JP2015138665A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery arranged so that the safety when it is overcharged can be ensured without using a current interrupt device (CID).SOLUTION: A nonaqueous electrolyte secondary battery comprises a battery exterior body with no CID, and in the battery exterior body, a positive electrode, a negative electrode, a separator and a nonaqueous electrolyte. The separator has a shutdown function. The positive electrode includes LiNiCoMO(where a+b+c=1; 0<a<1; 0<b<1; 0<c<1; M is at least one of Mn and Al). The negative electrode includes a graphite-based negative electrode active material. The nonaqueous electrolyte includes cyclohexylbenzene. Supposing that the total capacitance of the negative electrode is x, and the content of the cyclohexylbenzene in the nonaqueous electrolyte is y, a point (x,y) falls within a polygonal region having five apices consisting of: (14.82, 0.05); (34.19; 0.3); (34.19, 4.5); (19.95, 5.3) and (14.82, 5.5).

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

  Various attempts have been made to ensure safety during overcharging of nonaqueous electrolyte secondary batteries. For example, Japanese Patent Laying-Open No. 2013-149456 (Patent Document 1) discloses a battery in which a separator is softened and melted at a predetermined shutdown temperature (Ts) to lose its porosity.

JP 2013-149456 A

  In non-aqueous electrolyte secondary batteries, ensuring safety during overcharging is one of the important issues, and various strict standards have been established. Therefore, multiple measures have been taken for non-aqueous electrolyte secondary batteries for the purpose of interrupting current during overcharge. For example, in addition to the separator having a shutdown function disclosed in Patent Document 1, a battery exterior body having a current interruption mechanism (CID: Current Interrupt Device) is widely used.

  Here, CID is a mechanism or device that physically cuts the current path when the internal pressure of the battery reaches a predetermined value, and is generally used with an overcharge additive for increasing the internal pressure during overcharge. The overcharge additive is oxidatively decomposed at a predetermined voltage to generate gas, and thus the CID is activated, so that overcharge exceeding the voltage can be prevented.

  However, the CID may malfunction due to vibration or impact. In particular, in applications where vibration is inevitable, such as in-vehicle applications, there is concern about CID malfunction. In addition, it cannot be denied that multiple safety measures have led to an increase in battery prices.

  When the non-aqueous electrolyte secondary battery is configured not to have a CID, it is necessary to cut off the current by shutting down the separator. In this case, however, current interruption is incomplete due to thermal contraction of the separator. In other words, a temperature difference (temperature unevenness) occurs between the center and the outer periphery of the electrode body during overcharging, and the separator itself heat shrinks at the center of the electrode body at a high temperature, closing the pores of the separator. Even if it is made, the positive electrode and the negative electrode come into contact with each other, resulting in a short circuit.

In recent years, the shape of the battery for in-vehicle use has become the mainstream from the viewpoint of effective use of space. However, the square battery has poor heat dissipation compared to a laminated battery or the like, and temperature unevenness tends to occur in the thickness direction of the battery. This tendency becomes more prominent as the battery size increases. From the viewpoint of Li ⁺ acceptability, it is preferable that the capacitance of the negative electrode is large. However, as the negative electrode capacitance increases, the amount of heat generated by the negative electrode material also increases, which increases the increase in temperature unevenness. Under such circumstances, it has been extremely difficult to ensure safety during overcharge without using a CID.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a nonaqueous electrolyte secondary battery in which safety during overcharge is ensured without using CID. It is in.

  The present inventor conducted intensive research to solve the above-mentioned problems. As a result, cyclohexylbenzene (CHB: CycloHexylBenzene), which has been added to operate CID, and the total capacitance of the negative electrode satisfy a specific relationship. As a result, the inventors have obtained new knowledge that the temperature unevenness of the electrode body can be alleviated during overcharging, and have completed the present invention by further research based on the knowledge. That is, the nonaqueous electrolyte secondary battery of the present invention has the following configuration.

  (1) A nonaqueous electrolyte secondary battery includes a battery outer package, and a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte inside the battery outer package. This battery exterior body does not have a current interrupting mechanism that operates when the internal pressure increases.

The separator has a shutdown function of closing the pore size by increasing the temperature, the positive electrode is an _{LiNi a Co b M c O 2} ( provided that a + b + c = 1,0 < a <1,0 <b <1,0 <c <1 , M is at least one of Mn and Al.), The negative electrode includes a graphite-based negative electrode active material, and the non-aqueous electrolyte includes cyclohexylbenzene.

  When the total capacitance of the negative electrode when the frequency is 0.1 Hz in AC impedance measurement is x [unit: F], and the content of cyclohexylbenzene in the nonaqueous electrolyte is y [unit: mass%], xy orthogonality is obtained. In the coordinates, the point (x, y) is the point (14.82, 0.05), the point (34.19, 0.3), the point (34.19, 4.5), the point (19.95, 5 .3) and a point (14.82, 5.5) are included in a polygonal region having apexes at five points.

  In the above non-aqueous electrolyte secondary battery, CHB has a property of generating heat during overcharge. According to the research of the present inventor, when the content of CHB in the non-aqueous electrolyte and the total capacitance of the negative electrode satisfy the above relationship, the outer peripheral portion of the electrode body rises in temperature due to the heat generated by CHB. The temperature difference between the outer peripheral portion and the outer peripheral portion is reduced, and local heat shrinkage of the separator can be prevented. As a result, the separator can be shut down uniformly over the entire area, and thus safety during overcharging is ensured even for a battery that does not use CID.

  Here, the “total capacitance of the negative electrode” indicates the total amount of capacitance of the negative electrode mixture contained in the nonaqueous electrolyte secondary battery. A method for measuring the capacitance per unit mass of the negative electrode mixture (AC impedance measurement) will be described later.

  (2) The non-aqueous electrolyte secondary battery is a prismatic battery, and includes an electrode body that is wound so that the positive electrode and the negative electrode face each other with a separator interposed therebetween, and the positive electrode and the negative electrode are wound around the electrode body. It is preferable that a non-coating portion is provided at the end of the rotating shaft, and the non-coating portion constitutes a current collector.

  Conventionally, such a battery configuration has been particularly susceptible to temperature unevenness, so CID has been essential. However, since the total capacitance of the negative electrode and the content of CHB in the nonaqueous electrolyte satisfy the above relationship, CID Safety during overcharging can be ensured without using a battery.

  (3) The non-aqueous electrolyte secondary battery preferably has a rated capacity of 23 Ah or more. Conventionally, large high-capacity batteries with a rated capacity of 23 Ah or more have large temperature unevenness and CID is essential, but the total capacitance of the negative electrode and the content of CHB in the nonaqueous electrolyte satisfy the above relationship. Safety without overcharge can be ensured without using CID.

  ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte secondary battery with which the safety | security at the time of overcharge was ensured without using CID is provided.

It is a graph which shows the relationship between the total capacitance of the negative electrode in the nonaqueous electrolyte secondary battery which concerns on one Embodiment of this invention, the cyclohexylbenzene content of a nonaqueous electrolyte, and an overcharge test result. It is a graph which shows the result of the differential scanning calorimetry of the graphite type negative electrode active material concerning one Embodiment of this invention. It is a typical perspective view showing an example of the composition of the nonaqueous electrolyte secondary battery concerning one embodiment of the present invention. 1 is a schematic cross-sectional view illustrating a capacitance measurement cell according to an embodiment of the present invention.

  Hereinafter, an embodiment of the present invention (hereinafter referred to as “the present embodiment”) will be described in detail, but the present embodiment is not limited thereto.

<Nonaqueous electrolyte secondary battery>
FIG. 3 is a schematic perspective view showing an example of the configuration of the nonaqueous electrolyte secondary battery of the present embodiment. The battery 1000 shown in FIG. 3 is a square battery. The battery outer package 500 is an outer package that does not have a CID, and incorporates an electrode body 400 that is wound so that the positive electrode 100 and the negative electrode 200 face each other with the separator 300 interposed therebetween, and a nonaqueous electrolyte.

  The electrode body 400 has a positive electrode non-coated portion 100a where the positive electrode current collector is exposed at one end of the winding shaft, and a negative electrode non-coated portion 200a where the negative electrode current collector is exposed at the other end. doing. The positive electrode non-coated portion 100a is collectively welded to the positive electrode current collecting member 100b, and the negative electrode non-coated portion 200a is collectively welded to the negative electrode current collecting member 200b, and each constitutes a current collecting portion. The positive electrode current collecting member 100b is connected to the positive electrode terminal 100c provided in the battery outer package 500, and the negative electrode current collector member 200b is also provided in the battery outer package 500 and connected to the negative electrode terminal 200c. Hereinafter, each part which comprises the battery 1000 is demonstrated.

(Negative electrode)
The negative electrode 200 is a long strip-shaped sheet member, and a negative electrode mixture layer containing a graphite-based negative electrode active material is fixed on a negative electrode current collector (for example, Cu foil). The negative electrode 200 has a negative electrode non-coated portion 200a in which the negative electrode current collector is continuously exposed at one end in the width direction.

  The negative electrode mixture layer is composed of a negative electrode mixture containing a graphite-based negative electrode active material and a binder. The graphite-based negative electrode active material may be either natural graphite or artificial graphite. As the binder, for example, carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) can be used. The negative electrode mixture layer is formed, for example, by applying a negative electrode mixture slurry obtained by kneading a graphite-based negative electrode active material, CMC, and SBR in water onto a negative electrode current collector, drying, and further rolling. The

As shown in FIG. 1, in this embodiment, the total capacitance of the negative electrode 200 needs to be 14.82F or more and 34.19F or less. Here, since the total capacitance of the negative electrode 200 is equal to the total amount of charges that can be adsorbed to the negative electrode 200, it can be considered as an index indicating the reactivity of the negative electrode 200. As described above, when the total capacitance of the negative electrode is increased, the Li ⁺ acceptability is improved. On the other hand, the calorific value of the negative electrode is increased.

  FIG. 2 is a graph showing the results of differential scanning calorimetry (DSC) in a mixture of a negative electrode (SOC 100%) containing graphite-based negative electrode active material and ethylene carbonate (EC). The sample A and the sample B shown in FIG. 2 have different capacitances, and the sample A has a larger capacitance than the sample B. As can be seen from FIG. 2, the sample A having a large capacitance generates a larger amount of heat than the sample B in the range of 100 ° C. to 220 ° C. Therefore, it is considered that when the total capacitance of the negative electrode increases, the temperature unevenness of the electrode body increases. Therefore, in the prior art, the total capacitance of the negative electrode has been limited to a range of less than 14.82 F due to concern about the amount of heat generated during overcharging.

  However, the present inventor conducted a detailed investigation on the relationship between the total capacitance of the negative electrode and the safety during overcharge, and found that the total capacitance of the negative electrode was 14.82F or more and 34.19F or less, which was a much larger range than before. However, when CHB was added to the non-aqueous electrolyte in a specific range, a surprising result was obtained that the safety during overcharging was significantly improved.

  Specifically, when the total capacitance of the negative electrode is x [F] and the CHB content of the nonaqueous electrolyte is y [mass%], the point (x, y) is the point (14.82) in the xy orthogonal coordinates. 0.05), point (34.19, 0.3), point (34.19, 4.5), point (19.95, 5.3) and point (14.82, 5.5) It is clear that the safety at the time of overcharging is improved to the extent that no CID is required when it is included in a polygonal region having the five points as vertices (hereinafter referred to as “region α”). The reason for this is that by using a negative electrode with a large calorific value and adding CHB that generates heat during overcharging to the non-aqueous electrolyte, the temperature of the outer periphery of the electrode body 400 rises and temperature unevenness of the electrode body 400 is eliminated. This is considered to be because the separator 300 can be shut down uniformly at an early stage.

(Measurement method of capacitance)
The total capacitance of the negative electrode can be calculated by multiplying the “capacitance per unit mass of the negative electrode mixture” by the “total weight of the negative electrode mixture layer (total coating mass during drying)”. The capacitance per unit mass of the negative electrode mixture (at a frequency of 0.1 Hz) can be measured as follows.

First, two measurement samples (for example, 21.15 cm ² ) are cut out from the negative electrode 200. Next, referring to FIG. 4, the first measurement sample 62a and the second measurement sample 62b are opposed to each other with the measurement separator 61 interposed therebetween, and an electrode group is manufactured. Further, using the electrode group and a non-aqueous electrolyte (for example, LiPF ₆ = 1.0 mol / L, EC: DMC: EMC = 1: 1: 1), a measurement cell 60 having two measurement samples as counter electrodes. (A beaker cell or a laminate cell) is produced. Then, AC impedance measurement is performed in a 25 ° C. environment using the measurement cell 60, and the impedance Z (f) obtained with respect to the frequency (f) in a predetermined range is a group of relationships represented by the following formula (1). Using the equation, the electric double layer capacitance component C (f) for the frequency in the predetermined range is converted. Then, by dividing C ′ (f) at a frequency of 0.1 Hz among the obtained C (f) by the mass of the negative electrode mixture of the first measurement sample 62a or the second measurement sample 62b, “negative electrode” "Capacitance per unit mass of composite material". A conventionally known frequency response analyzer can be used for the AC impedance measurement. The measurement frequency range is, for example, about 0.1 to 100,000 Hz.

(Nonaqueous electrolyte)
The nonaqueous electrolyte of this embodiment is typically a liquid electrolyte in which a solute (lithium salt) is dissolved in an aprotic solvent. And in the nonaqueous electrolyte of this embodiment, CHB is added in the range of 0.05% by mass or more and 5.50% by mass or less, and the addition amount of CHB and the total capacitance of the negative electrode have the specific relationship described above. To meet. As long as the conditions are satisfied, the nonaqueous electrolyte may have any configuration.

  Examples of the aprotic solvent include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), γ-butyrolactone (GBL) and vinylene carbonate (VC), and dimethyl carbonate (DMC). , Chain carbonates such as ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) can be used. These aprotic solvents can be used in an appropriate combination of two or more from the viewpoint of electrical conductivity and electrochemical stability. In particular, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate, and the volume ratio of the cyclic carbonate to the chain carbonate is preferably about 1: 9 to 5: 5. Note that the nonaqueous electrolyte of the present embodiment may be in the form of a gel.

As the solute lithium salt, for example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N, Li (CF ₃ SO ₃ ) or the like can be used. Moreover, you may use 2 or more types together about these solutes. The concentration of the solute in the nonaqueous electrolyte is not particularly limited, but is preferably about 0.5 to 2.0 mol / L from the viewpoint of discharge characteristics and storage characteristics.

(Separator)
The separator 300 has a shutdown function. The shutdown temperature of the separator 300 is preferably about 110 ° C to 150 ° C, more preferably about 120 ° C to 140 ° C. For the separator 300, for example, a polyolefin-based microporous film, for example, a microporous film made of polyethylene (PE) or polypropylene (PP) is suitable. A plurality of microporous membranes may be laminated and used. The thickness of the separator 300 can be about 5-40 micrometers, for example. What is necessary is just to adjust suitably the hole diameter and porosity of the separator 300 so that air permeability may become a desired value.

(Positive electrode)
The positive electrode 100 is a long belt-like sheet member, and a positive electrode mixture layer containing a positive electrode active material is fixed on a positive electrode current collector (for example, an Al foil). The positive electrode 100 has a positive electrode non-coated portion 100a in which a positive electrode current collector is continuously exposed at one end portion in the width direction.

The positive electrode mixture layer is composed of a positive electrode mixture containing a positive electrode active material, a conductive additive, and a binder. In this embodiment, the positive electrode active material is a ternary positive electrode active material, that is, LiNi _a Co _b M _c O ₂ (where a + b + c = 1, 0 <a <1, 0 <b <1, 0 <c <1, M is at least one of Mn and Al. Examples of the positive electrode active material satisfying such a composition include LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.4 Co _0.3 Mn _0.3 O _2, LiNi _0.5 Co _0.3 Mn _0.2 O ₂ , LiNi _0.5 Co _0.3 Al _0.2. O ₂ etc. can be mentioned. The ternary positive electrode active material has a small calorific value near the shutdown temperature in a microporous membrane separator made of PE or PP. Therefore, by using the ternary positive electrode active material, the shutdown of the separator mainly depends on the heat generation on the negative electrode side. Therefore, for this embodiment in which the separator is shut down uniformly using the heat generation on the negative electrode side. convenient. In the above composition formula, M is more preferably Mn, and a, b, and c are more preferably 0.2 ≦ a ≦ 0.4, 0.2 ≦ b ≦ 0.4, 0.2 ≦ c ≦. It satisfies 0.4.

The positive electrode of the present embodiment may contain a positive electrode active material such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , and LiFePO ₄ in addition to the ternary positive electrode active material. The ratio of the ternary positive electrode active material to the total mass of the active material is preferably 50% by mass or more, and more preferably 75% by mass or more.

  For example, acetylene black (AB) or the like can be used as the conductive additive included in the positive electrode mixture, and polyvinylidene fluoride (PVdF) or the like can be used as the binder. For example, the positive electrode mixture layer is obtained by mixing a positive electrode mixture slurry obtained by kneading, for example, a positive electrode active material, a conductive additive, and a binder in a solvent such as N-methylpyrrolidone (NMP) on the positive electrode current collector. It is formed by coating, drying and rolling.

  Hereinafter, the present embodiment will be described in more detail using examples, but the present embodiment is not limited thereto.

<Example 1>
A rectangular non-aqueous electrolyte secondary battery having no CID was produced as follows, and an overcharge test was performed to evaluate safety.

(Preparation of positive electrode)
A positive electrode active material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), a conductive additive (AB), and a binder (PVdF) are kneaded in a solvent (NMP) to mix the positive electrode. A material slurry was obtained. The positive electrode mixture slurry was coated on a long strip-shaped Al foil, dried, and further rolled to obtain a positive electrode 100. The positive electrode 100 has a positive electrode non-coated portion 100a on one side in the width direction.

(Preparation of negative electrode)
A negative electrode mixture slurry was obtained by kneading a negative electrode active material (natural graphite powder), a thickener (CMC), and a binder (SBR) in water. The negative electrode mixture slurry was coated on a long strip of Cu foil, dried, and further rolled to obtain a negative electrode 200. The negative electrode 200 had the negative electrode non-coating part 200a on one side in the width direction.

Also as shown in Table 1 this time, one side basis weight of the negative electrode composite material layer was set to 7.3 mg / cm ^2, the coating area of the negative electrode material layer was 14500cm ^2. Moreover, when the capacitance per unit mass of the negative electrode composite material at a frequency of 0.1 Hz was measured according to the above-mentioned method, it was 0.14 F / g. Therefore, the total capacitance of the negative electrode is 14.82 F according to the following formula (2) (total capacitance of the negative electrode) = (capacitance per unit mass of the negative electrode mixture) × (weight per side) × (coating area). (2).

(Nonaqueous electrolyte adjustment)
EC, EMC, and DEC were mixed so that EC: EMC: DEC = 3: 5: 2 (volume ratio) to obtain an aprotic solvent. Next, a nonaqueous electrolyte was prepared by dissolving CHB (0.05 mass%) and LiPF ₆ (1.0 mol / L) in the aprotic solvent.

(assembly)
A microporous membrane separator (thickness 20 μm, shutdown temperature 130 ° C.) having a three-layer structure of PP / PE / PP was prepared as the separator 300. Then, referring to FIG. 3, a wound body is obtained by winding the separator 300 so that the positive electrode 100 and the negative electrode 200 face each other, and the wound body is press-molded to obtain an electrode body 400 (thickness). 20 mm). Here, the thickness of the electrode body 400 indicates the thickness in the direction of the arrow shown in FIG.

  Next, the prismatic nonaqueous electrolyte secondary battery according to Example 1 having a rated capacity of 23 Ah is obtained by inserting the electrode body 400 into the battery outer package 500 having no CID and injecting a nonaqueous electrolyte. It was.

<Examples 2-6 and Comparative Examples 1-7>
Change the capacitance per unit mass of the negative electrode mixture, the amount per unit area of the negative electrode, and the coating area so that the total capacitance of the negative electrode becomes the value shown in Table 1, and change the positive electrode and battery capacity design accordingly. Except for changing the amount of CHB added, prismatic nonaqueous electrolyte secondary batteries according to Examples 2 to 6 and Comparative Examples 1 to 7 were obtained in the same manner as Example 1.

<Evaluation>
The overcharge test of each battery was performed as follows, and the safety during overcharge was evaluated. The results are shown in Table 1. In the following description, “current value 1.0 C” indicates a current value for discharging the rated capacity of the battery in one hour.

(Overcharge test)
After performing CC-CV charging (current value: 1.0 C, CV voltage: 10 V, CV charging time: 10 minutes) in a 25 ° C. environment, the OCV was measured after being left for 10 minutes. And based on the measured OCV, the safety | security at the time of an overcharge was evaluated by the following 2 levels of "A" and "B".

A: OCV is 4.2 V or more B: OCV is 3.6 V or less Here, it can be evaluated that the higher the OCV after overcharging, the smaller the short circuit area and the better the safety during overcharging. In particular, if the OCV is 4.2 V or more, it can be said that a short circuit does not substantially occur and the safety is sufficient.

  The results were plotted on xy coordinates where the total capacitance of the negative electrode was x [F] and the CHB content of the nonaqueous electrolyte was y [mass%] (FIG. 1). In FIG. 1, the round legend indicates that “A: OCV is 4.2 V or higher”, and the rhombus legend indicates that “B: OCV is 3.6 V or lower”.

(Results and discussion)
(I) Comparative Example 2, Comparative Example 5, Comparative Example 6 and Comparative Example 7
In Comparative Examples 2, 5, 6 and 7, the OCV after overcharge was low, and the safety during overcharge was not sufficient. In the xy coordinates shown in FIG. 1, these comparative examples are located in a region that deviates upward from the region α (a lot of CHB) or a region that deviates to the right (the total capacitance of the negative electrode is large). Therefore, in these comparative examples, it is considered that the amount of heat generated due to CHB or the negative electrode becomes excessively large, and the thermal contraction of the separator occurs.

(Ii) Comparative Example 1 and Comparative Example 4
In Comparative Examples 1 and 4, the OCV after overcharging was low, and the safety during overcharging was not sufficient. In the xy coordinates shown in FIG. 1, these comparative examples are located in a region (the amount of CHB is small) deviated downward from the region α. Therefore, it is considered that the effect of suppressing temperature unevenness of the electrode body by CHB is small, the temperature unevenness is large, and the shutdown of the separator is not uniform.

(Iii) Examples 1-6
In Examples 1 to 6 in which the point (x, y) belongs to the region α with respect to these comparative examples, the OCV after the overcharge test is 4.2 V or more, and a short circuit has not substantially occurred. Therefore, it had sufficient safety. The reason for this is that by controlling the relationship between the amount of CHB added and the total capacitance of the negative electrode, the temperature unevenness in the thickness direction of the electrode body was greatly alleviated, and the shutdown of the separator occurred uniformly over the entire area. It is believed that there is.

From the above results, the battery exterior body includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte inside the battery exterior body, and the battery exterior body has a current blocking mechanism that is activated by an increase in internal pressure. not without having, the separator has a shutdown function of closing the pore size by increasing the temperature, the positive _{electrode, LiNi a Co b M c O} 2 ( provided that a + b + c = 1,0 < a <1,0 <b <1, 0 <c <1, M is at least one of Mn and Al.), The negative electrode includes a graphite-based negative electrode active material, the nonaqueous electrolyte includes cyclohexylbenzene, and AC impedance measurement Where the total capacitance of the negative electrode when the frequency is 0.1 Hz is x [F], and the content of the cyclohexylbenzene in the nonaqueous electrolyte is y [mass%], The point (x, y) is the point (14.82, 0.05), the point (34.19, 0.3), the point (34.19, 4.5), the point (19.95, 5. 3) and the nonaqueous electrolyte secondary battery according to the example included in the polygonal region having the five points consisting of the points (14.82, 5.5) as a vertex is safe at the time of overcharge without having a CID. It was confirmed that the battery was secured.

  Although the present embodiment and examples have been described as described above, it should be considered that the embodiments and examples disclosed this time are illustrative and not restrictive in all respects. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  60 measurement cell, 61 measurement separator, 62a first measurement sample, 62b second measurement sample, 100 positive electrode, 100a positive electrode non-coated portion, 100b positive current collecting member, 100c positive electrode terminal, 200 negative electrode, 200a Negative electrode non-coated portion, 200b negative electrode current collecting member, 200c negative electrode terminal, 300 separator, 400 electrode body, 500 battery outer body, 1000 battery, α region.

Claims (1)

A battery case;
Inside the battery exterior body, a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte,
The battery exterior body does not have a current interrupting mechanism that operates due to an increase in internal pressure,
The separator has a shutdown function that closes the hole diameter as the temperature rises,
The positive electrode is _{LiNi a Co b M c O 2} ( provided that a + b + c = 1,0 < a <1,0 <b <1,0 <c <1, M is at least one of Mn and Al. )
The negative electrode includes a graphite-based negative electrode active material,
The non-aqueous electrolyte includes cyclohexylbenzene,
In AC impedance measurement, when the total capacitance of the negative electrode when the frequency is 0.1 Hz is x [F] and the content of the cyclohexylbenzene in the non-aqueous electrolyte is y [mass%], in xy orthogonal coordinates The point (x, y) is the point (14.82, 0.05), the point (34.19, 0.3), the point (34.19, 4.5), the point (19.95, 5.3). ) And a point (14.82, 5.5), a non-aqueous electrolyte secondary battery included in a polygonal region having a vertex at five points.

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