JP2015176671A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous secondary battery in which a current interruption mechanism can be stably actuated.SOLUTION: A nonaqueous electrolyte secondary battery has an electrode body having a positive electrode in which a cathode active material layer containing cathode active material is held by a positive electrode collector, a negative electrode and a separator, a battery case in which the electrode body is accommodated together with nonaqueous electrolyte, an external terminal which is provided to the battery case and connected to the electrode body, and a current interruption mechanism for interrupting the electrical connection between the electrode body and the external terminal when the inner pressure of the battery case increases to a predetermined pressure or more. The nonaqueous electrolyte contains gas generating agent which is reacted with a predetermined voltage or more to generate gas, and the DBP absorption amount per 100 g of the cathode active material is not less than 23 mL to not more than 32 mL.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery containing a gas generating agent in a non-aqueous electrolyte.

  Lithium ion secondary batteries and other secondary batteries are becoming increasingly important as on-vehicle power supplies or personal computers and portable terminals. In particular, a lithium ion secondary battery that is lightweight and obtains a high energy density is preferably used as a high-output power source mounted on a vehicle. When such a secondary battery is overcharged, excessive charge carriers are released from the positive electrode, and excessive charge carriers are inserted into the negative electrode. For this reason, both the positive electrode and the negative electrode are thermally unstable. When both the positive electrode and the negative electrode become thermally unstable, the organic solvent of the electrolytic solution is eventually decomposed, and an exothermic reaction occurs, thereby impairing the stability of the battery.

  To deal with this problem, for example, the battery case is equipped with a current interruption mechanism that interrupts charging when the gas pressure inside the battery exceeds a predetermined pressure, and gas is generated when a predetermined overcharge state is reached in the nonaqueous electrolyte. A non-aqueous electrolyte secondary battery to which a gas generating agent to be added is added is disclosed. As such a gas generating agent, for example, cyclohexylbenzene (CHB) or biphenyl (BP) is used (for example, Patent Document 1). CHB and BP activate the polymerization reaction during overcharge and generate hydrogen gas. Thereby, the pressure in a battery case becomes high, an electric current interruption mechanism act | operates, and an overcharge electric current is interrupted | blocked.

JP 2012-119183 A

  In the overcharged state, in particular, since the potential of the positive electrode becomes high, the gas generating agent contained in the electrolyte that permeates the positive electrode active material layer reacts to generate gas. When the internal pressure of the battery case becomes higher than a predetermined pressure due to the generated gas, the current interrupt mechanism is activated to interrupt the current path and stop the battery reaction. However, according to the study by the present inventor, when a material having a large DBP absorption amount is used as the positive electrode active material, further adopting the above-described current interruption mechanism slows down the gas generation, and the current interruption mechanism operates. There were some late events. It is desirable that the current interruption mechanism operates stably when a predetermined condition is met.

  The proposed non-aqueous electrolyte secondary battery includes a positive electrode in which a positive electrode active material layer containing a positive electrode active material is held by a positive electrode current collector, and a negative electrode active material layer containing a negative electrode active material held in a negative electrode current collector. An electrode body comprising a negative electrode, a separator interposed between the positive electrode and the negative electrode, a battery case containing the electrode body together with a nonaqueous electrolyte, and provided in the battery case and connected to the electrode body And an electric current interruption mechanism that interrupts electrical connection between the electrode body and the external terminal when the internal pressure of the battery case becomes higher than a predetermined pressure. The non-aqueous electrolyte contains a gas generating agent that reacts at a voltage equal to or higher than a predetermined voltage to generate gas. The DBP absorption amount per 100 g of the positive electrode active material is 23 mL or more and 32 mL or less. According to such a configuration, the output at a low temperature can be secured by setting the DBP absorption amount of the positive electrode active material to 23 mL / 100 g or more. Moreover, the gas generation amount by a gas generating agent is more appropriately securable by making DBP absorption amount of a positive electrode active material into 32 mL / 100g or less. Therefore, the amount of gas generation can be increased while keeping the output characteristics high, and the current interrupt mechanism can be operated appropriately.

FIG. 1 is a diagram illustrating an example of the structure of a secondary battery. It is a graph which shows the relationship between DBP absorption amount, low temperature discharge resistance, and electric current interruption mechanism action | operation SOC.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. In the present specification, the “secondary battery” refers to a general power storage device that can be repeatedly charged and discharged, and is a term including a so-called storage battery such as a lithium ion secondary battery and a power storage element such as an electric double layer capacitor. The “lithium ion secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by the movement of lithium ions between positive and negative electrodes. The electrode active material refers to a material capable of reversibly occluding and releasing chemical species (lithium ions in a lithium ion secondary battery) serving as a charge carrier.

  Hereinafter, a non-aqueous secondary battery according to an embodiment of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected suitably to the member and site | part which show | play the same effect | action. Each drawing is schematically drawn and does not necessarily reflect the real thing. Each drawing shows an example only and does not limit the present invention unless otherwise specified. Hereinafter, embodiments of the present invention will be described by taking as an example the case where the present invention is applied to a lithium ion secondary battery, but it is not intended to limit the application target of the present invention.

  FIG. 1 shows a lithium ion secondary battery 100 according to an embodiment of the present invention. As shown in FIG. 1, the lithium ion secondary battery 100 includes a wound electrode body 20 and a battery case 30. As shown in FIG. 1, a lithium ion secondary battery 100 according to an embodiment of the present invention includes a flat rectangular battery case 20 having a flat wound electrode body 20 together with a liquid electrolyte (electrolytic solution) (not shown). That is, it is accommodated in the exterior container 30.

  The battery case 30 has a box-shaped (that is, bottomed rectangular parallelepiped) case body 32 having an opening at one end (corresponding to the upper end in a normal use state of the battery), and the opening attached to the opening. It is comprised from the cover body 34 which consists of a rectangular-shaped plate member which plugs up a part. The material of the battery case 30 is exemplified by aluminum, for example. As shown in FIG. 1, a positive electrode terminal 42 and a negative electrode terminal 44 for external connection are formed on the lid 34. A safety valve 36 is formed between both terminals 42 and 44 of the lid 34.

  The wound electrode body 20 includes a long sheet-like positive electrode (positive electrode sheet 50) and a long sheet-like negative electrode (negative electrode sheet 60) similar to the positive electrode sheet 50, in total, two long sheet-like separators (separators). 70).

  The positive electrode sheet 50 includes a strip-shaped positive electrode current collector 52 and a positive electrode active material layer 54. For the positive electrode current collector 52, for example, a strip-shaped aluminum foil having a thickness of about 15 μm is used. A positive electrode active material layer non-forming portion 52 a is set along an edge portion on one side in the width direction of the positive electrode current collector 52. In the illustrated example, the positive electrode active material layer 54 is held on both surfaces of the positive electrode current collector 52 except for the positive electrode active material layer non-forming portion 52 a set in the positive electrode current collector 52. The positive electrode active material layer 54 includes a positive electrode active material, a conductive material, and a binder.

  As the positive electrode active material, a material used as a positive electrode active material of a lithium ion secondary battery can be used. As an example of a positive electrode active material, an oxide (lithium transition metal) containing lithium and one or more transition metal elements (particularly at least one transition metal element of Ni, Co, and Mn) as constituent metal elements A positive electrode active material mainly composed of an oxide). For example, a conductive material such as acetylene black (AB) can be mixed with the positive electrode active material. In addition to the positive electrode active material and the conductive material, a binder such as polyvinylidene fluoride (PVdF), styrene butadiene rubber (SBR), or carboxymethyl cellulose (CMC) can be added. A positive electrode mixture (paste) can be prepared by dispersing these in a suitable dispersion medium and kneading. The positive electrode active material layer 54 is formed by applying this positive electrode mixture to the positive electrode current collector 52, drying it, and pressing it to a predetermined thickness.

  The negative electrode sheet 60 includes a strip-shaped negative electrode current collector 62 and a negative electrode active material layer 64. For the negative electrode current collector 62, for example, a strip-shaped copper foil having a thickness of about 10 μm is used. On one side in the width direction of the negative electrode current collector 62, a negative electrode active material layer non-formation part 62a is set along the edge. The negative electrode active material layer 64 is held on both surfaces of the negative electrode current collector 62 except for the negative electrode active material layer non-forming portion 62 a set in the negative electrode current collector 62. The negative electrode active material layer 64 includes a negative electrode active material, a thickener, a binder, and the like.

  As the negative electrode active material, one type or two or more types of materials conventionally used in lithium ion secondary batteries can be used without any particular limitation. Preferable examples include carbon-based materials such as graphite carbon. And like a positive electrode, this negative electrode active material is disperse | distributed to a suitable dispersion medium with binders, such as PVDF, SBR, and CMC (it can function also as a thickener), and knead | mixing a negative electrode mixture (paste). Can be prepared. The negative electrode active material layer 64 is formed by applying this negative electrode mixture to the negative electrode current collector 62, drying it, and pressing it to a predetermined thickness.

  The separator 70 is a member that separates the positive electrode sheet 50 and the negative electrode sheet 60. In this example, the separator 70 is composed of a strip-shaped base material having a predetermined width and having a plurality of minute holes. Examples of the base material include a sheet material having a single layer structure (for example, a single layer structure of polyethylene) made of a porous polyolefin-based resin, or a sheet material having a laminated structure (for example, a three-layer structure of polypropylene, polyethylene, and polypropylene). Can be used.

  The wound electrode body 20 is attached to electrode terminals 42 and 44 attached to the battery case 30 (in this example, the lid body 34). The wound electrode body 20 is housed in the battery case 30 in a state where the wound electrode body 20 is flatly pushed and bent in one direction orthogonal to the winding axis. In the wound electrode body 20, the positive electrode active material layer non-formed portion 52 a of the positive electrode sheet 50 and the negative electrode active material layer non-formed portion 62 a of the negative electrode sheet 60 protrude on the opposite sides in the winding axis direction. Among these, one electrode terminal 42 is fixed to the positive electrode active material layer non-forming portion 52 a of the positive electrode current collector 52 via the positive electrode current collector tab 42 a, and the other electrode terminal 44 is the negative electrode current collector 62. The negative electrode active material layer non-forming portion 62a is fixed via a negative electrode current collecting tab 44a. The wound electrode body 20 is accommodated in the flat internal space of the case body 32. The case body 32 is closed by the lid 34 after the wound electrode body 20 is accommodated.

As the non-aqueous electrolyte (typically a liquid non-aqueous electrolyte, hereinafter referred to as a non-aqueous electrolyte), the same non-aqueous electrolyte as that conventionally used for lithium ion secondary batteries is used without any particular limitation. be able to. Such a nonaqueous electrolytic solution has a composition in which a supporting salt is contained in a suitable nonaqueous solvent. As the non-aqueous solvent, for example, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, or the like can be used. Moreover, as said support salt, lithium salts, such as LiPF ₆ , can be used, for example.

  The non-aqueous electrolyte contains a gas generating agent that reacts and generates gas when the battery voltage becomes equal to or higher than a predetermined voltage. As such a gas generating agent, for example, cyclohexylbenzene (CHB) or biphenyl (BP) can be used. For example, when cyclohexylbenzene (CHB) and biphenyl (BP) are overcharged at about 4.35V to 4.6V, for example, the polymerization reaction is activated, and gas (here, hydrogen gas) is generated. Two or more kinds of gas generating agents are preferably used in combination, and one of them is preferably BP, and more preferably CHB and BP are used in combination. The amount of the gas generating agent added to the non-aqueous electrolyte is, for example, about 0.05% by mass to 4.0% by mass, preferably 0.1% by mass to 3% by mass. In addition, the addition amount of a gas generating agent is not limited to this, It is good to adjust so that a predetermined amount of gas may be generated on predetermined conditions. Further, the gas generating agent is not limited to cyclohexylbenzene (CHB) and biphenyl (BP).

  Further, the lithium ion secondary battery 100 includes a current interruption mechanism 90. The current interruption mechanism 90 is a mechanism that interrupts the current path when the pressure in the battery case becomes abnormally high. In this embodiment, as shown in FIG. 1, the current interruption mechanism 90 is constructed inside the positive electrode terminal 42 so that the conduction path of the battery current in the positive electrode is interrupted. The current interruption mechanism 90 is configured to interrupt the electrical connection between the electrode body 20 and the positive terminal 42 when the internal pressure of the battery case becomes higher than a predetermined pressure.

  Hereinafter, the lithium ion secondary battery 100 will be described in more detail. As described above, in the lithium ion secondary battery 100, the non-aqueous electrolyte contains a gas generating agent that reacts at a voltage equal to or higher than a predetermined voltage to generate gas. The DBP absorption amount per 100 g of the positive electrode active material in the positive electrode active material layer 54 is 23 (mL / 100 g) or more and 32 (mL / 100 g) or less.

  Here, the DBP absorption amount (mL / 100 g) is determined in accordance with JIS K6217-4 “Carbon black for rubber—Basic characteristics—Part 4: Determination of DBP absorption amount”. Here, DBP (dibutyl phthalate) is used as a reagent liquid, and the powder to be inspected is titrated with a constant speed burette, and a change in viscosity characteristics is measured with a torque detector. Then, the amount of reagent liquid added per unit weight of the inspection target powder corresponding to 70% of the generated maximum torque is defined as DBP absorption (mL / 100 g). The DBP absorption amount indicates how much the electrolytic solution impregnated in the positive electrode active material layer 54 can be absorbed by the positive electrode active material. That is, the higher the DBP absorption amount, the easier the electrolyte solution impregnated in the positive electrode mixture layer is absorbed by the positive electrode active material.

  According to the lithium ion secondary battery 100 according to the present embodiment, the DBP absorption amount of the positive electrode active material in the positive electrode active material layer 54 is 23 (mL / 100 g) or more. For this reason, the electrolytic solution impregnated in the positive electrode active material layer 54 is easily absorbed by the positive electrode active material, and the positive electrode active material layer 54 is unlikely to wither due to insufficient electrolyte. Therefore, output characteristics (particularly, output characteristics at a low temperature and a high rate at 10 C or higher) are improved. Furthermore, since the DBP absorption amount of the positive electrode active material in the positive electrode active material layer 54 is 32 (mL / 100 g) or less, the amount of gas generated by the gas generating agent can be more appropriately ensured. Therefore, the gas generation amount can be increased while keeping the output characteristics high, and the current interrupt mechanism 90 can be appropriately operated. That is, according to this configuration, in a lithium ion secondary battery containing a gas generating agent in the electrolyte, the amount of gas generation and output characteristics (especially low temperature) during overcharging are optimized by optimizing the DBP absorption amount of the positive electrode active material. In addition, it is possible to obtain an optimal lithium ion secondary battery that satisfies both of the output characteristics at a high rate of 10 C or more at a high level.

  From the viewpoint of improving the output characteristics, the DBP absorption amount of the positive electrode active material in the positive electrode active material layer 54 is suitably 23 (mL / 100 g) or more, preferably 25 (mL / 100 g) or more, Particularly preferably, it is 30 (mL / 100 g) or more. In addition, from the viewpoint of securing the amount of gas generated during overcharge, the DBP absorption amount of the positive electrode active material in the positive electrode active material layer 54 is suitably 32 (mL / 100 g) or less, preferably 30 ( mL / 100 g) or less, and particularly preferably 28 (mL / 100 g) or less. For example, a positive electrode active material having a DBP absorption amount of 25 (mL / 100 g) or more and 30 (mL / 100 g) or less is preferable from the viewpoint of satisfying both the gas generation amount and output characteristics during overcharge.

  The inventor conducted the following evaluation test. Then, the influence of the DBP absorption amount of the positive electrode active material on the output characteristics of the lithium ion secondary battery and the amount of gas generated during overcharge was examined. The evaluation cell was produced as follows.

The positive electrode of the evaluation cell was produced as follows. First, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ powder as a positive electrode active material, AB as a conductive material and PVdF as a binder have a mass ratio of 93: 4: 3. In this way, the mixture was mixed in NMP to prepare a positive electrode mixture. A positive electrode sheet having a positive electrode active material layer provided on both sides of the positive electrode current collector is prepared by applying the positive electrode mixture in a strip shape on both sides of a long sheet-like aluminum foil (positive electrode current collector) and drying it. did.

  The negative electrode of the evaluation cell was produced as follows. First, a negative electrode mixture was prepared by dispersing graphite as a negative electrode active material, SBR as a binder, and CMC as a thickener in water so that the mass ratio of these materials was 98: 1: 1. . This negative electrode mixture was applied to both sides of a long sheet-like copper foil (negative electrode current collector) to prepare a negative electrode sheet in which a negative electrode active material layer was provided on both sides of the negative electrode current collector.

  A porous polyethylene (PE) sheet was used as a separator for the evaluation cell.

As the non-aqueous electrolyte of the evaluation cell, a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3: 3: 4, and LiPF as a supporting salt. ₆ was used at a concentration of about 1 mol / liter. Further, 4% by mass of CHB and 1% by mass of BP were added to the nonaqueous electrolytic solution.

  The positive electrode sheet and the negative electrode sheet were wound through two separators, and the wound body was crushed from the side surface to produce a flat wound electrode body. The wound electrode body thus obtained was housed in a box-type battery case together with the non-aqueous electrolyte, and the opening of the battery case was hermetically sealed. Thus, a lithium ion secondary battery for evaluation was constructed. This lithium ion secondary battery includes a current interrupting mechanism that interrupts the current path when the pressure in the battery case increases.

  Samples 1 to 8 have different DBP absorption amounts (mL / 100 g) for the positive electrode active material. The configuration was the same except that the DBP absorption amount (mL / 100 g) of the positive electrode active material was different. Table 1 shows the DBP absorption of each sample.

<Output test>
A value obtained by dividing the voltage drop when the cell for evaluation of each sample was cooled at 0 ° C. for 10 seconds with a constant current of 10 C by the discharge current value was obtained as the low temperature discharge resistance. The results are shown in Table 1 and FIG. Here, the ratio is shown by the ratio of the discharge resistance when the low temperature discharge resistance of Sample 1 is 100%. This suggests that the lower the low-temperature discharge resistance, the better the output characteristics at low temperatures.

<Overcharge test>
The evaluation cell of each sample was charged with a current value of 1 C, and SOC (State Of Charge) at which the current interrupting mechanism was activated was measured. The results are shown in Table 1 and FIG. Here, the current interruption mechanism operation SOC of sample 1 is set to 0%, and the current interruption mechanism operation SOC of each sample is indicated by a difference from the current interruption mechanism operation SOC of sample 1. This suggests that the smaller the current interruption mechanism operation SOC, the more gas is generated during overcharge.

  As shown in Table 1 and FIG. 2, samples 1-4, 7, and 8 in which the DBP absorption amount (mL / 100 g) of the positive electrode active material was 23 or more were low-temperature discharge resistance compared to other samples 1 and 2 Is lower and the output characteristics are greatly improved. Thus, the tendency that the performance of the lithium ion secondary battery, in particular, the high-rate output characteristics at a low temperature was generally improved by setting the DBP absorption amount (mL / 100 g) of the positive electrode active material to 23 or more. Samples 1-6, in which the DBP absorption amount (mL / 100 g) of the positive electrode active material is 32 or less, have a lower current interruption mechanism operating SOC than the other samples 7 and 8, and gas generation during overcharge The amount has increased dramatically. From this result, the optimal amount of lithium ion that satisfies both the gas generation amount and the output characteristics at the time of overcharge at a high level by setting the DBP absorption amount (mL / 100 g) of the positive electrode active material to 23 or more and 32 or less. It was confirmed that the secondary battery was obtained.

  Although the lithium ion secondary battery according to one embodiment of the present invention has been described above, the secondary battery according to the present invention is not limited to any of the above-described embodiments, and various modifications can be made. For example, in the above-described embodiment, a lithium ion secondary battery has been described as a typical example of a non-aqueous electrolyte secondary battery. However, the embodiment is not limited to the non-aqueous electrolyte secondary battery. For example, a secondary battery using a metal ion (for example, sodium ion) other than lithium ion as a charge carrier may be used.

  Since the secondary battery according to the present invention exhibits good battery performance as described above, it can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile. Therefore, the present invention provides a vehicle (typically an automobile such as an automobile, particularly a hybrid automobile, an electric automobile, or a fuel cell automobile) provided with such a secondary battery (typically, a plurality of batteries connected in series) as a power source. Vehicle).

20 Winding electrode body 30 Battery case 42 Positive electrode terminal 44 Negative electrode terminal 50 Positive electrode sheet 52 Positive electrode current collector 60 Negative electrode sheet 62 Negative electrode current collector 64 Negative electrode active material layer 70 Separator 90 Current interruption mechanism 100 Lithium ion secondary battery

Claims (1)

A positive electrode in which a positive electrode active material layer containing a positive electrode active material is held in a positive electrode current collector, a negative electrode in which a negative electrode active material layer containing a negative electrode active material is held in a negative electrode current collector, and between the positive electrode and the negative electrode An electrode body comprising a separator interposed between,
A battery case containing the electrode body together with a non-aqueous electrolyte;
An external terminal provided in the battery case and connected to the electrode body;
When the internal pressure of the battery case becomes higher than a predetermined pressure, a current interruption mechanism that interrupts electrical connection between the electrode body and the external terminal,
The non-aqueous electrolyte includes a gas generating agent that reacts at a voltage equal to or higher than a predetermined voltage to generate a gas,
The non-aqueous electrolyte secondary battery, wherein the DBP absorption amount per 100 g of the positive electrode active material is 23 mL or more and 32 mL or less.

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