Secondary battery with non-aqueous electrolyte

Abstract

A secondary battery with a non-aqueous electrolyte is provided, enabling a current-cut-off mechanism to function while maintaining high battery performance. The secondary battery with a non-aqueous electrolyte according to the present invention comprises: a battery assembly provided with a positive electrode having a positive electrode active material layer held in place by a positive electrode current collector, a negative electrode, and a separator; a battery housing that accommodates the electrode assembly together with a non-aqueous electrolyte; and a current-cut-off mechanism. The positive electrode active material layer comprises a positive electrode active material and a conductive material. A compound comprising a saturated cyclic hydrocarbon group is held in at least a portion of the conductive material.The content of the compound comprising the saturated cyclic hydrocarbon group is 0.5% by mass or more, based on a value of 100% by mass or more for the total solids content of the positive electrode active material layer.

Description

BACKGROUND OF THE INVENTION 1. Field of the invention

[0001] The present invention relates to a secondary battery which is provided with a non-aqueous electrolyte (secondary battery with non-aqueous electrolyte). 2. State of the art

[0002] Lithium-ion secondary batteries and other secondary batteries with non-aqueous electrolyte are becoming increasingly important as vehicle-mounted power sources and power sources for personal computers, portable devices, and the like. In particular, lithium-ion secondary batteries are preferred as high-power vehicle-mounted power sources because they are lightweight and allow for high energy densities (see, for example, Japanese patent application number 2013-157139). When such secondary batteries with non-aqueous electrolyte are overcharged, an excessive amount of charge carrier is released from the positive electrode, while an excessive amount of charge carrier is transferred to the negative electrode. As a result, both the positive and negative electrodes become thermally unstable.If the positive and negative electrodes become thermally unstable, the organic solvent of the electrolyte eventually decomposes, leading to an exothermic reaction that impairs battery stability.

[0003] In response to this problem, a secondary battery with a non-aqueous electrolyte was disclosed, equipped with a current-cut-off mechanism in the battery casing that interrupts charging when, for example, the gas pressure in the battery casing reaches a predetermined pressure or higher. A gas generator is added that produces gas in the electrolyte when the battery reaches a predetermined overcharge state. For example, cyclohexylbenzene (CHB) or biphenyl (BP) are used as gas generators (see, for example, Japanese patent application number 2013-157139). CHB and BP produce hydrogen gas as a result of being activated by a polymerization reaction during overcharging. As a result, the pressure in the battery casing increases, the current-cut-off mechanism is activated, and the overcharge current is interrupted. List of cited documents Patent literature Patent literature 1: Japanese patent application with publication number 2013-157139 SUMMARY OF THE INVENTION

[0004] To enable the current cutoff mechanism to function efficiently, increasing the amount of the aforementioned added gas generator is effective. However, since the aforementioned gas generator acts as a resistive component of the battery, increasing the amount of added gas generator can lead to a decrease in battery performance. Conversely, reducing the amount of added gas generator to maintain a high level of battery performance decreases gas production during overcharging, potentially delaying the activation of the current cutoff mechanism. With this type of conventional design, it was difficult to achieve both ensuring an adequate amount of gas production and maintaining battery performance. The present invention solves the aforementioned problems.

[0005] The secondary battery with non-aqueous electrolyte provided by the present invention comprises: an electrode arrangement provided with a positive electrode in which a positive electrode active material layer is held on a positive electrode current collector, a negative electrode in which a negative electrode active material layer is held on a negative electrode current collector, and a separator interposed between the positive and negative electrodes; a battery housing that accommodates the electrode arrangement together with a non-aqueous electrolyte, an external terminal provided in the battery housing and connected to the electrode arrangement; and a current cut-off mechanism that interrupts the electrical connection between the electrode arrangement and the external terminal when the internal pressure of the battery housing reaches a predetermined pressure or more.The positive electrode active material layer mentioned above comprises at least one positive electrode active material and a conductive material. A compound comprising a saturated cyclic hydrocarbon group is trapped (charged) in at least a portion of the conductive material mentioned above. The content of the compound mentioned above is 0.5% by mass or more, based on a total solids content of 100% by mass of the positive electrode active material layer mentioned above. In a preferred mode thereof, the compound mentioned above is formulated to allow protons to detach from the saturated cyclic hydrocarbon group mentioned above when the voltage reaches a predetermined voltage or higher.This design allows a secondary battery to be provided, enabling the current cutoff mechanism to function properly during overcharging while maintaining advantageous battery performance.

[0006] The content of the aforementioned compound is approximately 0.5% by mass or more (and preferably 1% by mass or more) based on a value of 100% by mass for the total solids content of the aforementioned positive electrode active material layer. If the content of the aforementioned compound is excessively low, the amount of gas generated during overcharging will be insufficient, which may delay the operation of the current cutoff mechanism. Conversely, if the content of the aforementioned material is excessively high, the function of a conductive material will be impaired. 58The compound may impair performance, potentially leading to a decrease in battery efficiency (e.g., battery capacity). To ensure the conductive material functions adequately, the concentration of the aforementioned compound should be approximately 4% by mass or less (and preferably 2% by mass or less).

[0007] In a preferred mode, the secondary battery with non-aqueous electrolyte disclosed here, the aforementioned saturated cyclic hydrocarbon group is a cyclohexyl group. Since a cyclohexyl group facilitates the release of protons (H₂), + The fact that, when the voltage reaches a predetermined voltage or higher, this can preferably be used as a compound that satisfies the objective of the present invention. An example of a compound containing a cyclohexyl group is cyclohexylbenzene (CHB).

[0008] In a preferred mode of the secondary battery with non-aqueous electrolyte disclosed herein, the aforementioned non-aqueous electrolyte does not contain a gas generator that produces gas when the voltage reaches a predetermined voltage or higher. If a gas generator is included in the electrolyte, it inhibits the phoretic diffusion of the charge carrier (lithium ions in the case of a lithium-ion secondary battery) and the anions present in the electrolyte, potentially causing a decrease in battery performance. In contrast, with the design according to the present invention, an adequate amount of gas can be ensured even during overcharging when no gas generator is included in the electrolyte, since the aforementioned compound, which functions as a gas generator, is held in place by a conductive material.This allows the power cut-off mechanism to function properly during overcharging without causing a decrease in battery performance. BRIEF DESCRIPTION OF THE FIGURES

[0009] Fig. Figure 1 is a drawing that shows an example of the structure of a lithium-ion secondary battery according to one embodiment;

[0010] Fig. 2 is a drawing showing a wound electrode arrangement according to one embodiment;

[0011] Fig. 3 is a cross-sectional view showing along line III-III in Fig. 2 represents the removed cross-section;

[0012] Fig. Figure 4 is a schematic diagram representing a portion of a cross-section obtained by cutting a wound electrode arrangement in the radial direction;

[0013] Fig.Figure 5 is a drawing that shows an example of a conductive material that retains CHB; and

[0014] Fig. Figure 6 is a drawing that shows an example of a conductive material that holds CHB. DESCRIPTION OF PREFERRED EXECUTION FORMS

[0015] The following provides an explanation of preferred embodiments of the present invention. Furthermore, matters necessary for carrying out the present invention that are not specifically mentioned in this description can be understood as design matters for a person skilled in the art with ordinary abilities in the field, based on the prior art in the relevant area. The present invention can be carried out based on the content described in this description and common general technical knowledge in the relevant area. In addition, in this description, the term "secondary battery" refers to all electrically rechargeable devices that can be repeatedly charged and discharged, and it includes both so-called storage batteries such as lithium-ion secondary batteries and electrical storage elements such as electrical double-layer capacitors.Furthermore, "lithium-ion secondary battery" refers to a secondary battery that uses lithium ions as the electrolyte and is charged and discharged by the migration of lithium ions between positive and negative electrodes. Additionally, electrode active material refers to a material capable of reversibly absorbing and releasing chemical species (lithium ions in the case of a lithium-ion secondary battery).

[0016] The following provides an explanation of a secondary battery with a non-aqueous electrolyte according to an embodiment of the present invention, based on the figures. Furthermore, the same reference symbols are appropriately used to designate such elements and locations that exhibit the same function. The figures are intended as schematic representations and do not necessarily reflect actual objects. The figures are also intended as examples and do not limit the present invention unless expressly stated otherwise. Although the following provides an explanation of embodiments of the present invention by using the application of the present invention to a lithium-ion battery as an example, this is not intended to limit the scope of the present invention.

[0017] Fig. Figure 1 shows a lithium-ion secondary battery 100according to one embodiment of the present invention. As in Fig. Figure 1 shows this lithium-ion secondary battery. 100 with a wound electrode arrangement 20 and a battery housing 30 provided. Fig. 2 is a drawing showing the wound electrode arrangement 20 represents. Fig. 3 is a cross-sectional view, taken along line III-III in Fig. 2 is removed. In the lithium-ion secondary battery 100 according to one embodiment of the present invention, as in Fig. 1 and Fig. Figure 2 shows the flat-shaped wound electrode arrangement. 20 in the flat rectangular battery housing 30 (namely an outer casing) together with a liquid electrolyte (electrolyte solution) not shown.

[0018] The battery casing 30is formed by a box-shaped (namely the shape of a rectangular parallel flat with a base) housing body 32 with an opening in one end (corresponding to the upper end when the battery is in its normal operating state) and a sealing plate (cover) 34 formed, which is attached to the opening, which is formed from a rectangular plate component that covers the opening. An example of the battery casing material. 30 is aluminum. As in Fig. The figures shown in 1 are in the sealing plate 34 a positive electrode connection 42 and a negative electrode connection 44 Designed for creating external connections. A thin-walled safety valve. 36 is between the two connections 42 and 44 the sealing plate 34 formed, which is designed to maintain the pressure in the battery casing 30releases the water if it has risen to a predetermined level or higher.

[0019] The wound electrode arrangement 20 is equipped with a long, leaf-shaped positive electrode (positive electrode sheet) 50 ), a long, leaf-shaped negative electrode (negative electrode sheet) 60 ), which corresponds to the positive electrode sheet 50 resembles, and has a total of two long, leaf-shaped separators (separators). 70 and 72 ) provided.

[0020] The positive electrode sheet 50 is equipped with a band-shaped positive electrode current collector 52 and a positive electrode active material layer 54 provided. A strip-shaped aluminum foil with a thickness of 15 μm is used, for example, as the positive electrode current collector. 52 used. An uncoated area 52a is along an edge in the direction of the width of the positive electrode current collector 52provided. In the example shown in the figure, the positive electrode active material layer is 54 on both sides of the positive electrode current collector 52 with the exception of the uncoated area 52a recorded, which is on the positive electrode current collector 52 is provided. The positive electrode active material layer 54 It comprises a positive electrode active material, a conductive material and a binder.

[0021] A substance used as the positive electrode active material in a lithium-ion secondary battery can be used for the positive electrode active material. Examples of positive electrode active materials include lithium transition metal oxides such as lithium nickel cobalt manganese oxide (LiNiCoMnO2). For example, a conductive material can be mixed into the positive electrode active material. The conductive material is described below.

[0022] Furthermore, a binder such as polyvinylidene fluoride (PVdF), styrene-butadiene rubber (SBR), or carboxymethylcellulose (CMC) can be added to the positive electrode active material and the conductive material. A composition for forming the positive electrode active material layer (paste) can be prepared by dispersing it in a suitable dispersion medium and kneading. The positive electrode active material layer 54 Layering this composition forms the positive electrode active material layer on the positive electrode current collector. 52 followed by drying and pressing to a predetermined thickness.

[0023] As in Fig. The negative electrode sheet is shown in section 2. 60 with a ribbon-shaped negative electrode current collector 62 and a negative electrode active material layer 64It is equipped with a ribbon-shaped copper foil with a thickness of approximately 10 μm, which serves as the negative electrode current collector. 62 used. An uncoated area 62a is along an edge in the direction of the width of the negative electrode current collector 62 provided. The negative electrode active material layer 64 is applied to both sides of the negative electrode current collector 62 recorded, with the exception of the uncoated area 62a , which is on the negative electrode current collector 62 is provided. The negative electrode active material layer 64 It contains, for example, a negative electrode active material, a thickening agent and a binder.

[0024] One, two, or more substances conventionally used in lithium-ion secondary batteries can be used as the negative electrode active material without any special restrictions. Preferred examples include carbon-based materials such as graphite carbon. Similar to the positive electrode, a negative electrode mixture (paste) can be prepared by dispersing the negative electrode active material in a suitable dispersion medium together with a binder such as PVDF, SBR, PTFE, or CMC and kneading. The negative electrode active material layer 64 is applied to the negative electrode current collector 62 layered, followed by drying and pressing to a predetermined thickness.

[0025] The separators 70 and 72 are components that form the positive electrode sheet 50 and the negative electrode sheet 60 separate. In this example, the separators 70and 72 formed from a ribbon-like base material of a predetermined width with a multitude of small holes. A sheet material with a single-layer structure formed from a porous polyolefin-based resin (such as a polyethylene single-layer structure) or a sheet material with a laminated structure (such as a three-layer structure consisting of polypropylene, polyethylene, and polypropylene) can, for example, be used as the base material. As in Fig. 2 and Fig. Figure 3 shows a width b1 of the negative electrode active material layer. 64 wider than a width a1 of the positive electrode active material layer 54 Furthermore, the widths c1 and c2 of the separators are 70 and 72 wider than the width b1 of the negative electrode active material layer 64 (c1, c2 > b1 > a1).

[0026] The wound electrode arrangement 20is achieved by superimposing the positive electrode sheet 50 and the negative electrode sheet 60 with the separators 70 and 72 obtained, which are stored in between, so that the positive electrode active material layer 54 and the negative electrode active material layer 64 are in mutual opposition. Furthermore, the negative electrode current collector is used. 62 and the positive electrode current collector 52 superimposed, so that their uncoated areas on both sides 52a and 62a to the opposite side in the direction of the width of the wound electrode arrangement 20 protrude. The superimposed sheet materials (such as the positive electrode sheet) 50 ) are wound around a winding line WL which is oriented in the direction of the width.

[0027] The wound electrode arrangement 20 is at the electrode connections 42and 44 attached to the battery casing 30 are attached (in this example to the cover) 34 The wound electrode arrangement 20 is in a state by being pressed and bent into a flat shape in a direction perpendicular to the winding line, in the battery casing 30 accommodated. Furthermore, the wound electrode arrangement is designed such that the uncoated area 52a of the positive electrode sheet 40 and the uncoated area 62a of the negative electrode sheet 60 on opposite sides in the direction of the width of the separators 70 and 72 protrude. One of the electrode connections 42 is on the uncoated area 52a of the positive electrode current collector 52 attached, while the other electrode connection 44 on the uncoated area 62aof the negative electrode current collector 62 is attached. The wound electrode arrangement 20 is located in a flat space within the housing body 32 housed the housing body 32 will be covered 34 sealed after the wound electrode arrangement 20 was housed there.

[0028] A non-aqueous electrolyte similar to that conventionally used in lithium-ion secondary batteries can be used as the electrolyte (non-aqueous electrolyte) without any special restrictions. The non-aqueous electrolyte typically has a composition obtained by dissolving a conducting salt in a suitable non-aqueous solvent. Examples of the aforementioned non-aqueous solvent that can be used include one or more non-aqueous solvents selected from the group that includes, for example, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, and 1,3-dioxolane. Furthermore, examples of the aforementioned carrier salt that can be used include lithium salts such as LiPF6, LiBF4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2 or LiC(CF3SO2)3.An example of this is a non-aqueous electrolyte obtained by dissolving LiPF6 at a concentration of approximately 1 mol / L in a mixed solvent of ethylene carbonate and diethyl carbonate (in a mass ratio of, for example, 1:1). In this embodiment, the non-aqueous electrolyte does not contain a gas generator (such as cyclohexylbenzene (CHB) or biphenyl (BP)) that produces gas when the voltage reaches a predetermined voltage or higher.

[0029] Furthermore, this lithium-ion secondary battery is equipped with a current cut-off mechanism. 90 equipped. The power cut-off mechanism 90 This is a mechanism that interrupts the current path if the pressure inside the battery casing becomes abnormally high. In this embodiment, the current cut-off mechanism is located on the inside of the positive electrode terminal. 42formed, so that it interrupts the conductive path of the battery current in the positive electrode, as in Fig. 1 shown.

[0030] The following provides a detailed explanation of this lithium-ion secondary battery. 100 . Fig. Figure 4 schematically represents a cross-section obtained by cutting the positive electrode sheet. 50 and the separator 70 , which are in the wound electrode arrangement 20 are superimposed, in the direction of the winding line (as well as in the direction of the width of the positive electrode sheet) 50 ) will be received.

[0031] As in Fig. Figure 2 shows the positive electrode sheet. 50 with the positive electrode current collector 52 and the positive electrode active material layer 54 equipped with the positive electrode current collector 52 is recorded. The positive electrode active material layer 54includes a positive electrode active material 56 , the conductive material 58 and a binder (not shown). As previously described, the conductive material 58 It is formed from a powdered carbon material (such as AB). A compound comprising a saturated cyclic hydrocarbon group is attached to at least part of the conductive material. 58 held in place (chemically immobilized). In other words, the surface of the conductive material is... 58 chemically modified by the compound which includes a saturated hydrocarbon group.

[0032] In the area over which the effects of the present invention can be demonstrated, there are no special restrictions regarding the compound containing the saturated cyclic hydrocarbon group that is incorporated into the surface of the conductive material. 58is introduced and other molecular structures of the same, as long as it is a compound having at least one saturated cyclic hydrocarbon group and which may have any functional groups, bonding sites, halogen atoms, metal atoms, and the like. Furthermore, the compound is preferably structured such that it allows a proton to detach from the saturated cyclic hydrocarbon group when the latter is oxidized, when the strain reaches a predetermined strain or more. Examples of such saturated cyclic hydrocarbon groups include cycloalkyl groups with, for example, monocyclic, bicyclic, tricyclic, or tetracyclic structures, consisting of 5 to 10 (and preferably 6 to 8) carbon atoms.Examples of monocycloalkyl groups include, for example, a cyclopentyl group, a cyclohexyl group, a cycloheptanyl group, a cyclooctanyl group, a cycloononanyl group, and a cyclodecanyl group. Compounds in which one, two, or more of these cyclic hydrocarbon groups are directly or indirectly bonded to an aromatic ring (including a heteroaromatic ring) are also preferred.The compound can also be one in which hydrogen atoms in the aromatic ring (and typically a benzene ring) bonded to atoms forming the aromatic ring (such as carbon atoms) are each and independently exchanged with, for example, an aliphatic alkyl group (linear or branched with 1 to 10 carbon atoms), an alicyclic alkyl group (saturated or unsaturated with 1 to 10 carbon atoms), an oxygen atom (which may also be a hydroxyl group (OH)), or a halogen atom (such as F, Cl, or Br).

[0033] A particular example of a more preferred compound with a saturated cyclic hydrocarbon group in the technology disclosed herein is a compound in which the aforementioned cycloalkyl group is directly bonded to a benzene ring (cycloalkylbenzene). This cycloalkylbenzene has a monocyclic cycloalkyl group with 5 to 10 (preferably 6 to 8) carbon atoms. Particularly preferred examples include cyclohexolbenzene (CHB), cycloheptanylbenzene, and cyclooctanylbenzene. Of these, CHB is preferred. Fig. Figure 5 schematically represents the conductive material. 58 that CHB is holding (it is loaded with it). In the Fig. In example 5, the surface of the conductive material is shown. 58 chemically modified by CHB.

[0034] In the lithium-ion secondary battery using this design 100A compound containing a saturated cyclic hydrocarbon group (such as CHB) will be formed, which, as previously described, attaches to the conductive material. 58is held in place (is charged). According to this design, since the compound containing the saturated cyclic hydrocarbon group is normally held to the conductive material (namely, during the time the battery is used within its normal charge and discharge range), problems that can occur with a compound dispersed in the electrolyte (such as a decrease in power output characteristics due to the compound inhibiting the theoretical diffusion of lithium ions and anions in the electrolyte) can be avoided. Furthermore, the pressure in the battery casing rises very rapidly due to the generation of gas originating from the aforementioned compound when the battery is overcharged. As a result, the current cutoff mechanism can fail. 19 to be triggered at the right time. According to the current design, the lithium-ion secondary battery can be...100 will be provided that demonstrates high performance (for example, in terms of low resistance) as well as superior stability.

[0035] Furthermore, according to the present design, if the voltage reaches a predetermined voltage or more (overcharged state), even if gas can be generated that originates from the aforementioned compound comprising a saturated cyclic hydrocarbon group, this effect is assumed to be related to the dissolution of a proton (H). + ) is realized by the saturated cyclic hydrocarbon group included in the compound. As an example, if the aforementioned compound is cyclohexylbezene (CHB), as in Fig. 6 shown, although CHB is normally attached to the conductive material 58The voltage is held in place when it reaches a predetermined voltage or higher (overcharged state), allowing electrons to pass through the conductive material. 58 extracted from the CHB and thus H + from the CHB, resulting in the formation of a double bond. The H +The hydrocarbons released from the CHB migrate to the negative electrode, where they are reduced, and this is thought to result in the generation of hydrogen gas at the negative electrode. However, the present invention can be easily carried out based on the information disclosed herein (as well as the structure of the compound comprising a saturated cyclic hydrocarbon group or the conductive material). Thus, the mechanism of action of the compound of the present invention, which comprises a cyclic hydrocarbon group, insofar as it relates to the generation of gas during overcharging, does not need to be understood in order to carry out the present invention. The description relating to the aforementioned mechanism of action is intended merely to provide an example thereof and is not intended to limit the present invention to the mechanism of action explained herein.

[0036] Although this is already clear from the aforementioned mechanism of action, the modified conductive material revealed here makes it possible 58 This ensures an adequate amount of gas during overcharging, even when no gas generator such as CHB or PB is present in the electrolyte. Consequently, during normal battery use, detrimental effects associated with the presence of a gas generator like CHB or PB in the electrolyte (such as a reduction in power output characteristics due to inhibition of phoretic diffusion of lithium ions or anions in the electrolyte) are avoided, while the current cutoff mechanism functions correctly. 90during overcharging. The content of the aforementioned compound with a saturated cyclic hydrocarbon group used in the positive electrode active material layer of the lithium-ion secondary battery disclosed herein is suitably approximately 0.5% by mass or more, preferably 0.8% by mass or more, and particularly preferably 1% by mass or more, based on a value of 100% by mass for the total solids content of the positive electrode active material layer. If the content of the aforementioned compound is excessively low, the amount of gas generated during overcharging will be insufficient, which will delay the operation of the current cut-off mechanism. 90 ( Fig.1) can cause. On the other hand, if the content of the aforementioned compound is excessively high, the function of the conductive material will be hindered by the compound, potentially causing a decrease in battery performance (for example, with regard to battery capacity). From the perspective that the conductive material should be able to function properly, the content of the aforementioned compound is suitably approximately 8% by mass or less, preferably 4% by mass or less, and particularly preferably 2% by mass or less.

[0037] Various types of materials conventionally known to be suitable as conductive materials for lithium-ion secondary batteries, and which can be modified by the aforementioned compound containing a saturated cyclic hydrocarbon group, can be used without any particular restrictions as the conductive material (and typically in particulate form) employed in the lithium-ion secondary battery disclosed herein. Examples of conductive materials that can be used include carbon black, such as acetylene black (AB), Ketjen black, furnace black, or split carbon black, and other powdered carbon materials (such as graphite). AB is preferred. Although no particular restrictions exist in this regard, the mean particle diameter of the conductive material is approximately 100 nm to 1000 nm.Although there are also no particular restrictions on the proportion of conductive material present throughout the positive electrode active material layer (apart from the mass of the above-mentioned compound held to the conductive material), this proportion is usually approximately 0.5% by mass to 15% by mass (and preferably 1% by mass to 10% by mass and particularly preferably 2% by mass to 5% by mass).

[0038] Even if there are no particular restrictions on the process (chemical modification treatment) used to retain the aforementioned compound on the surface of the aforementioned conductive material, a process may preferably be used which, for example, consists of mixing an unmodified conductive material with a raw material of the aforementioned compound, followed by heating and stirring. For example, in the case of obtaining a conductive material by modifying its surface with CHB, the conductive material is placed in a reaction vessel equipped with a Liebig condenser and a stirrer, and the oxygen is removed from the interior of the oxidation vessel and replaced with argon, followed by the addition of 0-dichloromethane, tetrahydroforane (THF), and p-cyclohexylaniline and stirring at room temperature.After allowing cooling by standing, filtering, and washing the filtrate with acetone, the filtrate is dried to obtain a modified conductive material whose surface is modified with the aforementioned CHB. In this manufacturing process, the chemical modification of a conductive material using CHB can be carried out simply and efficiently, and the CHB-modified conductive material can be produced with advantageous productivity. Furthermore, the amount of the aforementioned compound (such as CHB) retained on the conductive material is determined by thermal analysis. For example, the amount can be determined by measuring the change in weight when an unmodified conductive material and a modified conductive material are scanned from 100°C to 500°C in the presence of flowing nitrogen using a thermogravimetric differential thermal analyzer (TG-DTA).In other words, the extent of the weight increase of the modified conductive material can be viewed as the amount of the aforementioned compound. Experimental examples

[0039] In the experimental examples, evaluation cells (lithium-ion secondary batteries) were fabricated using a modified conductive material chemically modified with CHB, followed by an overcharge test on the batteries and evaluation of their discharge characteristics. The following provides a detailed description of the procedure used.

[0040] The modified conductive material of the evaluation cell was prepared as described below. First, a conductive material in the form of acetylene carbon black (DENKI KAGAKU KOGYO KABUSHIKI KAISHA.) was placed in a reaction vessel equipped with a Liebig condenser and a stirrer. After removing oxygen and replacing the atmosphere in the reaction vessel with argon, 0-dichloromethane, tetrahydrophorane (THF, Aldrich INC.), and p-cyclohexylaniline (Wako Pure Chemical Industries, Ltd.) were added and stirred at room temperature. Isoamyl nitride was then added to the reaction product via syringe and heated. After allowing it to cool by standing, the reaction product was filtered, and the filtrate was washed with acetone, followed by drying to obtain a modified conductive material with CHB retained on it.

[0041] The positive electrode of the evaluation cells was manufactured as described below. First, a positive electrode active material in the form of LiNi was produced. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 powder, the aforementioned modified conductive material, and a binder in the form of PVDF in NMP were mixed in a mass ratio of 93:4:3 to produce a composition for a positive electrode active material layer. This composition for a positive electrode active material layer was applied in ribbon form to both sides of a long, sheet-shaped aluminum foil (positive electrode current collector) and dried to produce a positive electrode sheet with a positive electrode active material layer applied to both sides of the positive electrode current collector.

[0042] The negative electrode of the evaluation cells was manufactured as described below. First, a negative electrode active material (amorphous coated graphite), a binder (SBR), and a thickener (CMC) were mixed in water at a mass ratio of 98:1:1 to create a negative electrode active material layer. This negative electrode active material layer was then applied to both sides of a long, sheet-shaped copper foil (negative electrode current collector) to form a negative electrode sheet with a negative electrode active material layer on both sides of the current collector.

[0043] A porous polyethylene (PE) sheet was used for the separators of the evaluation cells. A non-aqueous electrolyte, obtained by taking a conducting salt in the form of LiPF6 at a concentration of approximately 1 mol / L in a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3:3:4, was used as the non-aqueous electrolyte for the evaluation cells.

[0044] A wound electrode assembly was fabricated by winding the positive and negative electrode sheets with two separator sheets sandwiched between them. The resulting wound electrode assembly was then placed, along with the non-aqueous electrolyte, into a cylindrical battery casing, followed by sealing the casing opening to achieve leak-tightness. The evaluation cells (lithium-ion secondary batteries) were assembled in this manner. The evaluation cells were equipped with a current-cut-off mechanism that interrupts the current flowing to the electrode assembly when the pressure inside the battery casing reaches or exceeds a predetermined level. Samples 1 to 11

[0045] In samples 1 to 10, evaluation batteries were fabricated while varying the CHB content based on a 100% by mass value for the total solids content of the positive electrode active material layer. Specifically, in samples 1 to 10, the CHB content was varied throughout the entire positive electrode active material layer from 1% by mass to 8% by mass. The other conditions were the same. Additionally, in sample 11, a conventional conductive material that did not retain CHB was used instead of the conductive material mentioned above that retained CHB. Furthermore, CHB was added to the non-aqueous electrolyte at 4% by mass. The other conditions were the same as for samples 1 to 10. Battery capacity measurement

[0046] Each of the resulting evaluation cells from the aforementioned samples 1 to 11 was charged to a battery voltage of 4.1 V at a constant current of 1 C and in an atmosphere of 25°C, followed by charging at a constant voltage of 4.1 V down to a charging current of 1 / 10 C. Subsequently, the samples were charged to a voltage of 3.0 V at a constant current of 1 C, and the discharge capacity at this time of the constant current discharge was defined as the battery capacity. The results are presented in Table 1. The values ​​are shown here as relative values ​​based on a value of 100 for the battery capacity of sample 11. Discharge characteristic test

[0047] Each of the resulting evaluation cells from the aforementioned samples 1 to 11 was charged to a battery voltage of 3.7 V at a constant current of 1 C in an atmosphere at 25°C, followed by charging at a constant voltage of 3.7 V up to a charging current of 1 / 10 C. Subsequently, the cells were allowed to discharge for 10 seconds at a constant current of 10 C. The discharge resistance was then calculated as (voltage immediately before discharge - voltage after 10 seconds of discharge) / discharge current. The results are presented in the corresponding columns of Table 1. The values ​​are shown here as relative values ​​based on a value of 100 for the discharge resistance of the battery of sample 11. Overload test

[0048] Each of the resulting evaluation cells from the aforementioned problems 1 to 11 was charged to a battery voltage of 4.1 volts at a constant current of 1 C in an atmosphere at 25°C, followed by charging at a constant voltage of 4.1 V up to a charging current of 1 / 10 C (state of charge: 100%). Subsequently, the batteries were overcharged to a state of charge of 160% at a constant current of 1 C, followed by marking the batteries in which the current cut-off mechanism functioned with an "O" and those in which it did not function with an "X". The results are presented in the corresponding columns of Table 1. [Table 1] sample CHB content (% by weight) discharge resistor Battery capacity Overload test evaluation Positive electrode active material layer electrolyte 1 0,1 - 81 100 x 2 0,2 - 79 99 x 3 0,3 - 80 101 x 4 0,4 - 81 100 x 5 0,5 - 82 101 O 6 0,6 - 81 100 O 7 1 - 80 99 O 8 2 - 79 97 O 9 4 - 81 96 O 10 8 - 82 93 O 11 - 4 100 100 O

[0049] As shown in Table 1, in the battery casing corresponding to Sample 11, CHB was added to the electrolyte without being bound to the conductive material. In this Sample 11, the discharge resistance tended to increase compared to Samples 1 to 11, even though the current cutoff mechanism functioned correctly in the overcharge test. In contrast, in the batteries corresponding to Samples 5 to 10, the conductive materials held the CHB in place, and the CHB content throughout the entire positive electrode active material layer was 0.5% by mass or more. In these Samples 5 to 10, the current cutoff mechanism functioned appropriately in the overcharge test, and an adequate amount of gas was generated. Furthermore, compared to Sample 11, in which CHB was added to the electrolyte without being held by the conductive material, the discharge resistance was lower, and the power output characteristics were superior.Based on these results, it was confirmed that a high-performance (low-resistance) battery with superior stability is obtained by using a conductive material with CHB bound to it and by adjusting the CHB content throughout the entire positive electrode active material layer to 0.5% by mass or more. Furthermore, in a comparison of samples 5 to 10, the battery capacity tended to decrease as the CHB content increased throughout the entire positive electrode active material layer. In the case of the batteries used in this experiment, an extremely high battery capacity of 96 or more was achieved compared to sample 11 by adjusting the CHB content throughout the entire positive electrode active material layer to 4% by mass or less.Based on this result, the CHB content throughout the entire positive electrode active material layer is preferably approximately 4% by mass or less, and more preferably approximately 2% by mass or less.

[0050] Although the above has provided an explanation of a lithium-ion secondary battery according to one embodiment of the present invention, the secondary battery according to the present invention is not limited to the embodiment mentioned above, but can be modified in various ways. QUOTES INCLUDED IN THE DESCRIPTION

[0051] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0052] JP 2013-157139 [0002, 0003]

Claims

[1] Secondary battery with non-aqueous electrolyte, comprising: an electrode arrangement comprising a positive electrode in which a positive electrode active material layer is held on a positive electrode current collector, a negative electrode in which a negative electrode active material layer is held on a negative electrode current collector, and a separator that is intermediately located between the positive electrode and the negative electrode; a battery casing that accommodates the electrode assembly along with a non-aqueous electrolyte; an external connection provided in the battery housing and connected to the electrode assembly; and, a current cut-off mechanism that interrupts the electrical connection between the electrode assembly and the external terminal when the internal pressure of the battery casing reaches a predetermined pressure or more, wherein the positive electrode active material layer comprises a positive electrode active material and a conductive material, a compound comprising a saturated cyclic hydrocarbon group, is retained in at least part of the conductive material, and The content of the compound is 0.5% by mass or more, based on a value of 100% by mass for the total solids content of the positive electrode active material layer. [2] Secondary battery with non-aqueous electrolyte according to claim 1, wherein the content of the compound is 4% by mass or less based on a value of 100% by mass for the total solids content of the positive electrode active material layer. [3] Secondary battery with non-aqueous electrolyte according to claim 1 or 2, wherein the compound is constructed such that it is possible for protons to detach from the saturated cyclic hydrocarbon group when the voltage reaches a predetermined voltage or more. [4] Secondary battery with non-aqueous electrolyte according to any one of claims 1 to 3, wherein the saturated cyclic hydrocarbon group is a cyclohexyl group. [5] Secondary battery with non-aqueous electrolyte according to any one of claims 1 to 4, wherein the compound is cyclohexylbenzene. [6] Secondary battery with non-aqueous electrolyte according to any one of claims 1 to 5, wherein the non-aqueous electrolyte does not include a gas generator which produces gas when the voltage reaches a predetermined voltage or more.