JPH11283623A - Lithium ion battery and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a cycle life, a low-temperature discharge characteristic and a high-rate discharge characteristic by providing a negative electrode mainly made of carbon, a separator, an organic electrolyte and a positive electrode mainly made of a lithium composite oxide, and covering part or the whole of the surface of the lithium composite oxide with a carbon material. SOLUTION: A child grain material of carbon is preferably mixed to parent grains made of a lithium composite oxide such as LiCoO2 , LiMn2 O4 or LiNiO2 or containing different elements such as Mg and Ti via a compressing or shearing action to cover part or the whole of the surface. When such a positive electrode mix is held on an aluminum foil, it is suitable for a positive electrode. Acetylene black, Ketien black, graphite or coke is used for the carbon material. A positive electrode active material is covered with the carbon material which is a conductive material, the conductivity between active material grains is improved, and charging/discharging reactions occur uniformly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium ion battery and a method of manufacturing the same, and more particularly, to a surface modification of a lithium composite oxide which is a main constituent material of a positive electrode.

[0002]

2. Description of the Related Art In recent years, electronic devices have been remarkably reduced in size and weight. Accordingly, there is a great demand for a battery that is a power source to be smaller and lighter. In the field of primary batteries, small and lightweight batteries such as lithium batteries have already been put to practical use, but since these are primary batteries, they cannot be used repeatedly, and their uses have been limited. On the other hand, in the field of secondary batteries, lead-acid batteries, nickel-cadmium storage batteries, nickel-metal hydride storage batteries, and the like have been used, but these have significant problems in terms of size and weight reduction.

[0003] Therefore, lithium-ion batteries have come into practical use as compact, lightweight, high-capacity, chargeable / dischargeable batteries, and are used in portable electronic and communication devices such as small video cameras, mobile phones, and notebook computers. It became so.
This type of lithium ion battery uses a carbon-based material capable of inserting and extracting lithium ions as a negative electrode active material, and uses LiCoO ₂ , LiNiO ₂ or LiM as a positive electrode active material.
Using a lithium composite oxide such as n ₂ O _4, an ionic conductor in which a lithium salt is dissolved as a solute in an organic solvent as an electrolytic solution, and assembling as a battery, lithium ions released from the positive electrode active material by the first charge Is a battery that can be charged and discharged by entering carbon particles.

In this lithium ion battery, a positive electrode plate and a negative electrode plate are formed by applying a positive electrode active material and a negative electrode active material to a metal core (foil), and a separator is inserted between them and wound to form an electrode. And After inserting the electrode body into a metal outer can, the outer can is filled with an electrolyte and sealed. As the metal outer can, an outer can made of iron or stainless steel or an outer can made of aluminum, an aluminum alloy, or the like is used.

[0005]

SUMMARY OF THE INVENTION Incidentally, lithium ion
The positive electrode active material used in on-battery
To make an electrode with improved conductivity,
LiCoO as active material _Two, LiNiO_TwoOr LiMn
_TwoO_FourTo the lithium composite oxide powder such as
Mix powder, knead with binder and paste
And apply it to a conductive core material such as aluminum foil.
It is common to dry and pressurize it to form an electrode.

However, in such a method, a lithium composite oxide powder as an active material and a carbon powder as a conductive agent are individually present. That is, when viewed microscopically, a certain portion contains only the lithium composite oxide, and a certain portion contains only the carbon powder, and is not necessarily in a uniformly mixed state. Therefore, there are problems such as the presence of the positive electrode active material particles that cannot exhibit uniform conductivity, a non-uniform reaction, and a decrease in the charge / discharge cycle life and a decrease in low-temperature discharge characteristics and high-rate discharge characteristics.

The present invention has been made in view of the above-mentioned problems, and a uniform distribution state is created by coating a part or the whole of the surface of a positive electrode active material with carbon powder, and the conductivity of the active materials is controlled. SUMMARY OF THE INVENTION It is an object of the present invention to improve the performance and prevent a decrease in cycle life and a decrease in low-temperature discharge characteristics and high-rate discharge characteristics.

[0008]

The lithium ion battery of the present invention comprises a positive electrode mainly composed of a lithium composite oxide, a negative electrode mainly composed of carbon, a separator, and an organic electrolyte. A part or the whole of the surface of the lithium composite oxide is coated with a carbon material.

Further, a method of manufacturing a lithium ion battery according to the present invention is directed to a lithium ion battery comprising a positive electrode mainly composed of a lithium composite oxide, a negative electrode mainly composed of carbon, a separator, and an organic electrolyte. In a method for manufacturing an ion battery, a part or all of the surface of the base particles is mixed with the base particles of the lithium composite oxide by compressing and mixing a child particle material made of carbon while giving a shearing action. It is characterized by being coated with child particles.

As the positive electrode active material, LiCoO ₂ , Li
Examples thereof include lithium composite oxides such as Mn ₂ O ₄ and LiNiO ₂ , but are not particularly limited thereto, as long as they function as a positive electrode of a lithium ion battery. For example, to improve the characteristics of the positive electrode active material itself, Mg, T
Those containing different elements such as i are also included.

As the carbon material, acetylene black,
Examples include Ketjen black, graphite, coke, and the like, but are not particularly limited thereto.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Example] Preparation of positive electrode plate LiCoO ₂ as a base particle was selected as an active material of a positive electrode, and a carbon powder as a child particle was compressed on the surface of the powder with a mechanofusion device made by Hosokawa Micron. An example in which coating is performed by causing an impact and a shearing action will be described.

First, 200 g of LiCoO ₂ was mixed with 5 wt% of acetylene black, and a mechanofusion device (AM) made by Hosokawa Micron, whose schematic structure was shown in FIG.
The active material surface was coated with −15F).

The main conditions during the coating treatment were as follows.

An argon gas as an inert gas was used as a processing atmosphere. The internal volume of the reaction processing case 1 of the rotating mechanofusion device is about 0.6 liter,
An arm is attached to a fixed shaft 2 disposed at the center of the case 1, the clearance between the stator 3 fixed to the tip of the arm and the inner wall of the case 1 is 3 mm, and the rotation speed of the case 1 is 1500
rpm. Further, a scraper 4 is disposed in front of the stator 3, and the rotating case 1 and the stator 3 are compressed and sheared by the rotating case 1 to scrape the sample stuck to the inner wall of the case 1.

Such a treatment was carried out for 20 minutes to complete the coating treatment of the base particles, thereby producing a positive electrode mixture of the present invention.

A solution prepared by dissolving the thus prepared positive electrode mixture mixture whose surface is coated with acetylene black and a binder made of polyvinylidene fluorolite (PVDF) in an organic solvent made of N-methylpyrrolidone or the like is used. Mix to form a slurry.

These slurries were uniformly applied to both sides of a 20 μm-thick aluminum foil by a doctor blade method and then rolled by a rolling mill to produce a 180 μm-thick positive electrode plate. The positive electrode plate thus manufactured is referred to as a positive electrode plate a of the present invention.

Preparation of Negative Electrode Plate A negative electrode active material composed of natural graphite and a binder composed of polyvinylidenefluoride (PVDF) dissolved in an organic solvent composed of N-methylpyrrolidone and the like are mixed.
Slurry. These slurries were uniformly applied to both surfaces of a copper foil having a thickness of 15 μm by using a doctor blade method, and then rolled by a rolling mill to produce a negative electrode plate having a thickness of 150 μm.

Preparation of Lithium Ion Battery A microporous polyethylene film is interposed between the negative electrode plate and the positive electrode plate prepared as described above to form a spiral electrode body, and this electrode body is made of an Fe-Ni plating outer can. Insert in
An electrolytic solution obtained by adding 1 mol / dm ³ of LiPF ₆ as an electrolyte salt to a mixed solvent consisting of 30 parts by weight of ethylene carbonate (EC) and 70 parts by weight of diethyl carbonate (DEC) was injected, sealed, and sealed with a book having a nominal capacity of 1200 mAh. The lithium ion battery of the invention was produced. The lithium-ion battery thus manufactured is referred to as Battery A of the present invention.

[Comparative Example 1] In the production method of Example 1 of the present invention, LiCoO ₂ particles and carbon particles were mixed by a V-type mixer and then passed through a roller compactor manufactured by Freund (roll gap: 1 mm). Comparative positive electrode plate b and comparative lithium ion battery B in the same manner as in Example 1 except that a positive electrode mixture was prepared by applying a compressive action, that is, except that the positive electrode mixture was prepared by applying only a compressive force without applying a shearing force.
Was prepared.

Comparative Example 2 The procedure of Example 1 was repeated except that LiCoO ₂ particles and carbon particles were mixed with a V-type mixer to produce a positive electrode mixture. Similarly, a comparative positive electrode plate c and a comparative lithium ion battery C were produced.

(Experiment 1) Using the electrode a of the present invention and the comparative electrodes b and c produced as described above, the surface resistance of the electrode was measured with a commercially available ohmmeter, and the results are shown in Table 1 below.

[0024]

[Table 1]

As is clear from Table 1, the electrode a of the present invention has a lower electrode surface resistance than the comparative electrode b and the comparative electrode c.

The reason why the characteristics of the comparative electrodes b and c are significantly lower than that of the electrode a of the present invention is that LiCoO ₂ and carbon particles as a conductive agent are present individually, and are nonuniform when viewed microscopically. This is considered to be due to the poor conductivity between the active material particles.

On the other hand, in the electrode a of the present invention, the surface of the active material is coated with carbon particles as the conductive agent by compressing, mixing and shearing the conductive agent such as carbon particles, and the active material is uniformly distributed. It is considered that the conductivity between the material particles was improved.

(Experiment 2) Next, high-rate discharge characteristics and low-temperature characteristics (−5 ° C.) were evaluated using the lithium ion battery A of the present invention and the lithium ion batteries B and C of the comparative examples. The results are shown in Tables 2 and 3 below.

The experimental conditions for the high rate discharge characteristics were a temperature of 25 ° C.
1C (= 1200 mA) -4.1 V constant current constant voltage charging was performed, and the charging was terminated when the current value became 0.02 C. Thereafter, constant current discharge was performed at a temperature of 25 ° C.

At this time, the current value of the discharge current is 0.2 C,
It was set in four ways: 1.0C, 2.0C, and 2.5C.

The experimental conditions for the low-temperature characteristics are as follows.
C., 1 C (= 1200 mA) -4.1 V constant current constant voltage charging was performed, and when the current value reached 0.02 C, the charging was terminated. Thereafter, a constant current discharge of 1.0 C was performed at a temperature of -5 ° C.

[0032]

[Table 2]

[0033]

[Table 3]

According to Tables 2 and 3, the battery A of the present invention has better discharge characteristics than the comparative battery B and the comparative battery C. In particular, the high-rate discharge characteristics at a discharge rate of 1.0 C or more and the low-temperature discharge characteristics Excellent characteristics.

The reason why the characteristics of the battery A of the present invention are excellent is that, as described in Experiment 1, the surface of the active material is coated with carbon particles as a conductive agent and is uniformly distributed. It is considered that the conductivity between the active material particles was improved.

(Experiment 3) Next, the charge / discharge cycle characteristics were evaluated using the lithium ion battery A of the present invention and the lithium ion batteries B and C of the comparative examples, and the results are shown in FIG.

The experimental conditions for the charge-discharge cycle characteristics were as follows:
Temperature 25 ° C., 1 C (= 1200 mA) -4.1 V constant current / constant voltage charging was performed, and when the current value became 0.02 C, charging was terminated.
The cycle of performing C constant current discharge was performed 500 times.

As is apparent from FIG. 3, the lithium ion battery A of the present invention has better charge / discharge cycle characteristics than the lithium ion batteries B and C of the comparative examples.

The reason why the characteristics of the battery A of the present invention is excellent is that, as described in Experiment 1, the surface of the active material is covered with the carbon particles as the conductive agent and is uniformly distributed. It is considered that the conductivity between the active material particles was improved.

In this embodiment, LiC is used as the active material.
Acetylene black was used as a material for coating the surface of oO ₂ , but the material is not limited to this, and Ketjen black, graphite, coke, and the like can be used.

In this embodiment, the active material LiC is used.
As a means for coating the surface of oO ₂ with carbon particles, a meso-fusion device made by Hosokawa Micron was used.

[0042]

As is clear from the above, the lithium ion battery of the present invention has an improved conductivity between active material particles because the active material is coated with a carbon material as a conductive agent. Since the discharge reaction occurs uniformly, high-rate discharge characteristics, low-temperature discharge characteristics, and charge / discharge cycle characteristics are improved, and the industrial value is extremely high.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a configuration of a mechanofusion device used for a coating process in an embodiment of the present invention.

FIG. 2 is a partially enlarged view of the apparatus shown in FIG.

FIG. 3 is a diagram showing cycle characteristics of the present invention and a comparative ion battery.

[Explanation of symbols]

 Reference Signs List 1 Reaction processing case of mechanofusion device 2 Fixed shaft 3 Stator 4 Scraper

Claims (3)

[Claims] 1. A lithium ion battery comprising: a positive electrode mainly composed of a lithium composite oxide; a negative electrode mainly composed of carbon; a separator; and an organic electrolyte, wherein the lithium composite oxide comprises A lithium ion battery characterized in that part or all of its surface is coated with a carbon material. 2. The positive electrode according to claim 1, wherein a positive electrode mixture obtained by coating a part or all of the surface of the lithium composite oxide with a carbon material is held on an aluminum foil. The lithium ion battery according to the above. 3. A method for manufacturing a lithium ion battery comprising: a positive electrode mainly composed of a lithium composite oxide; a negative electrode mainly composed of carbon; a separator; and an organic electrolyte. Lithium is characterized in that a part or all of the surface of the base particles is coated with the child particles by mixing a base particle material of the composite oxide with a compression and shearing action of a child particle material made of carbon. A method for manufacturing an ion battery.