JP2015122252A - Lithium ion secondary battery and manufacturing method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve power saving in a manufacturing process while securing charge/discharge capacity of a battery.SOLUTION: A cathode electrode structure 12A having a cathode electrode material layer 20 including a cathode active material 24 and a conductive assistant 26 formed on a collector is prepared. The cathode structure 12A is installed as a cathode 44 of an air battery 40 with a lithium metal as an anode 42. The air battery 40 is discharged so as to deposit lithium oxide 6 (LiO) on the cathode electrode material layer 20. The cathode 44 having the lithium oxide 6 deposited thereon is taken out from the air battery 40 and then installed as a cathode 12 of a lithium ion secondary battery 10. The lithium ion 2 produced by oxidative degradation of the lithium oxide 6 by firstly charging the lithium ion secondary battery 10 using an external power source B is taken into an anode 14 of the lithium ion secondary battery 10 so that the lithium ion secondary battery 10 is completed.

Description

  The present invention relates to a lithium ion secondary battery and a method for manufacturing the same.

A negative electrode of a lithium ion secondary battery is generally formed by fixing a negative electrode active material made of, for example, a carbon-based material to a current collector.
After the lithium ion secondary battery is assembled, lithium ions released from the positive electrode active material by the initial charge are taken into the negative electrode.
At this time, when a SEI (Solid Electrolyte Interphase) film, which is a reaction product of lithium ions and an electrolytic solution, is formed on the surface of the negative electrode active material, lithium ions released from the positive electrode active material are irreversible in the SEI film. The charge / discharge capacity of the battery is reduced.
Therefore, in Patent Document 1, an electrode material layer is prepared by preparing a lithium dope made of lithium oxide (Li ₂ O, Li ₂ O ₂ ) and a positive electrode active material in a paste form and applying the paste to a positive electrode current collector. A technology has been proposed in which lithium ions generated by an oxidative decomposition reaction of lithium oxide at the first charge are taken into a negative electrode.

JP 2010-225291 A

However, in the above prior art, since the lithium doping material made of lithium oxide and the positive electrode active material are simply mixed, the reactivity of lithium oxide (Li ₂ O, Li ₂ O ₂ ) is poor, and oxidative decomposition It is necessary to increase the voltage at the time of the first charge necessary for the reaction, which is disadvantageous in achieving power saving in the manufacturing process. Moreover, not all lithium oxides are oxidized and decomposed, and lithium oxide remains on the positive electrode. The charge / discharge capacity per positive electrode weight is reduced.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a lithium ion secondary battery that is advantageous in achieving power saving in the manufacturing process while securing the charge / discharge capacity of the battery, and a method for manufacturing the same. And

In order to achieve the above object, a first aspect of the present invention is a method for manufacturing a lithium ion secondary battery, wherein a positive electrode structure including a positive electrode material layer containing a positive electrode active material is formed on a positive electrode current collector. As a positive electrode of an air battery using a lithium metal as a negative electrode; a step of discharging lithium air to the positive electrode material layer by discharging the air battery; and taking out the positive electrode from the air battery and lithium ions A step of assembling as a positive electrode of a secondary battery, and a step of incorporating lithium ions generated by an oxidative decomposition reaction of the lithium oxide into the negative electrode of the lithium ion secondary battery by first charging the lithium ion secondary battery A method for manufacturing a lithium ion secondary battery.
The invention according to claim 2 is characterized in that the lithium oxide is electrochemically deposited, and in the step of depositing the lithium oxide, discharging is performed using a discharger that adjusts a discharge charge amount. The method for producing a lithium ion secondary battery according to claim 1.
The invention according to claim 3 is characterized in that the positive electrode material layer includes a positive electrode active material and a conductive auxiliary agent, and the conductive auxiliary agent has a catalytic function of oxidizing and decomposing the lithium oxide. 2. A method for producing a lithium ion secondary battery according to 2.
The invention according to claim 4 is the method for producing a lithium ion secondary battery according to claim 3, wherein the conductive additive is carbon and the lithium oxide is Li ₂ O ₂ .
The invention according to claim 5 is characterized in that the positive electrode active material is represented by lithium metal oxide Li _x MO _y (wherein component M is a transition metal element and 0 <x, 0 ≦ y). The method of manufacturing a lithium ion secondary battery according to claim 3 or 4.
The invention according to claim 6 is the method for producing a lithium ion secondary battery according to claim 5, wherein the positive electrode active material is Li ₂ MnO ₃ .
The invention described in claim 7 is a lithium ion secondary battery manufactured by the method for manufacturing a lithium ion secondary battery according to any one of claims 1 to 6.

According to the first aspect of the present invention, the lithium oxide is deposited on the positive electrode material layer of the positive electrode using an air battery, and then the positive electrode is assembled as the positive electrode of the lithium ion secondary battery and charged for the first time. The lithium ions were taken into the negative electrode of the lithium ion secondary battery.
Therefore, since the lithium oxide is generated electrochemically, the reactivity of the lithium oxide can be increased, so that the voltage at the first charge required for the oxidative decomposition reaction of the lithium oxide can be lowered. Therefore, it is advantageous in achieving power saving in the manufacturing process while securing the charge / discharge capacity of the lithium ion secondary battery.
According to the second aspect of the present invention, since the amount of precipitation is adjusted by the amount of discharge charge, the amount of precipitation of the lithium oxide compound can be easily increased or decreased simply by adjusting the charge. Can be manufactured.
According to the description of claim 3, since the conductive assistant has a catalytic function, it assists the power generation reaction when used as a lithium ion secondary battery, and an improvement in performance can be expected.
According to the description of claim 4, since carbon also functions as a catalyst, the reactivity of the lithium oxide Li ₂ O ₂ is further increased, and the voltage to be applied to the lithium ion secondary battery during charging is further increased. This can be reduced, and is further advantageous in terms of power saving.
According to the description of claim 5, the potential can be increased by using a lithium metal oxide as the positive electrode active material, and a high output secondary battery can be provided.
According to the description of claim 6, when the positive electrode active material is Li ₂ MnO ₃ , a part of lithium ions disappears by generating Li ₂ O by lithium / oxygen element co-desorption that occurs at the time of initial charge. Even so, new lithium ions can be reliably compensated at the first charge, which is advantageous in securing the charge / discharge capacity of the lithium ion secondary battery.
According to the seventh aspect of the present invention, it is advantageous to provide a lithium ion secondary battery in which charge / discharge capacity is ensured and cost is reduced by power saving.

It is a schematic diagram which shows the lithium ion secondary battery manufactured by the manufacturing method of the lithium ion secondary battery which concerns on this Embodiment. It is a schematic diagram which shows the state which assembled | attached the positive electrode structure as the positive electrode of an air battery in the manufacturing method of the lithium ion secondary battery which concerns on this Embodiment. It is a schematic diagram which shows the state which discharged the air battery in the manufacturing method of the lithium ion secondary battery which concerns on this Embodiment. It is a schematic diagram which shows the state which assembled | attached the positive electrode taken out from the air battery as a positive electrode of a lithium ion secondary battery, and performed the first charge in the manufacturing method of the lithium ion secondary battery which concerns on this Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, the configuration of the lithium ion secondary battery 10 manufactured by the manufacturing method of the present embodiment will be described.
As shown in FIG. 1, the lithium ion secondary battery 10 includes a positive electrode 12, a negative electrode 14, an electrolytic solution 16, and a case 18.
The positive electrode 12 includes a positive electrode material layer 20 and a positive electrode current collector 22 and is configured in a sheet shape.
The positive electrode material layer 20 includes a positive electrode active material 24 and a conductive additive 26.
In the present embodiment, the positive electrode active material 24 is Li ₂ MnO ₃ which is a lithium-rich positive electrode material. As the positive electrode active material 24, a layered oxide material (LiCoO ₂ , LiNiO ₂ , Li (Ni, Mn, Co) O ₂ ), a spinel structure material (LiMn ₂ O ₄ ), an olivine structure material (LiFePO ₄ ), etc. Various known materials for positive electrode active materials can be used.
In the present embodiment, the conductive auxiliary agent 26 is made of carbon. As such carbon, various conventionally known conductive materials such as carbon black (acetylene black, ketjen black), carbon nanotube, and graphene can be used.
The positive electrode current collector 22 is composed of a grid-like metal foil. As such a metal foil, various conventionally known metal foils such as an aluminum foil can be used.

The negative electrode 14 includes a negative electrode material layer 28 and a negative electrode current collector 30 and is configured in a sheet shape.
The negative electrode material layer 28 includes a negative electrode active material 32.
In the present embodiment, the negative electrode active material 32 includes graphite. As the negative electrode active material 32, various conventionally known materials for negative electrode active materials can be used.
The negative electrode current collector 30 is composed of a metal foil. As such a metal foil, various conventionally known metal foils such as a copper foil can be used.

  The electrolytic solution 16 moves lithium ions 2 and is impregnated in a separator (not shown) provided between the positive electrode 12 and the negative electrode 14.

  The case 18 accommodates the positive electrode 12, the negative electrode 14, and the separator, and a positive electrode terminal 34 connected to the positive electrode 12 and a negative electrode terminal 36 connected to the negative electrode 14 are provided on the surface of the case 18. .

Next, a method for manufacturing the lithium ion secondary battery 10 will be described.
The negative electrode 14, the separator, and the case 18 are manufactured by a conventionally known method, and thus the description thereof is omitted. Hereinafter, the manufacturing method of the positive electrode 12 will be described mainly. 2 to 4, the case 18, the positive terminal 34, and the negative terminal 36 are not shown.

As shown in FIG. 2, a positive electrode structure 12A in which a positive electrode material layer 20 containing Li ₂ MnO ₃ as a positive electrode active material 24 and carbon as a conductive additive 26 is formed on a current collector is prepared.
And this positive electrode structure 12A is assembled | attached as the positive electrode 44 of the air battery 40 which uses lithium metal as the negative electrode (negative electrode active material) 42. FIG.
In this case, the air battery 40 includes a negative electrode 42, a positive electrode 44 made of the positive electrode structure 12 </ b> A, and an electrolytic solution 46 disposed between the negative electrode 42 and the positive electrode 44, and part of the positive electrode 44 is opened to the atmosphere. Consists of.

Next, as shown in FIG. 3, the load R is connected between the positive electrode 44 and the negative electrode 42 to discharge the air battery 40, thereby depositing lithium oxide 6 on the positive electrode material layer 20.
That is, the lithium ions 2 dissolved in the electrolytic solution 16 from the negative electrode 42 move to the positive electrode 12 and are taken into the positive electrode 12, thereby reacting with oxygen 4 in the atmosphere and being Li ₂ O ₂ as the lithium oxide 6. (Lithium peroxide) precipitates. That is, the positive electrode 44 is electrochemically pre-doped with the lithium oxide 6. Note that Li ₂ O ₂ is precipitated as the lithium oxide 6 because the conductive additive 26 is made of carbon.
In this case, the lithium oxide 6 is deposited in a state of being attached in the vicinity of carbon as the conductive auxiliary agent 26.
The amount of lithium oxide 6 to be deposited is controlled by the amount of current during discharge, and the amount of lithium oxide 6 to be deposited depends on the required characteristics and specifications of the lithium ion secondary battery 10. Determined experimentally.
That is, lithium oxide is deposited by discharging using a discharger that adjusts the amount of discharge charge.

Next, the positive electrode 44 on which the lithium oxide 6 is deposited is taken out from the air battery 40 and assembled as the positive electrode 12 of the lithium ion secondary battery 10 as shown in FIG.
Then, when the lithium ion secondary battery 10 is charged for the first time by the external power source B, the lithium ions 2 generated by the oxidative decomposition reaction of the lithium oxide 6 are taken into the negative electrode 14 of the lithium ion secondary battery 10.
The oxidative decomposition reaction of Li ₂ O ₂ as the lithium oxide 6 is represented by the following reaction formula.
Li ₂ O ₂ → 2Li ⁺ + 2e ⁻ + O ₂ (1)
In this case, since the lithium oxide 6 is generated electrochemically, the lithium oxide 6 is deposited in the vicinity of the carbon particles serving as the conductive auxiliary agent 26, so that the conductive auxiliary agent 26 and the lithium oxide 6 are deposited. , The reactivity of the lithium oxide 6 is increased, and lithium ions 2 are efficiently generated.
Moreover, since the carbon as the conductive auxiliary agent 26 also functions as a catalyst, the reactivity of the lithium oxide 6 is further enhanced, and the lithium ions 2 are generated more efficiently.
In addition, by increasing the reactivity of the lithium oxide 6, it is possible to reduce the wasteful lithium oxide 6 that remains in the positive electrode 12 without undergoing an oxidative decomposition reaction.
The lithium ion secondary battery 10 is completed by performing the first charge as described above.

On the other hand, at the time of initial charge, a part of the lithium ions 2 disappears due to the following reaction occurring in Li ₂ MnO ₃ as the positive electrode active material 24.
Li ₂ MnO ₃ → x (MnO ₂ + Li ₂ O) + (1-x) Li ₂ MnO ₃ (2)
That is, Li ₂ MnO ₃ changes its form to MnO ₂ having a charge / discharge function. At the same time, Li ₂ O is generated by lithium / oxygen element co-desorption, whereby a part of lithium ions 2 (movable lithium ions (Li ⁺ )) disappears.
Further, the lithium ions 2 are also lost by irreversibly taking in the lithium ions 2 released from the positive electrode active material 24 into the SEI film formed on the surface of the negative electrode active material 32.

  An ideal charging / discharging reaction formula of the positive electrode 12 after the initial charging process is as follows.

In equation (2), the reaction from left to right corresponds to discharging, and the reaction from right to left corresponds to charging.
That is, when a part of the lithium ions 2 disappears, the charge / discharge reaction as represented by the formula (2) does not sufficiently occur, and the charge / discharge capacity of the battery decreases.
However, since the lithium ions 2 lost due to the generation of Li ₂ O and the action of the SEI film as described above are compensated by the lithium ions 2 newly generated by the oxidative decomposition reaction of the lithium oxide 6, Discharge capacity is secured.

As described above, according to the present embodiment, the positive electrode structure 12 </ b> A in which the positive electrode material layer 20 including the positive electrode active material 24 is formed on the positive electrode current collector 22 is assembled as the positive electrode 44 of the air battery 40. After the lithium oxide 6 is deposited on the electrode material layer 20, the positive electrode 44 is assembled as the positive electrode 12 of the lithium ion secondary battery 10, and the lithium ion 2 generated by first charging is used as the negative electrode of the lithium ion secondary battery 10. 14 to be incorporated.
In other words, conventionally, the lithium doping material made of lithium oxide and the positive electrode active material are simply mixed, so the distance between the lithium oxide and the conductive additive contained in the positive electrode active material is compared with that of the present embodiment. Therefore, the reactivity of the lithium oxide remains low. For this reason, it is difficult to reduce the voltage at the time of the first charge necessary for the oxidative decomposition reaction of the lithium oxide.
On the other hand, in this embodiment, since the lithium oxide 6 is generated electrochemically, the distance between the lithium oxide 6 and the conductive auxiliary agent 26 contained in the positive electrode active material 24 can be shortened. Since the oxide 6 is highly reactive, the voltage at the first charge required for the oxidative decomposition reaction of the lithium oxide 6 can be lowered.
Therefore, it is advantageous in achieving power saving in the manufacturing process while securing the charge / discharge capacity of the lithium ion secondary battery 10.
Moreover, it is advantageous in providing the lithium ion secondary battery 10 in which the charge / discharge capacity is ensured and the cost is reduced by power saving in the manufacturing process.

In the present embodiment, when the positive electrode active material 24 is Li ₂ MnO ₃ , movable lithium ions (Li ⁺ ) are generated by generating Li ₂ O by lithium / oxygen element co-desorption that occurs during the initial charge. Even if the disappearance of the lithium ion occurs, lithium ions can be reliably compensated at the first charge, which is advantageous in securing the charge / discharge capacity of the lithium ion secondary battery 10.

In the present embodiment, since the electrode material layer includes the conductive auxiliary agent 26 and carbon that functions as a catalyst, and the lithium oxide 6 is Li ₂ O ₂ , the carbon also functions as a catalyst. The reactivity of Li ₂ O ₂ as the product 6 is further enhanced, the voltage to be applied to the lithium ion secondary battery 10 at the time of charging can be further reduced, and this is further advantageous in achieving power saving.

In the present embodiment, the case where the lithium oxide 6 electrochemically pre-doped on the positive electrode 44 of the air battery 40 is Li ₂ O ₂ has been described. However, even if the lithium oxide 6 is LiO _2. In that case, the positive electrode material layer 20 only needs to contain platinum that functions as a catalyst.
However, when the lithium oxide 6 is LiO ₂ , the energy required for the oxidative decomposition reaction of the lithium oxide 6 (necessary for dissociating oxygen) compared to the case where the lithium oxide 6 is Li ₂ O _2. Energy) is high, the effect of lowering the voltage during the initial charge is reduced. From this point of view, as the lithium oxide 6, compared to the _{Li 2 O} Li ₂ O ₂ is more preferable.
In this embodiment, Li ₂ MnO is used for the positive electrode active material 24, but the present invention is not limited to this, and Li _x MO _y (0 <x, 0 ≦ y; using other transition metal elements). M = transition metal element). For example, LiCoO2 and LiNiO2 can be raised.

2 Lithium ion 4 Oxygen 6 Lithium oxide 10 Lithium ion secondary battery 12 Positive electrode 12A Positive electrode structure 14 Negative electrode 16 Electrolytic solution 20 Positive electrode material layer 22 Positive electrode current collector 24 Positive electrode active material 26 Conductive aid 40 Air battery 42 Negative electrode 44 Positive electrode

Claims (7)

A method for producing a lithium ion secondary battery, comprising:
Assembling a positive electrode structure in which a positive electrode material layer containing a positive electrode active material is formed on a positive electrode current collector as a positive electrode of an air battery using lithium metal as a negative electrode;
Depositing lithium oxide on the positive electrode material layer by discharging the air battery;
Removing the positive electrode from the air battery and assembling it as a positive electrode of a lithium ion secondary battery;
A step of incorporating lithium ions generated by the oxidative decomposition reaction of the lithium oxide by first charging the lithium ion secondary battery into the negative electrode of the lithium ion secondary battery;
The manufacturing method of the lithium ion secondary battery characterized by including. The lithium oxide is electrochemically deposited, and in the step of depositing the lithium oxide, discharge is performed using a discharge machine that adjusts the amount of discharge charge.
The method for producing a lithium ion secondary battery according to claim 1. The positive electrode material layer includes a positive electrode active material and a conductive additive, and the conductive additive has a catalytic function of oxidizing and decomposing the lithium oxide.
The method for producing a lithium ion secondary battery according to claim 1 or 2. The conductive assistant is carbon, and the lithium oxide is Li ₂ O ₂ ;
The method for producing a lithium ion secondary battery according to claim 3. The positive electrode active material is a lithium metal oxide Li _x MO _y (where component M is a transition metal element and is represented by 0 <x, 0 ≦ y),
The method for producing a lithium ion secondary battery according to claim 3 or 4, wherein: The positive electrode active material is Li ₂ MnO ₃ ;
The method for producing a lithium ion secondary battery according to claim 5. It was manufactured by the manufacturing method of the lithium ion secondary battery according to any one of claims 1 to 6.
The lithium ion secondary battery characterized by the above-mentioned.

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