JP2015037018A - Sealed type nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reliable sealed type nonaqueous electrolyte secondary battery which suppresses a failure accompanying manganese precipitation, and secures a sufficient amount of gas in the pressure rise inside a battery case.SOLUTION: In a sealed type nonaqueous electrolyte secondary battery 100, a positive electrode active material is composed of a lithium transition metal complex oxide including at least nickel, cobalt and manganese as transition metal elements. A nonaqueous electrolyte contains biphenyl and crown ether; the percentage of the biphenyl is 1-3 mass% to a total of 100 mass% of the nonaqueous electrolyte, and the percentage of the crown ether is 0.3-1 mass%. A battery case 50 is provided with a current interrupt device 30 which is activated when the pressure inside the battery case 50 is raised with generation of gas.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery. More specifically, the present invention relates to a sealed nonaqueous electrolyte secondary battery provided with a current interruption mechanism that operates by increasing internal pressure.

  As one form of a nonaqueous electrolyte secondary battery such as a lithium ion secondary battery, a sealed nonaqueous electrolyte secondary battery can be given. Typically, the battery is constructed in such a manner that an electrode body composed of positive and negative electrodes is accommodated in a battery case together with a non-aqueous electrolyte, and then a lid is attached and sealed (sealed). The positive electrode of the sealed nonaqueous electrolyte secondary battery is a substance (positive electrode active material) that can reversibly occlude and release chemical species (for example, lithium ions) serving as a charge carrier on a conductive member (positive electrode current collector). ) As a main component (hereinafter, the layered product is referred to as a “positive electrode active material layer”). One example of such a positive electrode active material is a composite oxide (hereinafter also referred to as “NiCoMn oxide”) containing at least nickel, cobalt, and manganese as transition metal elements, as shown in Patent Document 1. . Such a composite oxide is a positive electrode active material having a high capacity and excellent thermal stability.

Japanese Patent Application Laid-Open No. 2003-223887 JP 2003-187864 A

  By the way, the sealed nonaqueous electrolyte secondary battery is generally used in a state where the voltage is controlled so as to be within a predetermined region (for example, 3.0 V or more and 4.2 V or less). When supplied, it may overcharge beyond a predetermined voltage. As an overcharge countermeasure technique, a current interruption device (CID: Current Interrupt Device) that cuts off a charging current when the pressure in the battery case reaches a predetermined value or more is widely used. Generally, when a battery is overcharged, a non-aqueous solvent or the like in the non-aqueous electrolyte is electrolyzed to generate gas. The current interruption mechanism cuts off the charging path of the battery based on this gas generation, and can prevent further overcharge. In order to operate the current interruption mechanism more effectively, a compound (hereinafter referred to as “gas generating agent”) having an oxidation potential lower than that of the non-aqueous solvent of the non-aqueous electrolyte (that is, lower voltage at which the oxidative decomposition reaction starts) )) Is known in advance in a non-aqueous electrolyte.

  However, in a non-aqueous electrolyte secondary battery including a NiCoMn oxide as a positive electrode active material, when biphenyl as a gas generating agent is added to the non-aqueous electrolyte, a gas generation amount is ensured, but the NiCoMn oxide does not There is a risk that manganese will elute into the water electrolyte. When manganese eluted in the non-aqueous electrolyte is deposited on the surface of the negative electrode, there is a possibility that a short circuit may occur between the positive and negative electrodes or the battery capacity may be reduced.

  The present invention has been made in view of such a point, and the object thereof is to suppress defects associated with manganese precipitation and to ensure reliability in generating a sufficient amount of gas when the pressure in the battery case is increased. It is to provide a high hermetically sealed nonaqueous electrolyte secondary battery.

  The inventor of the present application has found that the precipitation of manganese on the negative electrode surface can be suppressed by further adding crown ether to the non-aqueous electrolyte to which biphenyl is added, and the present invention has been completed.

  That is, a sealed non-aqueous electrolyte secondary battery provided by the present invention includes an electrode body having a positive electrode and a negative electrode, a non-aqueous electrolyte, a battery case containing the electrode body and the non-aqueous electrolyte, Is a sealed nonaqueous electrolyte secondary battery. The positive electrode includes a positive electrode current collector and a positive electrode active material layer including at least a positive electrode active material formed on the positive electrode current collector. The positive electrode active material is a lithium transition metal composite oxide containing at least nickel, cobalt, and manganese as transition metal elements. The non-aqueous electrolyte contains biphenyl that can decompose to generate gas when a predetermined battery voltage is exceeded, and crown ether as an additive. The battery case is provided with a current interrupt mechanism that operates when the pressure in the battery case increases with the generation of the gas. Preferably, when the total amount of the non-aqueous electrolyte is 100% by mass, the ratio of the biphenyl is 1% by mass to 3% by mass. Preferably, when the total amount of the non-aqueous electrolyte is 100% by mass, the proportion of the crown ether is 0.3% by mass to 1% by mass.

In this specification, the “non-aqueous electrolyte secondary battery” includes a non-aqueous electrolyte (typically, an electrolyte containing a supporting salt (supporting electrolyte) in a non-aqueous solvent (organic solvent)). Battery.
In the present specification, the term “secondary battery” refers to a battery that can be repeatedly charged and discharged, and is a term that includes a so-called chemical battery such as a lithium ion secondary battery and a physical battery such as an electric double layer capacitor.

  In the nonaqueous electrolyte secondary battery provided by the present invention, a lithium transition metal complex oxide (hereinafter also referred to as “NCM oxide”) containing at least nickel, cobalt, and manganese as transition metal elements is used as a positive electrode active material. The non-aqueous electrolyte contains crown ether and biphenyl as a gas generating agent. Since biphenyl is contained in the non-aqueous electrolyte, manganese can be eluted from the NCM oxide into the non-aqueous electrolyte. However, since the nonaqueous electrolytic solution further contains crown ether, manganese ions eluted in the nonaqueous electrolytic solution are captured by the crown ether. That is, the crown ether forms a complex so as to enclose manganese ions. As a result, it is suppressed that the manganese ion eluted in the non-aqueous electrolyte is deposited as manganese on the negative electrode. Moreover, when the ratio of biphenyl is 1 mass%-3 mass%, generation | occurrence | production of sufficient gas amount can be ensured at the time of the pressure rise in a battery case. Furthermore, when the proportion of the crown ether is 0.3% by mass to 1% by mass, it is possible to further suppress the precipitation of manganese on the negative electrode. Reference 2 discloses a secondary battery in which a crown ether is contained in an electrolytic solution that is a liquid electrolyte. However, a problem that may occur when manganese is eluted from a positive electrode active material containing manganese. There is no disclosure about the above, and it does not contain crown ether in order to solve the problem. Therefore, it does not suggest or motivate the configuration of the present invention.

1 is a perspective view schematically showing an outer shape of a sealed nonaqueous electrolyte secondary battery according to an embodiment of the present invention. It is sectional drawing which follows the II-II line | wire in FIG. It is a graph which shows the relationship between the addition amount of a cryptand [2.2.2], and a capacity | capacitance maintenance factor.

  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 implementation 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 sealed nonaqueous electrolyte secondary battery disclosed herein, as described above, the positive electrode active material is a lithium transition metal composite oxide containing nickel, cobalt, and manganese as transition metal elements. Is characterized by containing biphenyl, which can decompose to generate gas when a predetermined battery voltage is exceeded, and crown ether as an additive. Hereinafter, the case where the sealed nonaqueous electrolyte secondary battery is a lithium ion secondary battery will be described in more detail as a typical example, but the application target of the present invention is not intended to be limited to such a battery.

  First, the positive electrode of the lithium ion secondary battery disclosed here will be described. The positive electrode disclosed here includes a positive electrode current collector and a positive electrode active material layer including at least a positive electrode active material formed on the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, a conductive material, a binder, and the like. As the positive electrode current collector, a conductive member made of a metal having good conductivity (for example, aluminum) can be suitably employed.

Examples of the positive electrode active material include lithium transition metal composite oxides containing at least manganese as a transition metal element. Preferably, a lithium transition metal complex oxide (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) containing nickel, cobalt, and manganese as the transition metal element can be used. As the conductive material, a carbon material such as carbon black (for example, acetylene black or ketjen black) can be adopted. As the binder, various polymer materials such as polyvinylidene fluoride (PVDF) and polyethylene oxide (PEO) can be adopted.

  The negative electrode disclosed here has a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, a binder, a thickener, and the like. As the negative electrode current collector, a conductive material made of a metal having good conductivity (for example, copper) can be suitably used. As the negative electrode active material, a carbon material such as graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), or the like can be used, and among them, graphite can be preferably used. As the binder, various polymer materials such as styrene butadiene rubber (SBR) can be adopted. As the thickener, various polymer materials such as carboxymethyl cellulose (CMC) can be employed.

  As shown in FIGS. 1 and 2, the lithium ion secondary battery according to this embodiment is a sealed lithium ion secondary battery 100. The battery case (outer container) 50 is a metal (for example, aluminum) battery case. The battery case 50 includes a bottomed flat rectangular battery case main body 52 having an open upper end, and a lid 54 that closes the opening. The lid 54 is provided with a positive electrode terminal 70 electrically connected to the positive electrode sheet 10 of the wound electrode body 80 and a negative electrode terminal 72 electrically connected to the negative electrode sheet 20 of the wound electrode body 80. Yes. In addition, the lid 54 is provided with a safety valve 55 for discharging the gas generated inside the battery case 50 to the outside of the battery case 50 as in the case of the battery case of the conventional lithium ion secondary battery. The safety valve 55 is typically set to be opened at a pressure higher than the pressure at which the current interrupt mechanism 30 operates. Inside the battery case 50, the positive electrode sheet 10 and the negative electrode sheet 20 are laminated together with a total of two separators 40A and 40B (for example, a porous sheet made of resin) and wound in the longitudinal direction. A flat wound electrode body 80 produced by crushing the body from the side direction and kidnapping it, and a non-aqueous electrolyte are accommodated. The positive electrode sheet (positive electrode) 10 includes a positive electrode current collector 12 and a positive electrode active material layer 14 including at least a positive electrode active material formed on the positive electrode current collector 12.

  Inside the battery case 50 is provided a current interrupt mechanism 30 that operates when the pressure in the battery case 50 rises. When the internal pressure of the battery case 50 increases, the current interruption mechanism 30 cuts off a conductive path (for example, a charging path) from at least one of the positive electrode terminal 70 and the negative electrode terminal 72 to the wound electrode body 80. It only has to be configured. As shown in FIG. 2, the current interrupt mechanism 30 is provided between the positive electrode terminal 70 fixed to the lid 54 and the wound electrode body 80, and is wound from the positive electrode terminal 70 when the internal pressure of the battery case 50 rises. The conductive path reaching the electrode body 80 is cut.

  More specifically, the current interrupt mechanism 30 may include a first member 32 and a second member 34, for example. When the internal pressure of the battery case 50 rises, at least one of the first member 32 and the second member 34 is deformed and separated from the other, thereby cutting the conductive path. The first member 32 is formed in an arch shape with a central portion curved downward, and a peripheral portion thereof is connected to the lower surface of the positive electrode terminal 70 via a current collecting lead terminal 35. Further, the tip of the curved portion 33 of the first member 32 is joined to the upper surface of the second member 34. A positive electrode current collector plate 74 is joined to the lower surface (back surface) of the second member 34, and the positive electrode current collector plate 74 is connected to the positive electrode sheet 10 (positive electrode current collector 12) of the wound electrode body 80.

  The current interrupt mechanism 30 includes an insulating case 38 made of plastic or the like. The insulating case 38 is provided so as to surround the first member 32, and hermetically seals the upper surface of the first member 32. The internal pressure of the battery case 50 does not act on the upper surface of the hermetically sealed curved portion 33. In the current interrupt mechanism 30, when the internal pressure of the battery case 50 increases, the internal pressure acts on the lower surface of the curved portion 33 of the first member 32, and the curved portion 33 curved downward is pushed upward. When the internal pressure of the battery case 50 exceeds the set pressure, the curved portion 33 is inverted so as to bend upside down and bend upward. Thereby, the junction point 36 between the first member 32 and the second member 34 is cut, the conductive path from the positive electrode terminal 70 to the wound electrode body 80 is cut, and the overcharge current is cut off. .

  The current interruption mechanism 30 is not limited to the mechanical cutting accompanied by the deformation of the first member 32 described above. For example, the internal pressure of the battery case 50 is detected by a sensor, and the internal pressure detected by the sensor sets the set pressure. An external circuit that cuts off the charging current when exceeded can be provided as a current cut-off mechanism.

As the non-aqueous electrolyte, an organic solvent (non-aqueous solvent) containing a supporting salt, a gas generating agent and an additive is used. As the supporting salt, a lithium salt, a sodium salt or the like can be used, and among them, a lithium salt such as LiPF ₆ or LiBF ₄ can be preferably used. As the organic solvent, aprotic solvents such as carbonates, esters and ethers can be used. Of these, carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) can be preferably used.

  Biphenyl is used as the gas generating agent. Biphenyl is a compound that can decompose and generate gas when it exceeds a predetermined battery voltage (that is, when the oxidation potential is higher than the operating voltage of the lithium ion secondary battery and the battery is overcharged) A compound that decomposes into a gas and generates gas). In addition to biphenyl, a gas generating agent (for example, cyclohexylbenzene) used for the same purpose may be used.

  When the total amount of the non-aqueous electrolyte is 100% by mass, the proportion of biphenyl is 0.1% by mass or more (typically 0.5% by mass or more, preferably 1% by mass or more, more preferably 2% by mass). Or more), and preferably 10% by mass or less (typically 5% by mass or less, preferably 3% by mass or less). When the proportion of biphenyl is too smaller than 0.1% by mass, the amount of gas generated during overcharge decreases, and the current interrupt mechanism may not operate normally. Moreover, when the ratio of biphenyl is too larger than 10 mass%, there exists a possibility that battery performance may fall.

The crown ether can be used without particular limitation as long as it is a compound capable of capturing (taking in) manganese ions eluted in the non-aqueous electrolyte. Examples thereof include macrocyclic ethers such as 12-crown-4, 15-crown-5, and 18-crown-6, and polycyclic ethers such as cryptands. As a preferred crown ether, a cryptand [2.2.2] represented by the following formula (I) (that is, 1,10-diaza-4,7,13,16,21,24-hexoxabicyclo [8,8 , 8] hexacon, N (CH ₂ CH ₂ OCH ₂ CH ₂ OCH ₂ CH ₂ ) ₃ N).

  When the total amount of the non-aqueous electrolyte is 100% by mass, the proportion of crown ether is 0.1% by mass or more (typically 0.2% by mass or more, preferably 0.3% by mass or more). 3 mass% or less (typically 2 mass% or less, preferably 1 mass% or less). When the proportion of the crown ether is less than 0.1% by mass, manganese eluted in the non-aqueous electrolyte cannot be sufficiently captured, and manganese may be deposited on the negative electrode.

  In the sealed lithium ion secondary battery 100 according to the present embodiment, a lithium transition metal composite oxide containing at least manganese as a transition metal element is used as a positive electrode active material, and biphenyl is used as a gas generating agent in a non-aqueous electrolyte. And crown ether. Since biphenyl is contained in the non-aqueous electrolyte, gas is generated at the time of overcharging, and the current interrupting mechanism 30 operates to provide a highly reliable secondary battery. However, since biphenyl is contained in the non-aqueous electrolyte, manganese is easily eluted from the lithium transition metal composite oxide into the non-aqueous electrolyte during normal charge / discharge. Here, since the non-aqueous electrolyte further contains crown ether, manganese ions eluted in the non-aqueous electrolyte are taken into the crown ether. As a result, even when manganese is eluted in the non-aqueous electrolyte, it is suppressed that manganese ions are precipitated as manganese on the surface of the negative electrode. As described above, the lithium ion secondary battery 100 according to the present embodiment suppresses the problems associated with the precipitation of manganese from the positive electrode active material and ensures the generation of a sufficient amount of gas when the pressure in the battery case increases. It can be a highly reliable secondary battery.

  EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.

<Example 1>
The mass ratio of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ as the positive electrode active material, acetylene black (AB) as the conductive material, and PVDF as the binder is 90: 8: 2. Thus, these materials were dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a paste-like composition for forming a positive electrode active material layer. The composition was applied onto an aluminum foil (positive electrode current collector) having a thickness of 15 μm. The coated material was dried and subjected to a press treatment to produce a positive electrode sheet having a positive electrode active material layer formed on a positive electrode current collector.

  Weigh so that the mass ratio of natural graphite, SBR as a binder, and CMC as a thickener is 98: 1: 1, and disperse these materials in ion-exchanged water to obtain a paste-like negative electrode active material. A composition for forming a material layer was prepared. The composition was applied onto a 10 μm thick copper foil (negative electrode current collector). The coated material was dried and subjected to a press treatment to prepare a negative electrode sheet in which a negative electrode active material layer was formed on the negative electrode current collector.

A wound electrode is formed by winding a separator sheet (a separator sheet having a three-layer structure in which a porous polypropylene layer is formed on both sides of a porous polyethylene layer) between the prepared positive electrode sheet and the negative electrode sheet, and winding it in an elliptical shape. The body was made. Electrode terminals are joined to the ends of the positive and negative electrode current collectors of the wound electrode body, and the wound electrode body is placed in an aluminum battery case having a length of 75 mm, a width of 120 mm, a thickness of 15 mm, and a case thickness of 1 mm. Accommodated. Next, the non-aqueous electrolyte solution according to Example 1 was injected into the battery case to produce a lithium ion secondary battery according to Example 1. The non-aqueous electrolyte according to Example 1 was prepared by dissolving LiPF ₆ as a supporting salt in a non-aqueous solvent having a volume ratio of EC, DMC, and EMC of 3: 4: 3. The concentration of LiPF ₆ in the nonaqueous electrolytic solution according to Example 1 was 1.1 mol / L.

<Example 2 to Example 4>
In the same manner as in Example 1, except that a non-aqueous electrolyte according to Example 2 was added to the non-aqueous electrolyte according to Example 1 and biphenyl as a gas generating agent was used. A secondary battery was produced. When the total amount of the nonaqueous electrolytic solution according to Example 2 was 100% by mass, the proportion of biphenyl was 1% by mass. Moreover, the lithium ion secondary battery concerning Example 3 and Example 4 was produced like Example 2 except having changed the ratio of biphenyl into what was shown in Table 1. FIG.

[Charge / discharge cycle test]
The lithium ion secondary batteries according to Examples 1 to 4 manufactured above were charged at a constant current up to 4.1 V at a current value (charge rate) of C / 5, and then the current value during constant voltage charging. The battery was fully charged (SOC 100%) by performing constant voltage charging up to a point where C becomes C / 50. Thereafter, under a temperature condition of 25 ° C., a discharge capacity (initial battery capacity) was measured when discharging was performed at a constant current up to 3 V at a current value of C / 5. Here, 1C means a current value that can charge the battery capacity (Ah) predicted from the theoretical capacity of the positive electrode in one hour. Charging / discharging was repeated 1000 cycles for each of the lithium ion secondary batteries of Examples 1 to 4 after the initial battery capacity measurement. The charge / discharge conditions for one cycle were a constant current charge to a voltage of 4.1V at a charge rate of 2C and a constant current discharge to a voltage of 3V at a discharge rate of 2C under a temperature condition of 60 ° C. For each lithium ion secondary battery after 1000 cycles, the discharge capacity after 1000 cycles (post-cycle battery capacity) was measured in the same manner as the initial capacity measurement. Here, the following formula: {(battery capacity after cycle) / (initial battery capacity)} × 100 was defined as the capacity retention rate [%] after 1000 cycles. The measurement results are shown in Table 1.

[Measurement of gas generation amount]
About the lithium ion secondary battery which concerns on the produced said Example 1-Example 4, volume A [mL] of each battery was measured by the Archimedes method. And about the lithium ion secondary battery which concerns on Example 1-Example 4 after 1000 cycles, the volume B [mL] of each battery was measured by the Archimedes method. Then, the volume A [mL] was subtracted from the volume B [mL], respectively, and the gas generation amount (BA) [mL] after 1000 cycles was calculated. The measurement results are shown in Table 1. In the Archimedes method, a measurement object (in this example, an assembly and a lithium ion secondary battery) is immersed in a liquid medium (for example, distilled water or alcohol), and the buoyancy that the measurement object receives is measured. This is a method for obtaining the volume of the measurement object.

  As shown in Table 1, it was confirmed that although the amount of gas generation increased as the proportion (added amount) of biphenyl increased, the capacity maintenance rate decreased as a contradiction. This is because as the amount of biphenyl added increases, the amount of manganese eluted from the positive electrode active material into the non-aqueous electrolyte increases, and as a result of the charge being consumed and manganese precipitating on the negative electrode surface, the total charge decreased. Conceivable.

<Example 5 to Example 9>
Example 5 is the same as Example 4 except that the nonaqueous electrolytic solution according to Example 5 is obtained by adding the cryptand [2.2.2] as an additive to the nonaqueous electrolytic solution according to Example 4. The lithium ion secondary battery which concerns on was produced. When the total amount of the nonaqueous electrolytic solution according to Example 5 was 100% by mass, the ratio of cryptand [2.2.2] was 0.1% by mass. Further, lithium ion secondary batteries according to Examples 6 to 9 were produced in the same manner as Example 5 except that the ratio of cryptand [2.2.2] was changed to that shown in Table 2.

[Charge / discharge cycle test]
About the lithium ion secondary battery which concerns on the said Example 5-Example 9, the test similar to the charging / discharging cycle test performed with respect to the lithium ion secondary battery which concerns on the said Example 1- Example 4 was done, and the capacity | capacitance maintenance after 1000 cycles The rate was measured. The measurement results are shown in Table 2 and FIG.

  As shown in Table 2 and FIG. 3, even when the proportion (addition amount) of biphenyl is the same, if the cryptand [2.2.2] is contained in the non-aqueous electrolyte, the capacity retention rate is A significant improvement was confirmed (see Examples 4 and 5). In particular, it was confirmed that a high capacity retention ratio was obtained when the amount of cryptand [2.2.2] added was 0.3% by mass or more. This is because even when the amount of manganese eluted from the positive electrode active material into the non-aqueous electrolyte is increased by increasing the amount of biphenyl added, the cryptand [2.2.2] is reduced in the non-aqueous electrolyte. This is probably because manganese is suppressed from being deposited on the negative electrode in order to capture the eluted manganese ions.

  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.

Claims (1)

A sealed non-aqueous electrolyte secondary battery comprising an electrode body having a positive electrode and a negative electrode, a non-aqueous electrolyte, and a battery case containing the electrode body and the non-aqueous electrolyte,
The positive electrode includes a positive electrode current collector, and a positive electrode active material layer including at least a positive electrode active material formed on the positive electrode current collector,
The positive electrode active material is a lithium transition metal composite oxide containing at least nickel, cobalt, and manganese as transition metal elements,
The non-aqueous electrolyte includes biphenyl that can decompose and generate gas when a predetermined battery voltage is exceeded, and crown ether as an additive,
When the total amount of the non-aqueous electrolyte is 100% by mass, the proportion of the biphenyl is 1% by mass to 3% by mass, and the proportion of the crown ether is 0.3% by mass to 1% by mass,
A sealed nonaqueous electrolyte secondary battery, wherein the battery case is provided with a current interrupting mechanism that operates when the pressure in the battery case increases as the gas is generated.

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