by the decomposition reaction of the electrolyte.

[0088] The type (structure) of lithium-titanium composite oxides is any oxide containing lithium and titanium as constituent elements; there are no particular restrictions. Specifically, lithium-titanium composite oxides contain lithium, titanium, and other elements as constituent elements, which are any one or more elements belonging to groups 2 to 15 of the long-period periodic table (excluding titanium). Furthermore, oxides containing lithium, titanium, and nickel as constituent elements are not lithium-nickel composite oxides, but rather lithium-titanium composite oxides.

[0089] More specifically, the lithium-titanium composite oxide contains any one or more of the compounds represented by formulas (1), (2), and (3) below. M1, as shown in formula (1), is a metallic element capable of becoming a divalent ion. M2, as shown in formula (2), is a metallic element capable of becoming a trivalent ion. M3, as shown in formula (3), is a metallic element capable of becoming a tetravalent ion. This is because the decomposition reaction of the electrolyte in the negative electrode 12 can be sufficiently suppressed, and therefore the generation of gas from the decomposition reaction of the electrolyte can also be sufficiently suppressed.

[0090] Li[Li x M1 (1-3x) / 2 Ti (3+x) / 2 ]O4…(1)

[0091] (M1 is at least one of Mg, Ca, Cu, Zn, and Sr. x satisfies 0 ≤ x ≤ 1 / 3.)

[0092] Li[Li y M2 1-3y Ti 1+2y ]O4…(2)

[0093] (M2 is at least one of Al, Sc, Cr, Mn, Fe, Ga, and Y. y satisfies 0 ≤ y ≤ 1 / 3.)

[0094] Li[Li 1 / 3 M3 z Ti (5 / 3)-z ]O4…(3)

[0095] (M3 is at least one of V, Zr, and Nb. z satisfies 0 ≤ z ≤ 2 / 3.)

[0096] From the range of possible values ​​for x in equation (1), it can be seen that the lithium-titanium composite oxide shown in equation (1) may contain other elements (M1) as constituent elements, or it may not contain other elements (M1) as constituent elements. From the range of possible values ​​for y in equation (2), it can be seen that the lithium-titanium composite oxide shown in equation (2) may contain other elements (M2) as constituent elements, or it may not contain other elements (M2) as constituent elements. From the range of possible values ​​for z in equation (3), it can be seen that the lithium-titanium composite oxide shown in equation (3) may contain other elements (M3) as constituent elements, or it may not contain other elements (M3) as constituent elements.

[0097] A specific example of the lithium-titanium composite oxide shown in equation (1) is Li 3.75 Ti 4.875 Mg 0.375 O 12 Etc. Specific examples of lithium-titanium composite oxides shown in equation (2) are LiCrTiO4, etc. Specific examples of lithium-titanium composite oxides shown in equation (3) are Li4Ti5O, etc. 12 and Li4Ti 4.95 Nb 0.05 O 12 wait.

[0098] It should be noted that the negative electrode active material only needs to contain the lithium titanium composite oxide mentioned above, and may also contain any one or more other negative electrode active materials.

[0099] Other anode active materials are not particularly limited in type, but specifically include carbon materials and metallic materials. Carbon materials include easily graphitized carbon, difficult-to-graphitize carbon, and graphite, such as natural graphite and artificial graphite. Metallic materials are materials containing one or more metallic elements and half-metallic elements capable of forming alloys with lithium. The types of metallic and half-metallic elements are not particularly limited, but specifically include silicon and tin. These metallic materials can be monomers, alloys, compounds, mixtures of two or more of them, or materials containing two or more of their phases. Furthermore, the metallic materials described here do not include the aforementioned lithium-titanium composite oxide.

[0100] Specific examples of metallic materials include SiB4, SiB6, Mg2Si, Ni2Si, TiSi2, MoSi2, CoSi2, NiSi2, CaSi2, CrSi2, Cu5Si, FeSi2, MnSi2, NbSi2, TaSi2, VSi2, WSi2, ZnSi2, SiC, Si3N4, Si2N2O, and SiO. v (0<v≤2), LiSiO, SnO w (0<w≤2), SnSiO3, LiSnO, and Mg2Sn, etc. Additionally, SiO v The value of v can also satisfy 0.2 < v < 1.4.

[0101] There is no particular limitation on the method of forming the negative electrode active material layer 12B. Specifically, it can be any one or more of the following methods: coating, gas phase, liquid phase, spraying, and firing (sintering).

[0102] It should be noted that when the positive electrode 11 and the negative electrode 12 are fabricated separately, the capacity ratio R1 can be adjusted by changing the relationship between the amounts of the positive electrode active material and the negative electrode active material. More specifically, in the process of fabricating the positive electrode 11 and the negative electrode 12 separately, the capacity ratio R1 can be adjusted by fixing the thickness of the positive electrode active material layer 11B and changing the thickness of the negative electrode active material layer 12B.

[0103] The "thickness of the negative electrode active material layer 12B" mentioned here refers to the total thickness of the negative electrode active material layer 12B. Therefore, since the negative electrode active material layer 12B is disposed on both sides of the negative electrode current collector 12A, when the negative electrode 12 includes two negative electrode active material layers 12B, the thickness of the negative electrode active material layer 12B is the sum of the thickness of one negative electrode active material layer 12B and the thickness of the other negative electrode active material layer 12B.

[0104] In this case, as described above, the capacity ratio R1 is 100% to 120%. Therefore, as will be explained later, even if the thickness of the negative electrode active material layer 12B is thin, the decomposition reaction of the electrolyte can be suppressed, thus suppressing the generation of gas due to the decomposition reaction of the electrolyte. More specifically, the thickness of the negative electrode active material layer 12B can be 130 μm or less.

[0105] (Diaphragm)

[0106] like Figure 2 As shown, the separator 13 is an insulating porous membrane located between the positive electrode 11 and the negative electrode 12, preventing contact between the positive electrode 11 and the negative electrode 12 while allowing lithium ions to pass through. The separator 13 contains any one or more of the following polymer compounds: polytetrafluoroethylene, polypropylene, and polyethylene.

[0107] (electrolyte)

[0108] The electrolyte contains a solvent and an electrolyte salt.

[0109] The solvent includes any one or more non-aqueous solvents (organic solvents), and the electrolyte containing such non-aqueous solvents is called a non-aqueous electrolyte. Specifically, non-aqueous solvents include dinitrile compounds and carboxylic acid esters.

[0110] Dianitrile compounds are chain-like compounds with nitrile groups (-CN) at both ends, thus containing two nitrile groups. These dinitrile compounds enhance the antioxidant properties of carboxylic acid esters when used in combination with them.

[0111] There is no particular limitation on the types of dinitrile compounds. Specifically, they are compounds formed by two nitrile groups bonded together by a straight-chain alkylene group. Specific examples of dinitrile compounds include malononitrile (1 carbon atom), succinic anionitrile (2 carbon atom), glutaronitrile (3 carbon atom), adiponitrile (4 carbon atom), heptacyanide (5 carbon atom), and octanoic anionitrile (6 carbon atom). The carbon atom number in parentheses above refers to the number of carbon atoms in the alkylene group.

[0112] The alkylene group preferably has 2 to 4 carbon atoms, therefore the dinitrile compound is preferably any one or more of succinic anionibacterium, glutaronitrile, and adiponitrile. This is because the dinitrile compound improves the solubility and compatibility, and also significantly enhances the antioxidant properties of the carboxylic acid ester.

[0113] Carboxylic acid esters are straight-chain esters of saturated fatty acids. Specific examples of carboxylic acid esters include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, and ethyl trimethylacetate.

[0114] The carboxylic acid ester is preferably one or both of ethyl propionate and propyl propionate. This is because the decomposition reaction of the carboxylic acid ester can be sufficiently suppressed during charging and discharging, thus also effectively suppressing the generation of gas from the decomposition reaction.

[0115] Furthermore, the content of the dinitrile compound in the solvent is set to be within a specified range relative to the content of the carboxylic ester in the solvent. Specifically, the molar ratio (molar proportion) R2 of the dinitrile compound to the carboxylic ester is 1% to 4%. This is to optimize the content of the dinitrile compound relative to the content of the carboxylic ester. Thus, even when the dinitrile compound and the carboxylic ester are used together, the decomposition reaction of the carboxylic ester can be suppressed, and therefore the generation of gas by the decomposition reaction of the carboxylic ester can also be suppressed. This molar proportion R2 is calculated by R2(%) = (molar number of dinitrile compound / molar number of carboxylic ester) × 100.

[0116] The content of carboxylic acid ester in the solvent is not particularly limited, but is preferably 50% to 90% by weight. Because the decomposition reaction of the carboxylic acid ester can be sufficiently suppressed during charging and discharging, the generation of gas by the decomposition reaction of the carboxylic acid ester can also be sufficiently suppressed.

[0117] It should be noted that the solvent only needs to contain the aforementioned dinitrile compounds and carboxylic acid esters, and may also contain any one or more other non-aqueous solvents.

[0118] Other non-aqueous solvents include esters and ethers, and more specifically, carbonate compounds and lactone compounds. This is because they can enhance the dissociation of electrolyte salts and result in high ion mobility.

[0119] Specifically, carbonate compounds include cyclic carbonates and chain carbonates. Specific examples of cyclic carbonates are ethylene carbonate and propylene carbonate, while specific examples of chain carbonates are dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0120] Lactone compounds are lactones, etc. Specific examples of lactones are γ-butyrolactone and γ-pentanolactone, etc. It should be noted that ethers, in addition to the lactone compounds mentioned above, can also be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, and 1,4-dioxane, etc.

[0121] In addition, non-aqueous solvents can also be unsaturated cyclic carbonates, halocarbonates, sulfonates, phosphate esters, acid anhydrides, mononitrile compounds, and isocyanate compounds, etc. This is because they can improve the chemical stability of the electrolyte.

[0122] Specific examples of unsaturated cyclic carbonates include vinylene carbonate (1,3-dioxacyclopenten-2-one), vinylene carbonate (4-vinyl-1,3-dioxacyclopenten-2-one), and methyleneene carbonate (4-methylene-1,3-dioxacyclopenten-2-one). Specific examples of halogenated carbonates include fluoroethylene carbonate (4-fluoro-1,3-dioxacyclopenten-2-one) and difluoroethylene carbonate (4,5-difluoro-1,3-dioxacyclopenten-2-one). Sulfonates include 1,3-propanesulfonolactone and 1,3-propenesulfonolactone. Specific examples of phosphate esters include trimethyl phosphate and triethyl phosphate.

[0123] Acid anhydrides include cyclic dicarboxylic acid anhydrides, cyclic disulfonic acid anhydrides, and cyclic carboxylic acid sulfonic anhydrides. Specific examples of cyclic dicarboxylic acid anhydrides include succinic anhydride, glutaric anhydride, and maleic anhydride. Specific examples of cyclic disulfonic acid anhydrides include 1,2-ethanedisulfonic anhydride and 1,3-propanedisulfonic anhydride. Specific examples of cyclic carboxylic acid sulfonic anhydrides include sulfobenzoic anhydride, sulfopropionic anhydride, and sulfobutyric anhydride.

[0124] Mononitrile compounds are compounds having a single nitrile group; specific examples of mononitrile compounds include acetonitrile. Specific examples of isocyanate compounds include hexamethylene diisocyanate.

[0125] The electrolyte salt is any one or more of light metal salts such as lithium salts. The lithium salt includes lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(fluorosulfonyl)imide (LiN(FSO2)2), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2), lithium tri(trifluoromethanesulfonyl)methylide (LiC(CF3SO2)3), lithium difluorooxalateborate (LiBF2(C2O4)), and lithium bis(oxalate)borate (LiB(C2O4)2), etc.

[0126] There is no particular limitation on the content of the electrolyte salt, but specifically, it is 0.3 mol / kg to 3.0 mol / kg relative to the solvent. This is because high ionic conductivity can be obtained.

[0127] The steps for determining the composition of the electrolyte (including the above molar ratio R2 and the content of carboxylic acid esters in the solvent) are as follows.

[0128] When examining the composition of the components (solvents) in an electrolyte, one or more analytical methods, such as gas chromatography and high-speed liquid gas chromatography, are used to analyze the electrolyte. This allows determination of the types of solvents present in the electrolyte.

[0129] In checking the content of components (solvents) in the electrolyte, firstly, the battery element 10 is recovered by disassembling the secondary battery, and then the electrolyte is recovered from the battery element 10. This electrolyte is used as a reference solution in subsequent processes. Next, the battery element 10, from which no electrolyte was recovered, is immersed in an organic solvent (dimethyl carbonate) (immersion time = 24 hours). Thus, the electrolyte immersed in the battery element 10 is extracted into the organic solvent, thereby obtaining an electrolyte extract. Finally, the electrolyte extract is analyzed using gas chromatography. In this case, the electrolyte recovered in the previous process is used as a reference solution. Furthermore, the peak areas of each component (each solvent contained in the electrolyte extract) are normalized based on the peak area of ​​propylene carbonate, thereby determining the residual amount of each component. Thus, the content of solvents contained in the electrolyte can be determined.

[0130] When examining the content of carboxylic acid esters in the solvent, the content of the carboxylic acid ester is calculated based on the content of the solvent contained in the electrolyte as described above. The content of the carboxylic acid ester is calculated using the formula: Carboxylic acid ester content (wt%) = (Weight of carboxylic acid ester / Weight of solvent) × 100. The "weight of solvent" is the sum of the weights of all solvents contained in the electrolyte.

[0131] When checking the molar ratio R3, the number of moles of the dinitrile compound and the number of moles of the carboxylic acid ester are determined based on the content of solvent (dianitronic compound and carboxylic acid ester) contained in the electrolyte. Then, the molar ratio R3 is calculated based on the number of moles of the dinitrile compound and the number of moles of the carboxylic acid ester.

[0132] [Positive and negative leads]

[0133] The positive lead 31 is the positive terminal connected to the positive electrode 11 (positive current collector 11A), and contains one or more conductive materials such as aluminum. Since the positive lead 31 is connected to the junction 11Z, it is electrically connected to multiple positive electrodes 11 through the junction 11Z. The shape of the positive lead 31 is not particularly limited, but specifically, it can be one or more of the following: a thin plate shape, a mesh shape, etc.

[0134] The negative lead 32 is the negative terminal connected to the negative electrode 12 (negative current collector 12A), and contains one or more conductive materials such as copper, nickel, and stainless steel. Since the negative lead 32 is connected to the junction 12Z, it is electrically connected to multiple negative electrodes 12 through the junction 12Z. The details regarding the shape of the negative lead 32 are the same as those regarding the shape of the positive lead 31 described above.

[0135] Here, as Figure 1 As shown, the positive electrode lead 31 and the negative electrode lead 32 are led out from the inside of the outer membrane 20 in the same direction. Alternatively, the positive electrode lead 31 and the negative electrode lead 32 can be led out in different directions.

[0136] <1-2. Actions>

[0137] During the charging of the secondary battery, lithium is deintercalated from the positive electrode 11 and intercalated into the negative electrode 12 via the electrolyte. Conversely, during the discharging of the secondary battery, lithium is deintercalated from the negative electrode 12 and intercalated into the positive electrode 11 via the electrolyte. During these charging and discharging processes, lithium is intercalated and deintercalated in an ionic state.

[0138] <1-3. Manufacturing Method>

[0139] In the case of manufacturing a secondary battery, a positive electrode 11 and a negative electrode 12 are fabricated according to the steps described below, and an electrolyte is prepared. The secondary battery is then manufactured using the positive electrode 11, negative electrode 12, and electrolyte. The following instructions will be consulted at any time. Figure 1 as well as Figure 2 .

[0140] [The production of the positive electrode]

[0141] First, a positive electrode active material containing lithium-nickel composite oxide is mixed with a positive electrode binder and a positive electrode conductive agent to prepare a positive electrode mixture. Next, a paste-like positive electrode mixture slurry is prepared by adding the positive electrode mixture to a solvent such as an organic solvent. Finally, the positive electrode mixture slurry is coated onto both sides of the positive electrode current collector 11A (excluding the protrusion 11AT) to form a positive electrode active material layer 11B. Thereafter, the positive electrode active material layer 11B can be compressed and molded using a roller press or the like. In this case, the positive electrode active material layer 11B can be heated, or the compression molding can be repeated multiple times. Thus, the positive electrode active material layer 11B is formed on both sides of the positive electrode current collector 11A, thereby producing the positive electrode 11.

[0142] [Making the negative electrode]

[0143] A negative electrode active material layer 12B is formed on both sides of the negative electrode current collector 12A through steps substantially the same as those used in the fabrication of the positive electrode 11. Specifically, a negative electrode active material containing a lithium-titanium composite oxide is mixed with a negative electrode binder and a negative electrode conductive agent to prepare a negative electrode mixture. This mixture is then added to a solvent such as an organic solvent to prepare a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry is coated onto both sides of the negative electrode current collector 12A (except for the protrusion 12AT) to form the negative electrode active material layer 12B. The negative electrode active material layer 12B can then be compressed and molded. Thus, the negative electrode active material layer 12B is formed on both sides of the negative electrode current collector 12A, thereby fabricating the negative electrode 12.

[0144] It should be noted that when fabricating the negative electrode 12, the thickness of the negative electrode active material layer 12B is adjusted so that the capacity ratio R1 is 100% to 120%.

[0145] [Preparation of Electrolyte]

[0146] An electrolyte is prepared by adding an electrolyte salt or the like to a solvent (containing a carboxylic acid ester), followed by adding another solvent (a dinitrile compound) to that solvent. The electrolyte salt or the like is thus dispersed or dissolved in the solvent.

[0147] It should be noted that, in the preparation of the electrolyte, the amount of dinitrile compound and carboxylic acid ester added should be adjusted so that the molar ratio R2 is 1% to 4%.

[0148] [Assembly of a secondary battery]

[0149] First, a positive electrode 11 containing protrusions 11AT and a negative electrode 12 containing protrusions 12AT are alternately stacked with a separator 13 to form a laminate. This laminate has the same structure as the battery element 10, except that the positive electrode 11, negative electrode 12 and separator 13 are not impregnated with electrolyte.

[0150] Next, multiple protrusions 11AT are joined together by welding or the like to form a joint 11Z, and multiple protrusions 12AT are joined together by welding or the like to form a joint 12Z. Next, the positive lead 31 is connected to the joint 11Z by welding or the like, and the negative lead 32 is connected to the joint 12Z by welding or the like.

[0151] Next, after housing the laminate inside the recess 20U, the outer film 20 (weld layer / metal layer / surface protective layer) is folded so that the outer films 20 are facing each other. Next, the outer periphery portions of two sides of the opposing outer films 20 (weld layers) are bonded together using a heat-sealing method or the like, thereby housing the laminate inside the bag-shaped outer film 20.

[0152] Finally, after injecting the electrolyte into the pouch-shaped outer membrane 20, the outer periphery of the remaining side of the outer membrane 20 (welded layer) is bonded together using a heat-sealing method or the like. In this case, the sealing film 21 is inserted between the outer membrane 20 and the positive electrode lead 31, and the sealing film 22 is inserted between the outer membrane 20 and the negative electrode lead 32. Thus, the electrolyte is impregnated in the laminate, thereby forming a battery element 10 as a laminated electrode body. Therefore, the battery element 10 is sealed inside the pouch-shaped outer membrane 20 and assembled into a secondary battery.

[0153] [Stabilization Process]

[0154] The assembled secondary battery is charged and discharged. Various conditions, such as ambient temperature, number of charge / discharge cycles, and charge / discharge conditions, can be arbitrarily set. Therefore, a coating is formed on the surface of the negative electrode 12, thereby stabilizing the electrochemical state of the secondary battery. Thus, a secondary battery using the outer membrane 20 is completed, i.e., a laminated membrane type secondary battery.

[0155] <1-4. Functions and Effects>

[0156] According to this secondary battery, the positive electrode 11 contains a lithium-nickel composite oxide, the negative electrode 12 contains a lithium-titanium composite oxide, and the electrolyte contains a dinitrile compound and a carboxylic acid ester. Furthermore, the capacity ratio R1 for the positive electrode 11 and the negative electrode 12 is 100%–120%, and the molar ratio R2 for the dinitrile compound and the carboxylic acid ester is 1%–4%.

[0157] In this case, firstly, since the electrolyte contains both a dinitrile compound and a carboxylic acid ester, the dinitrile compound improves the redox resistance of the carboxylic acid ester. Therefore, compared to the case where the electrolyte contains only the carboxylic acid ester and not the dinitrile compound, the potential window on the oxidation side is significantly expanded. Thus, even when using a lithium-nickel composite oxide with a high oxidizing capacity as the positive electrode active material, the decomposition reaction of the electrolyte (especially the carboxylic acid ester) during charging and discharging can be suppressed, thereby preventing the generation of gas in the positive electrode 11 due to the decomposition reaction of the electrolyte.

[0158] Secondly, since the decomposition reaction of the electrolyte can be suppressed in the positive electrode 11, even if lithium titanium composite oxide is used as the negative electrode active material, the formation of highly reducing byproducts caused by the decomposition reaction of the electrolyte in the positive electrode 11 can be suppressed. Therefore, since the reduction reaction of the byproducts in the negative electrode 12 can be suppressed, the generation of gas from the reduction reaction of these byproducts can be suppressed.

[0159] Third, since the molar ratio R2 is within the above range, the dinitrile compound at the interface between the negative electrode 12 (lithium-titanium composite oxide) and the electrolyte does not hinder the movement of lithium ions (Li / Li + The extent of the charge-movement reaction is selectively coordinated with respect to titanium in the lithium-titanium composite oxide. Thus, the dinitrile compound acts as a protective film to suppress the reduction reaction of the electrolyte at potentials below 1.5V relative to the lithium potential, thereby suppressing gas generation from the reduction reaction of the electrolyte even when the capacity ratio R1 is above 100%.

[0160] Fourth, because the dinitrile compound acts as a protective film, the thickness of the negative electrode 12 can be very thin. As a result, even when charging with a large current, the concentration distribution of the electrolyte is homogenized inside the negative electrode 12, making it easier for lithium ions to be inserted and extracted within the negative electrode 12.

[0161] Based on the above, even though the positive electrode 11 contains lithium-nickel composite oxide and the negative electrode 12 contains lithium-titanium composite oxide, a high energy density can be obtained because the capacity ratio R1 is within the aforementioned range, and the lithium-ion input performance can be improved while suppressing the expansion of the secondary battery because the molar ratio R2 is within the aforementioned range. Therefore, excellent expansion characteristics and excellent charging characteristics can be obtained while ensuring energy density.

[0162] In particular, if lithium-nickel composite oxides contain lithium, nickel, and other elements as constituent elements, and the molar ratio R3 is above 80%, higher energy density can be obtained, thus achieving better performance.

[0163] In addition, if the lithium titanium composite oxide contains any one or more of the compounds shown in formulas (1) to (3), the expansion of the secondary battery can be sufficiently suppressed, thus achieving a higher effect.

[0164] Furthermore, if the dinitrile compound includes succinate or the like, and the carboxylic acid ester includes ethyl propionate or the like, the expansion of the secondary battery can be sufficiently suppressed, thus achieving even better performance. In this case, in particular, even if ethyl propionate, which has a higher ionic conductivity than propyl propionate but is more prone to gas generation due to decomposition reactions, is used, gas generation can be suppressed by succinate or the like, thus achieving both improved lithium-ion input performance and suppression of secondary battery expansion.

[0165] Furthermore, if the electrolyte solvent contains carboxylic acid esters, and the content of carboxylic acid esters in the solvent is 50% to 90% by weight, then the decomposition reaction of the carboxylic acid esters can be sufficiently suppressed during charging and discharging, thus also sufficiently suppressing the generation of gas from the decomposition reaction of the carboxylic acid esters. That is, even when using a large amount of carboxylic acid esters (content in the solvent = 50% to 90% by weight), the generation of gas from the decomposition reaction of the carboxylic acid esters can be suppressed by the dinitrile compound, thus the secondary battery is less prone to expansion. Therefore, the expansion of the secondary battery can be sufficiently suppressed, resulting in higher performance.

[0166] Furthermore, in the battery element 10, if the positive electrode 11 and the negative electrode 12 are alternately stacked with a separator 13 in between, the electrolyte is supplied to the stack from four directions during the manufacturing process of the battery element 10. Therefore, even if the viscosity of the electrolyte increases due to the combined use of dinitrile compounds and carboxylic esters, the electrolyte is easily impregnated within the stack. Thus, the battery element 10 exhibits improved electrolyte retention, further enhancing its charging characteristics and resulting in superior performance. In this case, the electrolyte injection time into the stack is shortened during the secondary battery manufacturing process, further improving manufacturing efficiency.

[0167] Furthermore, if the secondary battery has a flexible outer membrane 20, and the battery elements 10 (positive electrode 11, negative electrode 12, and electrolyte) are housed inside the outer membrane 20, the secondary battery will not easily expand effectively even if an outer membrane 20, which is prone to significant expansion, is used, thus achieving higher performance. Additionally, by using the outer membrane 20, energy density can be further increased, and the cost of the secondary battery can also be reduced.

[0168] 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.

[0169] <2. Variations>

[0170] 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.

[0171] [Variation Example 1]

[0172] exist Figure 1 as well as Figure 2 In this process, a battery element 10 is used as a stacked electrode body. However, as with... Figure 1 corresponding Figure 3 and with Figure 2 corresponding Figure 4 As shown, a battery element 40, which is a wound electrode body, can be used instead of a battery element 10, which is a stacked electrode body.

[0173] Figure 3 as well as Figure 4 The laminated film type secondary battery shown, in addition to having battery element 40 (positive electrode 41, negative electrode 42, and separator 43), positive electrode lead 51, and negative electrode lead 52 replacing battery element 10 (positive electrode 11, negative electrode 12, and separator 13), positive electrode lead 31, and negative electrode lead 32, has the same... Figure 1 as well as Figure 2 The structure shown is the same as that of the laminated film secondary battery.

[0174] Except as described below, the structures of the positive electrode 41, negative electrode 42, separator 43, positive electrode lead 51, and negative electrode lead 52 are the same as those of the positive electrode 11, negative electrode 12, separator 13, positive electrode lead 31, and negative electrode lead 32.

[0175] In battery element 40, positive electrode 41 and negative electrode 42 are wound together with a separator 43 in between. More specifically, positive electrode 41 and negative electrode 42 are stacked with the separator 43 in between, and the positive electrode 41, negative electrode 42 and separator 43 are wound around a winding axis (an imaginary axis extending along the Y-axis). Therefore, positive electrode 41 and negative electrode 42 are positioned opposite each other with the separator 43 in between.

[0176] The positive electrode 41 includes a positive current collector 41A and a positive active material layer 41B, and the negative electrode 42 includes a negative current collector 42A and a negative active material layer 42B. Electrolyte is impregnated in each of the positive electrode 41, the negative electrode 42, and the separator 43.

[0177] Here, the three-dimensional shape of the battery element 40 is a flat shape. That is, the shape of the cross-section of the battery element 40 intersecting the winding axis (the cross-section along the XZ plane) is a flat shape defined by the major axis and the minor axis, more specifically, a flat, approximately elliptical shape. The major axis is an imaginary axis extending along the X-axis direction and having a relatively large length, and the minor axis is an imaginary axis extending along the Z-axis direction intersecting the X-axis direction and having a relatively small length.

[0178] The positive lead 51 is connected to the positive terminal 11 (positive current collector 11A), and the negative lead 52 is connected to the negative terminal 12 (negative current collector 12A). Here, there is one positive lead 51 and one negative lead 52.

[0179] Furthermore, there is no particular limitation on the number of positive leads 51, so there can be two or more. In particular, when the number of positive leads 51 is two or more, the resistance of the secondary battery decreases. This explanation regarding the number of positive leads 51 also applies to the number of negative leads 52, so the number of negative leads 52 is not limited to one, and can also be two or more.

[0180] Figure 3 as well as Figure 4 The manufacturing method of the laminated film type secondary battery shown, except that it uses battery element 40 instead of battery element 10, and uses positive electrode lead 51 and negative electrode lead 52 instead of positive electrode lead 31 and negative electrode lead 32, is similar to... Figure 1 as well as Figure 2 The manufacturing methods for the laminated film type secondary batteries shown are largely the same.

[0181] In manufacturing the battery element 40, firstly, a positive electrode 41 is manufactured by forming a positive electrode active material layer 41B on both sides of the positive electrode current collector 41A, and a negative electrode 42 is manufactured by forming a negative electrode active material layer 42B on both sides of the negative electrode current collector 42A. Next, a positive electrode lead 51 is connected to the positive electrode 41 (positive electrode current collector 41A) using a soldering method or the like, and a negative electrode lead 52 is connected to the negative electrode 42 (negative electrode current collector 42A) using a soldering method or the like.

[0182] Next, the positive electrode 41 and the negative electrode 42 are stacked on top of each other with the separator 43 in between, and then the positive electrode 41, the negative electrode 42, and the separator 43 are wound together to form a wound body. This wound body has the same structure as the battery element 40, except that each of the positive electrode 41, the negative electrode 42, and the separator 43 is not impregnated with electrolyte. Next, the wound body is pressed into a flat shape using a press or the like.

[0183] Finally, electrolyte is injected into the interior of the bag-shaped outer membrane 20 containing the wound body, and then the outer membrane 20 is sealed. Thus, the wound body is impregnated with electrolyte to fabricate the battery element 40.

[0184] In this battery element 40, the positive electrode 41 contains a lithium-nickel composite oxide, the negative electrode 42 contains a lithium-titanium composite oxide, the electrolyte contains a dinitrile compound and a carboxylic acid ester, and the capacity ratio R1 is 100% to 120%, and the molar ratio R2 is 1% to 4%. Therefore, even when using battery element 40, the same effect as when using battery element 10 can be obtained.

[0185] It should be noted that, in order to shorten the manufacturing time (electrolyte injection time) of the secondary battery, the battery element 10, which is a stacked electrode body, is preferred over the battery element 40, which is a wound electrode body. This is because, in the manufacturing process of the battery element 40, which is a wound electrode body, the electrolyte is supplied to the wound body from two directions (a portion of the direction around the wound body), while in the manufacturing process of the battery element 10, which is a stacked electrode body, the electrolyte is supplied to the stacked body from four directions (all the directions around the stacked body). Therefore, when using the battery element 10, the electrolyte impregnation rate is increased compared to the case of using the battery element 40, thus shortening the manufacturing time of the secondary battery.

[0186] [Variation Example 2]

[0187] Although no specific illustration is provided here, there is no particular limitation on the type of outer casing that houses the positive electrode 11, negative electrode 12, and electrolyte. Therefore, a metal can or the like, which is a rigid outer casing, can be used instead of the flexible outer casing membrane 20. In this case, the same effect can be achieved.

[0188] It should be noted that rigid metal cans, unlike flexible outer membranes 20, are inherently less prone to deformation. Therefore, when using metal cans, the secondary battery is inherently less likely to expand, and thus, compared to the case where outer membranes 20 are used, the expansion of this secondary battery may not be as noticeable.

[0189] [Variation Example 3]

[0190] A diaphragm 13 was used as a porous membrane. However, although not specifically illustrated here, a laminated diaphragm comprising layers of polymer compounds may be used instead of the porous membrane 13.

[0191] 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 11 and the negative electrode 12, the positional displacement of the battery element 10 is less likely to occur. Therefore, even if electrolyte decomposition reactions occur, the secondary battery is less likely to swell. The polymer compound layer contains polymer compounds such as polyvinylidene fluoride, which has excellent physical strength and is electrochemically stable.

[0192] 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.

[0193] In the case of fabricating a layered membrane, a precursor solution containing a polymeric compound and an organic solvent is prepared, and then the precursor solution is coated onto one or both sides of a porous membrane. Alternatively, the porous membrane can be impregnated in the precursor solution. In this case, multiple insulating particles can also be added to the precursor solution as needed.

[0194] When using this layered membrane, lithium ions can also move between the positive electrode 11 and the negative electrode 12, thus achieving the same effect. Although detailed descriptions are omitted here, it is of course possible to use a layered membrane including a polymer compound layer instead of the porous membrane 43.

[0195] [Variation Example 4]

[0196] The aforementioned secondary battery uses an electrolyte as a liquid electrolyte. However, although not specifically illustrated here, an electrolyte layer as a gel electrolyte can also be used instead of the liquid electrolyte.

[0197] In the battery element 10 using an electrolyte layer, the positive electrode 11 and the negative electrode 12 are alternately stacked with a separator 13 and an electrolyte layer in between. The electrolyte layer is located between the positive electrode 11 and the separator 13, and between the negative electrode 12 and the separator 13.

[0198] 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 of the electrolyte. The structure 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 the electrolyte, the 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.

[0199] Even with this electrolyte layer, lithium ions can move between the positive electrode 11 and the negative electrode 12 via the electrolyte layer, thus achieving the same effect. Although detailed explanations are omitted here, it is of course possible to apply the electrolyte layer to the battery element 40 instead of the battery element 10.

[0200] <3. Uses of Secondary Batteries>

[0201] Next, the uses (application examples) of the above-mentioned secondary batteries will be explained.

[0202] The application of a secondary battery is any machinery, equipment, appliance, device, or system (a collection of multiple devices, etc.) that can primarily use it as a power source for driving or as a power storage source for energy accumulation; there are no particular limitations. A secondary battery used as a power source can be either a main power source or an auxiliary power source. The main power source is the preferred power source, regardless of the availability of other power sources. An auxiliary power source can be used to replace the main power source or can be switched from the main power source as needed. When using a secondary battery as an auxiliary power source, the type of main power source is not limited to a secondary battery.

[0203] Specific examples of the uses of rechargeable batteries are as follows: Electronic devices (including portable electronic devices) such as camcorders, digital still cameras, mobile phones, laptops, cordless phones, stereo headphones, portable radios, portable televisions, and portable information terminals. Portable household appliances such as electric shavers. Backup power supplies and storage devices such as memory cards. Power tools such as electric drills and chainsaws. Battery packs that serve as detachable power sources for laptops, etc. Medical electronic devices such as pacemakers and hearing aids. Electric vehicles such as electric cars (including hybrid vehicles). Power storage systems such as home battery systems that pre-store power for emergencies. In these applications, one or multiple rechargeable batteries can be used.

[0204] Battery packs are effective for use in electric vehicles, energy storage systems, and larger equipment such as power tools. As described later, battery packs can use single cells or battery arrays. Electric vehicles are vehicles that operate (drive) using a secondary battery as a power source; as mentioned above, they can also be automobiles (hybrid vehicles, etc.) that have a power source other than a secondary battery. Energy storage systems are systems that use secondary batteries as a source of stored electricity. In household energy storage systems, since electricity is stored in the secondary battery that serves as the energy storage source, this electricity can be used to operate household electrical products, etc.

[0205] Here, a specific example of the application of secondary batteries is explained. The structure of the application example described below is only one example and can therefore be modified appropriately.

[0206] Figure 5 The frame structure of the battery pack is shown. The battery pack described here is a simplified type (so-called pouch) that uses a single rechargeable battery and is used in electronic devices such as smartphones.

[0207] like Figure 5 As shown, the battery pack includes a power supply 61 and a circuit board 62. The circuit board 62 is connected to the power supply 61 and includes a positive terminal 63, a negative terminal 64, and a temperature sensing terminal 65 (so-called T terminal).

[0208] The power supply 61 includes a secondary battery. In this secondary battery, the positive lead is connected to the positive terminal 63, and the negative lead is connected to the negative terminal 64. Since the power supply 61 can be connected to an external source through the positive terminal 63 and the negative terminal 64, it can be charged and discharged through these terminals. The circuit board 62 includes a control unit 66, a switch 67, a thermistor (Positive Temperature Coefficient (PTC)) element 68, and a temperature detection unit 69. Alternatively, the PTC element 68 may be omitted.

[0209] The control unit 66 includes a central processing unit (CPU) and memory, and controls the overall operation of the battery pack. The control unit 66 detects and controls the operating status of the power supply 61 as needed.

[0210] It should be noted that when the voltage of the power supply 61 (secondary battery) reaches the overcharge detection voltage or the over-discharge detection voltage, the control unit 66 cuts off the switch 67, thereby preventing the charging current from flowing through the current path of the power supply 61. Additionally, when a large current flows during charging or discharging, the control unit 66 cuts off the charging current by cutting off the switch 67. 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.

[0211] Switch 67 includes a charging control switch, a discharging control switch, a charging diode, and a discharging diode, etc., and switches the connection between power supply 61 and external devices according to the instructions of control unit 66. Switch 67 includes a metal-oxide-semiconductor field-effect transistor (MOSFET), etc., and detects the charging and discharging current based on the on-resistance of switch 67.

[0212] The temperature detection unit 69 includes a temperature detection element such as a thermistor, measures the temperature of the power supply 61 using the temperature detection terminal 65, and outputs the temperature measurement result to the control unit 66. The temperature measurement result measured by the temperature detection unit 69 is used for charging and discharging control by the control unit 66 when abnormal heating occurs, and for correction processing by the control unit 66 when calculating the remaining capacity.

[0213] Example

[0214] An embodiment of this technology will be described.

[0215] (Experimental Examples 1-52)

[0216] As described below, a secondary battery was fabricated, and its performance was then evaluated.

[0217] [Making a Second-hand Battery]

[0218] The following steps were followed to create the product. Figure 1 as well as Figure 2 The laminated film type secondary battery shown.

[0219] (The production of the positive electrode)

[0220] First, 98 parts by mass of the positive electrode active material (LiNi as a lithium-nickel composite oxide) 0.82 Co 0.14 Al 0.04O2 (LNCAO), 1 part by mass of positive electrode binder (polyvinylidene fluoride), and 1 part by mass of positive electrode conductive agent (carbon black) are mixed to prepare a positive electrode mixture. Next, the positive electrode mixture is added to an organic solvent (N-methyl-2-pyrrolidone) and the organic solvent is stirred to prepare a paste-like positive electrode mixture slurry. Next, the positive electrode mixture slurry is coated onto both sides of the positive electrode current collector 11A (aluminum foil with a thickness of 12 μm) (except for the protrusion 11AT) using a coating device, and then the positive electrode mixture slurry is dried to form a positive electrode active material layer 11B. Finally, the positive electrode active material layer 11B is compressed and molded using a roller press. Thus, a positive electrode 11 is formed by depositing a positive electrode active material layer 11B on both sides of the positive electrode current collector 11A.

[0221] In particular, when manufacturing the positive electrode 11, as shown in Tables 1 to 4, the molar ratio R3 related to the number of moles of nickel is varied by using a variety of lithium-nickel composite oxides with different nickel contents.

[0222] (Making the negative electrode)

[0223] First, 98 parts by mass of the negative electrode active material (Li4Ti5O as a lithium-titanium composite oxide) was added. 12 A negative electrode binder (polyvinylidene fluoride) and a negative electrode conductive agent (carbon black) are mixed to prepare a negative electrode mixture. Next, the negative electrode mixture is added to an organic solvent (N-methyl-2-pyrrolidone) and stirred to prepare a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry is coated onto both sides of the negative electrode current collector 12A (a copper foil with a thickness of 15 μm) using a coating apparatus (excluding the protrusion 12AT), and then dried to form a negative electrode active material layer 12B. Finally, the negative electrode active material layer 12B is compressed and molded using a roller press. Thus, a negative electrode 12 is formed by depositing a negative electrode active material layer 12B on both sides of the negative electrode current collector 12A.

[0224] In particular, when manufacturing the negative electrode 12, as shown in Tables 1 to 4, by changing the thickness (μm) of the negative electrode active material layer 12B according to the coating amount of the negative electrode slurry, the capacity ratio R1 related to the capacity of the positive electrode 11 and the negative electrode 12 is changed.

[0225] It should be noted that, for comparison purposes, the negative electrode 12 was fabricated using the same steps, except that carbon material (graphite) was used instead of lithium titanium composite oxide as the negative electrode active material. The procedure for determining the capacity ratio R1 when using carbon material as the negative electrode active material was the same as when using lithium titanium composite oxide as the negative electrode active material, except that the upper limit voltage during charging was changed to 0V and the lower limit voltage during discharging was changed to 1.5V when charging and discharging the test secondary battery to determine the capacity of the negative electrode 12.

[0226] (Preparation of electrolyte)

[0227] First, a solvent was prepared. A mixture of propylene carbonate (a cyclic carbonate) and carboxylic acid esters was used as the solvent. The types of carboxylic acid esters and their content (wt%) in the solvent are shown in Tables 1 to 4.

[0228] Methyl propionate (MtPr), ethyl propionate (EtPr), propyl propionate (PrPr), methyl acetate (MtAc), and ethyl acetate (EtAc) were used as carboxylic acid esters.

[0229] Next, an electrolyte salt (LiPF6 as a lithium salt) was added to the solvent, and the solvent was then stirred. In this case, the concentration of the electrolyte salt relative to the solvent was 1 mol / kg.

[0230] Finally, the dinitrile compound, other solvents (ethylene carbonate as an unsaturated cyclic carbonate), and other electrolyte salts (LiBF4 as a lithium salt) were added to the solvent containing the electrolyte salts, and then the solvent containing the electrolyte salts was stirred.

[0231] As dinitrile compounds, malononitrile (MN), succinic anionyl (SN), glutaronitrile (GN), adiponitrile (AN), heptanonitrile (PN), and octanoic anionyl (SBN) were used.

[0232] Thus, an electrolyte is prepared by dissolving or dispersing the dinitrile compound, other solvents, and other electrolyte salts in a solvent containing electrolyte salts. In this case, the content of other solvents in the electrolyte is 0.5% by weight, and the content of other electrolyte salts in the electrolyte is 1% by weight.

[0233] In particular, when preparing the electrolyte, as shown in Tables 1 to 4, by changing the amount of dinitrile compound added, the molar ratio R2 related to the molar number of the carboxylic ester and the dinitrile compound was changed.

[0234] It should be noted that, for comparison purposes, the electrolyte was prepared using the same steps, except that a chain carbonate was used instead of a carboxylic acid ester. Diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) were used as the chain carbonates. In Table 4, for convenience, the chain carbonates (DEC and EMC) are shown in the "Carboxylic Acid Esters" column. Furthermore, to clarify that DEC and EMC are not carboxylic acid esters, an asterisk (*) is added before DEC and EMC, respectively.

[0235] In addition, for comparison purposes, an electrolyte was prepared using the same steps, except that no dinitrile compound was used.

[0236] (Assembly of a secondary battery)

[0237] First, the positive electrode 11 and the negative electrode 12 are alternately stacked through a diaphragm 13 (a microporous polyethylene membrane with a thickness of 15 μm), thereby creating a laminate.

[0238] Next, a joint 11Z is formed by welding multiple protrusions 11AT together, and a joint 12Z is ​​formed by welding multiple protrusions 12AT together. Next, a positive electrode lead 31 made of aluminum is welded to the joint 11Z, and a negative electrode lead 32 made of copper is welded to the joint 12Z.

[0239] Next, the laminated body is housed inside the recess 20U provided in the outer film 20. The outer film 20 uses a laminated film, which sequentially layers a welding layer (a 30 μm thick polypropylene film), a metal layer (a 40 μm thick aluminum foil), and a surface protective layer (a 25 μm thick nylon film). In Tables 1 to 4, the term "laminated" in the "outer component" column indicates that the outer film 20 (laminated film) is used as the outer component. Next, the outer film 20 is folded so that the laminated body is sandwiched between the outer film 20 and the welding layer is located inside the outer film 20. Then, the outer periphery portions of two sides of the outer film 20 (welded layer) are thermally fused together, thereby housing the laminated body inside the bag-shaped outer film 20.

[0240] Finally, after injecting the electrolyte into the pouch-shaped outer membrane 20, the outer periphery of the remaining edge of the outer membrane 20 (welded layer) is thermally fused together under reduced pressure. In this case, a sealing film 21 (a polypropylene film with a thickness of 5 μm) is inserted between the outer membrane 20 and the positive electrode lead 31, and a sealing film 22 (a polypropylene film with a thickness of 5 μm) is inserted between the outer membrane 20 and the negative electrode lead 32. Thus, the electrolyte is impregnated in the laminate, thereby fabricating the battery element 10. In Tables 1 to 4, the term "laminated" in the "Battery Element (Element Structure)" column indicates that the battery element 10 uses laminated electrode bodies.

[0241] Therefore, the battery element 10 is sealed inside the outer membrane 20 and assembled into a secondary battery.

[0242] (Stabilization treatment)

[0243] The secondary battery was subjected to one charge-discharge cycle at room temperature (temperature = 25℃). During charging, a constant current of 0.01C was used until the voltage reached 2.7V. During discharging, a constant current of 0.2C was used. 0.01C refers to the current value required to fully discharge the battery (theoretical capacity) in 100 hours, and 0.2C refers to the current value required to fully discharge the battery in 5 hours.

[0244] Thus, a coating is formed on the surface of the negative electrode 12, thereby stabilizing the state of the secondary battery. Therefore, a laminated secondary battery using a flexible outer membrane 20 is completed.

[0245] [Making Other Secondary Batteries]

[0246] It should be noted that other secondary batteries were also made using the following steps.

[0247] (Changes in the structure of battery components)

[0248] Except that a battery element 40, which is a wound electrode body, is used instead of a battery element 10, which is a stacked electrode body, and a positive electrode lead 51 and a negative electrode lead 52 are used instead of a positive electrode lead 31 and a negative electrode lead 32, the same steps were followed to fabricate the battery. Figure 3 as well as Figure 4 The laminated film type secondary battery shown.

[0249] The manufacturing steps of battery element 40 are as follows. First, a positive electrode lead 51 made of aluminum is soldered to the positive electrode 41 (positive current collector 41A), and a negative electrode lead 52 made of copper is soldered to the negative electrode 42 (negative current collector 42A). Next, the positive electrode 41 and the negative electrode 42 are stacked on top of each other with a separator 43 (a microporous polyethylene membrane with a thickness of 15 μm) in between, and then the positive electrode 41, the negative electrode 42, and the separator 43 are wound together to form a wound body. Next, the wound body is stamped using a press to form a flat wound body. Finally, electrolyte is injected into the inside of the bag-shaped outer membrane 20 containing the wound body, so that the electrolyte is immersed in the wound body. In Tables 1 to 4, "winding" in the "Battery Element (Element Structure)" column indicates that the battery element 40 uses a wound electrode body.

[0250] (Changes to external components)

[0251] In addition, besides using a rigid metal can instead of the flexible outer membrane 20 as the outer casing, a square secondary battery was manufactured using the same steps. In Tables 1-4, "metal" in the "outer casing" column indicates that a metal can was used as the outer casing. This metal can has the same... Figure 1 The outer membrane 20 shown has a roughly flat, three-dimensional shape, and the wall thickness of the metal can is 0.15 mm.

[0252] The assembly steps of the secondary battery are as follows. First, a flat, coiled body is housed inside a stainless steel component with a flat, rectangular, three-dimensional shape, open at one end and closed at the other. Next, electrolyte is injected into the component, immersing the coiled body in the electrolyte. Thus, the electrolyte is immersed in the coiled body, forming a battery element 40. Finally, a stainless steel cap is welded to one end of the component. This seals the battery element 40 inside the metal container (component and cap).

[0253] [Performance Evaluation]

[0254] The performance (expansion characteristics, charging characteristics, and energy characteristics) of the secondary battery was evaluated, and the results are shown in Tables 1 to 4. The evaluation steps for each characteristic are described below.

[0255] (Expansion characteristics)

[0256] First, the thickness of the secondary battery was measured at room temperature (thickness before storage). Next, the secondary battery was charged and stored in a high-temperature environment (temperature = 60°C) for one month. The thickness of the secondary battery was then measured again in the same environment (thickness after storage). During charging, a constant current of 0.01C was used until the voltage reached 2.7V. Finally, the expansion rate (%) was calculated as: [(thickness after storage - thickness before storage) / thickness before storage] × 100.

[0257] It should be noted that, since a metal can was used as the outer casing, the increase in the thickness of the secondary battery after storage was minimal. The Archimedes method was used to measure the volume change of the secondary battery, and the thickness of the secondary battery after storage was calculated based on the measurement results of this volume change.

[0258] (Charging characteristics)

[0259] First, the battery capacity was measured by charging and discharging the secondary battery at room temperature. During charging, a constant current of 0.5C was applied until the voltage reached the upper limit. This upper limit voltage was 2.7V when lithium-titanium composite oxide was used as the negative electrode active material, and 4.2V when carbon material was used. During discharging, a constant current of 0.2C was applied until the voltage reached the lower limit. This lower limit voltage was 1.0V when lithium-titanium composite oxide was used as the negative electrode active material, and 2.5V when carbon material was used. 0.5C is the current value required to fully discharge the battery within 2 hours.

[0260] Next, the charging capacity was measured by charging the secondary battery in the same environment. During charging, a low current of 6C was applied until the voltage reached the upper limit voltage. Details regarding this upper limit voltage are as described above. 6C refers to the current value required to fully discharge the battery capacity in 1 / 6 hour.

[0261] Finally, the charge rate (%) is calculated as (charge capacity / battery capacity) × 100. This charge rate indicates what percentage of the battery capacity is equivalent to when the battery capacity is set to 100%.

[0262] (capacity characteristics)

[0263] First, the battery capacity and average discharge voltage were measured by charging and discharging the secondary battery at room temperature. The charging and discharging conditions were the same as those used when checking the charging characteristics (measuring the battery capacity). Next, the energy density (Wh) was calculated based on the battery capacity and average discharge voltage. Finally, the energy density per unit weight (E density, Wh / kg) was calculated based on the mass (kg) of the secondary battery.

[0264] (Injection status)

[0265] Here, in order to further inspect the electrolyte injection status during the secondary battery manufacturing process, the time required for the electrolyte to be immersed in the laminate and the wound body respectively was also measured. In this case, after the electrolyte was injected, the time required for the secondary battery to reach a certain thickness through the immersion in the electrolyte was measured (injection time (minutes)).

[0266] [Table 1]

[0267]

[0268] [Table 2]

[0269]

[0270] [Table 3]

[0271]

[0272] [Table 4]

[0273]

[0274] [Inspection]

[0275] As shown in Tables 1 to 4, in a secondary battery in which the positive electrode 11 contains lithium-nickel composite oxide, the negative electrode 12 contains lithium-titanium composite oxide, and the electrolyte contains carboxylic acid ester, the expansion characteristics, charging characteristics, and energy characteristics vary according to the capacity ratio R1 and the molar ratio R2, respectively.

[0276] Specifically, when both the capacity ratio R1 is 100%–120% and the molar ratio R2 is 1%–4% (Experimental Examples 1–24), compared with cases where both conditions are not met simultaneously (Experimental Examples 25–50), the expansion rate is significantly reduced and the charging rate is significantly increased while ensuring the energy density per unit weight.

[0277] In particular, when both of the above conditions are met simultaneously, the following tendency can be obtained.

[0278] First, when the molar ratio R3 is 80% or more (Experimental Examples 1, 9-11), compared with the case where the molar ratio R3 is less than 80% (Experimental Examples 7, 8), the energy density per unit weight is further increased while basically maintaining each of the expansion rate and the charge rate.

[0279] Second, when the dinitrile compound is succinic anion or the like (Experimental Examples 1, 13, 14), compared with the case where the dinitrile compound is malononitrile or the like (Experimental Examples 12, 15, 16), the expansion rate is further reduced and the charging rate is further increased while maintaining the energy density per unit weight.

[0280] Third, when the carboxylic acid ester is ethyl propionate or the like (Experimental Examples 1 and 18), compared with the case where the carboxylic acid ester is methyl propionate or the like (Experimental Examples 17, 19, and 20), the expansion rate is further reduced and the charging rate is further increased while maintaining the energy density per unit weight.

[0281] Fourth, when the content of carboxylic acid esters in the solvent is 50% to 90% by weight (Experimental Examples 1, 21, 22), sufficient energy density per unit weight can be obtained, while the expansion rate is sufficiently reduced and the charging rate is sufficiently increased.

[0282] Fifth, when using battery element 10 as a stacked electrode body (Experimental Example 1), the liquid injection time is significantly shortened compared to when using battery element 40 as a wound electrode body (Experimental Example 23). As a result, in the former case, the expansion rate is further reduced, the charging rate is further increased, and the energy density per unit weight is further increased compared to the latter case.

[0283] Sixth, when a rigid metal can is used as the outer casing (Experimental Example 24), the expansion rate hardly changes even when both of the above conditions are met. In contrast, when a flexible outer casing membrane 20 is used as the outer casing (Experimental Example 1), the expansion rate changes depending on whether both conditions are met, but the expansion rate is sufficiently suppressed.

[0284] Furthermore, if both of the above conditions are met simultaneously, the following tendency can also be obtained.

[0285] When the solvent contains chain carbonates (Experimental Examples 43-46), a sufficient energy density per unit weight is obtained, and although the charge rate is sufficiently increased, the expansion rate increases significantly. In this case, in particular, even when both of the above conditions are met simultaneously, the expansion rate is not sufficiently reduced.

[0286] In contrast, when the solvent contains carboxylic esters (Experimental Examples 1 and 25), compared to when the solvent contains chain carbonates, the charge rate increases and the expansion rate decreases while maintaining the energy density per unit weight. In this case, in particular, the expansion rate decreases significantly when both conditions are met.

[0287] Furthermore, when carbon materials were used as the negative electrode active material (Experimental Examples 51 and 52), although the energy density per unit weight increased significantly, the expansion rate increased and the charge rate decreased. In particular, even when both of the above conditions were met simultaneously, the expansion rate hardly decreased.

[0288] In contrast, when lithium-titanium composite oxide is used as the negative electrode active material (Experimental Examples 1 and 25), compared with the case where carbon material is used as the negative electrode active material, although the energy density per unit weight is reduced, the expansion rate is reduced and the charge rate is increased. In this case, in particular, sufficient energy density per unit weight can be obtained, and the expansion rate is significantly reduced when both conditions are met.

[0289] [Summarize]

[0290] As shown in Tables 1-4, when the positive electrode 11 contains lithium-nickel composite oxide, the negative electrode 12 contains lithium-titanium composite oxide, the electrolyte contains dinitrile compounds and carboxylic acid esters, and the capacity ratio R1 is 100%–120% and the molar ratio R2 is 1%–4%, the expansion characteristics, charging characteristics, and energy characteristics are all improved. Therefore, in secondary batteries, excellent expansion characteristics and excellent charging characteristics can be obtained while ensuring energy density.

[0291] The above description, while illustrating the present technology with an example of 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.

[0292] Specifically, although the case of a laminated film type battery structure for secondary batteries has been described, the battery structure is not particularly limited and can be other battery structures such as cylindrical, coin-shaped, and button-shaped.

[0293] Furthermore, although the battery element structure is described as a stacked type (stacked electrode body) and a wound type (wound electrode body), the battery element structure is not particularly limited, so other element structures can be used, such as a repeatedly folded type in which the electrodes (positive and negative electrodes) are folded into a Z-shape.

[0294] Furthermore, while the case where lithium is used as the electrode reactant has been described, this electrode reactant 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, the electrode reactant can also be other light metals such as aluminum.

[0295] 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, this technology can also achieve other effects.

Claims

1. A secondary battery, comprising: The positive electrode contains a lithium-nickel composite oxide; The negative electrode comprises lithium-titanium composite oxide; and The electrolyte contains dinitrile compounds and carboxylic acid esters. The ratio of the capacity of the positive electrode per unit area to the capacity of the negative electrode per unit area is more than 100% and less than 120%. The molar percentage of the dinitrile compound relative to the molar percentage of the carboxylic acid ester is 1% or more and 4% or less. The lithium-nickel composite oxide contains lithium, nickel, and at least one other element other than nickel from Groups 2 to 15 of the long-period periodic table as constituent elements. The ratio of the number of moles of nickel to the sum of the number of moles of nickel and the number of moles of the other elements is more than 80%.

2. The secondary battery according to claim 1, wherein, The lithium-titanium composite oxide comprises at least one of the compounds represented by formulas (1), (2), and (3) below, respectively. Li[Li x M1 （1-3x） / 2 You （3＋x） / 2 ]O4…(1) In equation (1), M1 is at least one of Mg, Ca, Cu, Zn, and Sr, and x satisfies 0 ≤ x ≤ 1 / 3. Li[Li y M2 1-3y Ti 1＋2y ]O4…(2) In equation (2), M2 is at least one of Al, Sc, Cr, Mn, Fe, Ga, and Y, and y satisfies 0 ≤ y ≤ 1 / 3. It[It 1 / 3 M3 z Small （5 / 3）-z ]O4…(3) In equation (3), M3 is at least one of V, Zr and Nb, and z satisfies 0≤z≤2 / 3.

3. The secondary battery according to claim 1 or 2, wherein, The dinitrile compound includes at least one selected from succinic anion, glutaronitrile, and adiponitrile. The carboxylic acid ester includes at least one of ethyl propionate and propyl propionate.

4. The secondary battery according to claim 1 or 2, wherein, The electrolyte contains a solvent. The solvent contains the carboxylic acid ester. The content of the carboxylic acid ester in the solvent is more than 50% by weight and less than 90% by weight.

5. The secondary battery according to claim 1 or 2, wherein, It also has a separator between the positive electrode and the negative electrode. The positive electrode and the negative electrode are alternately stacked with the membrane in between.

6. The secondary battery according to claim 1 or 2, wherein, It also has a flexible external component for housing the positive electrode, the negative electrode, and the electrolyte.

7. The secondary battery according to claim 1 or 2, wherein, The secondary battery is a lithium-ion secondary battery.

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