JP2000277095A - Lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the conductivity of the whole of a positive electrode material layer, and to improve the ion mobility by including a specified weight ratio of graphite powder and acetylene black powder to be used as a conductive assistant in the positive electrode material layer while mixing with the lithium transition metal double oxide. SOLUTION: Mean grain diameter of the graphite powder included in the conductive assistant so as to improve the conductivity is desirably formed at 5-20 μm, and mean grain diameter of the acetylene black powder for improving the ion mobility is desirably formed at 0.02-0.05 μm. Content percentage of the acetylene black powder in relation to the total quantity is set at 55-70 wt.%. They are desirably used for the conductive assistant included in a positive electrode material layer laminated with a negative electrode material layer, which is mainly composed of carbon material such as amorphous carbon powder or graphite capable of storing and discharging lithium, through an electrode layer including the organic electrolyte while being mixed with the cobalt acid lithium. With this structure, internal resistance of a battery is lowered, and efficient discharging characteristic is improved. Mn, Fe, Ni or Ti is used as a transition metal of the double oxide except for Co.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a lithium ion battery.

[0002]

_2. Description of the Related Art Lithium cobaltate (Li _x CoO ₂ )
And a negative electrode material layer containing a negative electrode material that occludes and releases lithium ions such as a carbon material via an electrolyte layer. Batteries are known. This electrolyte layer is configured such that an organic electrolyte in which a lithium salt is dissolved in an organic solvent such as ethylene carbonate or dimethyl carbonate is held by a separator. With this type of battery,
Since the conductivity of the lithium transition metal double oxide is low, a conductive auxiliary such as graphite powder is added to the positive electrode material layer.

[0003]

However, in the case of a conductive aid consisting only of graphite powder, the conductivity in the plane direction of the layer structure forming the graphite powder is high, but the conductivity in the thickness direction is low. Further, the ion mobility for moving lithium ions is low. Therefore, there is a limit in reducing the internal resistance of the battery and improving the high rate discharge characteristics of the battery.
In order to solve such a problem, it is conceivable to use acetylene black powder as a conductive additive. Acetylene black powder has good adhesion and many pores inside the powder, so that the electrolyte easily penetrates and has high ion mobility. In addition, there is no deviation due to direction in the conductivity. However, acetylene black powder has low conductivity.

Japanese Patent Application Laid-Open No. 8-153538 discloses a positive electrode comprising two layers: a graphite-containing layer using only graphite powder as a conductive aid, and a graphite-free layer using only acetylene black powder as a conductive aid. A lithium ion battery in which a material layer is formed and a graphite-containing layer is joined to an electrolyte layer has been proposed. However, even when the graphite powder and the acetylene black powder are used so as to form separate layers without being mixed as described above, the positive electrode material layer has locally high conductivity or high ion mobility. However, the conductivity and ion mobility of the entire positive electrode material layer cannot be increased.

An object of the present invention is to provide a positive electrode plate for a lithium ion battery and a lithium ion battery capable of improving the conductivity and ion mobility of the entire positive electrode material layer.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to improve a positive electrode plate for a lithium ion battery having a positive electrode material layer containing a lithium transition metal double oxide and a conductive additive. The lithium transition metal double oxide is a double oxide containing lithium and a transition metal. As this lithium transition metal double oxide, lithium cobalt oxide (Li _x CoO ₂ ) or the like can be used. Examples of transition metals other than cobalt include Ti,
There is at least one selected from V, Cr, Mn, Fe, Co, Ni, Mo, W, and Cu. In the present invention, graphite powder and acetylene black powder are used as the conductive assistant. Then, the graphite powder, acetylene black powder and lithium transition metal double oxide are mixed and contained in the positive electrode material layer, and the amount of acetylene black powder is 55 to 70 with respect to the total amount of graphite powder and acetylene black powder. % By weight.

As in the present invention, when a mixture of graphite powder and acetylene black powder is used as a conductive additive, the conductivity can be increased by the graphite powder, and the ion mobility can be increased by the acetylene black powder. it can. Therefore, the internal resistance of the battery can be reduced, and the high-rate discharge characteristics of the battery can be improved.

In order to enhance the conductivity and ion mobility of the entire positive electrode material layer, the amount of acetylene black powder is set to 55 to 70% by weight based on the total amount of graphite powder and acetylene black powder. If this amount is less than 55% by weight, ion mobility will decrease. On the other hand, if it exceeds 70% by weight, the amount of the graphite powder decreases, and the conductivity decreases.

The graphite powder has an average particle size of 5 to 20.
μm, and the acetylene black powder preferably has an average particle diameter of 0.02 to 0.05 μm. A lithium ion battery using the positive electrode plate of the present invention includes a positive electrode material layer containing a lithium transition metal complex oxide and a conductive auxiliary, and a negative electrode material layer mainly containing a carbon material capable of absorbing and releasing lithium. This is a lithium ion battery that is stacked with an electrolyte layer containing an organic electrolyte interposed therebetween, and uses graphite powder and acetylene black powder as conductive assistants. Then, the graphite powder, the acetylene black powder and the lithium transition metal double oxide are mixed and included in the positive electrode material layer, and the amount of the acetylene black powder with respect to the total amount of the graphite powder and the acetylene black powder is 55 to 70. % By weight.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Each lithium ion battery used for the test was manufactured as follows. First, a positive electrode plate was made. First, lithium cobalt oxide (Li _{x having} an average particle diameter of 10 μm) was used.
A cathode material made of CoO ₂ ), a conductive agent made of carbon powder, and a binder made of polyvinylidene fluoride (PVDF) are mixed at a weight ratio of 94: 3: 3, and this is mixed with N-methyl-2-pyrrolidone ( NMP) to prepare a positive electrode slurry. As shown in Table 1, the carbon powder used as the conductive additive has an average particle size of 15 μm.
m of graphite powder or a mixed powder obtained by mixing graphite powder with acetylene black powder having an average particle diameter of 0.035 μm. Next, each positive electrode slurry was
0μm aluminum foil is coated to a uniform thickness on both sides of the positive electrode current collector, then dried to remove NMP,
Rolling was performed with a roll press to form a positive electrode material layer. Then, this was cut into a width of 54 mm to produce a strip-shaped positive electrode plate.

Next, a negative electrode plate was prepared. First, average particle size 2
A negative electrode material made of a carbon material of 0 μm amorphous carbon powder and a binder made of polyvinylidene fluoride were mixed at a volume ratio of 90:
And mixed with N-methyl-2-pyrrolidone (N
MP) to prepare a negative electrode slurry.
As the carbon material, pitch coke, petroleum coke, graphite, carbon fiber, activated carbon, a mixture thereof, and the like can be used in addition to the amorphous carbon powder. Next, a negative electrode slurry was applied to both sides of a negative electrode current collector made of copper foil having a thickness of 10 μm to a uniform thickness, and then dried to remove NMP.
Rolling was performed with a roll press to form a negative electrode material layer. Then, this was cut into a width of 56 mm to produce a strip-shaped negative electrode plate.

Next, each positive electrode plate and each negative electrode plate shown in Table 1 were wound through a belt-like separator made of a microporous polyethylene (PE) film having a thickness of 25 μm and a width of 58 mm to form a wound type electrode plate group. Had made. Next, after disposing the wound electrode group in a cylindrical battery can made of Ni-plated iron, a nickel negative electrode tab terminal previously welded to the negative electrode current collector is welded to the bottom of the battery can. did. Next, an organic electrolyte (non-aqueous electrolyte) prepared by dissolving a lithium salt of LiPF _{6 at} a concentration of 1 mol / l in an organic solvent in which propylene carbonate (PC) and dimethyl carbonate (DMC) are mixed at a volume ratio of 1: 1. ) 5 ml was injected into the battery can.

Next, a positive electrode connecting terminal made of aluminum, which was previously welded to the positive electrode current collector, was welded to a battery lid provided with a safety valve and a pressure switch (current interrupting device). Next, the battery cover was placed on the upper portion of the battery can via a gasket made of insulating polypropylene, and then caulked to seal the inside of the battery can to seal each lithium ion for a cylindrical test having a nominal capacity of 1350 mAh. I made a battery.

[0014]

[Table 1] Next, the above lithium-ion batteries were charged at an ambient temperature of 25 ° C. with a charging current of 1350 mA and a limiting current of 4.15 V for 3 hours.
Time constant current constant voltage charge, then discharge current 0.5Cm
A (675 mAh), 1.0 CmA (1350 mA
h), 2.0 CmA (2700 mAh), 3.0 CmA
(4050 mAh) to discharge to a final voltage of 2.5 V, and the relationship between the discharge current and the discharge capacity ratio of each battery was examined. FIG. 1 shows the measurement results.

From FIG. 1, it can be seen that the batteries 1 and 2 of the embodiment have a lower discharge capacity during high-rate discharge and a higher high-rate discharge characteristic than the batteries of the comparative example.

Table 1 shows the relative internal resistance of each of the lithium ion batteries when the internal resistance of the battery of Example 1 at the time of full charge under the above charge and discharge conditions is 100.

From Table 1, it can be seen that the batteries 1 and 2 of the embodiment can suppress the internal resistance of the battery lower than that of the battery of the comparative example. Further, from FIG. 1 and Table 1, even when a mixed powder obtained by mixing graphite powder and acetylene black powder is used, if the ratio of the acetylene black powder to the mixed powder is less than 55% by weight or more than 70% by weight, a high ratio is obtained. It can be seen that the discharge characteristics deteriorate and the internal resistance of the battery increases. This is because when the ratio of the acetylene black powder to the mixed powder is less than 55% by weight, the ion mobility is reduced, and when it exceeds 70% by weight, the amount of the graphite powder is reduced, so that the conductivity is reduced. . Even if the ion mobility or the conductivity is reduced, the high-rate discharge characteristics are reduced. Also, the internal resistance of the battery increases even if the ion mobility decreases or the conductivity decreases.

[0018]

According to the present invention, since a mixed powder obtained by mixing graphite powder and acetylene black powder is used, the conductivity can be enhanced by the graphite powder, and the ion mobility can be enhanced by the acetylene black powder. . Therefore, the internal resistance of the battery can be reduced, and the high-rate discharge characteristics of the battery can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a discharge current and a discharge capacity ratio of a battery used in a test.

Claims (3)

[Claims] 1. A positive electrode plate for a lithium ion battery having a positive electrode material layer containing a lithium transition metal double oxide and a conductive auxiliary, wherein graphite powder and acetylene black powder are used as the conductive auxiliary, The powder, the acetylene black powder, and the lithium transition metal double oxide are contained in the positive electrode material layer in a mixed state, and the acetylene black powder with respect to the combined amount of the graphite powder and the acetylene black powder Is 55 to 70% by weight. 2. The graphite powder having an average particle size of 5
A positive electrode plate for a lithium ion battery, wherein the acetylene black powder has an average particle size of 0.02 to 0.05 μm. 3. A positive electrode material layer containing a lithium transition metal double oxide and a conductive auxiliary, and a negative electrode material layer mainly containing a carbon material capable of occluding and releasing lithium are interposed through an electrolyte layer containing an organic electrolyte. In the lithium ion battery formed by stacking, graphite powder and acetylene black powder are used as the conductive assistant, and the graphite powder, the acetylene black powder, and the lithium transition metal complex oxide are mixed. A lithium ion battery contained in the positive electrode material layer, wherein the amount of the acetylene black powder is 55 to 70% by weight based on the total amount of the graphite powder and the acetylene black powder.