JP2018137141A - Method for testing battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of a conventional test method that behaviors must be exactly grasped to determine a safety level in the event of an internal short circuit in considering uses and applications of a battery, but the safety of the internal short circuit cannot be evaluated correctly.SOLUTION: The invention is a method for evaluating the safety of a battery having an electrode group having a positive electrode, a negative electrode, and an insulator layer for electrical insulation between the positive and negative electrodes, an electrolyte solution, and an outer packaging body containing the electrode group and the electrolyte solution. The battery evaluating method comprises the steps of: assembling the battery in such a way that any one of the positive and negative electrodes is connected with the outer packaging body by a collector terminal of which the specific volume resistance is partially or totally 10×10Ωm or more to assemble; powering the battery to raise the temperature of the collector terminal, thereby causing the battery to generate heat; and evaluating the safety of the battery based on a state of heat generation by the battery.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a battery test method, a test apparatus, and a battery used for them.

  Among rechargeable batteries, lithium rechargeable batteries are small and have high energy density, so they have been attracting attention in recent years as power sources for portable devices and power sources for electric vehicles that require high capacity and high output. As a result, development has been actively conducted in each country, and there is an urgent need to realize safer and higher capacity batteries.

In a lithium secondary battery, there is an insulating layer between a positive electrode and a negative electrode that electrically insulates each electrode plate and holds an electrolyte.
When the lithium secondary battery is held in an extremely high temperature environment for a long time, the above-mentioned insulating layer easily contracts, so that the positive electrode and the negative electrode are in physical contact with each other to cause an internal short circuit, or the positive electrode, the negative electrode, and the insulating layer. Due to the conductive powder adhering to the surface, there was a tendency that the insulating layer was broken and the positive electrode and the negative electrode were electrically connected and an internal short circuit occurred.

  Particularly in recent years, the problem of internal short-circuiting is becoming more serious, coupled with the trend of thinning of the insulating layer accompanying the increase in capacity of lithium secondary batteries. Once an internal short circuit occurs, the short circuit part may further expand due to Joule heat associated with the short circuit current, and the battery may be heated and destroyed.

Even when an internal short circuit occurs in a battery, it is very important to ensure its safety, and techniques for improving the safety at the time of internal short circuit of a battery have been actively developed.
For example, a technique for printing an insulating layer made of ion-permeable ceramic particles and a binder on an electrode plate (see Patent Document 1) has been proposed.

  On the other hand, in order to ensure safety when an internal short circuit occurs, it is very important to correctly evaluate the safety of the battery when the internal short circuit occurs.

  Conventionally, as a safety evaluation item of a battery such as a lithium secondary battery, a battery evaluation test for evaluating a heat generation behavior at the time of an internal short circuit is UL standard for a lithium battery (UL1642), a guideline from a battery industry association (JIS B8714), etc. Has been enacted.

  These evaluation tests include, for example, a nail penetration test and a crush test.

  The nail penetration test is to observe changes in battery temperature, battery voltage, etc. based on Joule heat generated by a short-circuit current flowing through the nail through the nail by piercing the nail from the outside. . As a prior example of the patent (see Patent Document 2) (Fig. 4) is the closest to the nail penetration test method, the insulation resistance until reaching the current collector through the insulating layer with the nail is measured, and at the same time, the inside by foreign matter This is a test method that simulates a short circuit.

  In the crushing test, the battery is physically deformed by a round bar, a square bar, a flat plate or the like to cause an internal short circuit between the positive electrode and the negative electrode to observe changes in battery temperature, battery voltage, and the like.

Furthermore, a battery having a structure in which a destruction mechanism is provided inside the battery has been proposed in order to prevent smoke generation, ignition, and the like at the time of an internal short circuit in a single battery (see Patent Document 3).

  As shown in FIG. 5, when an external pressure is applied to a burr provided in the vicinity of the housing inside the battery, the burr is formed in a part of the second separator and spirally wound. An internal short circuit is generated between the outermost layer of the positive electrode and the outermost layer of the negative electrode of the electrode assembly, and the burrs provided on the negative electrode are also provided during the above-described crushing test by this destruction mechanism. However, since the battery voltage is lowered by opening a hole in the separator and causing a short circuit with the positive electrode plate, no smoke or ignition occurs.

  However, a battery provided with this destruction mechanism makes the manufacturing process of the battery difficult, and it cannot be denied that the provision of this destruction mechanism may reduce the safety of its own battery. In addition, since it is not possible to specify where in the battery an internal short circuit occurs due to contamination, the internal short circuit safety level of the battery evaluated by this destruction mechanism is not necessarily the internal short circuit safety level of the entire battery. Does not necessarily reflect. In addition, burrs charged inside the battery may cause a short circuit due to slight impact from the outside of the battery or expansion of the electrode plate due to charging, so it is a serious issue to ensure safety from battery manufacture to test execution. Exists.

Japanese Patent Laid-Open No. 10-106530 JP 2009-158266 A Japanese translation of PCT publication No. 2002-515637

  In considering the intended use of the battery, it is necessary to correctly grasp the behavior when an internal short circuit occurs and determine the level of safety.

  However, the conventional test method has a problem that the safety of the internal short circuit cannot be accurately evaluated.

  The reason for this is that conventional research has revealed that the behavior at the time of an internal short circuit varies greatly depending on the resistance of the short circuit point and the short circuit point in the battery.

  For example, a short circuit occurred simultaneously at the location where the positive and negative electrodes of the low resistance member in the vicinity of the current collector of the electrode are opposed to the location of the positive and negative electrodes of the high resistance member such as an electrode active material away from the current collector. At that time, most of the short-circuit current due to the short-circuit flows in the location facing the current collector with low resistance.

  As a result, the battery function (voltage) is reduced because most of the Joule heat is generated not at the active material facing part, which is not thermally stable, but at the facing part of the current collector, but it does not cause smoke or ignition, Apparently the safety of internal short circuit is judged high.

  Specifically, a battery having a configuration in which only the current collectors of both the positive electrode plate and the negative electrode plate are faced to the outer peripheral portion of the electrode group formed by winding the positive electrode plate, the separator, and the negative electrode plate. Exists. In such a configuration, in a test method using an external impact such as nail penetration or crushing, first, a short circuit occurs between the current collectors on the outer peripheral portion. As a result, a large amount of current flows through the current collector facing portion having low resistance, and the apparent internal short circuit safety is highly evaluated.

That is, in the conventional evaluation method, depending on the location where a short circuit occurs, even a battery that may be in a more dangerous state may be erroneously evaluated as a safe battery.

Furthermore, the burr described in Patent Document 3 is also very difficult to control the short-circuit resistance because the penetration level to the separator and the counter electrode differs depending on the micron-level shape of the burr tip. Since heat generation at the time of a short circuit depends on the resistance value generated by the Paris, it is very difficult to obtain a stable result even if a test is performed under the same conditions.
Therefore, in order to correctly evaluate the internal short-circuit safety of the battery, in view of the shape and components of the battery, avoid locations that would appear to be safely evaluated, and accurately control the amount of heat generated at the short-circuit point. is important.

  The present invention solves the above-mentioned conventional problems, can freely change the heat generation assuming an internal short circuit, can correctly grasp the behavior when an internal short circuit occurs, and further improve the safety of the battery at the time of the internal short circuit It is a battery testing method that enables accurate evaluation, and an object thereof is to provide a highly safe battery.

In order to achieve the above object, the present invention provides an outer package that includes a positive electrode, a negative electrode, an electrode group having an insulating layer that electrically insulates the positive electrode and the negative electrode, an electrolytic solution, and the electrode group and the electrolytic solution. A battery having a volume resistivity of 10 × 10 ⁻⁸ Ωm or more connected to either one of a positive electrode and a negative electrode, A battery evaluation method that evaluates the safety of the battery according to the heat generation state of the battery, and the process of heating the battery by raising the temperature of the current collecting terminal by passing a current through the battery. is there.

  By raising the temperature of the current collecting terminal by flowing current through the battery, it is possible to reproduce a heat generation state equivalent to Joule heat generated by an internal short circuit.

  The current collecting terminal that generates heat is configured by connecting materials having different volume resistivity in series so that heat is efficiently transmitted to the electrode group, and a portion of the current collecting terminal having a high volume resistance is connected to the electrode group. It is preferably in thermal contact.

  Similarly, in order to efficiently transfer heat to the electrode group, more than half of the portion between the electrode group and the exterior body of the current collecting terminal that generates heat is in contact with the electrode group. Preferably it is.

  Furthermore, in the current collecting terminal, when a portion other than the electrode group and the outer body electrically connected to the electrode group or the outer body is in electrical contact, the resistance of the current collecting terminal is expected to be reduced. The calorific value cannot be obtained, and the accuracy of the test may be reduced. Therefore, it is preferable that the portions other than the electrode group of the current collecting terminal and the externally connected body are electrically insulated.

  Another aspect of the present invention is an electrode group having a positive electrode, a negative electrode, an insulating layer that electrically insulates the positive electrode and the negative electrode, an electrolytic solution, and an outer package containing the electrode group and the electrolytic solution. A method for evaluating the safety of a battery having a positive electrode, a negative electrode, and a cross-sectional area that has a shape smaller in cross section than a connection portion connected to at least one of the positive electrode, the negative electrode, and an outer package. Connecting the current collector terminal so that the small portion of the battery contacts the electrode group, assembling the battery, raising the temperature of the current collector terminal by passing current through the battery, heating the battery, and heating the battery There is a battery evaluation method for evaluating the safety of the battery according to the state.

Furthermore, another aspect of the present invention provides a battery in which one or all of the positive electrode and the negative electrode are connected by a current collecting terminal having a volume resistivity of 10 × 10 ⁻⁸ Ωm or more, and a current is supplied to the battery. A battery testing device including a current source for flowing and a measuring device for measuring a heat generation state of the battery.

  With this configuration, it is possible to freely change the heat generation assuming an internal short circuit of the battery, it is possible to correctly grasp the behavior when an internal short circuit occurs, and to accurately evaluate the safety of the battery at the time of the internal short circuit The battery internal short circuit test method can be realized, and a highly safe battery can be provided.

  As described above, according to the battery testing method of the present invention, it is possible to freely change the heat generation assuming an internal short circuit, and more accurately grasp the behavior when an internal short circuit occurs, Safety can be accurately evaluated.

It is sectional drawing of the sealed secondary battery which has a general explosion-proof valve structure. It is a top view which shows the current collection terminal connection part which is an example of embodiment of this invention. It is a top view which shows the current collection terminal connection part which is an example of embodiment of this invention. It is a top view which shows the current collection terminal connection part which is an example of embodiment of this invention. It is a top view which shows the current collection terminal connection part which is an example of embodiment of this invention. It is a top view which shows the current collection terminal connection part which is an example of embodiment of this invention. It is a top view which shows the current collection terminal connection part which is an example of embodiment of this invention.

(battery)
In the battery of the present invention, a part or all of the positive and negative current collecting terminals use a material having a volume resistivity of 10 × 10 ⁻⁸ Ωm or more, more preferably 30 × 10 ⁻⁸ Ωm or more. It is characterized by. Generally, aluminum is used for the positive current collecting terminal, and copper or nickel is used for the negative current collecting terminal. Each volume resistivity, aluminum 2.8 × ^{10 -8} Ωm, copper 1.7 × ^{10 -8} Ωm, nickel is 6.9 × ^{10 -8} Ωm, to improve the output of the battery, and the battery A metal having a low resistance is used to reduce heat generation. In contrast, the battery of the present invention generates heat at the current collecting terminal using a material having a high volume resistivity. Examples of the material to be used include materials such as iron, SUS, nichrome, and Kanthal (iron chrome).

  When a part of the current collecting terminal is made of a material having a high volume resistivity, for example, nickel and nichrome are connected in series by a method such as ultrasonic welding or resistance welding. In this case, it is preferable to increase the ratio at which the material having a high volume resistivity contacts the electrode group. That is, in the case of a current collecting terminal in which nickel and nichrome are connected in series, a material having a higher volume resistivity of the current collecting terminal, that is, nichrome, is arranged and joined on the side electrically joined to the electrode group.

  An example of a current collecting terminal using materials having different volume resistivity is shown in FIG. The high resistance material using portion 203 of the current collecting terminal is connected to the current collector foil exposed portion 202 which is an uncoated portion of the electrode plate by the electrical connecting portion 204, and the low resistance material using portion 206 of the current collecting terminal is It is connected to the body case or the sealing plate by the electrical connection portion 207. The high resistance material using portion and the low resistance material using portion of the current collecting terminal are connected by a connecting portion 205 using ultrasonic welding or the like. A portion 208 between the electrode plate current collector foil of the current collecting terminal and the outer case is electrically insulated by an insulating tape 209.

  As shown in FIG. 3, an arrangement in which a high resistance material using portion 210 is sandwiched between low resistance material using portions 203 of current collecting terminals is also effective.

Furthermore, as shown in FIG. 4, it is more preferable that the high resistance member 210 is a wire and is bent to increase the resistance value and increase the heat generation efficiency.
In addition, the current collecting terminal of either the positive or negative electrode according to the present invention has a shape in which a terminal cross-sectional area is smaller than that around the connection portion in a part between the electrode group and the exterior body being electrically connected. Use electrical terminals.

  As an example of the current collecting terminal having the above-described shape, a shape in which the central portion of the current collecting terminal becomes narrow as shown in FIG. In creating the low cross-sectional area portion 212 in this way, the current collecting terminals are partially cut or created by electrically connecting current collecting terminals having different widths or thicknesses by ultrasonic welding or resistance welding. I can do it.

  Furthermore, the current collecting terminal that generates heat is positioned at the position of the electrical joint 204 between the current collecting terminal and the current collector foil exposed portion 202 of the electrode plate, as shown in FIG. 6, so that heat is efficiently transferred to the electrode group. It is preferable to adjust and increase the ratio at which the heat generating portion of the current collecting terminal contacts the electrode group. The heat generating portion refers to a portion having a high volume resistivity, a portion having a small cross-sectional area, or a central portion of the current collecting terminal between the electrical joints at both ends of the current collecting terminal.

  A resin sheet or tape can be used for the insulating tape 208 for electrically insulating the portions other than those electrically connected to the electrode group of the current collecting terminal and the exterior body. The resin is not particularly specified as long as it has insulating properties, but heat conduction such as imide resin or aramid resin is conducted to efficiently transmit heat generated at the current collector terminal to the electrode group and to ensure insulation even at high temperatures. It is preferable to use a resin material having a high degree of heat resistance.

  In recent years, lithium ion secondary batteries are mainly used as batteries. The negative electrodes of these lithium ion secondary batteries include graphite particles as a negative electrode active material. Here, the graphite particles are a general term for particles including a region having a graphite structure. Thus, the graphite particles include natural graphite, artificial graphite, graphitized mesophase carbon particles, and the like.

  The diffraction image of the graphite particles measured by the wide angle X-ray diffraction method has a peak attributed to the (101) plane and a peak attributed to the (100) plane. Here, the ratio of the peak intensity I (101) attributed to the (101) plane and the peak intensity I (100) attributed to the (100) plane is 0.01 <I (101) / I. (100) <0.25 is preferably satisfied, and 0.08 <I (101) / I (100) <0.2 is more preferably satisfied. The peak intensity means the peak height.

  The average particle size of the graphite particles is preferably 14 to 25 μm, and more preferably 16 to 23 μm. When the average particle diameter is within the above range, the slipping property of the graphite particles in the negative electrode mixture layer is improved, the filling state of the graphite particles is improved, and it is advantageous for improving the adhesive strength between the graphite particles. In addition, an average particle diameter means the median diameter (D50) in the volume particle size distribution of a graphite particle. The volume particle size distribution of the graphite particles can be measured by, for example, a commercially available laser diffraction type particle size distribution measuring apparatus.

The average circularity of the graphite particles is preferably 0.9 to 0.95, and more preferably 0.91 to 0.94. When the average circularity is included in the above range, the slipping property of the graphite particles in the negative electrode mixture layer is improved, which is advantageous in improving the filling properties of the graphite particles and the adhesion strength between the graphite particles. The average circularity is represented by 4πS / L ² (where S is the area of the orthographic image of graphite particles, and L is the perimeter of the orthographic image). For example, the average circularity of 100 arbitrary graphite particles is preferably in the above range.

The specific surface area S of the graphite particles is preferably 3 to 5 m ² / g, more preferably 3.5~4.5m ² / g. When the specific surface area is included in the above range, the slipperiness of the graphite particles in the negative electrode mixture layer is improved, which is advantageous for improving the adhesive strength between the graphite particles. Further, the preferred amount of the water-soluble polymer that covers the surface of the graphite particles can be reduced.

  In order to coat the surface of the graphite particles with a water-soluble polymer, it is desirable to produce a negative electrode by the following production method.

  A preferable method includes a step (step (i)) of mixing graphite particles, water, and a water-soluble polymer dissolved in water, and drying the obtained mixture to obtain a dry mixture. For example, a water-soluble polymer is dissolved in water to prepare a water-soluble polymer aqueous solution. The obtained water-soluble polymer aqueous solution and graphite particles are mixed, and then the water is removed and the mixture is dried. Thus, once the mixture is dried, the water-soluble polymer efficiently adheres to the surface of the graphite particles, and the coverage of the graphite particle surface with the water-soluble polymer is increased.

  The viscosity of the water-soluble polymer aqueous solution is preferably controlled to 1000 to 10,000 mPa · s at 25 ° C. The viscosity is measured using a B-type viscometer at a peripheral speed of 20 mm / s and using a 5 mmφ spindle. The amount of graphite particles mixed with 100 parts by weight of the water-soluble polymer aqueous solution is preferably 50 to 150 parts by weight.

A positive electrode will not be specifically limited if it can be used as a positive electrode of a nonaqueous electrolyte secondary battery. For the positive electrode, for example, a positive electrode mixture slurry containing a positive electrode active material, a conductive agent such as carbon black, and a binder such as polyvinylidene fluoride is applied to a positive electrode core material such as an aluminum foil, dried, and rolled. Can be obtained. As the positive electrode active material, a lithium-containing transition metal composite oxide is preferable. Typical examples of the lithium-containing transition metal composite oxide include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO _{2 and the} like.

  Especially, it is preferable that a positive electrode contains the complex oxide containing lithium and nickel from the point from which the effect which suppresses gas generation | occurrence | production while ensuring high capacity | capacitance is acquired more notably. In this case, the molar ratio of nickel to lithium contained in the composite oxide is preferably 30 to 100 mol%.

  The composite oxide preferably further contains at least one selected from the group consisting of manganese and cobalt, and the total molar ratio of manganese and cobalt to lithium is preferably 70 mol% or less.

  The composite oxide preferably further contains an element M other than Li, Ni, Mn, Co and O, and the molar ratio of the element M to lithium is preferably 1 to 10 mol%.

Specific lithium nickel-containing composite oxides include, for example, the general formula (1)
_{Li x Ni y M z Me 1-} (y + z) O 2 + d (1)
(M is at least one element selected from the group consisting of Co and Mn, Me is at least one element selected from the group consisting of Al, Cr, Fe, Mg, and Zn; 98 ≦ x ≦ 1.1, 0.3 ≦ y ≦ 1, 0 ≦ z ≦ 0.7, 0.9 ≦ (y + z) ≦ 1, −0.01 ≦ d ≦ 0 .01).

  As the separator, a microporous film made of polyethylene, polypropylene or the like is generally used. The thickness of the separator is, for example, 10 to 30 μm.

The present invention is applicable to batteries having various shapes such as a cylindrical shape, a flat shape, and a square shape, and the shape of the battery is not particularly limited. The electrode group is applicable not only to a wound type but also to an electrode group having a configuration in which a plurality of strip electrode plates are stacked.
(Safety evaluation)
A battery having such a configuration is manufactured, and a current source for supplying a current to the battery and a measuring device for measuring the heat generation state of the battery are connected to evaluate the safety of the battery.
Specifically, after adjusting to the target state of charge, the next test is performed.

  A charged battery is placed in a thermostatic chamber, and an ammeter for measuring current in the battery, a fixed resistor for adjusting the resistance of the circuit, and a switch for controlling connection of the circuit are connected in series. The circuit is short-circuited for a certain period of time with a switch while the ambient temperature is controlled. By gradually decreasing the fixed resistance of the circuit, the amount of heat generated at the heat generating portion of the current collecting terminal increases. At this time, by measuring the resistance of the heat generating portion of the current collecting terminal before assembling the battery, the amount of heat generated in the heat generating portion can be calculated from the current flowing in the short circuit.

  By determining the value of the fixed resistance that leads to thermal runaway by the above method and calculating the amount of heat at the heat generating part at that time, the safety of the battery can be accurately evaluated.

  In conducting the test, the battery charging voltage, environmental temperature, and short circuit time (heat generation time) can be changed according to the purpose of the evaluation.

  As a method of applying a current to the heat generation part, not only a short circuit of a circuit but also a method of applying a current by charging by arranging a power source instead of a fixed resistor is possible.

  The resistance of the heat generating part is better as the volume resistivity is higher for efficient heat generation. As a result, thermal runaway can occur without the state of charge of the battery changing significantly due to the application of current. However, when the battery is charged to the target state of charge before the test, it is necessary to reduce the charging current to a current value that does not ignite by increasing the resistance of the heat generating portion, so that a long charging time is required.

  For the above reasons, it is necessary to optimally adjust the resistance of the heat generating portion in view of the capacity of the battery, the amount of heat that leads to thermal runaway, and the time required for charging (test efficiency). That is, the optimum resistance value varies depending on the above factors.

  In addition, a heat_generation | fever location can be controlled by changing the welding position of a current collection terminal.

  Further, by using the internal short-circuit test method of the present invention, the following battery pack safety evaluation test can be performed.

  In other words, a battery pack is a battery pack in which a large number of batteries are connected in parallel and in series, but as mentioned in the background, in recent years, it has been actively developed for portable equipment power supplies and electric vehicles. The battery pack has been devised in various forms.

  However, due to the influence of high energy density, which is also a characteristic of lithium ion batteries, there is a problem that when one battery is destroyed and burned due to an internal short circuit, the adjacent batteries are also broken and burned.

  This is called the sinterability of the battery pack. Generally, in order to determine the sinterability of the battery pack, it is necessary to cause the battery serving as the base point to run out of heat.

  In order to generate a thermal runaway, a commonly used method is to pierce the battery with a nail to generate an internal short circuit. However, depending on the form of the battery pack, there are various levels such as two-stage and three-stage stacks, and it is impossible to pierce the battery hidden inside, and the sinterability of the battery pack cannot be correctly determined. There is.

  Furthermore, since the case is damaged by piercing with a nail, there is a possibility that similar firing spreads from the base point, and the accuracy of evaluation may be lowered.

  On the other hand, there is a method of mounting the heater on the side of the battery to cause thermal runaway, but the heat of the heater propagates to the pack structure and adjacent batteries in addition to the base battery, resulting in severe evaluation. .

  Furthermore, it is possible to cause thermal runaway by overcharging the battery, but the energy stored in the battery increases due to overcharging, which increases heat generation during thermal runaway, which is higher than the target condition. It becomes severe evaluation.

  As a means for evaluating the sinterability of this battery pack, a battery manufactured based on the internal short-circuit test method according to the present invention is incorporated in an arbitrary part of a battery pack used for an electric vehicle or the like, and this test method is used. By igniting and smoking the battery and evaluating whether or not other adjacent batteries are burnt down, the thermal effect on the pack structure and adjacent battery can be minimized and the nail can be inserted. It is possible to evaluate the firing based on the battery at the center of the pack that is not present.

  By performing a test using this method, it is possible to determine whether or not the sinterability is acceptable, and it is possible to take measures to improve the safety of the battery pack by improving the heat dissipation design and the layout design.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to a following example.

The battery 1 shown in FIG. 1 was produced as follows.
The positive electrode plate 101 used was an aluminum foil current collector coated with a positive electrode mixture, and the negative electrode plate 103 was a copper foil current collector coated with a negative electrode mixture.

The thickness of the separator 105 was 20 μm.
The positive electrode current collector terminal 102 and the aluminum foil current collector were laser welded. The positive electrode current collector terminal used had a width of 3 mm, a thickness of 0.3 mm, and a length of 50 mm.

The negative electrode current collector terminal 104 and the copper foil current collector were resistance welded. The negative electrode current collecting terminal had a width of 3 mm, a thickness of 0.3 mm, and a length of 50 mm. The negative electrode current collecting terminal 104 was electrically connected to the bottom of the metal bottomed case 108 by resistance welding.
As shown in FIG. 5, the electrical connection point is formed in a shape so that the distance 208 between the electrically connected copper foil current collector and the metal bottom case on the negative electrode current collector terminal is 20 mm. It was adjusted. Each electrical connection point was insulated using imide tape to prevent a short circuit other than at the connection point.

The positive electrode current collecting terminal 102 was electrically connected to the metal filter of the sealing plate 110 having an explosion-proof valve from the open end of the metal bottomed case 108 by laser welding. The position of the electrical connection point was adjusted so that the distance of the portion 208 between the electrical connection 204 and 207 between the electrode plate current collector foil of the current collector terminal and the outer case was 20 mm. Between each electrical connection point, the imide tape was insulated as the insulation tape 209 in order to prevent a short circuit other than a connection point like the negative electrode current collection terminal.

  A non-aqueous electrolyte was injected from the open end of the bottomed case 108 made of metal. A groove is formed in the open end of the metal bottomed case 108 to form a seat, the positive current collecting terminal 102 is bent, and a resin outer gasket 109 and a sealing plate 110 are attached to the seat of the metal bottomed case 108. Then, the entire periphery of the open end of the metal bottomed case 108 was caulked and sealed.

  (1) Fabrication of the negative electrode plate 103.

Step (i)
First, carboxymethyl cellulose (hereinafter, CMC, molecular weight 400,000), which is a water-soluble polymer, was dissolved in water to obtain an aqueous solution having a CMC concentration of 1% by weight. While mixing 100 parts by weight of natural graphite particles (average particle diameter 20 μm, average circularity 0.92, specific surface area 4.2 m ² / g) and 100 parts by weight of CMC aqueous solution, the temperature of the mixture is controlled at 25 ° C. Stir. Thereafter, the mixture was dried at 120 ° C. for 5 hours to obtain a dry mixture. In the dry mixture, the amount of CMC per 100 parts by weight of graphite particles was 1 part by weight.

Step (ii)
101 parts by weight of the obtained dry mixture, 0.6 parts by weight of a binder (hereinafter referred to as SBR) having a rubber elasticity, which is in the form of particles having an average particle size of 0.12 μm, and containing styrene units and butadiene units; .9 parts by weight of carboxymethyl cellulose and an appropriate amount of water were mixed to prepare a negative electrode mixture slurry. In addition, SBR was mixed with other components in the state of emulsion (BM-400B (trade name) manufactured by Nippon Zeon Co., Ltd., SBR weight ratio 40% by weight) using water as a dispersion medium.

Step (iii)
The obtained negative electrode mixture slurry was applied to both surfaces of an electrolytic copper foil (thickness 12 μm) as a negative electrode core material using a die coat, and the coating film was dried at 120 ° C. The weight of the applied negative electrode mixture was determined by designing so that the switching position between the 1st stage and the 2nd stage would be SOC 60% when the battery was charged at 4.2V. The switching position was designed based on the value obtained by preparing a battery using a negative electrode plate in advance and using a Li metal foil as a counter electrode, charging and discharging the battery, measuring the voltage and capacity, and the like.

Thereafter, the dried coating film was rolled with a rolling roller at a linear pressure of 0.25 ton / cm to form a negative electrode mixture layer having a thickness of 160 μm and a graphite density of 1.65 g / cm ³ . The negative electrode mixture layer was cut into a predetermined shape together with the negative electrode core material to obtain a negative electrode.

  (2) Fabrication of the positive electrode plate 101.

4 parts by weight of polyvinylidene fluoride (PVDF) as a binder is added to 100 parts by weight of LiNi _0.80 Co _0.15 Al _0.05 O _{2 as} a positive electrode active material, and an appropriate amount of N-methyl- It mixed with 2-pyro collector terminal (NMP), and the positive mix slurry was prepared. The obtained positive electrode mixture slurry was applied to both surfaces of a 20 μm thick aluminum foil as a positive electrode core material using a die coat, the coating film was dried, and further rolled to form a positive electrode mixture layer. . The positive electrode mixture layer was cut into a predetermined shape together with the positive electrode core material to obtain a positive electrode.

  (3) Preparation of non-aqueous electrolyte.

1 mol / liter in a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a weight ratio of V _EC : V _EMC : V _DMC = 20: 20: 60 LiPF ₆ was dissolved at a concentration of

  (4) Production of sealed secondary battery 1.

A separator 105 having a thickness of 20 μm is disposed between the positive electrode plate 101 and the negative electrode plate 103 and wound to form a cylindrical electrode group 112, which is then inserted into a metal bottomed case 108 and sealed to form a sealed nonaqueous electrolyte. A secondary battery 1 was obtained. This battery was a cylindrical battery having a diameter of 18 mm and a height of 65 mm, and the design capacity of the battery was 2750 mAh. The completed battery 1 was covered with a heat-shrinkable tube made of polyethylene terephthalate having a thickness of 80 μm as the battery can insulator 11 up to the outer edge of the top surface, and heat-shrinked with hot air of 90 ° C. to obtain a battery of Comparative Example 1.
Create evaluation battery pack.

  According to Table 1, the material and shape of the negative electrode current collector terminal (straight: Fig. 2, notch: Fig. 5), electrical connection position (20mm: Fig. 7, 40mm: Fig. 6), insulating tape (with or without sticking) As shown in FIG. 2, 1 to 5 batteries of comparative examples and 1 to 8 batteries of examples were prepared.

(test)
(1) Battery charging.

  The batteries of Comparative Examples and Examples in Table 1 can be charged at a constant current of 1.375 A (0.5 It) from the discharged state in the charging direction, and after 4.2 V is reached, the voltage can be maintained at 4.2 V. Thus, the current was reduced and constant voltage charging was performed. Charging was terminated when the current value reached 0.05A. (2) Exothermic test.

  The charged battery is placed in a thermostatic chamber, a power supply device for charging and discharging is connected to the battery, a thermocouple is attached to the center of the case so that the battery surface temperature can be measured, and 30 to 60 until it is stabilized at 25 ° C. Left for a minute.

  After the above preparation was completed, an exothermic test was performed by applying current to the batteries of Comparative Examples and Examples in Table 1. The test conditions performed and the results are shown in Table 2.

  In Comparative Examples 1 and 2, a material generally used in the past was used and a constant current of 10 A corresponding to 3 It was passed, but thermal runaway could not be generated. Similarly, in Comparative Example 3, although the current value and the energization time were increased, the battery temperature increased, but the state of charge of the cell changed due to the discharge, and the battery became safe (SOC 31% = SOC 100% −ΔSOC 69%). As a result, thermal runaway did not occur. When the current value was further increased, the current was interrupted by the safety mechanism of the battery and the test could not be performed. In Example 4, the test was carried out by repeating charging and discharging for 5 seconds each so that the SOC of the battery did not change due to thermal runaway current application. As a result, although the thermal runaway could be generated, the temperature of the battery reached 150 ° C. or higher, which was a test that is difficult to say as safety evaluation in an environment at 25 ° C.

  On the other hand, the battery of Example 1 of the present invention was able to generate thermal runaway by replacing the negative electrode lead with a nichrome material and energizing the current value 10A for 2 seconds. Since the thermal runaway could be generated in a very short time, the battery temperature and SOC could be tested in the same state as before energization.

In the same manner as in Example 1, in Examples 2 to 5, a thermal runaway test was performed on a battery prepared using metal materials having different volume resistivity for the current collector terminal of the negative electrode. Thermal runaway could be generated under the conditions shown in Table 2, but in the case of a material having a volume resistivity of 10 × 10 ⁻⁸ Ωm to 30 × 10 ⁻⁸ Ωm as in Example 2, the current value was increased. In addition, it was necessary to lengthen the energization time, and as a result, it was confirmed that the charging state and temperature of the battery were not affected. In addition, when the current is increased, it is difficult to apply a sufficient current in the discharging direction due to the battery voltage, and thus the current is applied in the charging direction. However, heat generation is equivalent to heat generation in both the charging direction and the discharging direction. As described above, since there is a concern about the influence on the state of the battery such as SOC and temperature, the volume resistivity is more preferably 30 × 10 ⁻⁸ Ωm or more.
On the other hand, in Example 6, a lead having a width of 3 mm is cut out to a width of 1 mm, and the line resistance is increased by reducing the cross-sectional area. Even with this method, thermal runaway could be generated.

  In Example 7, it was confirmed that the current value required for the thermal runaway increased by removing the insulation of the current collecting terminal. This is presumably because the current that should flow to the current collector terminal is shunted when the current collector terminal comes into contact with the case or the current collector foil to cause a short circuit, and the heat generation at the current collector terminal is reduced. For this reason, it is preferable to insulate the current collecting terminal in order to generate thermal runaway more efficiently.

  In Example 8, the change in the SOC of the battery was suppressed to the minimum by repeating the charging and discharging every 5 seconds, and a thermal runaway could be generated.

  Thus, it was confirmed that by using the test method of the present invention, it was possible to reproduce a phenomenon equivalent to an internal short circuit due to contamination of a battery.

  In the examples, the negative electrode side current collecting terminal was examined, but the same effect can be obtained also in the positive electrode side current collecting terminal.

  As described above, according to the present invention, there is provided a battery capable of accurately performing an evaluation assuming an internal short circuit test for battery safety evaluation.

DESCRIPTION OF SYMBOLS 1 Battery 11 Battery can insulator 101 Positive electrode plate 102 Positive electrode current collection terminal current collector 103 Negative electrode plate 104 Negative electrode current collection terminal current collector 105 Separator 106 Upper insulation plate 107 Lower insulation plate 108 Case 109 Gasket 109 Resin outer gasket 110 Sealing Plate 111 Positive electrode terminal 112 Electrode plate group 113 Groove 114 Gas discharge port 201 Mixture application part 202 Current collector foil exposed part 203 High resistance material use part 204 Electrical connection part 205 Connection part 207 Welding part 209 Insulation tape 210 High resistance member 212 Low cross-sectional area of current collector terminal

Claims (8)

Safety of a battery having a positive electrode, a negative electrode, an electrode group in which the positive electrode and an insulating layer that electrically insulates the negative electrode are laminated, an electrolytic solution, and an outer package containing the electrode group and the electrolytic solution A method for evaluating sex,
A process of assembling a battery by connecting to either one of the positive electrode and the negative electrode with a current collecting terminal having a volume resistivity of 10 × 10 ⁻⁸ Ωm or more.
Causing the battery to generate heat by raising the temperature of the current collector terminal by passing an electric current through the battery;
And a step of evaluating the safety of the battery according to the heat generation state of the battery. Safety of a battery having a positive electrode, a negative electrode, an electrode group in which the positive electrode and an insulating layer that electrically insulates the negative electrode are laminated, an electrolytic solution, and an outer package containing the electrode group and the electrolytic solution A method for evaluating sex,
Either one of the positive electrode and the negative electrode has a shape having a smaller cross section than a connecting portion connected to at least one of the positive electrode, the negative electrode, and the outer package, and a portion having a small cross-sectional area is in contact with the electrode group. Connecting the current collector terminals to assemble the battery,
Increasing the temperature of the current collecting terminal by passing an electric current through the battery, and heating the battery;
And a step of evaluating the safety of the battery according to the heat generation state of the battery.   The current collector terminal is configured by serially connecting materials having different volume resistivity, and a portion of the current collector terminal having a high volume resistance is in contact with the electrode group. 1 or 2 battery testing method.   The part between the said electrode group of the said current collection terminal and the said exterior body is contacting the said electrode group more than half, The said electrode group is characterized by the above-mentioned. Battery testing method.   The portion of the current collector terminal other than that electrically connected to the electrode group and the exterior body is electrically insulated from the electrode group, the exterior body, or both. The battery testing method according to any one of 1 to 4. The battery testing method according to claim 1, wherein the current collecting terminal is 30 × 10 ⁻⁸ Ωm or more. A battery having a positive electrode, a negative electrode, an electrode group in which the positive electrode and an insulating layer that electrically insulates the negative electrode are laminated, an electrolytic solution, and an outer package containing the electrode group and the electrolytic solution. And
A battery in which a current collector terminal having a volume resistivity of 10 × 10 ⁻⁸ Ωm or more is connected to one of the positive electrode and the negative electrode. A battery in which a collector terminal having a volume resistivity of 10 × 10 ⁻⁸ Ωm or more is connected to either one of the positive electrode and the negative electrode;
A current source for passing current through the battery;
A battery testing device including a measuring device for measuring a heat generation state of the battery.

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