JP3204358B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte battery such as a lithium secondary battery.

[0002]

2. Description of the Related Art In recent years, electronic devices such as a portable radio telephone, a portable personal computer, and a portable video camera have been developed, and various electronic devices have been reduced in size to be portable. Along with this, a battery having a high energy density and a light weight is also adopted as a built-in battery. A typical battery that satisfies such demands is an aprotic solution in which a lithium metal such as lithium metal, lithium alloy, or lithium ion is used as a negative electrode active material and a lithium salt such as LiClO ₄ or LiPF ₆ is dissolved. And a lithium secondary battery using the organic solvent as an electrolyte.

[0003] A lithium secondary battery has a negative electrode plate in which the above-mentioned negative electrode active material is held by a negative electrode current collector as a support, and a reversible electrochemical reaction with lithium ions like a lithium-cobalt composite oxide. A positive electrode plate holding the positive electrode active material to be supported on a positive electrode current collector as a support, and a separator that holds an electrolyte and intervenes between the negative electrode plate and the positive electrode plate to prevent a short circuit between the two electrodes. I have.

Meanwhile, in order to increase the charge / discharge voltage and energy density of this lithium secondary battery, a technique for specifying the average particle size of the positive electrode active material has been proposed (Japanese Patent Laid-Open No. 1-3).
04664, JP-A-4-162357).

[0005]

However, a study by the inventor of the present application has revealed that even if the average particle size is the same, a large difference occurs in battery performance depending on the particle size distribution. Therefore, an object of the present invention is to provide a non-aqueous electrolyte secondary battery having excellent battery performance by specifying a positive electrode active material from a viewpoint different from the prior art for specifying an average particle diameter.

[0006]

In order to achieve the object, a non-aqueous electrolyte secondary battery according to the present invention comprises a LiM _x Co _1-x
A positive electrode containing O ₂ (M represents at least one transition metal other than Co, and 0 ≦ x ≦ 1.0) as an active material, and containing a conductive agent and a binder in addition to the active material; In a secondary battery including a negative electrode, a separator interposed between the positive and negative electrodes, and a non-aqueous electrolyte held by the separator, the specific surface area of the positive electrode active material is 0.35 to 2.0 m ² / g. It is characterized by.

Here, specific examples of LiM _x Co _1-x O ₂ include LiCoO ₂ , LiMn _0.15 Co _0.85 O ₂ , LiN
i _0.10 Co _0.90 O ₂ , LiNi _0.37 Co _0.63 O _{2 and the} like.

Further, in this nonaqueous electrolyte secondary battery, both the (003) plane peak and the (104) plane peak in the X-ray diffraction pattern of the positive electrode active material are 0.10.
０．２0.20 .

[0009]

The electrode plate contains a conductive agent for electrically connecting the active materials and a binder for holding the active material on the current collector. Therefore, the content of the active material is relatively reduced by the content of the conductive agent and the binder, and the battery capacity is reduced as compared with a theoretical battery of the same volume that does not include the conductive agent and the binder. ing.

Therefore, the present invention focuses on the fact that it is sufficient that the conductive agent and the binder cover the surface of the active material, and the specific surface area of the positive electrode active material is set to 2.0 m ² / g or less. The content of the conductive agent and the binder in contact with the surface of the active material is set to the necessary minimum amount, particularly 8% by weight or less for the conductive agent,
The relatively high content of the active material can be secured.

On the other hand, if the specific surface area of the positive electrode active material is too small, the reaction area between the active material and the electrolytic solution becomes small, the current density becomes excessive, and the voltage decreases when discharging a large current. The capacity may be low. Therefore, in the present invention, the specific surface area of the positive electrode active material is set to 0.35 m ² / g or more.

That is, in the present invention, by limiting the specific surface area of the positive electrode active material to the range of 0.35 to 2.0 m ² / g, the content of the active material is increased while securing the required reaction area. Thus, the battery capacity and life were improved.

In addition, by limiting the half width of the X-ray diffraction peak as described above, the battery capacity and the service life are further improved. That is, it is known that the half width represents the degree of crystallinity, and that the smaller the half width, the higher the crystallinity, and the larger the half width, the lower the crystallinity. Therefore, by limiting the half width to the optimum range, the crystallinity of the active material is made appropriate, the packing density of the active material particles is maintained high, and the Li ions are easily moved, and as a result, a large capacity is obtained. And a large current discharge was made possible. Therefore, when the half width is larger than 0.50, the crystallinity is too low, so that the specific gravity of the active material particles is low, the packing density is low, and the capacity is small. On the other hand, when the half width is infinitely close to 0, the crystallinity is too high and there are no gaps, so that Li ions are difficult to move, and a large current cannot be discharged or the voltage drop when discharged is significantly large. Become.

[0014]

【Example】

-Example 1-An example in which the present invention is applied to a prismatic lithium ion secondary battery will be described. 20 μm thick as support for positive electrode plate
Was prepared. And, on a weight basis, a lithium cobalt composite oxide LiCoO ₂ as an active material
87%, 5% acetylene black powder as a conductive agent and 8% polyvinylidene fluoride PVDF as a binder
-Methylpyrrolidone was mixed with 44% to prepare a paste. Table 1 shows the specific surface area of the active material used and the half width of the X-ray diffraction peak.

[0015]

[Table 1] Next, the paste was applied to both sides of the support to a thickness of about 250 μm and dried. Subsequently, two hot rolls arranged in parallel at a spacing of 150 μm were rotated at a feed rate of 1 m / min, and the hot rolls were rolled through a support coated with a paste. The mandrel of the hot roll has a built-in heater, and the roll surface during rolling is 1
Conditions were set in advance so as to be 50 ° C.
After the rolling, the laminate of the paste and the support was cut into a width of 30 mm to produce three types of positive electrode plates of the same shape and the same shape except that the specific surface area and the crystallinity of the active material were different.

Separately, a support having a thickness of 20
A μm copper foil was prepared. Then, on a weight basis, 90% of graphite as an active material and 10% of PVDF as a binder were mixed together with 56% of n-methylpyrrolidone to prepare a paste. The paste was applied to both sides of the support, dried, rolled, and cut to a width of 31 mm in the same manner as in the method for producing the positive electrode plate, to produce a negative electrode plate.

As an electrolytic solution, LiPF ₆ was 1 mol / mol.
l containing ethylene carbonate: diethyl carbonate:
A mixed solution of dimethyl carbonate = 2: 1: 2 (volume ratio) was used. The separator has a thickness of 25 μm and a width of 3
What consisted of a 2.5 mm polyethylene microporous membrane was used.

Then, the positive electrode plate, the separator and the negative electrode plate are superimposed one after another and wound in an elliptical shape around the polyethylene core, and then electrically connected to the positive electrode lead or the negative electrode lead to form a battery. After being housed in a case and injecting the electrolytic solution, necessary parts were welded and covered, thereby producing a secondary battery.

The obtained battery was charged at a constant current and a constant voltage of 200 mA-4.1 V at 25 ° C. for 3 hours.
A cycle in which constant current discharging at 2.75 V at mA was performed at 25 ° C. was repeated, and the battery capacity was measured every 50 cycles.

FIG. 1 is a graph showing the relationship between the number of charge / discharge cycles and the battery capacity. In the figure, the symbols △, ● and ○ indicate No. 1, No. 2 and No. 3 shows data using the positive electrode active material of Example 3.

As can be seen from the figure, No. 1 having a smaller specific surface area and a larger half width than the range of the present invention. In the battery using the active material of No. 3, the capacity was significantly reduced as the number of cycles was increased. The battery using the active material of No. 2 has a gradual decrease in capacity and has a large specific surface area and a small half-value width. The battery using the active material of No. 1 had a tendency to maintain a high capacity.

Example 2 In this example, a specific surface area of 1.4 m ² /
g, a lithium-nickel-cobalt composite oxide L having a half width of 0.20 on (003) plane and 0.20 on (104) plane
iNi _0.10 Co _0.90 O ₂ was used. A battery was manufactured under the same conditions as in Example 1, and the charge / discharge cycle was repeated. As a result, the discharge capacity at the 300th cycle was 400 mAh. 1 Li
Almost the same performance as that of the battery using CoO ₂ was obtained.

Example 3 In this example, a specific surface area of 1.8 m ² /
g, Lithium-cobalt composite oxide LiC having a (003) plane half width of 0.105 and a (104) plane half width of 0.120
oO ₂ was used. Moreover, LiCoO ₂ 8 The composition of the positive electrode mixture
5%, acetylene black powder 7% and PVDF 8%. The other conditions were the same as in Example 1 to produce a battery, and the charge / discharge cycle was repeated. As a result, 300
The discharge capacity at the second cycle was 390 mAh. Almost the same performance as that of the battery using LiCoO ₂ was obtained.

Comparative Example 1 In this example, a specific surface area of 2.2 m ² /
g, a lithium-nickel-cobalt composite oxide LiNi _0.37 Co _0.63 O ₂ having a half-width of (003) plane of 0.220 and a half-width of (104) plane of 0.215 was used. The other conditions were the same as in Example 1 to produce a battery, and the charge / discharge cycle was repeated. As a result, the discharge capacity in the first cycle was 410 mAh, which was inferior in performance to any of the batteries using LiCoO ₂ of Example 1.

Comparative Example 2 In this example, the specific surface area was 0.28 m ² /
g, a lithium nickel cobalt composite oxide LiNi _0.37 Co _0.63 O ₂ having a half-width of 0.097 on the (003) plane and 0.100 on the (104) plane. The other conditions were the same as in Example 1 to produce a battery, and the charge / discharge cycle was repeated. As a result, the voltage increased only to 2.20 V from the time of the first cycle discharge.

Comparative Example 3 In this example, a specific surface area of 2.3 m ² /
g, a lithium-nickel-cobalt composite oxide L having a half width at (003) plane of 0.51 and a half width at (104) plane of 0.52
iNi _0.37 Co _0.63 O ₂ was used. The other conditions were the same as in Example 1 to manufacture the battery. However, the cathode active material was scattered during the preparation of the paste, and the cathode active material was aggregated in the paste. Therefore, the paste was uniformly applied to the support. could not.

[0027]

As described above, the non-aqueous electrolyte secondary battery of the present invention has a long life.

[Brief description of the drawings]

FIG. 1 is a graph plotting a relationship between a charge / discharge cycle and a battery capacity.

──────────────────────────────────────────────────の Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 4/36-4/62 H01M 10/40

Claims (2)

(57) [Claims] 1. An active material comprising LiM _x Co _1-x O ₂ (M represents at least one transition metal other than Co, and 0 ≦ x ≦ 1.0), and a conductive material other than the active material. In a secondary battery including a positive electrode containing an agent and a binder, a negative electrode, a separator interposed between the positive and negative electrodes, and a non-aqueous electrolyte held by the separator, the specific surface area of the positive electrode active material is about 0.1. 35 ~
2.0 m ² / g, and the half widths of the (003) plane peak and the (104) plane peak in the X-ray diffraction pattern of the positive electrode active material are both 0.10 to 0.20. Water electrolyte secondary battery. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the content of the conductive agent in the positive electrode is 8% by weight or less based on the whole solid substance constituting the positive electrode.