JP2009211965A - Lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the constitution of a lithium ion secondary battery making a distinction of polarity between a positive electrode and a negative electrode unnecessary. <P>SOLUTION: A lithium ion secondary battery 1 includes a lithium ion secondary battery base body 10 including a first electrode 11, a second electrode 12 and a solid electrolyte 13; and a housing member 20 housing the lithium ion secondary battery base body 10. Each active material of the first electrode and the second electrode of the lithium ion secondary battery base body 10 contains Li<SB>2</SB>FeS<SB>2</SB>. The housing member 20 includes an insulating substrate 21 having a surface on which the lithium ion secondary battery base body 10 is placed and a metallic cover member 22 joined with the insulating substrate 21 so as to cover the lithium ion secondary battery base body 10 placed on the surface of the insulating substrate 21. An insulator 30 is arranged in the inner space of the housing member 20 so as to surround the lithium ion secondary battery base body 10. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a lithium ion secondary battery.

  In recent years, lithium ion secondary batteries have been used as power sources for portable electronic devices such as mobile phones and portable personal computers. With the further miniaturization of portable electronic devices, it is required to further reduce the size of lithium ion secondary batteries and facilitate connection to an external electric circuit board.

In order to meet such a demand, a battery case and a battery that can be surface-mounted on an external electric circuit board are disclosed in, for example, Japanese Patent Laid-Open No. 2005-71889 (Patent Document 1). In this document, a lithium ion secondary battery is disclosed as a battery. As the positive electrode active material, lithium cobaltate (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), or the like is used. It is exemplified that carbon materials such as coke and carbon fiber are used.
JP 2005-71889 A

  However, when a lithium ion secondary battery is surface-mounted on an external electric circuit board, the positive electrode and the negative electrode may be installed incorrectly. If the positive electrode and the negative electrode are installed in reverse, the device may not operate normally, or it may cause failure or damage. Therefore, it is necessary to make it possible to distinguish between the positive electrode and the negative electrode by marking the outer surface of the lithium ion secondary battery, or to prevent the positive electrode and the negative electrode from being attached reversely using an image sensor or the like. .

  Accordingly, an object of the present invention is to provide a configuration of a lithium ion secondary battery in which it is not necessary to distinguish between polarities of positive electrode and negative electrode.

A lithium ion secondary battery according to one aspect of the present invention is a lithium ion secondary battery including a first electrode, a second electrode, and an electrolyte. The active material of the first electrode and the second electrode Each of which contains Li ₂ FeS ₂ .

In the lithium ion secondary battery according to one aspect of the present invention, the same material Li ₂ FeS ₂ is used as the active material of the first electrode and the second electrode. When one of the first electrode and the second electrode is a positive electrode and the other of the first electrode and the second electrode is a negative electrode, the following reactions are carried out at the positive electrode and the negative electrode.

  In the positive electrode, the following reaction is performed during charging.

Li ₂ FeS ₂ → Li _2-x FeS ₂ + xLi ⁺ + xe ⁻
In the positive electrode, the following reaction is performed during discharge.

Li _2−x FeS ₂ + xLi ⁺ + xe ⁻ → Li ₂ FeS ₂
In the negative electrode, the following reaction is performed during charging.

Li ₂ FeS ₂ + xLi ⁺ + xe ⁻ → Li _{2 + x} FeS ₂
In the negative electrode, the following reaction is performed during discharge.

_{Li 2 + x FeS 2 → Li} 2 FeS 2 + xLi + + xe -
In the above reaction formula, 0 <x ≦ 2.

  In the lithium ion secondary battery according to one aspect of the present invention, since the reaction is performed in the positive electrode and the negative electrode as in a kind of concentration battery, the first electrode and the second electrode are polar as the positive electrode and the negative electrode. Need not be used separately. For this reason, it is possible to prevent the occurrence of abnormal operation, failure, breakage, etc. of the apparatus due to the reverse attachment of the first electrode and the second electrode. Further, it is not necessary to mark the outer surface of the lithium ion secondary battery so that the positive electrode and the negative electrode can be distinguished from the first electrode and the second electrode.

  In the lithium ion secondary battery according to one aspect of the present invention, the electrolyte is preferably a solid electrolyte. If the electrolyte is a solid electrolyte, the lithium ion secondary battery can withstand the heating temperature in the reflow furnace and can be mounted on the external electric circuit board by reflow soldering.

A lithium ion secondary battery according to another aspect of the present invention contains a lithium ion secondary battery body including a first electrode, a second electrode, and a solid electrolyte, and a lithium ion secondary battery body A receiving member. Each of the active material of the first electrode and the second electrode of the lithium ion secondary battery element body includes Li ₂ FeS ₂ . The housing member is insulated so as to cover the insulating base material having a surface on which the lithium ion secondary battery body is placed, and the lithium ion secondary battery body placed on the surface of the insulating base material. A lid member joined to the substrate. An insulating material is disposed in the internal space of the housing member so as to surround the periphery of the lithium ion secondary battery body.

  In the lithium ion secondary battery according to another aspect of the present invention, it is possible to prevent the occurrence of abnormal operation, failure, breakage, etc. of the device by attaching the first electrode and the second electrode in reverse. In addition, since the housing member houses the battery element body containing the solid electrolyte instead of the liquid electrolyte, it is possible to withstand the heating temperature in the reflow furnace. Thereby, the lithium ion secondary battery according to another aspect of the present invention can be surface-mounted on a substrate by reflow soldering.

  By the way, in the lithium ion secondary battery according to another aspect of the present invention, since the battery body is composed of only a solid, the volume changes during charge and discharge. At this time, as the volume change of the battery body is repeated at the time of charging / discharging, the contact state of the electrode active material particles, the electrode active material particles and the electrolyte material particles changes. There is a problem that the voltage becomes unstable. In the lithium ion secondary battery according to another aspect of the present invention, since the insulating material is disposed so as to surround the battery element body in the internal space of the housing member, the above problem is solved. Can do. Therefore, the lithium ion secondary battery according to another aspect of the present invention can achieve voltage stability during charging and discharging of the battery. If the insulating material is made of a soft resin and the outer housing member is made of a hard material, it is possible to suppress deformation of the insulating material surrounding the battery body, thereby further enhancing the above effect. Can do.

  As described above, according to the lithium ion secondary battery according to one aspect of the present invention, it is possible to prevent the occurrence of abnormal operation, failure, damage, etc. of the apparatus by attaching the first electrode and the second electrode in reverse. can do. In addition, according to the lithium ion secondary battery according to another aspect of the present invention, the occurrence of abnormal operation, failure, breakage, etc. of the device due to the reverse attachment of the first electrode and the second electrode is prevented. In addition, the lithium ion secondary battery can be surface-mounted on the substrate by reflow soldering, and voltage stability can be achieved during charging and discharging of the battery.

  An embodiment of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing a configuration of a lithium ion secondary battery as one embodiment of the present invention.

  As shown in FIG. 1, the lithium ion secondary battery 1 includes a lithium ion secondary battery body 10 and a housing member 20 that houses the lithium ion secondary battery body 10.

As the lithium ion secondary battery body 10, for example, an all-solid secondary battery includes a solid electrolyte 13 sandwiched between a first electrode 11 and a second electrode 12, and an outer surface of the first electrode 11. A conductive adhesive 111 is attached to the second electrode 12, and a conductive adhesive 121 is attached to the outer surface of the second electrode 12. The first electrode 11 and the second electrode 12 can operate as either a positive electrode or a negative electrode, and Li ₂ FeS ₂ as an electrode active material of either the positive electrode active material or the negative electrode active material, and a solid electrolyte Li ₂ S—P ₂ S ₅ based composition. The solid electrolyte 13 sandwiched between the first electrode 11 and the second electrode 12 is a Li ₂ S—P ₂ S ₅ composition. The conductive adhesives 111 and 121 are, for example, silver (Ag) -epoxy conductive adhesives.

  The housing member 20 includes an insulating base material 21 and a metal lid member 22. The insulating base material 21 has a recess that accommodates the lithium ion secondary battery body 10. The lithium ion secondary battery body 10 is mounted and fixed to the bottom surface of the recess as the surface of the insulating base material 21 with the conductive adhesive 111 interposed therebetween. The metal lid member 22 is joined to the top surface of the concave portion of the insulating base material 21 with metallized layers 221 and 222 so as to cover the lithium ion secondary battery body 10 mounted on the surface of the insulating base material 21. Has been. The metallized layers 221 and 222 are formed, for example, by printing and applying a metal paste whose main component is a metal powder such as tungsten (W). Insulating base material 21 is formed from ceramics, such as alumina, for example. The metal lid member 22 is made of a metal such as aluminum (Al) or copper (Cu), or an alloy such as iron (Fe) -nickel (Ni) -cobalt (Co) alloy. Thus, since the lithium ion secondary battery body 10 is firmly fixed to the insulating base material 21, it is possible to suppress deterioration of characteristics due to a volume change of the lithium ion secondary battery body 10 during charging and discharging. .

  Moreover, in this embodiment, although the insulating base material 21 showed the example formed from ceramics, you may form with insulating materials, such as a synthetic resin which can endure the heating temperature in a reflow furnace. . In this case, it is preferable to form the insulating base material 21 using a synthetic resin having a heat distortion temperature of 270 ° C. or higher.

  An insulating material 30 is disposed and filled in the internal space of the housing member 20 so as to surround the lithium ion secondary battery body 10. The insulating material 30 is made of a material such as an epoxy resin or a polyimide resin, for example.

  Conductor portions 112 and 122 are disposed inside the insulating base material 21. The conductor portions 112 and 122 are formed as follows. First, for example, a metal paste mainly composed of a metal powder such as tungsten (W) is printed on the surface of the green sheet, or formed on the green sheet of the ceramic constituting the insulating base 21. The printed holes are printed and filled to form a printed pattern to be a conductor portion. Next, the insulating base material 21 which has the conductor parts 112 and 122 inside is produced by laminating | stacking and baking the green sheet in which these printing patterns were formed.

  Terminals 110 and 120 are disposed on the lower surface as the outer surface of one side of the insulating base material 21. The first electrode 11 of the lithium ion secondary battery body 10 is connected to the terminal 110 through the conductive adhesive 111 and the conductor portion 112. The second electrode 12 of the lithium ion secondary battery body 10 is connected to the terminal 120 through the conductive adhesive 121, the metal wire 123, and the conductor portion 122. The terminals 110 and 120 are formed as follows. First, a metal paste having a metal powder such as tungsten (W) as a main component is printed and applied to a ceramic green sheet constituting the insulating base 21 to form a printed pattern serving as a terminal. Next, the insulating base material 21 having the terminals 110 and 120 on the outer surface is produced by firing the green sheet on which these printed patterns are formed. The terminals 110 and 120 are formed in the same process as the conductor portions 112 and 122 described above. In order to improve the wettability with the solder, it is preferable that a nickel (Ni) layer and a gold (Au) layer are formed on the surfaces of the terminals 110 and 120 by a plating method or the like.

In one embodiment of the invention configured as described above, in the lithium ion secondary battery body 10, the same material Li ₂ FeS ₂ is used as the material of the positive electrode active material and the negative electrode active material, and at the time of charging and discharging. Since the reaction is performed in the positive electrode and the negative electrode like a kind of concentration cell, it is not necessary to distinguish the polarity of the first electrode and the second electrode as in the case of the positive electrode and the negative electrode. For this reason, it is possible to prevent the occurrence of abnormal operation, failure, breakage, etc. of the apparatus due to the reverse attachment of the first electrode and the second electrode. Further, it is not necessary to mark the outer surface of the lithium ion secondary battery body 10 so that the positive electrode and the negative electrode can be distinguished from the first electrode and the second electrode.

  Further, in the lithium ion secondary battery 1 of the present invention, since the housing member 20 houses the lithium ion secondary battery body 10 including the solid electrolyte 13 instead of the liquid electrolyte, the heating temperature in the reflow furnace Can withstand. Thereby, this lithium ion secondary battery 1 can be surface-mounted on a substrate by reflow soldering.

  By the way, when the lithium ion secondary battery body 10 is charged and discharged, the crystal structure of the electrode active material is changed and the volume is changed by the lithium ions entering and leaving. Since the lithium ion secondary battery body 10 in the present invention does not contain a liquid component and is composed only of a solid, it cannot absorb the volume change of the particles of the electrode active material, and the first electrode 11 and the second electrode 12. The volume changes during charging and discharging. At this time, as the volume change of the lithium ion secondary battery body 10 is repeated during charging and discharging, the contact states of the electrode active material particles, the electrode active material particles, and the electrolyte material particles change. Therefore, there is a problem that the voltage of the battery becomes unstable. In the lithium ion secondary battery 1 of the present invention, since the insulating material 30 is disposed in the internal space of the housing member 20 so as to surround the lithium ion secondary battery body 10, the above problem is solved. be able to. Therefore, the lithium ion secondary battery 1 of the present invention can achieve voltage stability during charging and discharging of the lithium ion secondary battery body 10. In addition, if the insulating material 30 is made of a soft resin and the outer housing member 20 is made of a hard material, deformation of the insulating material 30 surrounding the lithium ion secondary battery body 10 can be suppressed. The above effects can be further enhanced.

Furthermore, in the lithium ion secondary battery 1 of the present invention, each of the active materials of the first electrode and the second electrode constituting the lithium ion secondary battery body 10 contains Li ₂ FeS ₂ , and the solid electrolyte Includes Li ₂ S and P ₂ S ₅ . In this case, in the lithium ion secondary battery body 10, if the solid electrolyte contains Li ₂ S and P ₂ S ₅ and the active material of the first electrode and the second electrode contains Li ₂ FeS ₂ , The active material of the 1st electrode and 2nd electrode which consist of a thing has low reactivity with a solid electrolyte. In addition, even if the lithium ion secondary battery body 10 is subjected to heat treatment at a predetermined temperature, the rate at which the battery capacity and other characteristics decrease after the heat treatment is lower than that of a solid battery provided with a conventional solid electrolyte. Accordingly, in the lithium ion secondary battery body 10 of the present invention, the heat resistance can be increased as compared with the conventional solid battery, so that the solder is used in a reflow furnace having a relatively high heating temperature using Pb-free solder. Even if the attaching process is performed, deterioration of characteristics such as battery capacity can be suppressed to a low level.

  In the lithium ion secondary battery 1 according to the present invention, the conductor portions 112 and 122 are disposed inside the insulating base material 21, and the terminals 110 and 120 are disposed on the lower surface of the insulating base material 21. The first electrode 11 and the second electrode 12 of the secondary battery body 10 are connected to the terminals 110 and 120 through the conductor portions 112 and 122, respectively.

  Since it is configured in this way, the terminals 110 and 120 are arranged on the lower surface, which is the outer surface on one side of the insulating base material 21, so that a paste-like shape is previously formed on the wiring board connected to the terminals 110 and 120. The reflow soldering process can be performed by supplying the solder material.

  Examples of the present invention will be described below.

A lithium ion secondary battery body 10 shown in FIG. 1 was produced using a Li ₂ S—P ₂ S ₅ composition as a solid electrolyte.

The solid electrolyte was prepared by mixing Li ₂ S and P ₂ S ₅ in a molar ratio of 7: 3, vacuum-sealing the above mixture in a quartz tube whose inner surface was covered with carbon, heating at 900 ° C. for 2 hours, It was prepared by quenching with Li ₂ FeS ₂ as the active material of the first electrode and the second electrode is prepared by mixing Li ₂ S and FeS at a molar ratio of 1: 1 and mixing the above mixture into a quartz tube whose inner surface is coated with carbon. It was produced by vacuum-sealing and heating at 950 ° C. for 5 hours.

An electrode material was prepared by mixing Li ₂ FeS ₂ as an active material of the first electrode and the second electrode obtained above and a solid electrolyte in a weight ratio of 1: 1. This electrode material is a material common to the first electrode 11 and the second electrode 12.

The electrode material and the solid electrolyte obtained as described above were laminated in the order of electrode material / solid electrolyte / electrode material, and a three-layered pellet was press-molded at a pressure of 3000 kgf / cm ² . In this way, as shown in FIG. 1, a lithium ion secondary battery element body 10 including the solid electrolyte 13 sandwiched between the first electrode 11 and the second electrode 12 was obtained.

  On the other hand, as a ceramic green sheet constituting the insulating base 21 shown in FIG. 1, a metal paste mainly composed of tungsten (W) metal powder is printed and applied to an alumina compact as a conductor and terminals. A printed pattern was formed. Next, the green sheets on which these printed patterns were formed were stacked and baked to produce the insulating base material 21 having the conductor portions 112 and 122 inside and the terminals 110 and 120 on the outer surface. At this time, metallized layers 221 and 222 were formed on the top surface of the concave portion of the insulating base material 21. In order to improve the wettability with the solder, a nickel (Ni) layer and a gold (Au) layer were formed on the surfaces of the terminals 110 and 120 by a plating method.

  Using the lithium ion secondary battery body 10 and the insulating base material 21 obtained above, as shown in FIG. 1, the first electrode 11 side of the lithium ion secondary battery body 10 is turned down, The lithium ion secondary battery body 10 is placed on the bottom surface of the recess of the insulating base material 21 with a silver (Ag) -epoxy conductive adhesive as the conductive adhesive 111, and the adhesive is cured. It was. Thereby, the lithium ion secondary battery body 10 was joined to the insulating base material 21 so as to conduct between the conductor portion 112 and the first electrode 11.

  Thereafter, a part of the surface of the second electrode 12 was covered with a conductive adhesive 121 made of a silver (Ag) -epoxy conductive adhesive. The conductive adhesive 121 and the conductor portion 122 were connected by a metal wire 123. An epoxy resin as an insulating material 30 was disposed so as to surround and cover the periphery of the lithium ion secondary battery body 10.

  Next, the metal lid member 22 is interposed on the top surface of the concave portion of the insulating base material 21 with the metallized layers 221 and 222 so as to cover the lithium ion secondary battery body 10 mounted on the surface of the insulating base material 21. Arranged. Furthermore, the metal lid member 22 and the insulating base material 21 were joined by welding. Then, the metal lid member 22, the insulating material 30, and the insulating base material 21 were integrated by hardening the epoxy resin as the insulating material 30. In this way, a small lithium ion secondary battery 1 having a size of 4 mm × 4 mm square was produced.

The lithium ion secondary battery body 10 accommodated in the manufactured lithium ion secondary battery 1 is charged at a current density of 16 μA / cm ² using the first electrode 11 as a positive electrode, and then discharged to obtain a first The discharge capacity per unit weight of the active material was measured. Charging / discharging was performed according to the following procedure. After starting charging at the current density described above, charging was considered to be complete when the potential changed rapidly and charging was stopped. Thereafter, switching to discharging was performed, and when the potential became 0 V, it was considered that discharging was completed, and discharging was stopped. This charge / discharge test was performed under conditions where the ambient temperature was 20 ° C.

The measurement results of the charge / discharge test are shown in FIG. FIG. 2 shows that the fabricated lithium ion secondary battery body 10 exhibits a charge / discharge capacity of about 100 μAh. Since the mass of each of the active materials of the first electrode and the second electrode made of Li ₂ FeS ₂ was 0.3 mg, the measured value of the charge / discharge capacity per unit mass was about 350 mAh / g. . This measured value is about 75% with respect to the theoretical value of 400 mAh / g of charge / discharge capacity per unit mass.

  This measurement result is for the case where the first electrode 11 is a positive electrode and the second electrode 12 is a negative electrode, but the case where the second electrode 12 is a positive electrode and the first electrode 11 is a negative electrode. However, it goes without saying that similar results can be obtained.

On the other hand, when Li _0.5 CoO ₂ is used as a material for the positive electrode active material and the negative electrode active material and charge / discharge reaction is performed between LiCoO ₂ and CoO ₂ , the theory of charge / discharge capacity per unit mass is obtained. The value is 136 mAh / g. In addition, when Li _0.5 Mn ₂ O ₄ is used as a material for the positive electrode active material and the negative electrode active material and charge / discharge reaction is performed between LiMn ₂ O ₄ and Mn ₂ O ₄ , charge / discharge per unit mass is performed. The theoretical value of capacity is 74 mAh / g.

In the lithium ion secondary battery of the present invention, the charge / discharge capacity value per unit mass is Li _0.5 CoO ₂ or Li _0.5 Mn as the material of the positive electrode active material and the negative electrode active material, whether theoretical or measured. _This is a relatively large value compared to a lithium ion secondary battery using ₂ O ₄ .

In addition, Li _0.5 CoO ₂ and Li _0.5 Mn ₂ O ₄ as materials of the positive electrode active material and the negative electrode active material use LiCoO ₂ or LiMn ₂ O ₄ as one electrode active material, A battery is formed using another material as the other electrode active material, and is obtained by charging until a desired composition is obtained. However, it is not easy to synthesize Li _0.5 CoO ₂ and Li _0.5 Mn ₂ O ₄ from raw materials such as metal oxides.

On the other hand, Li ₂ FeS ₂ used for the material of the active material of the first electrode and the second electrode of the lithium ion secondary battery of the present invention can be easily synthesized from Li ₂ S and FeS.

Further, when a lithium ion secondary battery is configured using Li _0.5 CoO ₂ or Li _0.5 Mn ₂ O ₄ as a material for the positive electrode active material and the negative electrode active material, it is inserted into the negative electrode in order to increase the capacity. If the battery is charged until Li is excessive, the crystal structure changes. For this reason, the electrical resistance increases, and the voltage drops. Therefore, it is impossible to obtain a capacity higher than the theoretical value, and it is difficult to actually obtain a capacity as the theoretical value.

  In addition, the lithium ion secondary battery of the present invention has a lower voltage when compared with a conventional lithium ion secondary battery using a carbon material as the negative electrode active material, but the voltage for a memory backup or the like is relatively low. It can be used as a power source for applications that may be low.

  It should be considered that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is shown not by the above embodiments and examples but by the scope of claims, and is intended to include all modifications and variations within the meaning and scope equivalent to the scope of claims. .

It is typical sectional drawing which shows the structure of a lithium ion secondary battery as one embodiment of this invention. It is a figure which shows the measurement result of the charging / discharging test of the lithium ion secondary battery produced in one Example of this invention.

Explanation of symbols

  1: lithium ion secondary battery, 10: lithium ion secondary battery body, 11: first electrode, 12: second electrode, 13: solid electrolyte, 20: housing member, 21: insulating base material, 22: Metal lid member, 30: insulating material, 112, 122: conductor portion, 110, 120: terminal.

Claims (3)

In a lithium ion secondary battery comprising a first electrode, a second electrode, and an electrolyte,
Each of the active material of the first electrode and the second electrode is characterized in that it comprises a Li ₂ FeS _2, the lithium ion secondary battery.   The lithium ion secondary battery according to claim 1, wherein the electrolyte is a solid electrolyte. A lithium ion secondary battery element body including a first electrode, a second electrode, and a solid electrolyte; and a housing member that accommodates the lithium ion secondary battery element body,
Each of the active materials of the first electrode and the second electrode of the lithium ion secondary battery element body includes Li ₂ FeS ₂ ,
The housing member is
An insulating base material having a surface on which the lithium ion secondary battery body is placed;
A lid member joined to the insulating base material so as to cover the lithium ion secondary battery body placed on the surface of the insulating base material,
A lithium ion secondary battery in which an insulating material is disposed in the internal space of the housing member so as to surround the lithium ion secondary battery body.

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