JP4911938B2 - Reflow heat-resistant lithium secondary battery - Google Patents

Description

  The present invention relates to an improvement in a heat-resistant lithium secondary battery having reflow heat resistance and causing no sudden voltage drop even when discharged at a low temperature.

  In recent years, non-aqueous electrolyte secondary batteries have been used as a memory backup power source for electronic devices such as mobile phones and digital cameras. When mounting such a nonaqueous electrolyte secondary battery on an electronic device, a reflow soldering method is used to increase production efficiency. According to this method, although the battery temperature is 200 to 200 seconds, the reflow soldering method is used. Reach up to 260 ° C.

  For this reason, an electrode material having excellent heat resistance is used as the electrode material of the non-aqueous electrolyte secondary battery for reflow. For example, a manganese oxide is used as a positive electrode active material and a lithium-aluminum alloy is used as a negative electrode active material. It was. The secondary battery having this configuration can be efficiently discharged in the range of 2 to 3V.

  However, in recent years, there has been an increasing demand for power saving of electronic devices, and it is desired to reduce the driving voltage of semiconductor devices and the like incorporated in electronic devices to about 0.8 to 1.5V. Therefore, there is a demand for a secondary battery that has reflow heat resistance and can be stably driven at a low voltage of about 0.8 to 1.5V.

Under these circumstances, when a lithium-aluminum alloy is used as a negative electrode, a technique using titanium oxide that can be stably discharged at about 1.1 V as a positive electrode has attracted attention. When the reflow mounting method is used for a conventional battery, there is a problem that the electrolytic solution reacts with the electrode by heating to form a coating on the electrode surface, and this coating inhibits a smooth discharge reaction.
This problem is particularly noticeable when used in a low temperature environment of −10 ° C. to −30 ° C., and the discharge voltage drops sharply at the beginning of discharge, and the discharge voltage drops below the end-of-discharge voltage. Significantly decreases or adversely affects the operation of an electronic device mounted with this battery.

  Here, Patent Documents 1 to 4 can be cited as technologies related to batteries using titanium oxide.

Japanese Unexamined Patent Publication No. 2000-243445 Japanese Patent Laid-Open No. 2001-23697 JP 2005-135872 A Japanese Unexamined Patent Publication No. 7-302587

  The technique described in Document 1 is a technique that uses a lithium-containing manganese oxide as a positive electrode active material and at least one selected from molybdenum oxide, lithium titanate, iron sulfide, and niobium pentoxide as a negative electrode active material. According to this technique, the material is unlikely to react rapidly with the electrode, so that the battery performance can be maintained even when reflow mounting is performed.

  However, the discharge voltage of the battery is 2 to 2.5 V, and cannot meet the demand for lowering the battery voltage.

  The technique of the above-mentioned document 2 is a technique using a positive electrode active material obtained by adding spinel-structure lithium titanium oxide and / or niobium pentoxide to tungsten trioxide. According to this technique, crystal destruction of tungsten trioxide during overdischarge can be prevented, and charge / discharge cycle life and overdischarge characteristics can be improved.

  However, the above technique does not consider any reflow mounting, and there is room for improvement in this respect.

  The technique described in the above-mentioned document 3 has oxide particles including at least one element selected from the group consisting of Ti, Zr, V, Nb, Cr, Mo, and W, and covers the particles and has conductivity. And a coating layer containing a carbon material, and the coating layer is a technique using an electrode that is contained at a ratio of 5 wt% or less with respect to the total weight. According to this technology, it is said that a non-aqueous secondary battery having excellent cycle characteristics and heavy load discharge characteristics and high capacity can be realized.

  However, the above technique does not consider any reflow mounting, and there is room for improvement in this respect.

The technique of the above-mentioned document 4 is a technique that uses, as a negative electrode, a mixture of one or more of WO ₃ , LiWO ₂ , and Nb ₂ O ₅ with respect to spinel type lithium-titanium oxide. According to this technique, the discharge characteristics at the end of discharge can be improved.

  However, the above technique also does not consider any reflow mounting, and there is room for improvement in this respect.

  The present invention has been made in view of the above, and an object of the present invention is to provide a lithium secondary battery that has excellent heat resistance and can prevent a sudden drop in voltage at the initial stage of discharge.

The present invention for solving the above problems is a reflow heat-resistant lithium secondary battery having a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and a non-aqueous electrolyte including a non-aqueous solvent and an electrolyte salt. The positive electrode active material includes a titanium oxide and a metal oxide that discharges at a higher voltage than the titanium oxide in the initial stage of discharge, and the metal oxide includes niobium oxide, molybdenum oxide, tungsten It is 1 or more types of compounds selected from the group which consists of oxides, The mass ratio of the said metal oxide in the said positive electrode total mass is 1-30 mass%, It is characterized by the above-mentioned.

According to the above configuration, the metal oxide (one or more compounds selected from the group consisting of niobium oxide, molybdenum oxide, and tungsten oxide) that discharges at a higher voltage than titanium oxide is included. Since the metal oxide acts to raise the discharge voltage of the battery at the early stage of discharge, it is possible to prevent a sudden drop in voltage.
In addition, if the mass ratio of the metal oxide in the total mass of the positive electrode is less than 1% by mass, the effect of suppressing the voltage drop cannot be sufficiently obtained, while if it exceeds 30% by mass, the discharge capacity decreases. . Therefore, it restrict | limits in the said range.

  Here, the metal oxide that discharges at a higher voltage than the titanium oxide in the initial stage of the discharge means that the metal oxide is used for the positive electrode and the lithium-aluminum alloy is used for the negative electrode. This means that the voltage is higher than when titanium oxide is used for the positive electrode.

In the above structure, the titanium oxide may be a spinel-type lithium-titanium oxide represented by Li _{1 + x} Ti _2-x O ₄ (−0.2 ≦ x ≦ 1/3) .

In the above configuration, the metal oxide is one or more compounds selected from the group consisting of Nb ₂ O ₅ , MoO _y (2 ≦ y ≦ 3), and WO _z (2 ≦ z ≦ 3). can do.

  In the above configuration, the negative electrode active material may be a lithium-aluminum alloy.

According to the configuration of the present invention, it is possible to mount a reflow heat-resistant lithium secondary battery that can be stably discharged without causing a drop in the discharge voltage even by the reflow method.

  The best mode for carrying out the present invention will be described by taking a coin-type non-aqueous electrolyte battery as an example. FIG. 1 is a cross-sectional view showing the overall configuration of this battery.

  As shown in FIG. 1, a battery outer can (positive electrode can) 1 includes a positive electrode 2 using a titanium oxide to which molybdenum oxide is added as an active material, and a negative electrode 3 using a lithium-aluminum alloy as an active material. An electrode body composed of a separator 4 that separates both electrodes is housed. The separator 4 is impregnated with an electrolytic solution. In this battery, an opening of the positive electrode can 2 and a battery sealing can (negative electrode cap) 6 are caulked and sealed through a ring-shaped insulating gasket 5.

  The details of the nonaqueous electrolyte battery according to the present invention will be described more specifically with reference to examples.

Example 1
<Preparation of positive electrode>

93 parts by mass of titanium oxide (spinel type lithium titanium oxide: Li ₄ Ti ₅ O ₁₂ ), 1 part by mass of niobium oxide (Nb ₂ O ₅ ), 5 parts by mass of carbon as a conductive agent, and a binder As a positive electrode mixture, 1 part by mass of polytetrafluoroethylene was mixed. This mixture was press-molded at 5 ton / cm ² and dried to produce a disc-shaped positive electrode 2 having a diameter of 2 mm and a thickness of 0.7 mm.

<Preparation of negative electrode>
A negative electrode cap 6 made of a clad material in which a stainless steel plate and an aluminum plate were bonded together so that the inner surface was an aluminum plate was used. A disc-shaped metal lithium plate having a diameter of 2 mm and a thickness of 0.2 mm was pressure-bonded to the surface of the aluminum plate on the inner surface of the negative electrode cap 6 to produce the negative electrode 3. Since the alloying reaction occurs between the aluminum clad material and the metal lithium plate after charge and discharge after the battery is fabricated, the negative electrode active material is a lithium-aluminum alloy.

<Preparation of electrolyte>
LiN (CF ₃ SO ₂ ) ₂ as a solute was dissolved at a ratio of 1.0 M (mol / liter) in a mixed solvent in which propylene carbonate and diethylene glycol dimethyl ether were mixed at a volume ratio of 1: 1 to prepare an electrolytic solution. .

<Production of battery>
A separator 4 made of a non-woven fabric made of polyphenylene sulfide (PPS) was placed on the negative electrode 3, and the electrolyte solution was injected into the separator 4. Then, the said positive electrode 2 was mounted on the separator, and also the stainless steel positive electrode can 1 (thickness 0.15 mm) was covered on it. The positive electrode can 1 and the negative electrode cap 6 are caulked and sealed through an insulating gasket 5 made of polyphenylene sulfide (PPS), and the nonaqueous solution according to Example 1 having a battery diameter (diameter) of 4.0 mm and a thickness of 1.4 mm is used. An electrolyte battery was produced. PPS is a resin having high heat resistance (melting point: PPS, about 280 ° C.).

(Example 2)
A battery according to Example 2 was fabricated in the same manner as in Example 1 except that 84 parts by mass of titanium oxide and 10 parts by mass of niobium oxide were used.

Example 3
A battery according to Example 3 was fabricated in the same manner as in Example 1 except that 69 parts by mass of titanium oxide and 25 parts by mass of niobium oxide were used.

Example 4
A battery according to Example 4 was fabricated in the same manner as in Example 2 except that molybdenum oxide (MoO ₂ ) was used instead of niobium oxide.

(Example 5)
A battery according to Example 5 was fabricated in the same manner as in Example 2 except that tungsten oxide (WO ₃ ) was used instead of niobium oxide.

(Example 6)
A battery according to Example 6 was made in the same manner as Example 1 except that 69 parts by mass of titanium oxide, 12.5 parts by mass of niobium oxide, and 12.5 parts by mass of molybdenum oxide were used. did.

(Comparative Example 1)
A battery according to Comparative Example 1 was fabricated in the same manner as in Example 1 except that the titanium oxide was 94 parts by mass and the niobium oxide was not added.

  The batteries according to Examples 1 to 6 and Comparative Example 1 produced above were reflowed under the following conditions, and the following tests were performed on each battery after reflow. Note that the number of specimens is two.

<Reflow>
Each battery was placed twice in a reflow furnace set so that the surface temperature of the battery was 250 ° C. at maximum.
Here, the reason why the reflow furnace was charged twice is that the soldering is performed twice on the front and back surfaces of the double-sided mounting board.

<Measurement of low-temperature discharge characteristics>
Each battery after the reflow resistance test is discharged at −20 ° C. with a fixed resistance of 300 kΩ until the battery voltage becomes 0.8 V, and the discharge capacity is measured, and the relationship between the discharge time and the battery voltage is measured. did.

  The test results (average values) are shown in Table 1 below, and the relationship between discharge time and voltage in Comparative Example 1 and Example 2 is shown in FIG.

From Table 1 and FIG. 2, in Examples 1 to 6 including a metal oxide (one or more compounds selected from the group consisting of niobium oxide, molybdenum oxide, and tungsten oxide) together with titanium oxide , After the start of discharge, the voltage gradually drops to about 1.1 V, and then stable discharge at 1.1 V, whereas in Comparative Example 1 that does not include a metal oxide, the discharge voltage is 0 after the start of discharge. It can be seen that it has dropped rapidly until it reaches .95V.

  This is considered as follows. In Examples 1 to 6, a metal oxide (such as niobium oxide) that discharges at a higher voltage than titanium oxide is added to titanium oxide, and this metal oxide increases the discharge voltage at the initial stage of discharge. The discharge voltage does not drop suddenly. On the other hand, in Comparative Example 1, since the metal oxide is not included, smooth discharge is hindered by the coating generated by reflow, and the discharge voltage drops rapidly.

  In the above experiment, the final discharge voltage was set to 0.8 V. However, when this is set to 1.0 V, the discharge capacity of Comparative Example 1 is extremely small. Is not suitable.

  In the case where reflow was not performed, a sudden drop in voltage was not observed even when no metal oxide was added. Therefore, this phenomenon is caused by reflow.

  Moreover, it turns out that discharge capacity becomes small as the addition amount of a metal oxide increases from the comparison of Examples 1-3.

  This is presumably because the discharge capacity of the metal oxide is smaller than that of the titanium oxide.

  Here, in order to obtain the effect of the present invention, when the total mass of the positive electrode (titanium oxide + metal oxide + binder + conductive agent) is 100, 1 part by mass or more of the metal oxide is included. It is preferable. From the viewpoint of discharge capacity, the upper limit of the amount of metal oxide added is preferably 30 parts by mass.

[Other matters]
As the titanium oxide used in the present invention, it is preferable to use a spinel type lithium-titanium oxide represented by Li _{1 + x} Ti _2-x O ₄ (−0.2 ≦ x ≦ 1/3). Further, it is preferable to use Nb ₂ O ₅ as the niobium oxide, MoO _y (2 ≦ y ≦ 3) as the molybdenum oxide, and WO _z (2 ≦ z ≦ 3) as the tungsten oxide. The metal oxide may contain lithium.

  Moreover, although lithium-aluminum alloy was used as a negative electrode active material, it is not limited to this, You may use other lithium alloys, such as a lithium- silicon alloy and a lithium- tin alloy. Moreover, the alloy which contains trace amount of other metals in these alloys may be sufficient.

In addition to LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiPF ₆ , LiBF ₄ , LiClO _4, etc. can be used as the electrolyte salt, and a mixture thereof. Also good. Among these, LiN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) ₂ are preferably used because of excellent thermal stability.

  In addition, the non-aqueous solvent is not limited to those used in the above examples, but it should be noted that if a large amount of a solvent having a low boiling point is used, the solvent volatilizes during reflow and the battery may rupture.

  In the above embodiment, a caulking sealing method using a gasket is used to seal the opening of the battery outer can, but besides this method, a sealing method by laser irradiation, a sealing made of resin You may use the method of heat-welding a member.

  Further, as the material of the separator, the heat-resistant temperature (melting point / decomposition temperature) is preferably higher than 150 ° C., more preferably higher than the melting temperature of reflow solder (185 ° C.), and during reflow It is more preferable that the temperature is higher than the minimum temperature (200 ° C.), and it is most preferable that the temperature is higher than the maximum temperature (260 ° C.) during reflow.

  As a specific example of such a heat-resistant resin, in addition to the above polyphenylene sulfide, a heat-resistant resin such as polyether ether ketone, polyether ketone, polybutylene terephthalate, and cellulose, or a filler such as glass fiber is added to the resin material Thus, a resin having a further improved heat resistant temperature can be exemplified.

  Moreover, when crimping sealing with a gasket or welding a resin, the materials used in the separator can be used as these materials.

As described above, according to the present invention, a reflow heat-resistant lithium secondary that can prevent a sudden drop in voltage at the initial stage of discharge and stably discharge in the range of 0.8 to 1.5 V even if reflow is performed. A battery is obtained. Therefore, industrial applicability is great.

1 is a cross-sectional view schematically showing a coin-type nonaqueous electrolyte battery according to the present invention. It is a graph which shows the relationship between the discharge time and voltage of Example 2 and Comparative Example 1.

Explanation of symbols

1 Battery outer can (positive electrode can)
2 Positive electrode 3 Negative electrode 4 Separator 5 Insulating gasket 6 Battery sealing can (negative electrode cap)

Claims (5)

In a reflow heat-resistant lithium secondary battery having a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and a nonaqueous electrolyte including a nonaqueous solvent and an electrolyte salt,
The positive electrode active material includes titanium oxide, and a metal oxide that discharges at a higher voltage than the titanium oxide in the initial stage of discharge ,
The metal oxide is one or more compounds selected from the group consisting of niobium oxide, molybdenum oxide, and tungsten oxide;
The mass ratio of the metal oxide in the total mass of the positive electrode is 1 to 30% by mass.
A reflow heat-resistant lithium secondary battery characterized by the above. The reflow heat-resistant lithium secondary battery according to claim 1,
The titanium oxide is a spinel type lithium-titanium oxide represented by Li _{1 + x} Ti _2-x O ₄ (−0.2 ≦ x ≦ 1/3).
A reflow heat-resistant lithium secondary battery characterized by the above. The reflow heat-resistant lithium secondary battery according to claim 1 or 2,
The metal oxide is one or more compounds selected from the group consisting of Nb ₂ O ₅ , MoO _y (2 ≦ y ≦ 3), WO _z (2 ≦ z ≦ 3).
A reflow heat-resistant lithium secondary battery characterized by the above. In the reflow heat-resistant lithium secondary battery according to claim 1, 2, or 3,
The negative electrode active material is a lithium-aluminum alloy;
A reflow heat-resistant lithium secondary battery characterized by the above. A circuit board on which a lithium secondary battery is mounted by reflow soldering,
A circuit board, wherein the lithium secondary battery is the reflow heat-resistant lithium secondary battery according to claim 1.

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