JP3966254B2 - Secondary battery with surface mount terminals - Google Patents

Description

  The present invention is a secondary battery in which a terminal for connecting to a device is mounted on at least one electrode terminal that also serves as a battery container, has a high capacity, and eliminates the thermal effect associated with the mounting of the battery on the device. The present invention relates to a secondary power supply with a terminal that has improved performance.

  In recent years, small coin-type lithium secondary batteries have come to be used as a memory backup power source for mobile phones, mobile terminals, information devices, and the like. As a coin-type lithium secondary battery system, a lithium manganese composite oxide is combined with a positive electrode and a lithium aluminum alloy is combined with a negative electrode, and the discharge voltage is about 3V (hereinafter referred to as 3V class, the same applies to other discharge voltages). A secondary battery or a 2.5 V class lithium secondary battery in which niobium pentoxide is combined in the positive electrode and a lithium aluminum alloy in the negative electrode is used.

  As a method of mounting the battery on the circuit board of the device, manual soldering or a method of inserting the battery into a battery holder previously mounted on the circuit board is employed. Recently, automatic mounting by a reflow method has been adopted in response to miniaturization of devices and batteries and mounting at high density. In this reflow method, solder cream is supplied to the circuit board and the terminal portion of the battery, and the battery and the board are passed through a high temperature atmosphere to melt the solder, thereby ensuring the connection between the battery and the board. In the case of using conventional lead-containing solder, the maximum temperature reaches about 220 ° C. to 240 ° C. in the process including the reflow method (hereinafter referred to as the reflow process). In some cases, the temperature reaches 250 to 260 ° C.

  In order to solve the problems in the reflow process, high-boiling organic electrolytes and heat-resistant materials are used as the constituent materials of the battery, and heat resistance is given to the entire battery, so that it can be automatically mounted on a substrate using the reflow method. Various lithium secondary batteries have been proposed, and as an example, it is proposed to use sulfolane having a boiling point of 260 ° C. or higher, 3 methylsulfolane, and tetraglyme as an organic solvent.

  However, depending on the combination of the positive and negative electrode materials and the organic electrolyte, the decomposition of the organic electrolyte caused by the reaction between the two when exposed to a high temperature atmosphere, leakage due to gas generation due to this decomposition, the electrode Problems such as capacity reduction due to deterioration of the material will occur. These problems are not observed in the normal temperature range and are unique to the reflow process.

For example, Patent Document 1 discloses that a battery using niobium pentoxide as a positive electrode is mixed and fired with boron oxide for the purpose of suppressing gas generation under a high temperature atmosphere and capacity reduction. It discloses that covering a part of the surface of the niobium reduces the contact area with the organic electrolyte, suppresses decomposition of the organic electrolyte, and reduces gas generation.
JP 2002-203545 A

  However, in the battery using niobium pentoxide for the positive electrode, boron oxide is coated on the positive electrode surface even in a normal temperature range, and the state in which the contact area between the electrolytic solution and the positive electrode is reduced is maintained. The electrode reaction is lowered and the battery characteristics are deteriorated. Further, the positive electrode is not uniformly coated with boron oxide, and only a part of the surface is coated with boron oxide, and gas generation in a high temperature atmosphere cannot be sufficiently suppressed. In particular, depending on the conditions (temperature, time) of the reflow process and the type of the electrolytic solution, a decomposition reaction of the electrolytic solution is recognized, which is not a fundamental solution.

  The present invention has been made in view of the above-described conventional situation, and an object thereof is to provide a secondary battery with a terminal that has a high capacity and excellent reliability and is suitable for surface mounting by a reflow method.

  In order to achieve the above-mentioned object, the present inventors diligently studied to suppress the reaction between niobium pentoxide and an organic electrolyte under a high temperature atmosphere.

  As a result, in a battery using monoclinic niobium pentoxide for the positive electrode and a lithium aluminum alloy for the negative electrode, the battery voltage is set to 1.7 V or less prior to the reflow process, so that a high temperature atmosphere during reflow can be obtained. It was found that the decomposition reaction of the electrolyte below can be suppressed.

  Even when the battery is subjected to a reflow process in a high-temperature atmosphere using lead-free solder according to the present invention, the organic electrolyte and niobium pentoxide are stably present, and the surface has high capacity and excellent reliability. A secondary battery with a terminal for mounting can be provided.

  Hereinafter, preferred embodiments of the present invention will be described.

The invention according to claim 1 of the present application is configured such that a power generation element composed of positive and negative electrodes, a separator, and an organic electrolyte is housed in a battery container, and a connection terminal is provided on at least one electrode of the battery container. A secondary battery mounted on a device by a reflow method, using a monoclinic niobium pentoxide for the positive electrode and a lithium aluminum alloy for the negative electrode, and the battery before mounting on the device A secondary battery with a surface-mounting terminal having a voltage of 1.7 V or less.

  Depending on the firing temperature, niobium pentoxide has a hexagonal structure in the low temperature range, an orthorhombic structure in the intermediate temperature range, and a monoclinic structure in the high temperature range. From the viewpoint of charge / discharge cycle performance and capacity, the monoclinic system fired in a high temperature range is the most excellent.

  When fired in a high temperature region, many oxygen defects are generated on the surface due to the oxygen partial pressure of niobium pentoxide. After firing, a crystal layer having many thin oxygen defects that cannot be identified by X-ray diffraction different from bulk is formed on the surface of niobium pentoxide. Even when firing in an oxygen atmosphere, it is impossible to completely suppress this oxygen defect.

  The reactivity of this surface layer is higher than that of the internal bulk, and a gas generation reaction due to decomposition of the electrolytic solution proceeds in a high temperature atmosphere of 200 ° C. or higher. It was found that by inserting 10% or more of lithium with respect to the theoretical capacity of niobium pentoxide, the reactivity of the surface layer was lowered, and niobium pentoxide and the electrolyte existed stably even in a high temperature atmosphere.

  As the means, a method of discharging the assembled battery by constant current or constant resistance discharge, a method of inserting lithium into the positive electrode by electrochemically shorting lithium to the positive electrode at the time of battery production, niobium pentoxide, There is a method of obtaining a compound of lithium and niobium pentoxide by firing with a predetermined amount of lithium source such as lithium hydroxide or lithium carbonate. Preferably, it is a method of discharging after producing the battery.

The lithium aluminum alloy used for the negative electrode is preferably lithium / aluminum (molar ratio) = 1 or less in which two phases of α phase and β phase excellent in charge / discharge cycle performance coexist.
The potential of the lithium aluminum alloy having the molar ratio is about 0.4 V with respect to metallic lithium, and the potential of the positive electrode in which lithium is inserted into niobium pentoxide by 10% or more of the theoretical capacity is 2.1 V with respect to metallic lithium. By setting the battery voltage to 1.7 V or less, it is possible to suppress the reaction between the positive electrode and the electrolytic solution at a high temperature. The state of the positive electrode can be known from the battery voltage, and confirmation is easy.
The positive electrode material is not subjected to a treatment for reducing the capacity, and can be increased in capacity. Further, the same effect can be obtained with niobium pentoxide partially coated with boron oxide.

In the invention according to claim 2, the specific surface area of the niobium pentoxide measured by the BET method is 3.0 m ² / g or less. The BET method is a method for measuring the specific surface area based on the nitrogen adsorption amount. When the specific surface area is 3.0 m ² / g or less, the reaction area with the electrolytic solution decreases, and the reaction with the electrolytic solution can be further suppressed by combining with the lithium insertion reaction of niobium pentoxide. is there.

  The invention according to claim 3 contains at least one sulfolane or tetraglyme in the organic solvent of the organic electrolyte. Since the boiling point of sulfolane and tetraglyme is 260 ° C. or higher, and the reactivity to niobium pentoxide and lithium aluminum alloy is lower than other organic solvents, the characteristics after passing through reflow can be maintained. . In addition, mixing with the above solvents 1,2 dimethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, butyl diglyme, and other glymes, and chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and the like, further reflow passes. Later discharge characteristics and charge / discharge cycle performance are improved.

In the invention according to claim 4, the solute of the organic electrolyte is LiN (CF ₃ SO ₂ ) _2.
At least one of LiN (C ₂ F ₅ SO ₂ ) ₂ is contained. Less reactive to niobium pentoxide and lithium aluminum alloys than other solutes, so the properties after reflow can be maintained, and even better results can be obtained by combining with the above organic solvents .

  The invention according to claim 5 is a gasket made of an organic resin containing at least one of polyetheretherketone, polyphenylene sulfide, and a liquid crystal polymer. Gaskets containing polyetheretherketone, polyphenylene sulfide, and liquid crystal polymer are stable against high temperatures during surface mounting and are used as a packing material that plays an important role in battery liquid sealing. The sealing portion can be stably maintained against an increase in internal pressure. Preferably, by using an inorganic fiber such as glass fiber or potassium titanate as a filler, the strength of the resin itself is improved and a highly reliable battery can be obtained.

The invention described in claim 6 is a separator made of polyphenylene sulfide or polyfluorinated ethylene . Polyphenylene sulfide or polyfluorinated ethylene is stable and does not react with niobium pentoxide of the positive electrode, lithium aluminum of the negative electrode, organic solvent, and gasket in a high temperature environment, and can maintain battery performance.

  Hereinafter, preferred embodiments of the present invention will be described in detail. FIG. 1 is a cross-sectional view of a secondary battery with a terminal having a thickness of 1.4 mm and a diameter of 4.8 mm manufactured in Examples and Comparative Examples of the present invention. In FIG. 1, a coin-type battery container that houses a power generation element includes a positive electrode can 1 made of stainless steel having excellent corrosion resistance, a negative electrode can 2 made of stainless steel, and a gasket 3. In addition to the function of insulating the power generation element, the power generation element is physically sealed in the battery container.

The gasket 3 interposed between the positive electrode can 1 and the negative electrode can 2 was made of a polyether ether ketone (PEEK) resin. A solution obtained by diluting butyl rubber with toluene was applied between the gasket 3 and the positive electrode can 1, and the negative electrode can 2 and the gasket 3, and the toluene was evaporated to obtain a sealant made of a butyl rubber film.
The positive electrode 4 is composed of monoclinic niobium pentoxide (BET specific surface area 1.5 m ² / g) obtained by firing niobium hydroxide at 1000 ° C. as an active material, carbon black and binder as a conductive agent. A fluororesin powder is mixed as an agent, formed into a pellet having a diameter of 2 mm and a thickness of 0.9 mm, and then dried at 250 ° C. for 12 hours. The obtained pellet-like positive electrode material is in contact with the positive electrode current collector 7 formed by applying a carbon paint on the inner surface of the positive electrode can 1.
In the negative electrode 5, aluminum is punched into a disk shape having a diameter of 2.5 mm and a thickness of 0.2 mm, and a lithium metal sheet is pressure-bonded to the aluminum surface inside the negative electrode can 2. When the battery is assembled, by injecting the electrolytic solution, lithium and aluminum are short-circuited, and lithium is occluded electrochemically in the aluminum metal. The lithium aluminum alloy obtained by this reaction was used as the negative electrode 5. In addition, polyphenylene sulfide (PPS) was used for the separator 6 disposed between the positive electrode 4 and the negative electrode 5. Furthermore, for the electrolyte, sulfolane was used with LiN (CF ₃ SO ₂ ) ₂ as a solute. The battery container is filled with 3 μl of electrolyte by volume. The battery thus obtained was discharged at 50 μA to a depth of 10% of the theoretical capacity of the positive electrode to obtain a battery A according to Example 1. The battery voltage was 1.69V.

  A battery B having the same configuration and the same depth of discharge as the battery A was prepared except that tetraglyme was used in place of sulfolane as the solvent of the organic electrolyte used in the battery A. The battery voltage was 1.67V.

A battery having the same configuration and the same depth of discharge as battery A except that LiN (C ₂ F ₅ SO ₂ ) ₂ was used instead of LiN (CF ₃ SO ₂ ) ₂ which is the solute of the organic electrolyte used for battery A C was produced. The battery voltage was 1.68V.
Battery D was obtained by discharging at 50 μA to the depth of 25% of the theoretical capacity of the positive electrode in the same configuration as battery A. The battery voltage was 1.45V.
Battery E was obtained by discharging at 50 μA to a depth of 50% of the theoretical capacity of the positive electrode. The battery voltage was 1.40V.

  A comparative battery F having the same configuration and the same depth of discharge as that of the battery A was prepared except that propylene carbonate was used instead of sulfolane as the solvent of the organic electrolyte solution of the battery A. The battery voltage was 1.68V.

A battery B having the same configuration as that of battery A but in an undischarged state was designated as comparative battery G. The battery voltage was 2.22V .

  A comparative battery H was obtained by discharging at 50 μA to the depth of 5% of the theoretical capacity of the positive electrode in the same configuration as the battery A. The battery voltage was 1.80V.

An undischarged comparative battery I was produced in the same configuration as battery A except that propylene carbonate was used in place of sulfolane as the solvent of the organic electrolyte solution of battery A. The battery voltage was 2.12V .

Instead of niobium pentoxide for the positive electrode of battery A, monoclinic niobium pentoxide obtained by firing niobium hydroxide at 1000 ° C. and boron oxide were mixed at a weight ratio of 95: 5, and 375 An undischarged comparative battery J was produced in the same configuration as the battery A except that niobium pentoxide obtained by firing for 1 hour at ° C and having boron oxide adhered to the surface was used. The battery voltage was 2.18V .

About the batteries A, B, C, D, E, and F of the obtained examples and the comparative batteries G, H, I, and J, the positive electrode terminal 7 and the negative electrode terminal 8 were terminal welded by laser welding, and then in a reflow furnace The high temperature environment characteristic test was conducted. The temperature profile inside the reflow furnace through which each battery passes is exposed to an environment of 180 ° C. for 2 minutes as a preheating process, and after passing through 180 ° C., 245 ° C. and 180 ° C. for 30 seconds as a heating process. Naturally cooled down to room temperature. After passing through this reflow process twice, it inspected about the generation | occurrence | production state of a liquid leak. Thereafter, charge and discharge were performed, and the discharge capacity (load 2 μA−cut voltage 1.0 V) was examined. In addition, a charge / discharge test was performed in the range of 2.5 to 1.0 V (charge protection resistance 10 kΩ, charge time: 60 hours). The cycle in which the capacity is 0.4 mAh or less (half the design capacity) is defined as the cycle life number. Table 1 shows the state of occurrence of liquid leakage after passing through the reflow furnace, the discharge capacity, and the results of the charge / discharge cycle test.

  The batteries A to F of the examples did not leak after passing through reflow, and almost half or more of the comparative batteries G, H, I, and J leaked. In addition, the battery of the example had a larger discharge capacity than the comparative battery. From the results of the charge / discharge cycle life test, the battery of this example had 15 cycles or more, whereas the comparative battery had less than 10 cycles. By reducing the battery voltage to 1.7 V or less, the reactivity between the positive electrode niobium pentoxide and the organic electrolyte can be reduced, and further performance can be achieved by combining a high boiling point solvent such as sulfolane or tetraglyme. Improved.

  The positive electrode niobium pentoxide has a BET specific surface area of 10.0, 5.0, 3.0, and 1.0 m 2 / g, respectively, and the other configurations are the same as those of Example Battery A, and batteries J, K, L, and M are used. Produced. Battery A and batteries K, L, M, and N were terminal-attached in the same manner as in Example 1 and then passed through a reflow furnace to examine the leakage performance. In addition, a charge / discharge cycle test was performed. Table 2 shows the number of leaks after reflow and the results of the charge / discharge cycle test.

As is apparent from Table 2, no leakage was observed in all the batteries, but the number of charge / discharge cycles improved as the specific surface area decreased. When the specific surface area was large, the reaction between niobium pentoxide and the organic electrolyte occurred, and the charge / discharge cycle life was shortened due to consumption of the electrolyte. When the specific surface area is 3.0 m ² / g or less, 20 or more charge / discharge cycles are possible.

  In the secondary battery with a surface mounting terminal in which niobium pentoxide is combined in the positive electrode and lithium aluminum alloy in the negative electrode, a part of the positive electrode is reacted with lithium so that the battery voltage is 1.7 V or less. Thus, it becomes possible to stabilize the niobium pentoxide and the organic electrolyte even under a reflow high temperature atmosphere, and it is possible to provide a secondary battery with a terminal for surface mounting that has high capacity and excellent reliability.

  In addition, even the reflow method using lead-free solder, which is essential for the environment, can be mounted, and its industrial value is extremely high.

Sectional drawing of the secondary battery with a terminal in a present Example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode can 2 Negative electrode can 3 Gasket 4 Positive electrode 5 Negative electrode 6 Separator 7 Positive electrode terminal 8 Negative electrode terminal

Claims (6)

A power generation element composed of positive and negative electrodes, a separator, and an organic electrolyte is housed in a battery container, and a connection terminal is provided on at least one electrode of the battery container, and the connection terminal is attached to a device by a reflow method. A secondary battery,
A secondary battery with surface-mounting terminals that uses monoclinic niobium pentoxide for the positive electrode and a lithium aluminum alloy for the negative electrode, and has a battery voltage of 1.7 V or less before being attached to the device. The secondary battery with a terminal for surface mounting according to claim 1, wherein the niobium pentoxide has a specific surface area of 3.0 m ² / g or less as measured by the BET method. The secondary battery with a terminal for surface mounting according to claim 1 or 2, wherein the organic solvent of the organic electrolyte contains at least one of sulfolane and tetraglyme. Solute organic _{electrolyte, LiN (CF 3 SO 2)} 2, and _{LiN (C 2 F 5 SO 2} ) 2 of either surface mounting terminal with the secondary battery according to claim 1 comprising at least one . The secondary battery with a terminal for surface mounting according to any one of claims 1 to 4, wherein the gasket is made of at least one organic resin selected from polyether ether ketone, polyphenylene sulfide, and liquid crystal polymer. The secondary battery with a terminal for surface mounting according to any one of claims 1 to 5, wherein the separator is formed of at least one of polyphenylene sulfide and polyfluorinated ethylene .

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