JP2017050156A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery in which heating is suppressed during overcharge.SOLUTION: A nonaqueous electrolyte secondary battery 100 includes an electrode body 20 having a negative electrode 60 including a negative electrode active material layer 64 and a positive electrode 50. On the surface of the negative electrode active material contained in the negative electrode active material layer 64, a first coat derived from the nonaqueous solvent and/or an additive of the nonaqueous electrolyte is formed, and a second coat derived from the support salt of the nonaqueous electrolyte is formed on the first coat.SELECTED DRAWING: Figure 1

Description

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

  Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are lighter and have higher energy density than existing batteries, and have recently been used as so-called portable power sources for vehicles and personal computers and power sources for driving vehicles. ing. In particular, lithium-ion secondary batteries that are lightweight and provide high energy density will become increasingly popular as high-output power sources for driving vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). It is expected to do.

  In order to improve the cycle life of the non-aqueous electrolyte secondary battery, the non-aqueous electrolyte secondary battery is initially charged to form a passive film called SEI (Solid Electrolyte Interface) film on the negative electrode active material surface. (For example, refer to Patent Document 1). The coating is generated by reductive decomposition of the non-aqueous electrolyte during initial charging. The coating suppresses decomposition of the nonaqueous electrolytic solution and enables smooth insertion and removal of lithium ions.

JP 2013-232413 A

  However, as a result of intensive studies by the present inventors, when a film is formed on the surface of the negative electrode active material as in the prior art, the battery characteristics are improved during normal use of the nonaqueous electrolyte secondary battery. However, it has been found that the amount of the coating on the negative electrode surface increases as the battery capacity decreases, and heat is easily generated during overcharge.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a non-aqueous electrolyte secondary battery in which heat generation during overcharge is suppressed.

The non-aqueous electrolyte secondary battery disclosed herein includes an electrode body having a negative electrode and a positive electrode including a negative electrode active material layer, and a non-aqueous electrolyte. In the non-aqueous electrolyte secondary battery, a first film derived from the non-aqueous solvent and / or additive of the non-aqueous electrolyte is formed on the surface of the negative electrode active material included in the negative electrode active material layer. In addition, a second coating derived from the supporting salt of the non-aqueous electrolyte is formed on the first coating.
Thus, by forming the second film derived from the supporting salt on the first film derived from the nonaqueous solvent and / or additive on the surface of the negative electrode active material, the nonaqueous electrolyte secondary battery is formed. Heat generation during overcharging can be suppressed.

It is sectional drawing which shows typically the internal structure of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is a schematic diagram which shows the structure of the winding electrode body of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is a graph which shows the relationship between the quantity of the coating derived from the nonaqueous solvent etc. of the negative electrode active material surface in the lithium ion secondary battery of a prior art, and the emitted-heat amount. No. examined 1-No. 3 is a graph showing a measurement result of a calorific value when an overcharge of the lithium ion secondary battery of No. 3 is performed. No. examined 4-No. It is a graph which shows the measurement result of the emitted-heat amount at the time of the overcharge of the lithium ion secondary battery of 6.

  Embodiments according to the present invention will be described below with reference to the drawings. Note that matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention (for example, a general configuration and manufacturing process of a non-aqueous electrolyte secondary battery that does not characterize the present invention) ) Can be understood as a design matter of those skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. Moreover, in the following drawings, the same code | symbol is attached | subjected and demonstrated to the member and site | part which show | plays the same effect | action. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

  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. Hereinafter, an embodiment of the present invention will be described in detail by taking a flat rectangular lithium ion secondary battery as an example. However, the present invention is not intended to be limited to that described in the embodiment. .

  The lithium ion secondary battery 100 shown in FIG. 1 has a flat wound electrode body 20 and a non-aqueous electrolyte (not shown) accommodated in a flat rectangular battery case (that is, an exterior container) 30. This is a sealed lithium ion secondary battery 100 to be constructed. The battery case 30 is provided with a positive terminal 42 and a negative terminal 44 for external connection, and a thin safety valve 36 set so as to release the internal pressure when the internal pressure of the battery case 30 rises above a predetermined level. Yes. In addition, the battery case 30 is provided with an inlet (not shown) for injecting a non-aqueous electrolyte. The positive terminal 42 is electrically connected to the positive current collector 42a. The negative electrode terminal 44 is electrically connected to the negative electrode current collector plate 44a. As the material of the battery case 30, for example, a light metal material having good thermal conductivity such as aluminum is used.

  The nonaqueous electrolytic solution contains a nonaqueous solvent and a supporting salt. As the non-aqueous solvent, aprotic solvents such as carbonates, esters and ethers can be used. Of these, carbonates can be preferably used. Examples of carbonates include ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). Further, fluorinated carbonates such as monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyl difluoromethyl carbonate (F-DMC), trifluorodimethyl carbonate (TFDMC), and the like can also be used.

As the supporting salt, a lithium salt, a sodium salt, or the like can be used. Among them, a lithium salt such as LiPF ₆ or LiBF ₄ is preferable, and LiPF ₆ is more preferable. The concentration of the supporting salt in the nonaqueous electrolytic solution is preferably 0.7 mol / L or more and 1.3 mol / L or less.

  The nonaqueous electrolytic solution may further contain an additive. As the additive, an additive capable of forming a film on the negative electrode surface is preferable, and examples thereof include an oxalato complex compound (eg, lithium bisoxalate borate), vinylene carbonate, vinyl ethylene carbonate, and the like.

  As shown in FIGS. 1 and 2, the wound electrode body 20 has a positive electrode active material layer 54 formed along the longitudinal direction on one side or both sides (here, both sides) of an elongated positive electrode current collector 52. The positive electrode sheet 50 and the negative electrode sheet 60 in which the negative electrode active material layer 64 is formed along the longitudinal direction on one side or both sides (here, both sides) of the long negative electrode current collector 62 are two long shapes. The separator sheet 70 is overlapped and wound in the longitudinal direction. It should be noted that the positive electrode active material non-forming portion 52a (that is, the positive electrode active material) formed so as to protrude outward from both ends in the winding axis direction of the wound electrode body 20 (referred to as the sheet width direction perpendicular to the longitudinal direction). The portion where the positive electrode current collector 52 is exposed without forming the material layer 54) and the negative electrode active material layer non-forming portion 62a (that is, the portion where the negative electrode current collector 62 is exposed without forming the negative electrode active material layer 64). The positive electrode current collector plate 42a and the negative electrode current collector plate 44a are joined to each other.

Examples of the positive electrode current collector 52 constituting the positive electrode sheet 50 include aluminum foil. Examples of the positive electrode active material included in the positive electrode active material layer 54 include lithium transition metal oxides (eg, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNiO ₂ , LiCoO ₂ , LiFeO ₂ , LiMn ₂ O). ₄ , LiNi _0.5 Mn _1.5 O ₄ etc.), lithium transition metal phosphate compounds (eg, LiFePO ₄ etc.) and the like. The positive electrode active material layer 54 can include components other than the active material, such as a conductive material and a binder. As the conductive material, for example, carbon black such as acetylene black (AB) and other (eg, graphite) carbon materials can be suitably used. As the binder, for example, polyvinylidene fluoride (PVDF) can be used.

  Examples of the negative electrode current collector 62 constituting the negative electrode sheet 60 include copper foil. As the negative electrode active material contained in the negative electrode active material layer 64, for example, a carbon material such as graphite, hard carbon, or soft carbon can be used. The negative electrode active material layer 64 can include components other than the active material, such as a binder and a thickener. As the binder, for example, styrene butadiene rubber (SBR) can be used. As the thickener, for example, carboxymethyl cellulose (CMC) can be used.

  In the present embodiment, a first coating derived from the non-aqueous solvent of the non-aqueous electrolyte and / or the additive of the non-aqueous electrolyte is formed on the surface of the negative electrode active material included in the negative electrode active material layer 64 (hereinafter referred to as the first coating). , Also referred to as a “first coating derived from a non-aqueous solvent”), and a second coating derived from the supporting salt of the non-aqueous electrolyte is formed on the first coating. Has been. Preferably, a first film derived from the nonaqueous solvent of the nonaqueous electrolytic solution is formed on the surface of the negative electrode active material included in the negative electrode active material layer 64. Further, on the first film, A second film derived from the supporting salt of the nonaqueous electrolytic solution is formed.

  The first coating derived from the non-aqueous solvent and / or the additive is electrically charged with the non-aqueous solvent and / or the additive that is optionally contained in the non-aqueous electrolyte when the lithium ion secondary battery is constructed. It is a film formed by a chemical reaction (typically a decomposition reaction). When the first coating is derived from a non-aqueous solvent and an additive, and when the first coating is derived from an additive, the non-aqueous electrolyte contains an additive when the lithium ion secondary battery is constructed. After the formation of the first film, the additive may disappear from the nonaqueous electrolytic solution. The second coating derived from the supporting salt of the non-aqueous electrolyte is formed by electrochemical reaction (typically decomposition reaction) of the supporting salt contained in the non-aqueous electrolyte when the lithium ion secondary battery is constructed. It is a coating.

The inventors of the present invention, on the surface of the negative electrode active material contained in the negative electrode active material layer as in the prior art, also referred to as a film derived from a non-aqueous solvent and / or additive (hereinafter referred to as “film derived from a non-aqueous solvent or the like”). First, a lithium ion secondary battery in which only the battery is formed was examined.
The present inventors prepared lithium ion secondary batteries having different amounts of coating derived from the nonaqueous solvent on the surface of the negative electrode active material, and studied the amount of heat generated during overcharge. FIG. 3 is a graph showing the result of the study, that is, the relationship between the amount of the coating derived from the nonaqueous solvent on the surface of the negative electrode active material and the calorific value. FIG. 3 shows that the amount of heat generation increases as the amount of the coating derived from the non-aqueous solvent on the surface of the negative electrode active material increases.
On the other hand, the present inventors prepared lithium ion secondary batteries having different capacity deterioration rates (a film derived from a nonaqueous solvent or the like is formed on the negative electrode surface), and the amount of heat generated during overcharging. Study was carried out. FIG. 4 is a graph showing the result of the study, that is, the relationship between the capacity deterioration rate of the lithium ion secondary battery and the heat generation amount. FIG. 4 shows that the amount of heat generation increases as the capacity deterioration rate of the lithium ion secondary battery increases.
Based on the results of these studies, the present inventors have found that in a lithium ion secondary battery in which a coating derived from a nonaqueous solvent or the like is formed on the negative electrode surface, the nonaqueous solvent on the surface of the negative electrode active material increases as the capacity deteriorates. It has been found that the amount of the coating derived from, etc. increases, and the amount of heat generated during overcharge increases. A large amount of heat generated during overcharging adversely affects the overcharge resistance of the lithium ion secondary battery.

As a result of further investigation by the present inventors, as shown in the results of the examples described later (particularly FIG. 5), a first film derived from a nonaqueous solvent or the like is formed on the surface of the negative electrode active material. According to the lithium ion secondary battery in which the second coating derived from the supporting salt of the nonaqueous electrolyte solution is formed on the first coating, it has been experimentally found that heat generation during overcharge can be suppressed. .
Therefore, the lithium ion secondary battery 100 according to the present embodiment is one in which heat generation during overcharge is suppressed, and is excellent in overcharge resistance. Moreover, the lithium ion secondary battery 100 according to the present embodiment also has an effect of improving battery characteristics during normal use, which is an effect obtained by forming a film on the surface of a conventional negative electrode active material.

  Examples of the separator 70 include a porous sheet (film) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. Such a porous sheet may have a single-layer structure or a laminated structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). A heat resistant layer (HRL) may be provided on the surface of the separator 70.

  In the lithium ion secondary battery 100 according to the present embodiment, a first film derived from a nonaqueous solvent or the like is formed on the surface of the negative electrode active material included in the negative electrode active material layer 64, and the first film In addition, as long as the second coating derived from the supporting salt is formed, the production method is not particularly limited. For example, a nonaqueous electrolyte solution containing a nonaqueous solvent, a supporting salt, and an additive as necessary is prepared, and a lithium ion secondary battery assembly in which the electrode body 20 and the nonaqueous electrolyte solution are accommodated in a battery case 30 is manufactured. Then, a voltage is applied between the positive and negative electrodes 50 and 60 of the lithium ion secondary battery assembly under such a condition that a first film derived from a nonaqueous solvent or the like is formed, and then derived from the supporting salt. What is necessary is just to apply a voltage on the conditions that a 2nd film is formed.

  As described above, in a lithium ion secondary battery in which a coating derived from a nonaqueous solvent or the like is formed on the negative electrode surface, the amount of the coating derived from the nonaqueous solvent or the like on the negative electrode active material surface increases as capacity deterioration proceeds. Increases the amount of heat generated during overcharge. Therefore, a lithium ion secondary battery having a capacity deteriorated and having a first film derived from a nonaqueous solvent or the like formed on the surface of the negative electrode active material is prepared. In the lithium ion secondary battery, It is extremely effective to form a second film derived from the supporting salt.

As a particularly effective method, a lithium ion secondary battery in which a first film derived from a nonaqueous solvent or the like is formed on the surface of a negative electrode active material having a capacity deterioration rate (percentage) of x% is 0.9 V. Treat with voltage 5 x 2 ^{x / 10} seconds. By such treatment, a second film derived from the supporting salt is formed on the first film. When the voltage is too high (for example, 1.0 V or more), the second coating derived from the supporting salt is not formed on the first coating. On the other hand, if the treatment time is too short, the second coating derived from the supporting salt is not formed on the first coating.

For example, a nonaqueous solvent is formed on the surface of the negative electrode active material by utilizing the effect of suppressing heat generation during overcharging by forming the second film derived from the supporting salt on the first film derived from the nonaqueous solvent or the like. Each time the capacity is deteriorated by 10%, the lithium ion secondary battery having the first film derived from the above is 5 × 2 ^{x / 10} at a voltage of 0.9 V (where x is the capacity deterioration rate (%)). It may be processed for seconds).
For example, when a lithium ion secondary battery in which a first film derived from a non-aqueous solvent or the like is formed on the surface of the negative electrode active material is used as a power source for driving a vehicle, the vehicle is normally run (a lithium ion secondary battery is When the capacity deteriorates by 10%, it is processed at a voltage of 0.9 V for 5 × 2 seconds. This process can be performed when the lithium ion secondary battery is not used, such as when the vehicle is running using gasoline, when the vehicle is stopped using gasoline, or when the engine of the vehicle is stopped. By this treatment, a second film derived from the supporting salt is formed on the first film derived from the nonaqueous solvent or the like on the surface of the negative electrode active material, and the effect of suppressing heat generation during overcharging of the lithium ion secondary battery is achieved. can get. After that, the vehicle travels normally. As the vehicle travels normally, the capacity of the lithium ion secondary battery decreases, so that when the lithium ion secondary battery is overcharged, it tends to generate heat. Therefore, when the capacity of the lithium ion secondary battery is further deteriorated by 10% (i.e., when the capacity of the lithium ion secondary battery has degraded 20%) to be treated with 0.9V voltage 5 × 2 ² seconds. By this treatment, a film derived from the supporting salt is formed again, and the effect of suppressing heat generation during overcharging of the lithium ion secondary battery is obtained again. Thereafter, when the vehicle is driven normally and the capacity of the lithium ion secondary battery further deteriorates by 10% (that is, when the capacity of the lithium ion secondary battery deteriorates by 30%), the voltage of 0.9V is 5 × 2 Process for ³ seconds. In this way, every time the capacity of the lithium ion secondary battery deteriorates by 10%, an effect of suppressing heat generation during overcharging by forming a coating derived from the supporting salt can be obtained. Heat generation during overcharging can be suppressed over a long period of time.

  The lithium ion secondary battery 100 configured as described above can be used for various applications. Suitable applications include driving power sources mounted on vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). The lithium ion secondary battery 100 can also be used in the form of a battery pack typically formed by connecting a plurality of lithium ion secondary batteries 100 in series and / or in parallel.

  In the above description, the rectangular lithium ion secondary battery 100 including the flat wound electrode body 20 has been described as an example of the nonaqueous electrolyte secondary battery disclosed herein. However, the nonaqueous electrolyte secondary battery disclosed herein may include a laminated electrode body. Moreover, the non-aqueous electrolyte secondary battery disclosed herein can also be configured as a cylindrical lithium ion secondary battery.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this invention is not limited to this Example.

A lithium ion secondary battery having the following configuration with a capacity deterioration rate of 10%, 20%, and 30% was prepared.
Non-aqueous electrolyte: a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) as a non-aqueous solvent in a volume ratio of EC: DMC: EMC = 30: 40: 30, Use what dissolved LiPF ₆ as a supporting salt.
Positive electrode: Lithium / nickel / cobalt / manganese composite oxide is used as the positive electrode active material.
Negative electrode: A carbon material is used as the negative electrode active material. On the surface of the negative electrode active material, a film derived from the nonaqueous solvent of the nonaqueous electrolytic solution is formed.

The above lithium ion secondary battery having a capacity deterioration rate of 10% was No. 1 lithium ion secondary battery. Further, the lithium ion secondary battery having a capacity deterioration rate of 20% is No. No. 2 lithium ion secondary battery. Further, the lithium ion secondary battery having a capacity deterioration rate of 30% is No. No. 3 lithium ion secondary battery.
On the other hand, a battery obtained by treating the above-described lithium ion secondary battery with a capacity deterioration rate of 10% at a voltage of 0.9 V for 10 seconds was No. No. 4 lithium ion secondary battery. In addition, when the above lithium ion secondary battery having a capacity deterioration rate of 20% was treated with a voltage of 0.9 V for 20 seconds, No. No. 5 lithium ion secondary battery. A battery obtained by treating the above-described lithium ion secondary battery with a capacity deterioration rate of 30% at a voltage of 0.9 V for 40 seconds was obtained as a No. 1 battery. No. 6 lithium ion secondary battery was obtained. That is, no. 4-No. The lithium ion secondary battery of No. 6 was treated at a voltage of 0.9 V for 5 × 2 ^{x / 10} (x represents a capacity deterioration rate (%)) for 2 seconds. By this treatment, non-water on the surface of the negative electrode active material was obtained. A film derived from the supporting salt is formed on the film derived from the solvent.

  No. above. 1-No. The lithium ion secondary battery of No. 6 was charged to 5 V, and the calorific value was measured. No. 1-No. The measurement results for the lithium ion secondary battery No. 3 are shown in FIG. 4-No. The measurement result about the lithium ion secondary battery 6 is shown in FIG. The evaluation results of the capacity deterioration rates of 10%, 20%, and 30% on the horizontal axis of the graph of FIG. 1-No. 3 and the evaluation results of the capacity deterioration rates of 10%, 20% and 30% on the horizontal axis of the graph in FIG. 4-No. 6 corresponds to the evaluation result of the lithium ion secondary battery.

No. 1-No. 3 is a conventional lithium ion secondary battery in which a coating derived from a non-aqueous solvent is formed on the surface of the negative electrode active material. 4-No. In the lithium ion secondary battery of No. 6, a film derived from a nonaqueous solvent is formed on the surface of the negative electrode active material, and a film derived from a supporting salt is formed on the film derived from the nonaqueous solvent. 1 is a lithium ion secondary battery according to an embodiment. From FIG. 1-No. In the lithium ion secondary battery No. 3, the calorific value is large, and it can be seen that the calorific value increases as the capacity deterioration rate increases. In particular, the calorific value increases at a magnification close to 2 ^{x / 10} when the capacity deterioration rate is x%.
On the other hand, from FIG. 4-No. In the lithium ion secondary battery of No. 6, it can be seen that the calorific value is extremely low. In particular, it can be seen that the amount of heat generation is sufficiently suppressed even when the capacity deterioration rate increases.
From the above, it can be seen that the lithium ion secondary battery according to the present embodiment suppresses heat generation during overcharge.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

20 wound electrode body 30 battery case 36 safety valve 42 positive electrode terminal 42a positive electrode current collector plate 44 negative electrode terminal 44a negative electrode current collector plate 50 positive electrode sheet (positive electrode)
52 Positive Electrode Current Collector 52a Positive Electrode Active Material Layer Non-Forming Portion 54 Positive Electrode Active Material Layer 60 Negative Electrode Sheet (Negative Electrode)
62 Negative electrode current collector 62a Negative electrode active material layer non-formed portion 64 Negative electrode active material layer 70 Separator sheet (separator)
100 Lithium ion secondary battery

Claims (1)

An electrode body having a negative electrode and a positive electrode each including a negative electrode active material layer;
A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte,
On the surface of the negative electrode active material included in the negative electrode active material layer, a first film derived from the nonaqueous solvent and / or additive of the nonaqueous electrolyte is formed, and the first film is formed on the first film. The second coating derived from the supporting salt of the non-aqueous electrolyte is formed,
Non-aqueous electrolyte secondary battery.

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