JP2003197180A - Nonaqueous electrolyte battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte battery with high energy density by increasing the filling amount of a positive active material while the penetration of the electrolyte is ensured. <P>SOLUTION: This nonaqueous electrolyte battery has a positive electrode 5 prepared by forming a positive active material layer on a positive current collector, a negative electrode 6, and a nonaqueous electrolyte containing lithium ions, and the positive active material layer is composed of two active material layer parts comprising active materials having different absolute specific gravities, a first active material part 22 arranged on the positive current collector side is made of spinel lithium manganate having low absolute specific gravity and a second active material layer 23 arranged on the positive electrode surface side is made of lithium cobaltate having high absolute specific gravity. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte battery provided with a positive electrode having a positive electrode active material layer formed on the surface of a positive electrode current collector, a negative electrode, and a non-aqueous electrolyte containing lithium ions.

[0002]

2. Description of the Related Art Conventionally, as positive electrode active materials for non-aqueous electrolyte batteries, lithium cobalt oxide, lithium nickel oxide,
Alternatively, lithium manganate or the like has been proposed, but the positive electrode material currently in the mainstream is lithium cobalt oxide. This is advantageous in that the lithium nickel oxide has a high capacity, but has a problem that it is inferior to lithium cobalt oxide in safety and performance. In addition, the lithium manganate is equivalent in performance to lithium cobalt oxide, and has the advantage of being inexpensive and excellent in safety, but it also has the problem that manganese itself dissolves at high temperatures, and low energy consumption. This is because it has the problem of density. Here, the reason why lithium manganate has a low energy density is as follows. That is, regarding the packing density of the positive electrode active material, the influence of the physical properties (true specific gravity) of the positive electrode active material itself is strongly influenced, as well as the pressing pressure, the pressing method, and the mixing ratio of the positive electrode mixture (the ratio of the carbon conductive additive). receive. Generally, the true specific gravity of lithium cobalt oxide is 5.04 g / cc,
The true specific gravity of lithium manganate is said to be 4.29 g / cc. Therefore, both have a ratio of 1 per volume.
Since it is about 0: 8 (5.04: 4.29), and the capacity ratio per unit mass is also about 10: 8, the capacity per unit volume is practically 10: 6 (exactly Is 1
This is because a difference of about 00:64) occurs.

Therefore, in order to use the above lithium nickel oxide or the above lithium manganate as a positive electrode active material, it is necessary to improve various characteristics thereof. Here, recently, not only for consumer use such as mobile phones and personal computers such as hybrid automobiles but also for secondary batteries ranging from small size to large size, small amount of output and expensive cobalt have been used. Lithium manganate, which uses manganese, which has a higher yield and is cheaper than lithium cobaltate, is gaining attention.

Therefore, in order to improve the high temperature characteristics of lithium manganate, many studies have been made to stabilize the crystal structure by adding a different element (substitution element) to lithium manganate, but an effective substitution element is No practical improvement measures have been found, such as a reduction in energy density due to the addition of harmful elements such as chromium or the addition of many different elements. In order to solve the problems of deterioration of high temperature characteristics and deterioration of capacity of the positive electrode active material at the same time, the applicant of the present application discloses in Japanese Patent Laid-Open No. 2000-215884.
And as shown in Japanese Patent Laid-Open No. 2001-143705,
It has been proposed to use a composite electrode in which lithium cobalt oxide and lithium manganate are mixed. As a result, the above problem can be solved to some extent, but it is not sufficient, and there is room for improvement, particularly in terms of reduction in capacity.

Here, the positive electrode is manufactured by applying a positive electrode active material to a positive electrode current collector to prepare an electrode sheet and then compressing the electrode sheet. The compression method is as follows.
A roll press system in which the electrode sheet is poured into a gap between two rotating roll heads and is compressed by a so-called line,
There is a full-pressing method in which the whole surface of the electrode sheet is compressed at once with a plate-like pressing device. In the former case, since the electrode sheet can be continuously processed by being wound in a roll shape, the processing efficiency is good, and in addition, since it is compressed by a wire, it has an advantage that a force required for compression is small. hand,
In the latter case, a large compressive force is required in proportion to the pressing area, and the processing efficiency is low.
The former compression method is the mainstream.

However, in the roll press system, as shown in FIG. 12, when the roll heads 31 are rotated in the arrow F direction, the surface of the electrode sheet is
Since the load is applied not only in the pressing direction (arrow C direction in the figure) but also in the counter traveling direction of the positive electrode current collector (arrow D direction in the figure), the pressing direction and the counter traveling direction of the positive electrode current collector are While the load is applied in the direction of the vector sum (E direction in the figure),
Inside the electrode sheet, the force in the anti-progression direction of the positive electrode current collector (direction of arrow D in the figure) is exhausted on the surface and in the vicinity thereof, so that the load is applied only in the pressing direction (direction of arrow C in the figure). . For this reason, the compressive force becomes strong on the surface of the electrode sheet, but the compressive force becomes weak inside the electrode sheet, so that there is a problem that the packing density becomes low inside the electrode (on the side close to the positive electrode current collector). That is, although the packing density of the entire electrode is a target value, the compression density of the electrode surface is actually higher than the target value and the inside of the electrode is lower than the target compression density. As a result, in the surface layer in which the electrolytic solution is first impregnated, the compression density is too high, and the absorbing speed of the electrolytic solution is rapidly reduced, so that the electrolytic solution cannot penetrate into every corner of the electrode. This tendency becomes more remarkable as the pressing pressure becomes higher, so that the penetration of the electrolytic solution becomes insufficient when the pressing pressure is increased. From this, in order to maintain the battery characteristics, it is necessary to regulate the filling amount of the positive electrode active material to some extent, and there is a problem that it is difficult to increase the energy density. In particular, this tendency is remarkable when an active material having a low true specific gravity such as lithium manganate is used as the active material, and as described above, a mixture of lithium manganate and lithium cobalt oxide is used as the positive electrode active material. The same problem was encountered when used as.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-mentioned conventional problems. By increasing the filling amount of the positive electrode active material while ensuring the permeability of the electrolytic solution, It is an object of the present invention to provide a non-aqueous electrolyte battery capable of achieving high energy density and improved battery performance.

[0008]

In order to achieve the above object, a non-aqueous electrolyte battery of the present invention comprises a positive electrode having a positive electrode active material layer formed on the surface of a positive electrode current collector, a negative electrode, and a non-aqueous electrolyte. In the non-aqueous electrolyte battery comprising, the positive electrode active material layer is composed of a plurality of active material layer portions made of active materials each having a different true specific gravity, and the active material layer portion on the positive electrode surface side. The true specific gravity is larger than the true specific gravity of the lower active material layer portion.

The sheet density and the true specific gravity of the positive electrode active material when a positive electrode is manufactured are not proportionally linked, but an approximate correlation can be obtained. That is, the higher the true specific gravity of the active material, the higher the sheet density, and the higher the density, the better the electrolyte absorbability. Therefore, when an active material having a relatively high true specific gravity is used on the surface of the positive electrode as in the above structure, the surface of the positive electrode is highly compressed, but the active material exhibits a high liquid absorption property with respect to high compression, and thus is high. Even at the packing density, it becomes easy to absorb the electrolyte solution. On the other hand, when an active material having a relatively low true specific gravity is used inside the positive electrode (on the side of the positive electrode current collector), since the inside of the positive electrode has low compression, the problem of liquid absorption does not occur. From these, it becomes possible to improve the impregnation property of the electrolyte into the positive electrode while increasing the packing density of the positive electrode active material. Therefore, it is possible to increase the filling amount of the positive electrode active material while ensuring the permeability of the electrolytic solution, so that the energy density of the battery can be increased and the battery performance can be improved.

According to a second aspect of the present invention, in the first aspect of the invention, the positive electrode active material layer comprises two active material layer portions, and the positive electrode active material layer is arranged on the positive electrode current collector side with respect to the total mass of the positive electrode active material layer. The mass ratio of the formed first active material layer portion is less than 70 mass%, and the mass of the second active material layer portion arranged on the positive electrode surface side with respect to the total mass of the positive electrode active material layer is 30.
It is characterized in that it is regulated so that the content is at least mass%.

The reason for restricting in this way is that when the mass ratio of the second active material layer portion arranged on the positive electrode surface side is 30 mass%, a large force applied to the positive electrode active material on the positive electrode surface side. , Extends to near the boundary between the first active material layer portion and the second active material layer portion arranged on the positive electrode current collector side. Therefore,
This is because if the mass ratio of the second active material layer portion is less than 30 mass%, a large force is applied to the first active material layer portion having a small true specific gravity, which is not preferable.

According to a third aspect of the invention, in the first or second aspect of the invention, the positive electrode active material of the first active material layer portion is spinel type lithium manganate, and the positive electrode of the second active material layer portion is the positive electrode. The nonaqueous electrolyte battery according to claim 1, wherein the active material is lithium cobalt oxide. In this way, because the shape of the discharge curve and the discharge operating voltage of the spinel-type lithium manganate and the lithium cobalt oxide are substantially the same, compared with the case where lithium cobalt oxide is used alone as the positive electrode active material. This is because the discharge curve profile of the positive electrode is substantially the same, which makes it easier to use as a battery.
Further, with such a configuration, lithium manganate using manganese, which has a large amount of production and is inexpensive, can be used as the positive electrode active material, so that the manufacturing cost of the battery is reduced.

According to a fourth aspect of the invention, in the third aspect of the invention, the packing density d of the positive electrode active material in the positive electrode active material layer is restricted to 2.85 ≦ d <3.30 g / cc. Is characterized by. As described above, it is desirable that the ratio of the second active material layer portion is 30% by mass or more, but the maximum packing density at this point is 2.85 g / cc, so that the positive electrode active material is regulated. The lower limit of the packing density of the substance is preferably regulated to 2.85 g / cc or more, while the battery having the maximum packing density of 3.30 g / cc is the positive electrode whose positive electrode active material is only lithium cobalt oxide.
This is because in order to use lithium manganate as the positive electrode active material, the upper limit of the packing density needs to be less than 3.30 g / cc.

According to the invention of claim 5, in the invention of claim 4, when an ionic electrolyte is used as the non-aqueous electrolyte, the packing density d of the cathode active material in the cathode active material layer is d.
Is regulated to 3.11 ≦ d <3.30 g / cc. When an ionic electrolyte is used as the non-aqueous electrolyte, the viscosity of the electrolyte is low, so that the electrolyte easily penetrates. Therefore, if the content is regulated within the above range, the permeability of the electrolyte is not hindered.

According to the invention of claim 6, in the invention of claim 4, when a polymer electrolyte is used as the non-aqueous electrolyte, the density d of the positive electrode active material in the positive electrode active material layer is
Is regulated to 2.85 ≦ d <3.11 g / cc. When a polymer electrolyte is used as the non-aqueous electrolyte, the viscosity of the electrolyte is high, which makes it difficult for the electrolyte to permeate. Therefore, if you do not regulate within the above range,
This is because the permeability of the electrolyte is hindered.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS. 1 is a front view of a non-aqueous electrolyte battery according to the present invention, FIG. 2 is a cross-sectional view taken along the line AA of FIG. 1, and FIG. 3 is a cross-sectional view of an aluminum laminate exterior body used for the non-aqueous electrolyte battery according to the present invention. FIG. 4 is a perspective view of an electrode body used in the non-aqueous electrolyte battery according to the present invention, and FIG. 5 is a cross-sectional view showing the structure of the positive electrode used in the non-aqueous electrolyte battery according to the present invention.

As shown in FIG. 2, the thin battery of the present invention has an electrode body 1, which is arranged in a storage space 2. This storage space 2 is, as shown in FIG.
It is formed by sealing the upper and lower ends and the central portion of the aluminum laminate outer casing 3 with sealing portions 4a, 4b and 4c, respectively. Further, as shown in FIG. 4, the electrode body 1 is a spinel type lithium manganate (LiMn ₂ O ₄₎ ,
Hereinafter, a positive electrode 5 mainly composed of a positive electrode active material composed of lithium manganate) and a positive electrode active material composed of lithium cobalt oxide (LiCoO ₂ ), a negative electrode 6 composed mainly of a negative electrode active material composed of natural graphite, It is produced by winding a separator (not shown in FIG. 4) separating these two electrodes in a flat spiral shape.

The specific structure of the positive electrode is, as shown in FIG. 5, positive electrode active material layers 24.2 on both sides of the positive electrode current collector 21.
4 are formed, and these positive electrode active material layers 24, 24 are formed.
Are each composed of two active material layer portions 22 and 23. Of the active material layer portions 22 and 23, the first active material layer portions 22 and 22 arranged on the positive electrode current collector side (inside the positive electrode) are made of lithium manganate (true specific gravity: 4.29 g).
/ Cc, average particle size: 10 μm, tap density 1.8 g / c
The second active material layer portions 23, 23 mainly composed of (c) and arranged on the positive electrode surface side are lithium cobalt oxide (true specific gravity: 5.04 g / cc, average particle diameter: 9.1 μm, tap density 2. 3 g / cc) is the main constituent. The mass ratio of lithium manganate in the first active material layer portion to lithium cobalt oxide in the second active material layer portion is 50:50.

In the separator, a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a mass ratio of 30:70 was added with 1 M of LiPF ₆ as an electrolyte salt (lithium salt). It is impregnated with the electrolyte solution added at a ratio of (mol / l).

Further, as shown in FIG. 3, the concrete structure of the aluminum laminate exterior body 3 is as follows.
Resin layers 13 and 13 (thickness: 3) made of polypropylene with adhesive layers 12 and 12 (thickness: 5 μm) made of modified polypropylene on both sides of (thickness: 30 μm) respectively.
0 μm) is bonded. Further, the positive electrode 5 is a positive electrode lead 7 made of aluminum, and the negative electrode 6 is
Are connected to negative electrode leads 8 made of copper, respectively, so that chemical energy generated inside the battery can be taken out as electric energy to the outside.

Here, the battery having the above structure was produced as follows. (Production of Positive Electrode) First, lithium manganate and carbon and graphite which are conductive agents are mixed at a mass ratio of 92: 5 to obtain a first positive electrode mixture powder, and a mixing device [eg, Hosokawa Micron mechanofusion device ( AM-15
F)] is filled with 100 g. This is the rotation speed 150
The mixture is operated at 0 rpm for 10 minutes to cause compression, impact and shearing action, and mixed to obtain the first positive electrode active material. Then, the first positive electrode active material and the fluororesin binder (PVd
The first positive electrode mixture slurry was prepared by mixing the two in an N-methylpyrrolidone (NMP) solvent such that the mass ratio with F) was 97: 3. In parallel with this, a second positive electrode mixture slurry was prepared in the same manner as above except that lithium cobalt oxide was used instead of the above lithium manganate.

Thereafter, the first positive electrode material mixture slurry is applied on both sides of an aluminum foil and dried, and then the second positive electrode material mixture slurry is applied, dried, and further rolled by a roll pressing method to produce a positive electrode. 5 was produced. When the first positive electrode mixture slurry and the second positive electrode mixture slurry are applied, the mass ratio of lithium manganate and lithium cobalt oxide is 50:50.
Both slurries were applied so that

(Preparation of Negative Electrode) First, the negative electrode active material made of graphite and the styrene-based binder were mixed in a N-methylpyrrolidone solvent so that the mass ratio was 98: 2, and the negative electrode was mixed. A mixture slurry was prepared. Next, this negative electrode mixture slurry was uniformly applied over both surfaces of a negative electrode core body made of a copper foil, dried and rolled to prepare a negative electrode 6.

(Production of Electrode Body) After attaching the positive electrode lead 7 or the negative electrode lead 8 to the positive electrode 5 and the negative electrode 6 produced as described above, respectively, the both electrodes 5 and 6 are put through a polyethylene separator. Overlaid. Then, it was wound by a winder, and the outermost periphery was taped and pressed to produce a flat spiral electrode body 1.

(Preparation of Battery) First, after preparing a sheet-shaped aluminum laminate material, the vicinity of the end portions of the aluminum laminate material are overlapped with each other, and the overlapped portion is welded to form the sealing portion 4c. did. Next, the electrode body 1 was inserted into the storage space 2 for the cylindrical aluminum laminate material. At this time, the electrode body 1 was arranged such that both current collecting tabs 7 and 8 were projected from one opening of the cylindrical aluminum laminate material. Next, in this state, the aluminum laminate material in the opening from which both the current collecting tabs 7 and 8 protrude was welded and sealed to form the sealing portion 4a. At this time, the welding was performed using a high frequency induction welding apparatus.

Then, an electrolyte solution was prepared by adding 1M LiPF ₆ as an electrolyte salt to a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed in a volume ratio of 3: 7. The liquid was poured into the storage space 2. Thereafter, the end of the aluminum laminate material on the side opposite to the sealing portion 4a is welded to form the sealing portion 4b, thereby forming a non-aqueous electrolyte battery (battery capacity: 600 mAh).
Was produced.

[Other Matters] (1) Lithium cobalt oxide and lithium manganate were used as the positive electrode active material, but the present invention is not limited to these. For example, manganese is partially replaced with a different element. Lithium manganate [Li (Mn _2-x M _x ) O ₄
(However, M is a metal element other than Mn selected from Li, Mg, Al, Co, Zr, Fe, etc.)], and lithium nickel oxide [LiNiO ₂ , true specific gravity 4.7]
8 g / cc] or olivine-type lithium phosphate [LiMPO ₄
(M is a metal element selected from Fe, Co, Mn, Ni, etc., and when M = Fe, the true specific gravity is 3.60 g / c.
c)] or the like. However, when lithium manganate is used for the first active material layer portion and lithium nickelate or olivine-type lithium is used for the second active material layer portion, the shape of the discharge curve of lithium manganate and lithium nickelate, etc. And the discharge operating voltage are different, the discharge curve profile of the mixed positive electrode changes greatly,
It becomes difficult to use as a battery. Therefore, the first
The most desirable combination is lithium manganate for the active material layer portion and lithium cobaltate for the second active material layer portion.

(2) The negative electrode active material is not limited to the above graphite, and any material capable of inserting and releasing lithium ions such as graphite, coke, tin oxide, metallic lithium, silicon, and a mixture thereof can be used. good. (3) The mixing of the positive electrode active material and the conductive agent is not limited to the mechanofusion method, and these materials may be mixed in a slurry state or may be mixed by another method.

(4) The shape of the battery is not limited to the thin battery using the aluminum laminate described above, and it is needless to say that the battery can be applied to a square or cylindrical battery using an iron or aluminum material for the outer can. In addition, there is no particular limitation on the size. (5) The electrolytic solution is not limited to the above, and examples of the lithium salt include LiClO ₄ and Li.
BF ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C
₂ F ₅ ) ₂ , LiPF _6-X (Cn F _{2n + 1} ) x [however, 1
≦ x ≦ 6, n = 1 or 2] and the like.
One kind or a mixture of two or more kinds can be used. The concentration of the lithium salt is not particularly limited, but is preferably 0.2 to 1.5 mol per liter of the electrolytic solution. Examples of the solvent for the electrolytic solution include propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and γ-butyrolactone.
One kind or a mixture of two or more kinds can be used. Among these, it is desirable to use a mixture of a cyclic carbonate and an acyclic (chain) carbonate, and it is particularly desirable to use ethylene carbonate as the cyclic carbonate and diethyl carbonate as the chain carbonate.

(6) The present invention is not limited to the above-mentioned liquid type battery, and comprises a polyether solid polymer, a polycarbonate solid polymer, a polyacrylonitrile solid polymer, or two or more of these. Of course, the present invention can be applied to a polymer battery using a solid electrolyte in which a copolymer or a crosslinked polymer is combined with a lithium salt and an electrolyte to form a gel. Here, an example of production of the polymer battery will be described. First, an electrolyte solution was prepared in which LiPF ₆ as an electrolyte salt was added at a ratio of 1M to a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a mass ratio of 3: 7. An acrylate (molecular weight: about 300) and an electrolytic solution were mixed at a mass ratio of 1:15, and 5000 ppm of t-hexylperoxypivalate as a polymerization initiator was added to the mixed solution, and the mixture was placed in the storage space. Injection (5
After that, it is produced by heating at 50 ° C. for 3 hours to carry out a curing treatment. The mixing ratio of the polypropylene glycol diacrylate and the electrolytic solution is not limited to the above ratio, but considering the conductivity and the liquid retaining property, the mass ratio is about 1: 6 to 1:25. Is desirable.

[0031]

EXAMPLES (First Example) [Examples 1 to 4] The mass ratios of lithium manganate and lithium cobalt oxide were 90:10 and 80: 2, respectively.
A positive electrode was produced in the same manner as in the above-described embodiment of the invention except that the ratio was 0, 70:30, and 60:40. The positive electrodes produced in this manner are hereinafter referred to as positive electrodes A1 to A4 of the present invention, respectively.
Called. [Example 5] As Example 1, a positive electrode prepared in the same manner as in the first embodiment (the mass ratio of lithium manganate and lithium cobalt oxide was 50:50) was used. The positive electrode thus manufactured is hereinafter referred to as a positive electrode A5 of the invention.

[Examples 6 to 9] The mass ratio of lithium manganate and lithium cobalt oxide was 40: 6, respectively.
Other than 0, 30:70, 20:80, 10:90,
A positive electrode was produced in the same manner as in the embodiment of the invention described above. The positive electrodes thus manufactured are hereinafter referred to as present invention positive electrodes A6 to A9, respectively.

Comparative Example 1 A positive electrode was prepared in the same manner as in Example 1 except that only the lithium manganate was used as the positive electrode active material without providing the first active material layer portion and the second active material layer portion. Was produced. The positive electrode thus manufactured is
Hereinafter, it is referred to as a comparative positive electrode X1. [Comparative Example 2] A mixed active material of lithium manganate and lithium cobalt oxide (the mass ratio of lithium manganate and lithium cobalt oxide was 90%) without providing the first active material layer portion and the second active material layer portion. : 10) was used as the positive electrode active material, and a positive electrode was produced in the same manner as in Example 1 above. Hereinafter, the positive electrode manufactured in this manner will be referred to as comparative positive electrode X.
2.

[Comparative Examples 3 to 10] The mass ratio of lithium manganate to lithium cobalt oxide was 80: 2, respectively.
0, 70:30, 60:40, 50:50, 40: 6
Other than 0, 30:70, 20:80, 10:90,
A positive electrode was produced in the same manner as in Comparative Example 2 above. The positive electrodes produced in this manner are hereinafter referred to as comparative positive electrodes X3 to X, respectively.
It is called 10. [Comparative Example 11] A positive electrode was prepared in the same manner as in Example 1 except that only lithium cobalt oxide was used as the positive electrode active material without providing the first active material layer portion and the second active material layer portion. . The positive electrode thus manufactured is hereinafter referred to as a comparative positive electrode X11.

Comparative Examples 12 to 20 Lithium cobalt oxide was used for the first active material layer portion (active material layer portion on the inside of the positive electrode), and the second active material layer portion (active material layer portion on the surface of the positive electrode).
Positive electrodes were produced in the same manner as in Examples 1 to 9 except that lithium manganate was used as the cathode. The positive electrodes produced in this manner are hereinafter referred to as comparative positive electrodes Y1 to Y1, respectively.
It is called Y9. Here, for ease of understanding, the above-described positive electrodes A1 to A9 of the present invention, comparative positive electrodes X1 to X11, and Y1 to Y9.
Table 1 shows the structure of the electrode plate.

[0036]

[Table 1]

[Meaning of Experiment 1 and Experiment 2 below] There are two important points regarding the positive electrode packing density. The first is how to increase the packing density of the positive electrode active material to achieve a high energy density, and the second is how quickly the electrolyte can penetrate into the electrode. ,this is,
It is necessary to make every corner of the electrode react (since the liquid-free part does not react, it is necessary to increase the utilization rate of the positive electrode active material). These two important points are
Each tends to conflict. That is, the higher the packing density, the lower the liquid content inside the electrode. vice versa,
If the packing density is low, the liquid content is good, but the energy density is low. From these things, in designing the battery,
It is necessary to strike a good balance between the two. Therefore,
The following Experiment 1 and Experiment 2 were conducted to examine the balance between the two.

[Experiment 1] Under the condition that the positive electrodes A1 to A9 of the present invention and the comparative positive electrodes X1 to X11 and Y1 to Y9 satisfy the following aging conditions, the highest packing density (maximum packing density) is investigated. Therefore, the results are shown in Tables 2 to 4 and FIG. Aging condition Under the closed condition without wind, the same electrolytic solution as the electrolytic solution shown in the embodiment of the present invention (EC and DEC in a mass ratio of 30: 7).
10 μl of an electrolytic solution obtained by adding LiPF ₆ at a ratio of 1 M to a mixed solvent mixed at a ratio of 0) was dropped on each positive electrode,
The electrolyte should disappear from the surface of the positive electrode within 2 minutes. still,
The reason for setting such a condition is as follows. That is, when the test is performed under the above conditions and the electrolytic solution disappears, it is possible to obtain the result that the capacity almost equal to the designed capacity can be obtained even when the battery is manufactured (after that, the electrolytic solution is immersed in the electrolytic solution for a certain time. Then, by calculating the amount of electrolyte contained in the electrode plate and confirming whether the disappearance rate of the electrolyte is permeation toward the inside of the positive electrode, it has been confirmed that it is not diffusion to the positive electrode surface). If it takes more than 2 minutes, when the battery is actually manufactured, the electrolyte does not sufficiently penetrate into the inside of the electrode plate (details), resulting in a non-uniform reaction, so that the capacity should be increased. Because it cannot be achieved.

[0039]

[Table 2]

[0040]

[Table 3]

[0041]

[Table 4]

As shown in Table 3 and FIG. 6, the comparative positive electrode X1
When using a positive electrode active material in which lithium cobalt oxide and lithium manganate are mixed as in the case of X11 to X11, since the true specific gravities of the respective active materials are reflected to some extent, the liquid absorbing property of the electrolytic solution (aging step) However, there is a proportional relationship between the compression density of the positive electrode material mixture and the proportion of lithium cobalt oxide. That is, the maximum packing density improves as the proportion of lithium cobalt oxide increases. On the other hand, as shown in Table 2 and FIG. 6, in the positive electrodes A1 to A9 of the present invention in which the positive electrode surface side is coated with a positive electrode active material (lithium cobalt oxide) having a high liquid absorbing property even when filled, Since lithium cobalt oxide is present in the surface portion where the compressive force is strong, it is recognized that the liquid absorbency can be maintained in a relatively high state even when the surface is highly filled.

As shown in Table 4 and FIG. 6, in the comparative positive electrodes Y1 to Y9, in which the positive electrode surface side was coated with lithium manganate, which is highly filled and the liquid absorbency is lowered, Since lithium manganate is present, the liquid absorbency is extremely reduced, and the permeability of the electrolytic solution into the electrode is almost the same as that of the positive electrode using lithium manganate alone. I can ask.

Next, the positive electrodes A1 to A9 of the present invention will be examined in detail. As shown in FIG. 6, when the proportion of lithium cobalt oxide is about 30% by mass, the liquid content rapidly increases. Has improved. The reason for this is that when the proportion of lithium cobalt oxide is about 30 mass%, a large force applied to the positive electrode active material on the positive electrode surface side during compression extends to the vicinity of the boundary between lithium cobalt oxide and lithium manganate. it seems to do. Therefore, if the proportion of lithium cobalt oxide is smaller than that, it is presumed that, in the end, a large force acts even on the surface of the lithium manganate to reduce the liquid content.

Although this is influenced by the extent to which the positive electrode slurry is applied onto the aluminum core, it is usually tested this time in the electrode design aiming at high capacity (commercial level). It is considered that the coating amount is the minimum required, and in order to secure the packing density, the ratio of the mass of lithium cobalt oxide to the total mass of the positive electrode active material is preferably 30 mass% or more. Further, as described above, the displacement point is the time when the proportion of lithium cobalt oxide reaches 30 mass%, and the maximum packing density at this point is 3.1.
Since it is 1 g / cc (refer to the positive electrode A3 of the present invention in Table 2), it is desirable that the maximum packing density is 3.11 g / cc or more, while in the battery with the maximum packing density of 3.30 g / cc, the positive electrode active material is cobalt acid. Comparative positive electrode X11 consisting only of lithium
Therefore, in the present invention, the maximum packing density is 3.3.
It must be less than 0 g / cc.

Although not shown here, a mixed slurry of lithium cobalt oxide and lithium manganate having a high content of lithium cobalt oxide is applied to the surface of the positive electrode, while a mixed slurry of lithium manganate is used. Even when a mixed slurry with a high content is applied to the inside of the positive electrode,
Although a large effect as shown in FIG. 6 is not obtained, it has been confirmed that the packing density is higher than that obtained by coating a slurry prepared by simply mixing lithium cobalt oxide and lithium manganate.

[Experiment 2] The highest packing density (maximum packing density) was examined under the condition that the positive electrodes A1 to A9 of the present invention and the comparative positive electrodes X1 to X11 satisfy the aging conditions shown in the first test. The results are shown in Tables 5 and 6 and FIG. However, as the electrolytic solution to be dropped, a prepolymer electrolytic solution obtained by mixing the electrolytic solution shown in the above Experiment 1 and polypropylene glycol diacrylate (having a molecular weight of about 300) in a mass ratio of 1:15 is used. I was there.

[0048]

[Table 5]

[0049]

[Table 6]

As shown in Table 6 and FIG. 7, the comparative positive electrode X1
In the case of ~ X11, as in the case of Experiment 1, there is a proportional relationship between the compression density of the positive electrode mixture and the proportion of lithium cobalt oxide, in which the liquid absorbency of the electrolyte solution (aging step) is not a problem. In the positive electrodes A1 to A9, as shown in Table 5 and FIG. 7, since lithium cobalt oxide is present on the surface portion having a strong compressive force, the liquid absorbing property can be maintained in a relatively high state even when highly filled. Is recognized.

Next, the positive electrodes A1 to A9 of the present invention will be examined in detail. As shown in FIG. 7, when the mixed amount of lithium cobalt oxide is about 30% by mass, the liquid content rapidly increases. Has improved. It is considered that the reason for this is the same as the reason shown in Experiment 1 above. However, as compared with the case of Experiment 1, the maximum packing density is lowered as a whole. It is considered that this is because the prepolymer electrolyte solution used in this experiment has a higher viscosity than the normal electrolyte solution used in Experiment 1.

As described above, the displacement point is when the proportion of lithium cobalt oxide is 30% by mass.
The highest packing density at this point is 2.85 g / cc (Table 5
Therefore, the maximum packing density is preferably 2.85 g / cc or more, while the maximum packing density is 3.11 g when the prepolymer electrolyte is used.
In the present invention, since the battery of / cc is the comparative positive electrode X11 in which the positive electrode active material is only lithium cobalt oxide,
The highest packing density needs to be less than 3.11 g / cc.

(Second Example) [Examples 1 to 5] In Examples 1 to 5, a battery (battery using an ionic electrolyte as a non-aqueous electrolyte) was prepared in the same manner as the method described in the above embodiment. Was produced. The packing density of the active material in each positive electrode was 3.00 g / cc,
3.10 g / cc, 3.20 g / cc, 3.30 g / c
c, 3.40 g / cc. The positive electrode active material of the battery thus produced was the same as the positive electrode A5 of the present invention shown in Example 5 of the first example, and
Since the ionic electrolyte is used as the non-aqueous electrolyte, the batteries produced as described above will be referred to as the present invention battery ai51, the present invention battery ai52, and the present invention battery ai5, respectively.
3, the present invention battery ai54, the present invention battery ai55.

[Examples 6 to 10] In Examples 6 to 10, using the positive electrode of the present invention shown in Example 5 of the first example, a polymer electrolyte was used as a non-aqueous electrolyte as shown below. The battery used was produced. The packing density of the active material in each positive electrode was 2.80 g / cc and 2.9, respectively.
0 g / cc, 3.00 g / cc, 3.10 g / cc,
It was specified to be 3.20 g / cc.

A method for producing a battery using a polymer electrolyte is an electrolytic solution in which LiPF6 as an electrolyte salt is added at a ratio of 1M to a mixed solvent in which EC and DEC are mixed at a mass ratio of 3: 7. Was further prepared, and polypropylene glycol diacrylate (molecular weight: about 300) was mixed with the electrolytic solution in a mass ratio of 1:15, and the mixed solution was mixed with t-hexylperoxypiper as a polymerization initiator. It was prepared by injecting (5 ml) a solution containing 5000 ppm of barrate into the storage space, and then heating at 50 ° C. for 3 hours to perform a curing treatment. The positive electrode active material of the battery thus manufactured was the same as the positive electrode A5 of the present invention shown in Example 5 of the first example, and the polymer electrolyte was used as the non-aqueous electrolyte. The batteries thus produced are referred to below as the present invention battery ap51, the present invention battery ap52, the present invention battery ap53, and the present invention battery ap, respectively.
54, battery of the present invention ap55.

Comparative Examples 1-5 As Comparative Examples 1-5,
A battery (battery using an ionic electrolyte as the non-aqueous electrolyte) was produced by the same method as the method shown in Comparative Example 5 of the first example. The packing density of the active material in each positive electrode was 2.80 g / cc, 2.90 g / cc, 3.00 g, respectively.
/ Cc, 3.10 g / cc, 3.20 g / cc. The positive electrode active material of the battery thus manufactured was the comparative positive electrode X5 shown in Comparative Example 5 of the first embodiment.
Since the same as the above and using an ionic electrolyte as the non-aqueous electrolyte, the batteries produced as described above are referred to as Comparative Battery xi51, Comparative Battery xi52, Comparative Battery xi53, Comparative Battery xi54, and Comparative Battery, respectively. xi55
Called.

[Comparative Examples 6 to 10] As Comparative Examples 6 to 10, the positive electrode of the present invention shown in Comparative Example 5 of the first embodiment was used, and the same method as in Examples 6 to 10 was performed. A battery using a polymer electrolyte as a non-aqueous electrolyte was prepared. The packing density of the active material in each positive electrode was 2.60 g / cc, 2.70 g / cc, 2.80 g, respectively.
/ Cc, 2.90 g / cc, 3.00 g / cc. The positive electrode active material of the battery thus manufactured was the comparative positive electrode X5 shown in Comparative Example 5 of the first embodiment.
The same as the above, and since the polymer electrolyte is used as the non-aqueous electrolyte, the battery produced as described above is
Hereinafter, comparative battery xp51, comparative battery xp52,
Comparative battery xp53, Comparative battery xp54, Comparative battery xp5
It is called 5.

[Experiment] The batteries of the present invention ai51 to ai5
5, ap51 to ap55 and comparative batteries xi51 to xi5
5, xp51 to xp55 were charged and discharged under the following conditions, and the ratio of the initial capacity of each battery to the discharge capacity when discharged at a current of 3C to the discharge capacity when discharged at a current of 1C (hereinafter, 3C / 1C ratio Abbreviated) was examined, and the results are shown in Tables 7 and 8 and FIGS.

[Charging / Discharging Conditions] -Charging conditions Charging is performed with a constant current at a charging current of 1 C (600 mA) until the battery voltage reaches 4.2 V, and after reaching 4.2 V, the charging current is constant until the current value becomes 30 mA or less. It was charged with voltage. This was followed by a 10 minute rest.・ Discharge conditions: discharge current 1C (600mA), discharge current 3C
At (1800 mA), the battery was discharged at a constant current until the battery voltage reached 2.75V.

[0060]

[Table 7]

[0061]

[Table 8]

As is clear from Tables 7 and 8 and FIGS. 8 to 11, the proper compression values obtained from the results of the liquid absorption test in Experiment 1 and Experiment 2 of the above-mentioned first embodiment for each battery. (Inventive battery ai53 and comparative battery xi, respectively)
53, the present invention battery ap53, the comparative battery xp53)
Up to the vicinity, the capacity of the battery is closest to the design value, and if the packing density exceeds it, the capacity lower than the design value can be obtained because the liquid content decreases. Therefore, it can be seen that the energy density per unit volume is the maximum at an appropriate value. Further, as also shown in Tables 7 and 8 and FIGS. 8 to 11, when the packing density is too low, the electrode plate resistance increases, so that the high rate characteristics (3C / 1C ratio) are particularly high. It tends to decrease. Therefore, if the packing density of the positive electrode is too low, not only the energy density is lowered, but also the high rate characteristics are deteriorated. Therefore, it is desirable that the packing density be as high as possible.

[0063]

As described above, according to the present invention,
By increasing the filling amount of the positive electrode active material while ensuring the permeability of the electrolytic solution, it is possible to achieve a high energy density and to provide a non-aqueous electrolyte battery having excellent battery performance. Produce an effect.

[Brief description of drawings]

FIG. 1 is a front view of a non-aqueous electrolyte battery according to the present invention.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is a cross-sectional view of an aluminum laminate exterior body used in the non-aqueous electrolyte battery according to the present invention.

FIG. 4 is a perspective view of an electrode body used in the non-aqueous electrolyte battery according to the present invention.

FIG. 5 is a cross-sectional view showing a structure of a positive electrode used in the non-aqueous electrolyte battery according to the present invention.

FIG. 6 is a graph showing the relationship between the ratio of lithium cobalt oxide and the maximum packing density.

FIG. 7 is a graph showing the relationship between the ratio of lithium cobalt oxide and the maximum packing density.

FIG. 8 is a graph showing the relationship between positive electrode packing density, initial capacity and 3C / 1C ratio.

FIG. 9 is a graph showing the relationship between positive electrode packing density, initial capacity and 3C / 1C ratio.

FIG. 10 is a graph showing the relationship between positive electrode packing density, initial capacity, and 3C / 1C ratio.

FIG. 11 is a graph showing the relationship between the positive electrode packing density, the initial capacity, and the 3C / 1C ratio.

FIG. 12 is an explanatory diagram when manufacturing a positive electrode by a roll pressing method.

[Explanation of symbols]

1: Electrode body 2: Storage space 3: Aluminum laminated exterior body 5: Positive electrode 6: Negative electrode 22: First active material layer portion 23: Second active material layer portion 24: Positive electrode active material layer

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5H029 AJ02 AJ03 AK03 AK18 AL02                       AL06 AL07 AL11 AL12 AL18                       AM03 AM05 AM07 AM16 BJ03                       BJ12 BJ14 CJ22 DJ16 DJ17                       HJ01 HJ08 HJ12                 5H050 AA02 AA08 BA16 BA17 CA07                       CA08 CA09 CA29 CB02 CB07                       CB08 CB11 CB12 CB29 DA02                       FA02 FA05 FA17 FA19 GA22                       HA01 HA08 HA12

Claims (6)

[Claims] 1. A non-aqueous electrolyte battery comprising a positive electrode having a positive electrode active material layer formed on the surface of a positive electrode current collector, a negative electrode, and a non-aqueous electrolyte, wherein each of the positive electrode active material layers has a true specific gravity. It is characterized in that it is composed of a plurality of active material layer portions made of different active materials, and the true specific gravity of the active material layer portion on the positive electrode surface side is larger than the true specific gravity of the lower active material layer portion. Non-aqueous electrolyte battery. 2. The positive electrode active material layer comprises two active material layer portions, and the mass ratio of the first active material layer portion disposed on the positive electrode current collector side to the total mass of the positive electrode active material layer is 70. Less than 3% by mass, and the mass of the second active material layer portion arranged on the positive electrode surface side with respect to the mass of the entire positive electrode active material layer is 3
The non-aqueous electrolyte battery according to claim 1, which is regulated to be 0% by mass or more. 3. The positive electrode active material of the first active material layer portion is spinel type lithium manganate, and the positive electrode active material of the second active material layer portion is lithium cobalt oxide. Non-aqueous electrolyte battery. 4. The non-aqueous electrolyte battery according to claim 3, wherein the packing density d of the positive electrode active material in the positive electrode active material layer is regulated to 2.85 ≦ d <3.30 g / cc. 5. When an ionic electrolyte is used as the non-aqueous electrolyte, the packing density d of the positive electrode active material in the positive electrode active material layer is restricted to 3.11 ≦ d <3.30 g / cc,
The non-aqueous electrolyte battery according to claim 4. 6. The packing density d of the positive electrode active material in the positive electrode active material layer is regulated to 2.85 ≦ d <3.11 g / cc when a polymer electrolyte is used as the non-aqueous electrolyte. The non-aqueous electrolyte battery described.