JPH10255807A - Lithium ion secondary battery - Google Patents

Abstract

(57) [Problem] To produce a high-capacity lithium secondary battery having excellent current characteristics. SOLUTION: By mixing ceramic particles in a negative electrode, the ionic conductivity in the electrode is improved, and the internal resistance of the battery is reduced. As a result, a higher capacity lithium secondary battery was obtained in high-rate discharge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium secondary battery, and more particularly to a negative electrode thereof.

[0002]

2. Description of the Related Art In recent years, lithium batteries, especially rechargeable lithium secondary batteries, have been actively researched and developed as a new type of secondary battery having a high voltage and a high energy density. In early research, lithium secondary batteries using lithium metal for the negative electrode had great expectations as high energy density batteries. However, when lithium metal is used for the negative electrode, dendritic lithium (dendrites) generated during charging grows by charging and discharging the battery, causing internal short-circuiting of the battery,
Further, a problem such as an abnormal temperature rise of the battery is caused. These safety issues have not yet been resolved.

In order to solve the above problems, attempts have been made to use not only lithium metal alone but also an alloy of lithium and a low-melting-point metal such as aluminum, lead, indium, behimath and cadmium for the negative electrode. However, also in this case, the alloy which has been refined due to charge / discharge penetrates through the separator, causing an internal short circuit, and the practicality is difficult, and the problem could not be solved.

On the other hand, recently, as a solution to the above problem, lithium ion secondary batteries using carbon for the negative electrode and a transition metal compound containing lithium for the positive electrode have become mainstream. In this battery system, charge and discharge are performed by inserting and extracting lithium ions into the carbon of the negative electrode, so that no dendrite is generated upon charging. Therefore, the battery has good cycle characteristics and excellent safety.

[0005]

As described above, in a lithium ion secondary battery at present, carbon is used as an active material for a negative electrode, and charging and discharging are performed by inserting and extracting lithium ions into carbon. When the powder is used as the active material as described above, the requirements required for the negative electrode of the battery include:
Along with the ability of carbon itself to absorb and release lithium ions, the filling ability of how much carbon can be packed in a limited volume of a battery can be cited. In a lithium ion secondary battery, usually, a mixed paste of carbon and an adhesive is applied to both sides or one side of a metal thin film as a current collector, and the electrode plate is dried and then rolled to form an electrode. In such a high-capacity electrode plate having a high filling property, it is technically important to make the ion conduction in a limited gap existing in the active material grain boundary more rapid. That is, by obtaining smoother ion diffusion inside the negative electrode, the internal resistance of the electrode is reduced, and a high-capacity lithium ion secondary battery can be obtained even during high-rate discharge.

The present invention solves such a problem, and proposes a new high-capacity lithium-ion secondary battery having excellent high-rate discharge characteristics.

[0007]

In order to solve the above-mentioned problems, according to the present invention, the negative electrode is made of Al ₂ O ₃ , SiO ₂ , ZrO ₂ ,
By containing 0.01 to 20 parts by weight of a ceramic that does not participate in the charge / discharge reaction of a battery made of at least one selected from the group consisting of MgO and Na ₂ O with respect to 100 parts by weight of the active material, lithium can be smoothly formed. The purpose of the present invention is to increase the capacity, particularly during high-rate discharge, by obtaining ion diffusion and reducing the internal resistance of the battery. At the same time, the strength of the electrode plate is improved by adding the ceramic particles to the electrode plate, whereby a lithium ion secondary battery having particularly excellent cycle life characteristics can be manufactured.

Japanese Patent Application Laid-Open No. Hei 7-235293 reports that an active material doped with a compound mainly composed of a semi-metal belonging to Group IV-B or VB of the periodic table has been used to improve electron conductivity. This is a modification of the negative electrode active material itself,
The purpose and means are different from those of the present application. In Japanese Patent Application Laid-Open No. 7-153495, Al ₂ O ₃ , In
_In Japanese Patent Application Laid-Open No. Hei 7-153496, BaO, MgO, and CaO are added to and mixed with ₂ O ₃ , SnO ₂ , and ZnO to increase the stability of the positive electrode active material in which lithium ions are undoped in the charged state. It is reported that the capacity deterioration accompanying the charge / discharge cycle is improved. This is added to the positive electrode to improve the stability of the positive electrode active material, and is fundamentally different in configuration, function and purpose from the present application added to the negative electrode.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a method for forming a negative electrode on Al ₂ O ₃ , Si.
0.01 to 20 parts by weight of ceramic particles which do not participate in the charge / discharge reaction of a battery made of at least one selected from the group consisting of O ₂ , ZrO ₂ , MgO and Na ₂ O based on 100 parts by weight of the active material The present invention relates to a lithium ion secondary battery. By mixing ceramic fine particles inside the electrode, the liquid retention property and the ionic conductivity are improved, and an electrode having a low internal resistance can be manufactured. In addition, by configuring a battery using this electrode, it has excellent high-rate charge / discharge characteristics,
Furthermore, since the mechanical strength of the electrode plate is also increased, a lithium ion secondary battery having excellent charge / discharge characteristics at the end of charge / discharge is obtained. When the addition amount of the ceramic particles is 0.01 part by weight or less, no effect is observed, and when the addition amount is 20 parts by weight or more, the capacity is reduced. Therefore, 0.01 to 20 parts by weight is preferable. This is because when the amount is more than 20 parts by weight, the volume of the electrolyte serving as an ion transfer path is drastically reduced due to the presence of a large amount of ceramic in the electrode, and the capacity is reduced. it is conceivable that.

Further, the ceramic particles have a particle size of 10 μm.
m or less.

[0011]

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

Example 1 Alumina (Al) of the present invention
_A cylindrical lithium ion secondary battery was constructed using a negative electrode mixed with ₂ O ₃ ) particles.

FIG. 1 is a longitudinal sectional view of a cylindrical lithium ion secondary battery of the present invention. In the figure, reference numeral 1 denotes a negative electrode mixed with Al ₂ O ₃ particles, which was produced by the following method. First, 90 parts by weight of graphite powder as a negative electrode active material, 10 parts by weight of polyvinylidene fluoride as a binder and N-methyl-2-pyrrolidone as a solvent were mixed, and a predetermined amount of Al ₂ O ₃ particles having a predetermined particle size was added. It was mixed and kneaded to form a paste. A predetermined amount of the mixture was applied to both surfaces of a copper foil as a negative electrode current collector, dried and rolled, and then cut into a predetermined size, thereby producing a negative electrode 1 for a lithium ion secondary battery. Reference numeral 3 denotes a positive electrode, which was produced by the following method. First, LiC
3 parts by weight of acetylene black and 9 parts by weight of an aqueous dispersion of polytetrafluoroethylene were added to 100 parts by weight of the oO ₂ positive electrode active material to form a kneaded paste. This was applied to both sides of an aluminum foil as a positive electrode current collector, dried and rolled, and then cut into a predetermined size to obtain a positive electrode 3 for a lithium ion secondary battery. Reference numeral 5 denotes a separator made of a polyethylene microporous film, which is interposed between the positive electrode 3 and the negative electrode 1, and forms a spirally-shaped electrode plate group as a whole. An upper insulating plate 6 and a lower insulating plate 7 made of polypropylene are arranged on the upper and lower ends of the electrode plate group, respectively, and inserted into a case 8 plated with nickel on iron. Then, the positive electrode lead plate 2 is attached to the sealing plate 10 made of titanium, and the negative electrode lead plate 2 is attached to the case 8.
Are spot-welded to the bottom of the case, a predetermined amount of electrolyte is injected into the case, and the battery is sealed with a sealing plate 10 via a gasket 9 to obtain a cylindrical lithium ion secondary battery of the present invention. The dimensions of the battery are 14 mm in diameter and 50 mm in height. Reference numeral 11 denotes a positive electrode terminal of the battery, and the negative electrode terminal is also used by the battery case 8. Here, LiPF ₆ was added to a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 25:75 in an electrolytic solution at 1.5 mol / mol.
A non-aqueous electrolyte obtained by dissolving 1 liter was used.

(Example 2) The particle size of Al ₂ O ₃ particles to be mixed with the negative electrode was fixed at 0.5 μm, and the addition ratio was 0.01, 5 to 90 parts by weight of graphite and 10 parts by weight of the binder. 10, 2
A cylindrical lithium ion secondary battery of the present invention was constructed in the same manner as in Example 1 except that four types of 0 and 30 parts by weight were used.

Example 3 The addition ratio of Al ₂ O ₃ particles to be mixed in the negative electrode was 5 parts per 90 parts by weight of graphite and 10 parts by weight of binder.
Parts by weight, and the particle size of the Al ₂ O ₃ particles is 0.5, 1.
A cylindrical lithium-ion secondary battery of the present invention was constructed in the same manner as in Example 1, except that three types of 0, 10, and 20 μm were used.

Comparative Example 1 A cylindrical lithium ion secondary battery of Comparative Example 1 was constructed in the same manner as in Example 1 except that the negative electrode did not contain Al ₂ O ₃ particles.

The characteristics of the batteries of Examples 1 to 3 and Comparative Example 1 were evaluated. The results are shown in FIGS.

FIG. 2 shows a discharge curve at the 10th cycle of the lithium ion secondary batteries obtained in Example 1 and Comparative Example 1. The battery test was performed at a constant current charge / discharge of 100 mA charge and 500 mA discharge, a charge end voltage of 4.2 V, a discharge end voltage of 3.0 V, and a cycle test in a 20 ° C. environment. As a result, while the battery of Comparative Example 1 had a capacity of 405 mAh, the battery of Example 1 of the present invention in which Al ₂ O ₃ particles were mixed in the negative electrode also had a capacity of 430 mAh, an increase of 6%. This is because the internal resistance of the battery is low, the voltage drop during discharging is small, and a high voltage is maintained.

FIG. 3 shows the current-capacity characteristics of the lithium ion secondary batteries obtained in Example 1 and Comparative Example 1 as a discharge capacity with respect to a discharge current value. Battery test is 100 charge
mA, constant current of 100, 250, 500, 1
000 mA. At a low-rate discharge of 100 mA, the battery of Example 1 in which Al ₂ O ₃ particles were mixed in the negative electrode had a 4% reduction in capacity compared to the battery of Comparative Example 1 due to a decrease in the amount of active material, but a high current of 250 mA or more. The capacity was improved by the rate discharge. Further, the battery of Comparative Example 1 showed about 83% capacity at a discharge of 100 mA at a discharge of 1000 mA, while the battery of Example 1 exhibited a capacity retention rate as high as 90%.

FIG. 4 is a diagram showing the discharge capacity with respect to the addition ratio of Al ₂ O ₃ particles mixed in the negative electrode of the lithium ion secondary battery obtained in Example 2. Battery test is charging 100
The measurement was performed at 20 ° C. at a current value of 500 mA at a discharge of 500 mA. As a result, the discharge capacity increased with the addition amount of the Al ₂ O ₃ particles, and showed a maximum value of 430 mAh at 5% by weight. But,
On the other hand, when the content was 20% by weight or more, the capacity was decreased by the addition. It is considered that this is because the presence of a large amount of ceramic fine particles in the electrode drastically reduces the volume of the electrolyte serving as an ion transmission path. Therefore, the content of the ceramic fine particles to be mixed in the electrode is suitably 20% by weight or less, and at this time, a high capacity lithium secondary battery can be obtained.

FIG. 5 shows the lithium ion obtained in Example 3.
Al mixed in the negative electrode of the secondary battery_TwoO_ThreeFor particle size
FIG. As a result, mixed Al
_TwoO _ThreeAs the particle diameter decreased, the discharge capacity increased, and the
A high capacity of 420 mAh or more was obtained at μm or less. This
This is the table of ceramic particles for lithium ion transmission.
The surface porous part is more related to the porous volume,
Use ceramic particles with small diameter and large surface area.
It is because more effective ion diffusing ability was obtained with
Conceivable.

In both the charging and discharging states, no difference in the Al ₂ O ₃ peak was observed in the X-ray analysis of the negative electrode after charging and discharging. From this, it is considered that Al ₂ O ₃ is not involved in the insertion and extraction of lithium.

Further, the cycle characteristics of the lithium ion secondary batteries of Example 1 and Comparative Example 1 were examined. In the battery test, the discharge current was set to 500 mA, the upper limit cutoff voltage was 4.2 V,
The test was performed under a 20 ° C. environment with a lower limit end voltage of 3.0 V.
As a result, the discharge capacities at 0, 100, and 500 cycles are shown in (Table 1).

[0024]

[Table 1]

According to Table 1, the battery of Comparative Example 1 had 93% of the initial capacity at 100 cycles, and 90% at 500 cycles.
On the other hand, in the battery of the present invention of Example 1, the capacity of 94% of the initial capacity was maintained even at 500 cycles. When the battery was disassembled after 500 cycles and the negative electrode was observed, the negative electrode mixture was less likely to fall off and the strength was high compared to the electrode plate of Comparative Example 1 in which the electrode plate of Example 1 to which Al ₂ O ₃ was added was not added. Was.

[0026] Incidentally, although this embodiment used LiPF ₆ as a solute of the nonaqueous electrolyte solution, which is LiCF ₃ SO _3, Li
Other lithium salts such as ClO ₄ , LiN (CF ₃ SO ₂ ), LiAsF ₆ or LiBF ₄ may be used.

In this embodiment, a mixed solvent of ethylene carbonate and ethyl methyl carbonate is used as the solvent of the non-aqueous electrolyte. However, this may be another organic solvent alone or a mixed solvent.

In this embodiment, Li is used as the positive electrode active material.
CoO ₂ was used, which was obtained from Li _{1 + x} Mn ₂ O ₄ (0 ≦ x ≦
0.1), LiNiO ₂ , Li _x MnO ₂ (0 <x ≦ 0.
5).

In this embodiment, graphite powder is used as the carbon material for the negative electrode, but other carbonaceous materials, metal oxides, metal nitrides, and the like may be used.

In this example, Al ₂ O ₃ was used as ceramic particles. However, similar effects were observed with SiO ₂ , ZrO ₂ , MgO and Na ₂ O.

In this embodiment, ceramic particles are used. However, the shape of the particles is not limited to a spherical shape, and similar effects can be obtained with a fibrous ceramic having a large specific surface area.

[0032]

As described above, according to the present invention, by mixing ceramic particles in the negative electrode plate, the ionic conductivity of the electrode plate is improved, and in particular, lithium having improved electrode capacity during high-rate discharge is improved. An ion secondary battery was obtained. Furthermore, a high capacity lithium secondary battery having excellent cycle characteristics was obtained by increasing the electrode strength.

[Brief description of the drawings]

FIG. 1 is a structural longitudinal sectional view of a lithium ion secondary battery using an electrode of the present invention.

FIG. 2 is a diagram showing discharge curves of a lithium ion secondary battery of the present invention and a lithium ion secondary battery of Comparative Example 1.

FIG. 3 is a diagram showing rate characteristics of the lithium ion secondary battery of the present invention and the lithium ion secondary battery of Comparative Example 1.

FIG. 4 is a diagram showing a discharge capacity with respect to an addition rate of Al ₂ O ₃ particles mixed in a negative electrode.

FIG. 5 is a view showing a discharge capacity with respect to a particle diameter of Al ₂ O ₃ particles mixed in a negative electrode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Negative electrode 2 Negative electrode lead plate 3 Positive electrode 4 Positive electrode lead plate 5 Separator 6 Upper insulating plate 7 Lower insulating plate 8 Case 9 Gasket 10 Sealing plate 11 Positive electrode terminal

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Nobuo Eda 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A positive electrode using a lithium transition metal composite oxide as an active material, a negative electrode containing at least one active material selected from the group consisting of carbon, metal oxides and polymers capable of inserting and extracting lithium, and an organic material. In a lithium ion secondary battery mainly composed of an electrolyte, Al ₂ O ₃ , Si
0.01 to 20 parts by weight of a ceramic which does not participate in the charge / discharge reaction of a battery made of at least one selected from the group consisting of O ₂ , ZrO ₂ , MgO and Na ₂ O based on 100 parts by weight of the active material Lithium ion secondary battery. 2. The lithium ion secondary battery according to claim 1, wherein the ceramic has a particle size of 10 μm or less. 3. A positive electrode using a lithium-transition metal composite oxide as an active material, a negative electrode containing at least one active material selected from the group consisting of carbon capable of absorbing and releasing lithium, a metal oxide, and a polymer; In a lithium ion secondary battery mainly composed of an electrolytic solution, Al ₂ O ₃ particles having a particle size of 10 μm or less are used in an amount of 0.01 to 2 parts by weight per 100 parts by weight of the active material.
A lithium ion secondary battery containing 0 parts by weight.