JP5699890B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly, to a non-aqueous electrolyte secondary battery including a current interruption mechanism that prevents overcharge and an electrolyte containing a gas generating additive.

  In recent years, secondary batteries have been used in various fields such as electronic devices such as mobile phones and personal computers, vehicles such as hybrid cars and electric cars. An example of this secondary battery is a lithium ion secondary battery. Lithium ion secondary batteries have high energy density and no memory effect. Therefore, it is suitable for mounting on various devices.

  When charging the lithium ion secondary battery, if there is a malfunction due to the presence of a defective battery or a failure of the charging device, a current higher than normal may be supplied, resulting in an overcharged state. In this case, the battery reaction proceeds rapidly, gas is generated inside the sealed battery case, and the internal pressure of the battery increases. As a result, deformation of the battery case, abnormal heat generation, etc. may occur. In order to cope with such an abnormality, a battery having a current interruption mechanism that interrupts charging when a pressure inside the battery becomes a predetermined value or more has been proposed.

  As a non-aqueous electrolyte secondary battery equipped with this current interruption mechanism, for example, the following Patent Document 1 describes an electrolyte containing a gas generating additive such as biphenyl or alkylbenzene. In the non-aqueous electrolyte secondary battery described in Patent Document 1 below, during overcharge, the gas generating additive undergoes oxidative decomposition on the positive electrode plate side, generating a large amount of gas (mainly hydrogen gas). Thereby, the pressure rise inside a battery is accelerated | stimulated and it can operate | move an electric current interruption mechanism at an early stage.

JP 2004-087168 A

  However, the nonaqueous electrolyte secondary battery described in Patent Document 1 has the following problems. In order to increase the amount of gas generated and activate the current interruption mechanism at an early stage, it is necessary to increase the amount of gas generating additive contained in the electrolyte. However, when the amount of the gas generating additive is increased, the gas generating additive is easily decomposed in a high-temperature storage state, and the battery capacity and the like are reduced by self-discharge or product deposition due to decomposition (side reaction of the gas generating additive). The battery characteristics deteriorate. That is, there is a problem that if the amount of the gas generating additive is small, the current interruption mechanism cannot be operated early, and if the amount of the gas generating additive is large, the battery characteristics are deteriorated.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a non-aqueous electrolyte secondary battery capable of operating a current interruption mechanism early while preventing deterioration of battery characteristics. And

The non-aqueous electrolyte secondary battery of the present invention has a positive electrode plate in which a positive electrode mixture layer containing a positive electrode active material is formed on a positive electrode core material, and a state in which a separator is interposed between the positive electrode plate and the negative electrode plate An electrode body laminated or wound with an electrolyte, an electrolytic solution containing a gas generating additive that oxidizes and decomposes to generate gas during overcharging, and current interruption that interrupts charging when the internal pressure of the battery exceeds a predetermined value be those having a mechanism, wherein the between the positive electrode core member the positive-electrode mixture layer, have a carbon particles consisting of expanded graphite obtained by expanding the pre interlayer, and to have a conductivity A carbon coat layer is formed.

  In this case, since the carbon particles of the carbon coat layer are expanded graphite, the area where the gas generating additive decomposes during overcharge is large. For this reason, the gas generating additive is efficiently oxidized and decomposed during overcharge, and a large amount of gas can be generated. In other words, since the carbon coat layer of expanded graphite is formed, the pressure increase inside the battery can be increased without increasing the amount of the gas generating additive. Therefore, the current interruption mechanism can be activated early while preventing deterioration of battery characteristics.

  In the nonaqueous electrolyte secondary battery according to the present invention, the thickness of the carbon coat layer is preferably 1 μm or more and 20 μm or less. This is because the current interruption mechanism can be reliably operated in a state where the SOC (battery charge state) is low during overcharge.

  In particular, in the non-aqueous electrolyte secondary battery according to the present invention, the thickness of the carbon coat layer is preferably 3 μm or more and 10 μm or less. This is because the increase in pressure inside the battery can be increased during overcharging while suppressing a decrease in battery capacity.

  ADVANTAGE OF THE INVENTION According to this invention, the non-aqueous-electrolyte secondary battery which can operate an electric current interruption mechanism at an early stage, preventing the deterioration of a battery characteristic is provided.

It is sectional drawing which showed the schematic structure of the battery which concerns on this embodiment. It is an enlarged view of the electric current interruption mechanism shown in FIG. It is the figure which showed the state which the electric current interruption mechanism shown in FIG. 2 act | operated. FIG. 2 is a schematic perspective view of a wound electrode body shown in FIG. 1. It is the perspective view which expand | deployed the negative electrode plate among the winding electrode bodies shown in FIG. It is the perspective view which expand | deployed the positive electrode plate among the winding electrode bodies shown in FIG. It is the figure of the positive electrode plate which showed typically the content of the carbon coat layer and positive electrode compound material layer which were shown in FIG. (A) It is a figure of the positive electrode plate in which the carbon coat layer shown in FIG. 7 is not formed and the positive electrode mixture layer contains expanded graphite. (B) It is the figure of the positive electrode plate which replaced the expanded graphite contained in the carbon coat layer shown in FIG. 7 with carbon black. In the battery of Examples 1-5 and Comparative Examples 1-3, it is the figure which showed the experimental result of the continuous overcharge test. It is the figure which showed the experimental result of the capacity | capacitance confirmation test in the battery of Examples 1-5 and Comparative Examples 1-3.

  The nonaqueous electrolyte secondary battery according to the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing a schematic configuration of a battery 1 according to the present embodiment. The battery 1 is a lithium ion secondary battery, and includes a current interruption mechanism 10 and a wound electrode body 20 in the battery container 2 as shown in FIG. The battery container 2 includes a battery container body 3 and a sealing plate 4. The sealing plate 4 closes the opening of the battery container body 3 and is joined to the upper edge of the battery container body 3.

  An electrolytic solution is injected into the battery container 2. This electrolytic solution is obtained by dissolving an electrolyte in an organic solvent. Examples of the organic solvent include propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), 1,2-dimethoxyethane, 1,1-diethoxyethane. , Tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, acetonitrile, propionitrile, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, γ-butyrolactone, etc. A solvent or a combination of these can be used.

Further, as a salt that is an electrolyte, lithium perchlorate (LiClO ₄ ), lithium borofluoride (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium hexafluoroarsenate (LiAsF ₆ ), LiCF ₃ SO ₃ LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiI and other lithium salts can be used.

  In addition, the electrolytic solution contains a gas generating additive that oxidizes and decomposes to generate gas (mainly hydrogen gas) during overcharge. As gas generating additives, biphenyl (BP), cyclohexylbenzene (CHB), diphenyl ether, cyclopentylbenzene, pyrrole, N-methylpyrrole, thiophene, furan, indole, 3-chlorothiophene, 3-bromothiophene, 3-fluorothiophene, 1,2-dimethoxybenzene, 1-methyl-3-pyridinium tetrafluoroborate, cumene, 1,3-diisopropylbenzene, 1,4-diisopropylbenzene, 1-methylpropylbenzene, 1,3-bis (1-methyl) Propyl) benzene, 1,4-bis (1-methylpropyl) benzene, and the like can be used. Further, two or more kinds of the above-mentioned gas generating additives may be used in combination.

  Further, as shown in FIG. 1, the battery 1 includes a positive electrode terminal 5, a negative electrode terminal 6, a positive electrode insulating member 7, and a negative electrode insulating member 8. The positive electrode insulating member 7 is a member for insulating the positive electrode terminal 5 and the sealing plate 4. The negative electrode insulating member 8 is a member for insulating the negative electrode terminal 6 and the sealing plate 4. The sealing plate 4 is provided with a liquid injection hole 4a for injecting an electrolytic solution therein, and a lid 9 is attached to the liquid injection hole 4a. The lid body 9 is seam welded to the sealing plate 4 from the outside of the sealing plate 4.

  The positive electrode terminal 5 is connected to the positive electrode end portion 21 of the wound electrode body 20 through the current interruption mechanism 10, the connection metal 11, and the positive electrode tab 12. The negative electrode terminal 6 is connected to the negative electrode end portion 22 of the wound electrode body 20 via the connection metal 13 and the negative electrode tab 14. Here, FIG. 2 is an enlarged view of the current interrupt mechanism 10 shown in FIG.

  The current interrupting mechanism 10 interrupts charging when the pressure in the battery container 2 exceeds a predetermined value during overcharging, and includes a deformed metal plate 15 and a support member 16 as shown in FIG. Yes. The deformed metal plate 15 is for making the connection metal 11 connected to the positive electrode tab 12 and the positive electrode terminal 5 contact or non-contact. The deformed metal plate 15 includes a dome-shaped curved portion 15 a that swells downward, and an edge portion 15 b that is connected to the positive electrode terminal 5. The support member 16 is a member for supporting and insulating the edge portion 15b of the deformed metal plate 15.

  In the current interruption mechanism 10, as shown in FIG. 2, the curved portion 15 a of the deformed metal plate 15 is in contact with the connection metal 11 when the pressure in the battery container 2 is less than a predetermined value. When the pressure in the battery container 2 reaches a predetermined value or more, as shown in FIG. 3, the curved portion 15a of the deformed metal plate 15 is deformed so as to be reversed by receiving an upward force. Thereby, the curved part 15a of the deformation | transformation metal plate 15 and the connection metal 13 become non-contact, and charge is interrupted | blocked. The pressure (operating pressure) at which this current interrupting mechanism 10 operates is set to 0.7 MPa, for example. Here, FIG. 4 is a schematic perspective view of the wound electrode body 20 shown in FIG.

  The wound electrode body 20 has a flat shape as shown in FIG. A positive electrode end portion 21 projects from one end portion of the wound electrode body 20. As will be described later, the positive electrode end portion 21 is a portion where the positive electrode core material 41 of the positive electrode plate 40 (see FIG. 6) protrudes. A negative electrode end 22 protrudes from the other end of the wound electrode body 20. The negative electrode end 22 is a portion where the negative electrode core 31 of the negative electrode plate 30 (see FIG. 5) protrudes, as will be described later. The wound electrode body 20 is obtained by winding a positive electrode plate 40, a separator (not shown), and a negative electrode plate 30 in order.

  Here, FIG. 5 is a perspective view in which the negative electrode plate 30 is developed in the wound electrode body 20 shown in FIG. The negative electrode plate 30 is obtained by applying a negative electrode paste containing a negative electrode active material capable of occluding and releasing lithium ions to a negative electrode core material 31 that is a copper foil. As shown in FIG. 5, the negative electrode plate 30 includes a strip-shaped negative electrode core material 31 and a negative electrode mixture layer 32 formed on part of both surfaces of the negative electrode core material 31. The negative electrode composite material layer 32 is not formed on the right side of FIG. 5 in the negative electrode core material 31, and the negative electrode core material 31 protrudes.

  The negative electrode mixture layer 32 is a layer formed by drying the negative electrode paste applied to the negative electrode core material 31. The negative electrode paste includes a binder and a thickener in addition to the negative electrode active material. As the negative electrode active material, a carbon-based material containing a graphite structure at least partially is used. For example, amorphous carbon, non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), natural graphite, artificial graphite, or a carbon-based material having a combination thereof can be used.

  The binder for the negative electrode is preferably a polymer that is insoluble (or hardly soluble) in the electrolyte and is dispersed in the solvent used for the negative electrode paste. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoro Fluorine resin such as ethylene copolymer (ETFE), vinyl acetate copolymer, styrene butadiene rubber (SBR), acrylic acid-modified SBR resin (SBR latex), rubber such as gum arabic can be used. Alternatively, a combination of these may be used. However, the binder is not necessarily limited to the above polymer.

  As the thickener for the negative electrode, cellulose such as carboxymethylcellulose (CMC), methylcellulose (MC), cellulose acetate phthalate (CAP), hydroxypropylmethylcellulose (HPMC), and hydroxypropylmethylcellulose phthalate (HPMCP) can be used. However, the thickener is not necessarily limited to the cellulose described above. Water is mentioned as a solvent for negative electrodes. In addition, N-methyl-2-pyrrolidone (NMP) may be used. Further, other lower alcohols and lower ketones may be used.

  Here, FIG. 6 is a perspective view of the positive electrode plate 40 in the wound electrode body 20 shown in FIG. The positive electrode plate 40 is obtained by applying a conductive paste containing expanded graphite to a positive electrode core material that is an aluminum foil and a positive electrode paste containing a positive electrode active material capable of occluding and releasing lithium ions. As shown in FIG. 4, the positive electrode plate 40 includes a strip-shaped positive electrode core material 41, a carbon coat layer 42 formed on a part of both surfaces of the positive electrode core material 41, and each surface of the carbon coat layer 42. And a positive electrode mixture layer 43 formed on the substrate. The carbon coat layer 42 and the positive electrode mixture layer 43 are not formed on the left side of FIG. 6 in the positive electrode core material 41, and the positive electrode core material 41 is in a protruding state.

  The carbon coat layer 42 is a layer formed by drying a conductive material paste applied to the positive electrode core material 41. The conductive material paste is obtained by kneading expanded graphite as carbon particles, for example, polyvinylidene fluoride (PVDF) as a binder, and N-methyl-2-pyrrolidone (NMP) as a solvent. The conductive paste is applied to both surfaces of the positive electrode core 41 to a uniform thickness and dried, so that the carbon coat layer 42 is formed with a uniform thickness of about 5 μm.

  As shown in FIG. 6, the carbon coat layer 42 is formed between the positive electrode core material 41 and the positive electrode mixture layer 43, and adheres to the positive electrode active material contained in the positive electrode mixture layer 43 and the positive electrode core material 41. It improves the performance and assists current collection. The carbon coat layer 42 prevents corrosion of the positive electrode core material 41 that is an aluminum foil when the positive electrode paste contains an aqueous binder such as polytetrafluoroethylene (PTFE) using water as a solvent. .

  Here, the expanded graphite contained in the carbon coat layer 42 will be described. Expanded graphite is obtained by inserting sulfuric acid or the like (intercalation) between layers such as scaly graphite and heating it at a temperature of 800 to 1000 degrees to greatly expand the layers. For this reason, the expanded graphite has a wide interlayer, has a wider reaction area with the gas generating additive described above, and is more reactive than ordinary graphite and carbon black. In addition, expanded graphite is more excellent in conductivity and formability than ordinary graphite.

The positive electrode mixture layer 43 is a layer formed by drying the positive electrode paste applied to the surface of the carbon coat layer 42. The positive electrode paste includes a conductive material, a binder, and a thickener in addition to the positive electrode active material. Lithium composite oxidation such as lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium cobaltate (LiCoO ₂ ), LiNi _1/3 Co _1/3 Mn _1/3 O ₂ as the positive electrode active material Things are used. The thickness of the positive electrode mixture layer 43 is about 150 μm. The positive electrode mixture layer 43 does not include the above-described expanded graphite.

  Carbon materials such as carbon powder and carbon fiber can be used as the conductive material for the positive electrode. Examples thereof include carbon black such as acetylene black, furnace black, and ketjen black, and carbon powder such as graphite powder. As the binder, the thickener, and the solvent for the positive electrode, those mentioned above as the binder, the thickener, and the solvent for the negative electrode can be used.

The effect of the battery 1 configured as described above will be described with reference to FIG. FIG. 7 is a view of the positive electrode plate 40 schematically showing the contents of the carbon coat layer 42 and the positive electrode mixture layer 43 shown in FIG. In FIG. 7, expanded graphite 42 a is shown as the carbon particles contained in the carbon coat layer 42, and NCM (LiNi _1/3 Co _1/3 Mn _1/3 O ₂₎ is used as the positive electrode active material contained in the positive electrode mixture layer 43. 43a and carbon black 43b as a conductive material.

  In the present embodiment, as shown in FIG. 7, since the carbon particles of the carbon coat layer 42 are expanded graphite 42a, the area where the gas generating additive decomposes during overcharge is large. For this reason, the gas generating additive is efficiently oxidized and decomposed during overcharge, and a large amount of gas can be generated. Thereby, the pressure rise inside the battery case 2 can be increased, and the current interrupting mechanism 10 can be activated early.

  The expanded graphite 42 a is included in the carbon coat layer 42, but is not included in the positive electrode mixture layer 43. That is, the expanded graphite 42a exists only in the carbon coat layer 42 and does not exist in the vicinity of the NCM 43a that is the positive electrode active material. For this reason, the gas generating additive is hardly decomposed in a high-temperature storage state, and there is almost no deterioration in battery characteristics due to self-discharge due to decomposition of the gas generating additive, product deposition, etc. (side reaction of the gas generating additive). Therefore, according to the battery 1 of the present embodiment, the current interrupt mechanism 10 can be activated early while preventing deterioration of battery characteristics.

  Here, in order to compare this embodiment, a prior art example is demonstrated using FIG. FIG. 8A is a view of a positive electrode plate 40A in which the carbon coat layer 42 shown in FIG. 7 is not formed and the positive electrode mixture layer 43 includes expanded graphite 43c. This positive electrode plate 40A is referred to as Conventional Example 1. FIG. 8B is a view of a positive electrode plate 40B in which the expanded graphite 42a included in the carbon coat layer 42 shown in FIG. 7 is replaced with carbon black 42b. This positive electrode plate 40B is referred to as Conventional Example 2.

  In the case of Conventional Example 1, as shown in FIG. 8A, since the positive electrode mixture layer 43 contains the expanded graphite 43c, the gas generating additive is easily decomposed in a high temperature storage state, and the gas generating additive is added. Battery characteristics deteriorate due to side reactions of the agent. For this reason, even if the positive electrode mixture layer 43 contains the expanded graphite 43c, the content of the expanded graphite 43c cannot be increased from the viewpoint of deterioration of battery characteristics. As a result, the gas generating additive does not efficiently undergo oxidative decomposition during overcharge, and the current interrupt mechanism 10 cannot be activated early.

  In the case of Conventional Example 2, as shown in FIG. 8B, since the carbon particles contained in the carbon coat layer 42 are carbon black 42b, the gas generating additive efficiently reacts with the carbon black 42b during overcharge. do not do. This is because the carbon black 42b does not have a sufficient reaction area (edge surface) that reacts with the gas generating additive unlike the expanded graphite 42a (see FIG. 7). Therefore, the current interrupting mechanism 10 cannot be operated early during overcharging.

  Thus, in this embodiment, the carbon particles contained in the carbon coat layer 42 are expanded graphite 42a, and the expanded graphite 42a is included only in the carbon coat layer 42, so that gas is generated in a high temperature storage state. The side reaction of the additive can be suppressed to prevent deterioration of battery characteristics, and the gas generation additive can be efficiently oxidized and decomposed at the time of overcharging to activate the current interrupting mechanism 10 at an early stage. Since the gas generating additive can be efficiently oxidatively decomposed in this way, the amount of the gas generating additive can be reduced to suppress deterioration of battery characteristics.

The nonaqueous electrolyte secondary battery according to the present invention has been described above. However, the present invention is not limited to this, and various modifications can be made without departing from the spirit of the present invention.
For example, as a current interruption mechanism that cuts off charging when the pressure inside the battery exceeds a predetermined value, an external circuit that stops charging by detecting the pressure inside the battery with a sensor, An external circuit that detects deformation with a sensor and stops charging may be used.
In the present embodiment, the electrode body is a flat wound electrode body 20, but is not limited to the wound electrode body 20, and may be, for example, a cylindrical wound electrode body. Moreover, the laminated electrode body which does not wind by laminating | stacking the positive electrode plate 40, a separator, and the negative electrode plate 30 in order may be sufficient.

  The relationship between the pressure in the battery container of each battery (lithium ion secondary battery) and the SOC (battery charge state) when the overcharge test is performed will be described. In this test, continuous overcharge was performed for each of the batteries of Examples 1 to 5 and the batteries of Comparative Examples 1 to 3 whose SOC was 30%. At this time, an internal pressure sensor was attached to the liquid injection hole (see FIG. 1), and the current interruption mechanism 10 was set not to operate, and changes in internal pressure during overcharge were observed. Below, the battery of Example 1 which is a test object will be described.

Positive electrode core material = 1085-H aluminum foil,
Thickness of positive electrode core material = 15 μm,
Carbon particles of conductive paste = expanded graphite (BPS-5AS manufactured by Chuetsu Graphite Industry),
Binder for conductive paste = PVDF,
Solvent of conductive paste = NMP,
Expanded graphite: PVDF = 100: 8 (wt%)
The conductive paste described above is applied to both surfaces of the positive electrode core material described above and dried at 120 degrees. Thereby, the positive electrode core material with a coat layer in which the carbon coat layer is formed on both surfaces of the positive electrode core material is created. In the battery of Example 1, the thickness of the carbon coat layer is 5 μm.

Positive electrode active material = NCM111
Conductive material = Denka Black (AB),
Binder for positive electrode paste = PVDF,
Solvent of paste for positive electrode = NMP,
NCM111: Denka Black: PVDF = 100: 5: 3 (wt%)
The positive electrode paste described above is applied to both surfaces of the positive electrode core material with a coat layer described above and dried at 120 degrees. And after pressing to predetermined thickness, it cuts. Thereby, the positive electrode plate in which the positive electrode mixture layer is formed on the surface of the carbon coat layer is created.
The thickness of the positive electrode mixture layer = 150 μm,
Width of positive electrode mixture layer = 94 mm,
Length of positive electrode plate = 4500 mm,

Negative electrode core material = copper foil,
Negative electrode core thickness = 14 μm,
Negative electrode active material = graphite,
Thickener for negative electrode paste = CMC,
Negative electrode paste binder = SBR,
Graphite: CMC: SBR = 100: 1: 1 (wt%)
The negative electrode paste described above is applied to both sides of the negative electrode core material and dried at 120 degrees. Thereby, the negative electrode plate in which the negative electrode mixture layers are formed on both surfaces of the negative electrode core material is created.

The separator has a three-layer separator structure of polypropylene (PP), polyethylene (PE), and polypropylene (PP). The thickness of this separator is 20 μm.
In the electrolytic solution, the salt that is an electrolyte is lithium hexafluorophosphate (LiPF ₆ ). The organic solvent contains ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), and EC: DMC: EMC = 3: 4: 3 (wt%). The gas generating additives contained in the electrolytic solution are biphenyl (BP) and cyclohexylbenzene (CHB), and BP: CHB = 1: 1 (wt%).

  The above-described positive electrode plate, separator, and negative electrode plate are sequentially stacked and wound to form a flat wound electrode body. Thereafter, the wound electrode body is accommodated in a battery container. Finally, the above-described electrolytic solution is injected into the battery container body from the injection hole. In this way, the battery of Example 1 was produced. The rated capacity of this battery is 24.0 Ah, and the upper limit voltage is 20V.

Then, the battery of Examples 2-5 and the battery of Comparative Examples 1-3 are demonstrated.
<Battery of Example 2>
The thickness of the carbon coat layer containing expanded graphite is 3 μm. Other configurations are the same as those of the battery of Example 1.
<Battery of Example 3>
The thickness of the carbon coat layer containing expanded graphite is 10 μm. Other configurations are the same as those of the battery of Example 1.
<Battery of Example 4>
The thickness of the carbon coat layer containing expanded graphite is 1 μm. Other configurations are the same as those of the battery of Example 1.
<Battery of Example 5>
The thickness of the carbon coat layer containing expanded graphite is 20 μm. Other configurations are the same as those of the battery of Example 1.

<Battery of Comparative Example 1>
The positive electrode plate does not have a carbon coat layer, and is composed of a positive electrode core material and a positive electrode mixture layer. Other configurations are the same as those of the battery of Example 1.
<Battery of Comparative Example 2>
The carbon particles in the carbon coat layer are not blackened graphite but carbon black (Denka black). Other configurations are the same as those of the battery of Example 1. In the conductive paste, carbon black: PVDF = 100: 8 (wt%).
<Battery of Comparative Example 3>
The positive electrode plate does not have a carbon coat layer, and is composed of a positive electrode core material and a positive electrode mixture layer. And the electrically conductive material of a positive electrode compound-material layer is not a Denka black (AB) but expanded graphite. Other configurations are the same as those of the battery of Example 1. In the positive electrode paste, NCM111: expanded graphite: PVDF = 100: 5: 3 (wt%).

  FIG. 9 shows experimental results of continuous overcharge tests in the batteries of Examples 1 to 5 and Comparative Examples 1 to 3. In the continuous overcharge test, charging is performed at 24A (1C), and the temperature is room temperature. In FIG. 9, the operating pressure of the current interrupting mechanism is 0.7 MPa ± 0.1 MPa, and the pressure in the battery container (hereinafter referred to as “internal pressure P”) is 0.6 MPa or more in a safety region where the SOC is 170% or less. See if or not. This is because it has been found as a knowledge that if the current interruption mechanism operates when the SOC is 170% or less, the battery does not cause abnormal heat generation or thermal runaway, and the safety can be sufficiently secured.

  As shown in FIG. 9, in the batteries of Example 1, Example 2, Example 3, and Example 5, the increase of the internal pressure P is remarkable in the region where the SOC is 130% or more, and the SOC is 140 to 160%. The internal pressure P has reached 6 MPa or more in the region. This is because the gas generating additive efficiently oxidatively decomposes and generates a large amount of gas on the edge surface of the expanded graphite (reaction area that reacts with the gas generating additive) of the carbon coat layer.

  On the other hand, in the battery (1 μm) of Example 4 in which the carbon coat layer containing expanded graphite is thin, the internal pressure P when the SOC is 170% is about 0.6 MPa. As described above, the degree of increase in the internal pressure P is small as compared with the batteries of Example 1, Example 2, Example 3, and Example 5. This is because the edge surface of the expanded graphite contained in the carbon coat layer is small. In the batteries of Examples 1 to 5, the greater the carbon coat layer thickness, that is, the degree of increase in internal pressure in the order of the batteries of Example 5, Example 3, Example 1, Example 2, and Example 4. Is getting bigger.

  Further, as shown in FIG. 9, in the battery of Comparative Example 1 having no carbon coat layer, the internal pressure P when the SOC is 170% is about 0.5 MPa. Thus, when the carbon coat layer is not present, the current interruption mechanism cannot be accurately operated when the SOC is 170% or less.

  In the battery of Comparative Example 2 in which the carbon particles contained in the carbon coat layer are carbon black, the internal pressure P when the SOC is 170% is about 0.55 MPa. This means that the carbon black of the carbon coat layer has a small reaction area that reacts with the gas generating additive, and the gas generating additive cannot be efficiently oxidized and decomposed, resulting in insufficient gas generation. doing.

  Moreover, in the battery of Comparative Example 3 using expanded graphite as the conductive material contained in the positive electrode mixture layer, the internal pressure P when the SOC is 170% is about 0.45 MPa. This is because the amount of expanded graphite contained in the positive electrode mixture layer is small and the reaction area that reacts with the gas generating additive is small. Furthermore, it is because there is no carbon coat layer.

  From the above, in a battery having a carbon coat layer and the carbon particles of the carbon coat layer are expanded graphite, the gas generating additive can be efficiently oxidized and decomposed using the edge surface of the expanded graphite. Can do. And in the battery of Examples 1-5 whose thickness of a carbon coat layer is 1-20 micrometers, SOC can be operated reliably with SOC of 170% or less.

  Next, when the capacity check test is performed, the capacity maintenance rate of each battery will be described. In this test, each of the batteries of Examples 1 to 5 and Comparative Examples 1 to 3 was first charged to 4.1 V at C rate (1C), paused for 5 minutes, discharged to 3.0 V, and then 5 Paused for a minute. And CCCV charge (4.1V, rate 1C, 0.1C cut) and CCCV discharge (3.0V, rate 1C, 0.1C cut) were performed. The battery capacity of each battery at this time is defined as the initial capacity. Then, 1000 cycles of 2C CC cycle charge / discharge were performed in a 50 degree constant temperature layer. The battery capacity of each battery at this time is defined as a post-cycle capacity. Thus, the ratio of the capacity after the cycle to the initial capacity (capacity after the cycle / initial capacity) was calculated to obtain the capacity maintenance ratio (%).

  FIG. 10 shows the capacity retention ratio values of the batteries of Examples 1 to 5 and Comparative Examples 1 to 3. As shown in FIG. 10, in the batteries of Examples 1 to 4, the capacity retention rate is 86% or more, and the decrease in battery capacity is small. This means that the side reaction of the gas generating additive hardly occurred during the cycle test because the thickness of the carbon coat layer containing expanded graphite was 1 to 10 μm and was relatively thin. In addition, since the batteries of Comparative Examples 1 and 3 do not have the carbon coat layer, the side reaction of the gas generating additive hardly occurs during the cycle test, and the decrease in battery capacity is small.

  On the other hand, in the battery of Example 5 (20 μm) in which the carbon coat layer containing expanded graphite is thick, the capacity retention rate is 60%, and the battery capacity is greatly reduced. This is based on the following reason. Since the amount of expanded graphite contained in the carbon coat layer is large, the total area of the edge surface of the expanded graphite is increased. Thereby, a side reaction of the gas generating additive is likely to occur during the cycle test, and a large amount of gas is generated. As a result, it is considered that the electrode reaction was inhibited by the gas cage, and the capacity retention rate was lowered.

  Further, in the battery of Comparative Example 2 in which the carbon particles of the carbon coat layer are carbon black, the capacity retention rate is 75%, and the battery capacity is greatly reduced. This is because carbon black easily reacts with the gas generating additive during the cycle test, and the capacity retention rate is reduced by the gas cage. Thus, among the carbon particles contained in the carbon coat layer, carbon black has low storage stability at a high temperature compared to expanded graphite, and expanded graphite easily reacts with the gas generating additive only during overcharge. It can be said that there is.

  As described above, from the experimental result of the overcharge test shown in FIG. 9 and the experimental result of the capacity confirmation test shown in FIG. 10, the thickness of the carbon coat layer made of expanded graphite is 3 μm or more and 10 μm or less. In this case, it is possible to increase the pressure increase inside the battery during overcharge while suppressing the decrease in battery capacity. In addition, although the mixture of biphenyl (BP) and cyclohexylbenzene (CHB) was used as the gas generating additive contained in the electrolyte, BP alone, CHB alone, or a mixture in which both are mixed at an arbitrary ratio may be used. Similar results were obtained in the overcharge test and the capacity confirmation test.

DESCRIPTION OF SYMBOLS 1 Battery 10 Current interruption | blocking mechanism 20 Winding electrode body 30 Negative electrode plate 40 Positive electrode plate 41 Positive electrode core material 42 Carbon coat layer 42a Expanded graphite 43 Positive electrode compound material layer

Claims (3)

A positive electrode plate in which a positive electrode mixture layer containing a positive electrode active material is formed on a positive electrode core material;
The positive electrode plate and the negative electrode plate are laminated or wound with a separator interposed therebetween, and
An electrolyte containing a gas generating additive that generates gas by oxidative decomposition during overcharge; and
In a non-aqueous electrolyte secondary battery comprising a current interruption mechanism that interrupts charging when the internal pressure of the battery exceeds a predetermined value,
Between the positive-electrode mixture layer and the positive electrode core member, it has a carbon particles consisting of expanded graphite obtained by expanding the pre interlayer, and wherein the carbon coating layer to have a conductive property is formed Non-aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery according to claim 1,
The non-aqueous electrolyte secondary battery according to claim 1, wherein a thickness of the carbon coat layer is 1 μm or more and 20 μm or less. The nonaqueous electrolyte secondary battery according to claim 2,
The non-aqueous electrolyte secondary battery according to claim 1, wherein the carbon coat layer has a thickness of 3 μm or more and 10 μm or less.

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