JP3533893B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in high-temperature storage characteristics of a non-aqueous electrolyte secondary battery. 2. Description of the Related Art In recent years, portable and cordless electronic devices have been rapidly advanced, and there is an increasing demand for small, lightweight, high-energy-density batteries that serve as driving power supplies for these devices. From this point of view, non-aqueous secondary batteries, especially lithium ion secondary batteries, are high-voltage, high-energy density batteries such as notebook computers, mobile phones,
Alkaline aqueous solution-based nickel-cadmium batteries or nickel-metal hydride batteries have been replaced by alkaline aqueous solution-based nickel-cadmium batteries or nickel-metal hydride batteries, mainly for AV equipment, and large growth is expected in the future. At present, a lithium-ion secondary battery that has been put into practical use is a battery system using a lithium-containing transition metal oxide such as LiCoO ₂ as a positive electrode active material and a carbon material capable of occluding and releasing lithium as a negative electrode. Is commercially available. In such a battery system, the lithium ion is deintercalated from the positive electrode during charging and intercalated into carbon as the negative electrode, whereby the charging reaction is completed. In the discharge, a reaction reverse to the charge reaction proceeds, and the lithium ion deintercalated from the carbon negative electrode returns to the positive electrode active material, thereby completing the discharge reaction. The positive electrode active material is Li _1-x CoO
₂ (where 0 ≦ x ≦ 1.0), the number of reactive electrons of lithium that can be deintercalated during charging is x = 0.
It is about 5 electrons, which translates into about 130
mAh / g. However, LiCoO ₂ is 4.3 Vvs. Since lithium having a high potential of about Li / Li + and x = 0.5 is deintercalated, its crystal structure is in a very unstable state. A battery in such a charged state is, for example,
It is known that when left at a high temperature of about 85 ° C., not only does the property of the positive electrode active material deteriorate, but also because it is reactive, it decomposes the organic solvent in the electrolytic solution and generates gas. In general, in order to ensure safety during overcharge in a lithium ion secondary battery, when the internal pressure of the battery exceeds a certain value, a safety mechanism provided in a sealing plate is activated to cut off an external current. Often, a safety structure is used. However, leaving such batteries at high temperatures,
If a large amount of gas is generated, the safety mechanism may be activated and the function as a battery may be lost. Therefore, in order to achieve both reliability when the battery is left at a high temperature and safety during overcharging, it is required to strictly control a safety mechanism provided within the sealing plate and operating at a certain range of internal pressure. On the other hand, attempts have been made to minimize the amount of gas generated during high-temperature storage, and it has been proposed to control the physical properties of the positive electrode material, reduce the reactivity, and use an electrolytic solution having good withstand voltage characteristics. Was. Recently, LiNiO ₂ or a part of Ni element has been replaced with another element such as Co or Al or Mn or B as a cathode active material in place of LiCoO ₂ in order to further increase the capacity of a lithium ion secondary battery. A solid solution substituted by, for example, has been proposed (for example, see JP-A-6-60887), and its development is in progress. LiNiO ₂ has a large amount of lithium that can be deintercalated at the time of charging and is 180 mA.
Although h / g~200mAh / g of the expected since the specific capacity is obtained is large, the state of charge LiCoO ₂
Further, since the crystal structure is more unstable and reactive, it is further necessary to suppress the generation of gas when left at high temperature. [0006] As described above, when a non-aqueous electrolyte secondary battery using a lithium-containing transition metal oxide as a positive electrode active material is left at a high temperature in a charged state, decomposition of the electrolyte occurs. The internal pressure of the battery rises due to the gas generation accompanying it, and there is a possibility that the malfunction of interrupting the current by the operation of the safety mechanism may occur.To avoid this, control the material properties of the positive electrode active material, Attempts have been made to reduce the specific surface area of the electrode and to select an electrolyte that produces less gas. However, when such measures are taken, in many cases, the battery capacity is reduced, the high-rate charge / discharge characteristics are reduced, and it is difficult to obtain satisfactory battery characteristics. Therefore, the present invention solves the above-mentioned problems, and does not impair battery characteristics such as battery capacity and high-rate charge / discharge characteristics without lowering battery internal pressure when the battery is left at high temperatures. It is an object to provide a water electrolyte secondary battery. [0008] In order to solve the above-mentioned problems, the present invention provides a positive electrode mainly composed of a lithium-containing transition metal oxide, a negative electrode mainly composed of lithium, and a non-aqueous electrolyte.
In a non-aqueous electrolyte secondary battery provided with: SrO capable of reacting with a gas generated in the battery system to generate a carbonate does not come into direct contact with an electrode and an electrolyte in a solid state such as a powder or a molded body. The non-aqueous electrolyte secondary battery is arranged as described above . According to the present invention, when a charged battery is left at a high temperature, the gas generated by the decomposition of the electrolytic solution reacts with the added oxide to reduce the gas, thereby suppressing an increase in the internal pressure of the battery. It is possible to do. In order to prevent an increase in the internal pressure of the battery due to gas generation when left at a high temperature without causing a decrease in the battery characteristics, the generated gas is absorbed before the safety mechanism in the sealing plate operates to increase the internal pressure of the battery. It is effective to prevent this. Then, as a result of analyzing the composition of the generated gas, it was found that most of the components of the gas were carbon dioxide. In addition, it was clarified that the amount of gas originating from the positive electrode was dominant as the generation source. Further, as for the gas generation amount, for example, when the battery was left at 85 ° C., the gas amount increased in proportion to the time, and the gas generation amount was substantially constant from several hours to about 10 hours, and no more gas was generated. Therefore, in the present invention, a material that reacts slowly with carbon dioxide and does not adversely affect battery performance is provided in the battery system so as not to come into direct contact with the battery and the electrolyte. As a result, it has been found that the effect of the present invention can be obtained by adding at least one oxide selected from the group consisting of SrO, CaO, BaO, and MgO as an oxide for generating a carbonate. . Japanese Patent Application Laid-Open No. Hei 7-153496 discloses that the cycle characteristics of a battery are improved by adding and mixing an active material and at least one oxide selected from BaO, MgO, and CaO into a positive electrode. However, the present invention does not add and mix at least one oxide selected from SrO, BaO, MgO, and CaO into a positive electrode, but instead uses a solid state such as a powder or a molded body to form an electrode and an electrolytic solution. It is arranged so that it does not come into direct contact with the liquid,
Both have completely different problems, and therefore have different oxide arrangements. Since these oxides react slowly with carbon dioxide to form carbonates and exist stably in the battery system,
It does not cause a decrease in battery performance. With respect to ensuring safety at the time of overcharging as described above, at the time of overcharging, oxygen generation occurs due to decomposition of the positive electrode active material itself in preference to gas generation due to decomposition of the electrolytic solution, and the reaction speed is high when left at high temperature. It is overwhelmingly faster than the gas generation rate. Therefore, the internal pressure of the battery rises and the safety mechanism operates, so that safety against overcharging is ensured. [0015] [Embodiment of the Invention The present invention can be implemented in the form described 請 Motomeko, as described in claim 1, a positive electrode consisting mainly of lithium-containing transition metal oxide, lithium a negative electrode and an active material, a non-aqueous non-aqueous electrolyte secondary battery comprising an electrolytic solution, Sr O a powder or molded body capable of producing carbonate by reacting with carbon dioxide generated in the battery system By arranging it so that it does not come into direct contact with the electrode and electrolyte in a solid state, this oxide can serve as a positive electrode, negative electrode,
When present in the battery system separately from the electrolytic solution, it reacts with carbon dioxide gas generated when the battery is left at a high temperature to generate SrCO ₃ . SrCO ₃ which generated is relatively inert, stable present in the cell system, does not adversely affect the subsequent battery characteristics. The present invention will be described in detail below with reference to examples. (Example 1) FIG. 1 shows a cutaway perspective view of a cylindrical battery used in this example, a conventional example and a comparative example.
In FIG. 1, reference numeral 1 denotes a negative electrode plate to which a negative electrode lead plate 2 is attached, and 3 denotes a positive electrode plate to which a positive electrode lead plate 4 is attached. The negative electrode plate 1 and the positive electrode plate 3 are housed in a battery case 7 which also serves as a negative electrode terminal with an electrode plate group spirally wound via a separator 5 with insulating plates 6 arranged above and below the electrode plate group. The upper edge of the battery case 7 is sealed via an insulating packing 8 with a sealing plate 9 also serving as a positive electrode terminal provided with a valve.
The inside of the sealing plate 9 is 10 kg / cm ² at a battery internal pressure of 20 ° C.
Is exceeded, conduction between the positive electrode terminal and the positive electrode lead plate 4 is stopped so that external current is cut off. Hereinafter, a method of manufacturing the positive electrode plate and the negative electrode plate will be described in detail. As the positive electrode active material, LiNi _0.8 Co _0.2 O ₂ was used. First, nickel hydroxide, cobalt hydroxide, and lithium hydroxide are mixed at an atomic ratio of Ni: Co: Li of 0.8:
It was weighed so as to be 0.2: 1.0, and was sufficiently mixed by a ball mill. Then, this mixture was put into a crucible made of alumina and heat-treated in oxygen at 750 ° C. for 10 hours. After natural cooling, pulverization and classification were performed to obtain a positive electrode active material powder having an average particle size of about 10 μm. 6 parts by weight of artificial graphite powder was added to 100 parts by weight of this active material, and N-
A solution in which polyvinylidene fluoride (hereinafter, referred to as PVDF) as a binder was dissolved in a solvent of methylpyrrolidone (hereinafter, referred to as NMP) was kneaded to form a paste. The amount of the added PVDF was adjusted to 4 parts by weight with respect to 100 parts by weight of the active material. Next, this paste was applied to both sides of an aluminum foil, dried, and rolled to obtain a positive electrode plate having a thickness of 0.14 mm, a width of 37 mm, and a length of 380 mm. In addition, in producing the positive electrode plate, a series of steps after kneading were performed in dry air. As the negative electrode, a mesophase small sphere having an average particle size of 6.0 μm, which was heat-treated at 2800 ° C. and graphitized, was used. 100 parts by weight of the graphitized mesophase was mixed with 3 parts by weight of styrene / butadiene rubber as a binder, and an aqueous carboxymethyl cellulose solution was added and kneaded to form a paste. This paste is coated on both sides of the copper foil, dried, and rolled to a thickness of 0.20 mm, a width of 39 mm,
A negative electrode plate having a length of 420 mm was used. Then, a lead plate was attached to each of the positive electrode plate and the negative electrode plate, and the thickness was 0.025 mm, the width was 45 mm, and the length was 1
It was spirally wound through a 000 mm separator and housed in a battery case having a diameter of 17.0 mm and a height of 50 mm. As an oxide to be subsequently added, SrO having an average particle size of about 8 μm was added to NMP in the same manner as in the preparation of the positive electrode plate.
A solution obtained by dissolving PVDF as a binder in the above solvent was kneaded to form a paste. This paste was applied to one side of an aluminum foil, dried and rolled, and then punched into a circle having a diameter of 8 mm, and the aluminum foil side was welded to the bottom of the sealing plate. The thickness of the oxide layer was set to 0.08 mm including the thickness of the aluminum foil. Further, the amount of SrO charged is _{0.1 to} 1 gram of LiNi _0.8 Co _0.2 O ₂ , which is a positive electrode active material.
It was 1 mmol. As the electrolyte, ethylene carbonate (hereinafter, referred to as ethylene carbonate)
EC and dimethyl carbonate (hereinafter referred to as DMC) were mixed at a volume ratio of 20:80, and a solution obtained by dissolving 1 mol / liter of LiPF ₆ as an electrolyte was injected. At that time, the electrolyte was prevented from contacting the oxide layer disposed on the bottom of the sealing plate. Then, after the electrolyte solution was sufficiently absorbed by the electrode plate group, the battery was sealed to obtain a completed battery, and 20 cells were produced as the battery of Example 1. (Conventional example) A battery was manufactured in exactly the same manner as in Example 1 except that the SrO oxide was not disposed in the battery system, and 20 cells were manufactured as a conventional battery. (Comparative Example) The same amount of SrO powder as in Example 1 was added to the battery system in a state where it was previously mixed in the positive electrode, instead of being arranged at the bottom of the sealing plate. A battery was produced in exactly the same manner as in Example 1 except that SrO was added to the positive electrode, and 20 cells were produced as batteries of the comparative example. The batteries of Example 1, Conventional Example and Comparative Example were subjected to charge / discharge tests. The charging was performed at a constant current voltage, and the battery was charged to 4.2 V at a constant current of 630 mA.
After reaching 2 V, conversion to constant voltage charging was performed, and charging was completed in 2 hours. Discharge was performed at a constant current of 900 mA, and the discharge end voltage was set to 2.5 V. Such charging and discharging is performed for 20
Five cycles were performed in an environment of ° C., and the capacity at the third cycle was used as the initial capacity. Then, the battery in the charged state was left in a thermostat at 85 ° C. for 15 hours. Thereafter, the battery was returned to an environment of 20 ° C. and the conduction of the battery was measured. Thereafter, the battery with conduction was charged and discharged again, and the capacity at the third cycle was taken as the capacity after standing. When the internal pressure of the battery exceeded about 10 kg / cm ² , the safety mechanism provided in the sealing plate 9 was activated, and the conduction between the positive electrode and the negative electrode was lost. Table 1 shows the results together with the average values of the initial capacity and the capacity after leaving. [Table 1] The battery capacity after being left at a high temperature was measured for a battery in which the safety mechanism did not operate. In the battery of Example 1, all cells remained conductive even after being left at a high temperature, indicating that the safety mechanism was not operating. In other words, it is considered that the internal pressure of the battery has fallen below the predetermined value due to the absorption of the gas generated during the high temperature storage by the SrO provided inside. The battery capacity after high temperature storage is as large as 938 mAh,
It can be seen that the reaction product of SrO does not adversely affect the battery characteristics. On the other hand, in the conventional battery, 15 cells have lost their function as a battery because the safety mechanism has been activated together with an increase in battery internal pressure due to high temperature storage. In addition, in the battery of the comparative example, almost the same 14 cells resulted in the operation of the safety mechanism. Also, the battery capacity tends to be somewhat smaller, which is not preferable. From the above, the purpose of the present invention cannot be achieved by adding and mixing SrO into the positive electrode in order to obtain the effects of the present invention, and the SrO is disposed in the battery system so as not to come into direct contact with the electrode and the electrolytic solution. It turns out to be important. In addition, another 10 batteries similar to the battery of Example 1 were prepared and subjected to an overcharge test at a constant current of 1 A. In all batteries, the safety mechanism was activated after 18 to 20 minutes, and the external current was shut off. No ignition, rupture or white smoke of the battery was observed, and the battery surface temperature was about 50 ° C. In other words, even if SrO is present in the battery system, it is expected that gas absorption at the time of overcharging does not occur or its speed is slow, and the present invention does not impair the safety at the time of overcharging. I understand. REFERENCE EXAMPLE A battery was prepared in which BaO was used in place of SrO as the oxide to be added in the battery of Example 1, and the amount of addition was as shown in Table 2 with respect to 1 gram of the positive electrode active material. And Battery A, Battery B, Battery C, Battery D, Battery E, and Battery F, respectively. These batteries were charged and discharged in the same manner as the battery of Example 1, and left at a high temperature in a charged state. Thereafter, the continuity of the battery was measured, and the results are shown in Table 2. [Table 2] In any of the batteries B, C, D, and E, the safety mechanism does not operate, and the effect of the present invention is obtained. However, in the battery A having a small addition amount of 0.03 mmol, the safety mechanism of about half of the cells was activated, and it can be seen that the suppression of the battery internal pressure was insufficient. On the other hand, even in the battery F having the largest addition amount of 0.25 mmol, a battery in which a part of the safety mechanism was operated was observed.
This is considered to be because the volume of voids in the battery became extremely small due to the increase in the volume of the added BaO, and the rate of increase of the battery internal pressure was faster than the gas absorption reaction, and the safety mechanism was activated. . From these results, it was found that the amount of oxide to be added was 0.0% per gram of the positive electrode active material.
It can be said that it is important that the amount is 4 mmol to 0.20 mmol. Although LiNi _0.8 Co _0.2 O ₂ was used as the positive electrode active material in Example 1 and Reference Example , LiNi _0.8 Co _0.2 O ₂ was used.
Al or Mn as part of Ni including O ₂ as another element
Or a solid solution substituted with B, LiCoO ₂ , LiMn ₂ O
_A similar effect was obtained when ₄ was used. The present invention is applicable to a non-aqueous electrolyte secondary battery using a lithium-containing transition metal oxide for a positive electrode. The negative electrode is made of graphitized mesophase spheres. However, other carbon materials such as artificial graphite, cokes, carbon fibers and the like, and lithium such as metal oxides are inserted and released. The present invention can be applied to a nonaqueous electrolyte secondary battery using lithium as an active material, for example, when a lithium alloy or lithium metal is used. As the electrolytic solution, a mixed solvent of EC and DMC was used as a solvent in this embodiment, but other solvents such as cyclic carbonates such as propylene carbonate and butylene carbonate, diethyl carbonate and ethyl carbonate Chain carbonates such as methyl carbonate, 1,2-
Any known compounds such as ethers such as dimethoxyethane and 2-methyltetrahydrofuran can be used alone or as a mixed solvent. LiBF for solute
₄ , LiClO _{4 and the} like can be used. As described above, according to the present invention, the battery function is satisfied by satisfying the battery characteristics, and even when the battery is left at a high temperature in a charged state, the internal pressure of the battery is prevented from rising. Has the advantageous effect of not causing the loss of

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cutaway perspective view of a cylindrical battery used in the present embodiment, a conventional example, and a comparative example. [Description of References] 1 negative electrode plate 2 negative electrode lead plate 3 positive electrode plate 4 positive electrode lead plate 5 Separator 6 Insulating plate 7 Battery case 8 Insulating packing 9 Sealing plate

Continuation of the front page (56) References JP-A-10-255860 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/40 H01M 4/02 H01M 10/52

Claims (1)

(57) [Claim 1] A non-aqueous electrolyte secondary comprising a positive electrode mainly composed of a lithium-containing transition metal oxide, a negative electrode mainly composed of lithium, and a non-aqueous electrolyte. In the battery, SrO capable of reacting with carbon dioxide gas generated in the battery system to form a carbonate is disposed in a solid state such as a powder or a molded body so as not to directly contact the electrode and the electrolyte. Non-aqueous electrolyte secondary battery.