JP2007123237A - Nonaqueous electrolyte battery, electrode for nonaqueous electrolyte battery, and manufacturing method of this electrode for nonaqueous electrolyte battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte battery or the like capable of improving such characteristics of a battery as high-rate charge/discharge characteristics, high-temperature cycle characteristics, and preservation characteristics while reducing manufacturing cost of a battery and satisfying request for higher capacity of the battery. <P>SOLUTION: A porous layer 14 with more excellent permeability of a nonaqueous electrolyte than at least a TD of a separator is arranged between an anode 13 and the separator, and at the same time, excess electrolyte solution is contained at least in a part of a site excluding an electrode body in an inside space of a battery container, and moreover, the excess electrolyte solution and at least a part of the porous layer 14 are in contact with each other. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte battery such as a lithium ion battery or a polymer battery, a non-aqueous electrolyte battery electrode, and a method for producing the non-aqueous electrolyte battery electrode. Batteries with excellent liquid properties and battery characteristics (cycle characteristics, storage characteristics, safety) related to electrolyte permeability and high reliability even in battery configurations characterized by high capacity and high output It relates to the structure.

In recent years, mobile information terminals such as mobile phones, notebook personal computers, and PDAs have been rapidly reduced in size and weight, and batteries as drive power sources are required to have higher capacities. A non-aqueous electrolyte battery that performs charge / discharge by moving lithium ions between the positive and negative electrodes along with charge / discharge has a high energy density and high capacity. As widely used. However, at present, the demand is not fully met.
Recently, using these features, not only mobile applications such as mobile phones, but also medium- to large-sized battery applications such as electric tools, electric vehicles, and hybrid vehicles are being developed. Along with this trend, the demand for higher safety is also increasing.

  Against this background, in order to increase the capacity of the battery, the electrode material is highly charged, and the current collector, separator, or battery storage case that is not directly involved in power generation is made thinner (for example, the following patents) In addition, in order to increase the output of the battery, the electrode area has been increased, and the battery configuration is a problem related to the penetration of the electrolyte into the electrode and the liquid retention. However, the surface is beginning to surface compared to the initial development of lithium-ion batteries. For this reason, it is necessary to establish a new battery configuration in order to solve this problem in securing the performance and reliability of the battery.

JP 2002-141042 A

A conventional battery configuration includes an electrode body in which a positive electrode and a negative electrode are opposed to each other with a separator interposed therebetween. For example, when the electrode body is a take-up electrode body, It is considered that the penetration and diffusion of the electrolytic solution into the film occur through the following three routes.
1) Gap inside the electrode 2) Gap of the separator 3) Gap between the electrode and the separator However, in the above-described path, it can sufficiently play a role as an electrolyte penetration and diffusion path for the following reasons. Absent.

・ Reason why the path 1) cannot fully play the role of electrolyte penetration and diffusion path As described above, in recent batteries, the active material has to be highly filled in order to achieve higher battery capacity. This is probably because the gap inside the electrode tends to decrease.

・ Reason that the path 2) cannot fully play the role of electrolyte penetration and diffusion path The currently used polyolefin-based separator is the ability to absorb electrolyte in the direction of electrode winding width (TD, Transverse direction). This is considered to be due to the reason that the gap portion tends to decrease due to the thinning of the separator due to the recent increase in capacity due to the manufacturing process.

・ Reason why the path 3) cannot fully play a role as an electrolyte penetration and diffusion path. In recent years, in a battery using a winding electrode body, the winding tension has increased, and the tension of the electrode body has been increased. This is probably because the penetration and diffusion of the electrolyte solution is unlikely to occur.

  By the way, in the initial stage of battery assembly, a decompression process and a pressurization process are performed in the battery manufacturing process, so that the penetration of the electrolyte into the electrode is ensured to some extent by optimizing the process conditions. . However, if the electrolyte in the battery is consumed by repeated charge / discharge cycles or by storing the battery for a long period of time, it is charged with the electrolyte that was originally in the electrode and the electrolyte retained by the separator. Although it is necessary to guarantee the discharge reaction, as described above, due to the thinning of the separator and the increase in the amount of active material applied, the above-mentioned electrolyte alone cannot adequately guarantee the charge / discharge reaction, and the battery performance deteriorates due to insufficient electrolyte. Will be increasingly accelerated.

  In addition, lithium cobaltate and graphite materials used as battery constituent materials exhibit a behavior of expanding by charging and contracting by discharging, and in particular, expansion and contraction of the negative electrode are increased. When these materials are used as electrode materials, the expansion of the battery is suppressed by a buffering action that the separator is thinned (shrinks) against expansion due to charging. In addition, since the gap inside the electrode decreases from the initial assembly (discharged state) to charging, the electrolyte is released from the electrode. However, the electrolyte is absorbed by the gap of the separator, and the electrolyte that cannot be absorbed is the electrode. It will be released outside the body. However, if the separator does not have the amount of electrolyte suitable for the absorption and release of the electrolyte in the electrode plate due to charge and discharge, or if the electrolyte is consumed due to side reactions on the electrode and is insufficient, the conventional structure In the battery, the permeability in the TD direction (electrolyte permeation direction) in the separator is inferior, and it is difficult to rapidly permeate the electrolyte discharged outside the electrode body over the entire area of the separator. For the reason, there has been a problem that the winding electrode body works in the direction of exhaustion of the electrolyte, and as a result, the charge / discharge performance is lowered. This tendency is particularly noticeable in test environments where electrolytes are likely to be consumed in side reactions such as high-temperature cycle tests and storage tests, and in test environments where the electrode absorbs electrolytes such as high-rate charge / discharge, where the speed changes quickly. .

  Furthermore, when the electrode width is increased in order to increase the capacity and output of the battery, the permeability of the electrolytic solution into the center portion of the electrode plate is particularly inferior. For this reason, it is necessary to ensure the permeability of the electrolyte not only during the charge / discharge cycle but also at the initial stage of assembly, and aging must be performed for a long time, but this increases the manufacturing cost of the battery. Therefore, in order to shorten the manufacturing process of the battery and reduce the cost, in order to ensure the penetration and diffusion path for smooth penetration and diffusion of the electrolyte into the electrode, and to further improve the characteristics of the battery In addition, it was essential to secure an amount of electrolyte that was commensurate with the amount of positive and negative active materials.

  Further, in recent years, there is a technology that enables the battery to have a higher capacity and higher output by charging the positive electrode until it becomes 4.40 V or higher with respect to the lithium reference electrode potential. If the battery is charged to 4.40 V or more, the cycle characteristics are significantly deteriorated.

  In the case of the above battery design, since the negative electrode charging depth does not change as compared with the conventional case where the positive electrode is charged to 4.30 V with respect to the lithium reference electrode potential, the expansion and contraction rate of the negative electrode However, since the positive electrode further expands when the charge potential is increased, the expansion / contraction rate as an electrode increases. For this reason, if the positive electrode is charged to 4.40 V or more with respect to the lithium reference electrode potential, the electrode expands and contracts and the amount of electrolyte in the separator becomes insufficient. Further, since the potential is high, the electrolytic solution is easily oxidized and decomposed in the positive electrode, and the electrolytic solution in the electrode is remarkably insufficient. Therefore, the charge / discharge battery characteristics are greatly deteriorated.

  Regarding the expansion and contraction of the electrode when lithium cobaltate is used for the positive electrode, FIG. Ozuku et. al, J. et al. Electrochem. Soc. Vol. 141, 2972 (1994)]. As is apparent from FIG. 20, the positive electrode is charged to 4.40V to 4.50V with respect to the lithium reference electrode potential (4.30V to 4.40V because the battery voltage is 0.1V lower than the lithium reference electrode potential) or more. Then, the crystal lattice constant on the a-axis hardly changes, but the crystal lattice constant on the c-axis increases. For this reason, the positive electrode expands further, and the expansion / contraction rate of the positive electrode during charge / discharge increases, while the expansion rate of the negative electrode does not change. As a result, the amount of electrolyte solution that permeates and diffuses into the positive electrode increases, while the amount of electrolyte solution that permeates and diffuses into the negative electrode decreases (this is shown in Preliminary Experiment 3 of Examples described later). Thus, it is considered that the positive electrode is superior in diffusibility and liquid absorption of the electrolytic solution. As a result, the charge / discharge battery characteristics are greatly deteriorated due to insufficient electrolyte in the negative electrode.

  In addition, in the battery configuration proposed in the past, there is no application focusing on this point, and there is a method for increasing the gap of the separator and a method for increasing the separator thickness to ensure the liquid retention amount and the buffering action. Although generally known, when such a method is taken, the occupied volume of the separator, which is a member that does not directly participate in power generation, increases, so that it is not possible to satisfy the demand for higher battery capacity. There are challenges.

  Therefore, the present invention can improve various battery characteristics such as high-rate charge / discharge characteristics, high-temperature cycle characteristics, and storage characteristics while reducing the battery manufacturing cost and satisfying the demand for higher battery capacity. An object of the present invention is to provide a water electrolyte battery, a nonaqueous electrolyte battery electrode, and a method for producing the nonaqueous electrolyte battery electrode.

  To achieve the above object, the present invention provides an electrode body comprising a positive electrode having a positive electrode active material layer, a negative electrode having a negative electrode active material layer, and a separator interposed between the two electrodes, and supplying the electrode body A non-aqueous electrolyte and a battery housing for housing the electrode body and the non-aqueous electrolyte, and in the separator, the separator is divided into two types, MD and TD, which is less permeable to the non-aqueous electrolyte than the MD. Directionality exists, and the nonaqueous electrolyte is supplied to the electrode body mainly along the TD. In the nonaqueous electrolyte battery, between at least one of the positive and negative electrodes and the separator, A porous layer having at least a non-aqueous electrolyte permeability than the TD is disposed, and at least a part of the portion excluding the electrode body in the internal space of the battery housing includes an excess electrolyte. One, characterized in that at least part is in contact of the excess electrolyte and the porous layer.

  As in the above configuration, if a porous layer having better non-aqueous electrolyte permeability than the TD of the separator is formed between at least one of the positive and negative electrodes and the separator, the presence of the porous layer causes an electrolyte solution. Electrolytic solution penetration and diffusion path that smoothly penetrates and diffuses can be secured, so that the void inside the electrode is reduced by charging, and the electrolytic solution that can not be absorbed in the gap of the separator is released out of the system of the electrode body Even if it is a case, the electrolyte solution discharged | emitted out of the system of the electrode body can osmose | permeate rapidly again over the whole region of a separator, and can be supplied to an electrode. Therefore, the electrolyte solution can be permeated into the electrode in a short time, so that the charge / discharge performance can be prevented from being deteriorated. In particular, the high-rate charge / discharge characteristics in which the electrode absorbs the electrolyte solution quickly changes. Etc. is drastically suppressed.

  Moreover, since at least a part of the portion excluding the electrode body in the internal space of the battery housing body contains the surplus electrolyte solution, and the surplus electrolyte solution and at least a part of the porous layer are in contact with each other, By repeating the charge / discharge cycle or storing the battery for a long time, the electrolyte solution inside the battery is consumed, so that the electrolyte solution originally contained in the electrode is charged with the electrolyte solution held by the separator. Even when the discharge reaction cannot be ensured, the surplus electrolyte solution penetrates into the porous layer and is quickly supplied to the electrode, so that it is possible to suppress the deterioration of the charge / discharge performance from this point. In particular, a decrease in high-temperature cycle characteristics, storage characteristics, etc., which tend to consume the electrolyte solution due to side reactions, is greatly suppressed.

  Furthermore, even when the electrode width is increased in order to increase the capacity and output of the battery, the presence of the porous layer provides excellent permeability of the electrolytic solution to the center of the electrode plate. Therefore, since the permeability of the electrolyte is sufficiently ensured not only during the charge / discharge cycle but also at the initial stage of assembly, it is not necessary to perform aging for a long time, and the manufacturing cost of the battery can be reduced.

  In addition, electrolyte penetration and diffusion path that smoothly penetrates and diffuses electrolyte without using a method to increase the gap of the separator or a method to increase the separator thickness and ensure a liquid retention amount and a buffering action. Therefore, the occupied volume of the separator, which is a member not directly involved in power generation, is not increased. Therefore, the capacity of the battery can be increased. That is, when the amount of electrolyte solution that can be retained in the separator is too small, it has been difficult to reduce the thickness of the separator due to the deterioration of cycle characteristics and the like, but by forming a porous layer as in the present invention, Since it is possible to secure a supply path for the electrolytic solution, the amount of electrolytic solution that must be retained in the separator can be reduced. As a result, the separator can be made thinner, that is, the capacity of the battery can be increased. is there. Although the separator is thinned, a new porous layer is required, so it may be considered that the capacity of the battery cannot be sufficiently increased. However, with the configuration of the present invention, the separator can be significantly thinned, while the thickness of the porous layer is insignificant. Therefore, as a whole, the occupied volume of the members not directly involved in the power generation is reduced, so that the capacity of the battery can be increased as described above.

  In addition, although there is a porous layer that is more excellent in nonaqueous electrolyte permeability than TD of the separator, in a battery using a laminated electrode body, etc., the nonaqueous electrolyte is more permeable than MD as well as MD. A porous layer is desirable. This is because, in a battery using a laminated electrode body or the like, unlike a battery using a winding electrode body, nonaqueous electrolyte penetrates not only from TD but also from MD (that is, from four sides). This is because the use of a porous layer having better non-aqueous electrolyte permeability than the non-aqueous MD makes the non-aqueous electrolyte permeate and diffuse more smoothly.

The MD means Machine Direction (machine direction), and the TD means Transverse Direction (right angle direction).
Furthermore, it is possible to form a polyamide microporous layer on the separator for the purpose of improving heat resistance. JP-A-10-6453, JP-A-10-324758, JP-A2000-100408, JP-A-2001-266949. It is reported in gazettes. Furthermore, forming a microporous layer on the electrode for the purpose of preventing internal short circuit is disclosed in Japanese Patent No. 3371301, Japanese Patent Laid-Open No. 7-20135, Japanese Patent Laid-Open No. 11-102730, Japanese Patent Laid-Open No. 2005-174792. Have been reported. However, all of these proposals are focused on the safety of preventing a short circuit between the positive and negative electrodes due to the shrinkage of the separator at a high temperature by providing a resin layer, etc. The battery structure is not optimized for the diffusion path. That is, there is no description in the above application regarding the point of providing a porous layer that is more excellent in the permeability of the nonaqueous electrolyte than the TD of the separator and the point that the surplus electrolyte is disposed in the battery housing. From these facts, it is added that the present invention and the above-mentioned application are completely different in configuration, operation and effect.

The electrode body is preferably a wound electrode body in which the positive and negative electrodes and the separator are wound.
In the wound electrode body, since the tension of the electrode body has been increased due to the recent increase in winding tension and the penetration and diffusion of the electrolyte is difficult to occur, such a battery When the present invention is applied to the above, the above-mentioned actions and effects are further exhibited.

It is desirable that the battery housing is cylindrical or rectangular.
A battery with a cylindrical or square battery housing has a larger surplus space than a thin battery housing such as a laminated battery, and can be filled with a large amount of surplus electrolyte. As a result, the above-described actions and effects are further exhibited.

It is desirable that the porous layer is composed of at least one selected from inorganic material-based fine particle groups composed of alumina and titania and a binder.
When these materials are used, the porous layer is composed of a non-oriented and particulate material, so that an appropriate space (gap) that can ensure the penetration of the electrolyte can be secured, Since these materials have high mechanical strength and high thermal stability, deterioration in the battery can be suppressed.
However, it is not limited to alumina and titania, and may be other ceramic materials such as zirconia.

It is desirable that the porous layer is composed of at least one selected from a resin-based material group consisting of polyamide and polyamideimide.
When these materials are used, the porous layer is composed of a non-oriented and fibrous substance, so that an appropriate space (gap) that can ensure the permeation of the electrolyte can be secured, Since these materials have high mechanical strength and high thermal stability, deterioration in the battery can be suppressed.
However, it is not limited to polyamide or polyamideimide, but may be polyimide or the like.

Although it can be applied to a battery in which the positive electrode is charged until it becomes less than 4.40 V with respect to the lithium reference electrode potential, it is 4.40 V or more, preferably 4.45 V or more, particularly preferably with respect to the lithium reference electrode potential. Is preferably applied to a battery having a configuration in which the positive electrode is charged until it reaches 4.50 V or higher.
This is because even in a battery configured such that the positive electrode is charged at less than 4.40 V with respect to the lithium reference electrode potential, there are sufficient differences in cycle characteristics and storage characteristics at high temperatures depending on the presence or absence of the porous layer. This is because, in a battery that is charged at a voltage of 4.40 V or more with respect to the lithium reference electrode potential, a difference in cycle characteristics at a high temperature appears remarkably depending on the presence or absence of the porous layer. In particular, in a battery in which the positive electrode is charged at 4.45 V or more, or 4.50 V or more with respect to the lithium reference electrode potential, this difference appears more remarkably.

It is desirable that the porous layer is disposed only between an electrode and a separator having a large volume change rate during charging and discharging.
On the electrode side where the volume change rate during charging / discharging is large, it is necessary to replenish the electrolyte solution inside the electrode plate by absorbing the electrolyte solution due to contraction due to discharge. When the porous layer is provided between the large electrode and the separator, the above-described functions and effects are further exhibited.

The porous layer is preferably formed on the surface of an electrode having a large volume change rate during charge / discharge.
The porous layer is not limited to being formed on the surface of the electrode having a large volume change rate at the time of charge / discharge, and may be formed on the separator surface on the electrode side having a large volume change rate at the time of charge / discharge. .

It is desirable that the negative electrode active material is mainly composed of graphite, and the porous layer is disposed only between the negative electrode and the separator.
When graphite is used as the negative electrode active material, the negative electrode often has a larger volume change rate during charge / discharge than the positive electrode. Therefore, when the porous layer is formed between the negative electrode and the separator, the above-described functions and effects are further exhibited.
Note that “mainly composed of graphite” means that 50% by mass or more of graphite is contained.

  It is desirable that the porous layer is formed on the surface of the negative electrode.

In a battery in which the positive electrode is charged at 4.40 V or more with respect to the lithium reference electrode potential, the porous layer may be disposed not only between the negative electrode and the separator but also between the positive electrode and the separator. desirable.
In the case where the end-of-charge voltage is 4.40 V or more, not only the electrolyte in the negative electrode is insufficient, but also the charge potential of the positive electrode is increased, so that the expansion / contraction rate at the positive electrode is increased and the charged state of the positive electrode is higher. Therefore, as a result of the oxidative decomposition of the electrolytic solution, the consumption of the electrolytic solution becomes very fast. As a result, the shortage of the electrolytic solution at the positive electrode also becomes serious. If a porous layer is also arranged between the separator and the separator, desired cycle characteristics can be obtained.

The positive electrode active material preferably contains at least lithium cobaltate in which aluminum or magnesium is dissolved, and zirconia is preferably fixed to the surface of the lithium cobaltate.
The reason for such a structure is as follows. That is, when lithium cobaltate is used as the positive electrode active material, the crystal structure becomes unstable as the charging depth increases, and the deterioration is accelerated in a high temperature atmosphere. Thus, aluminum or magnesium is dissolved in the positive electrode active material (inside the crystal) to reduce crystal distortion in the positive electrode. However, although these elements greatly contribute to the stabilization of the crystal structure, the initial charge / discharge efficiency is lowered and the discharge operating voltage is lowered. Therefore, in order to alleviate such a problem, zirconia is fixed to the lithium cobalt oxide surface.

In order to achieve the above object, the present invention has two directions, MD and TD, which is less permeable to the nonaqueous electrolyte than MD, and the nonaqueous electrolyte mainly follows the TD. A negative electrode for a non-aqueous electrolyte battery disposed opposite to a positive electrode through a permeating separator is characterized in that a porous layer having a non-aqueous electrolyte that is more permeable than the TD is formed on the surface.
In the battery using the negative electrode having such a configuration, the same operations and effects as those described above are exhibited.

It is desirable that the porous layer is composed of at least one selected from inorganic material-based fine particle groups composed of alumina and titania and a binder.
In the battery using the negative electrode having such a configuration, the same operations and effects as those described above are exhibited.

In order to achieve the above object, the present invention has two directions, MD and TD, which is less permeable to the nonaqueous electrolyte than MD, and the nonaqueous electrolyte mainly follows the TD. A positive electrode for a non-aqueous electrolyte battery disposed opposite to a negative electrode through a permeating separator is characterized in that a porous layer having a non-aqueous electrolyte that is more permeable than the TD is formed on the surface.
In the battery using the positive electrode having such a configuration, the same operations and effects as those described above are exhibited.

It is desirable that the porous layer is composed of at least one selected from inorganic material-based fine particle groups composed of alumina and titania and a binder.
In the battery using the positive electrode having such a configuration, the same operations and effects as those described above are exhibited.

In order to achieve the above object, the present invention provides a first step of forming a negative electrode active material layer on the surface of a negative electrode current collector, and a slurry containing fine particles of an inorganic material on the surface of the negative electrode active material layer. And a third step of drying the slurry.
If it is the said method, the above-mentioned negative electrode can be produced easily.

In order to achieve the above object, the present invention provides a first step of forming a positive electrode active material layer on the surface of a positive electrode current collector, and a slurry containing fine particles of an inorganic material on the surface of the positive electrode active material layer. And a third step of drying the slurry.
If it is the said method, the above-mentioned positive electrode can be produced easily.

  According to the present invention, a high-temperature charge / discharge cycle can be achieved by forming a novel electrolyte solution permeation and diffusion path with a porous layer, and securing an excess electrolyte solution that can be supplied to the inside of the electrode body. Since it is possible to suppress the shortage of the electrolytic solution during consumption of the electrolytic solution due to high temperature storage, the battery performance can be maintained even in a harsh environment. Further, conventionally, when the active material coating amount or the active material filling density does not match the liquid retention amount of the separator, there is a problem that the cycle life is likely to be reduced, and it is difficult to reduce the thickness of the separator. However, the capillary phenomenon of the porous layer according to the present invention has a very high penetration rate and diffusion speed of the electrolyte solution, and does not require a buffer portion of the separator so quickly that the electrolyte solution from the outside of the electrode body can be rapidly applied to both the positive and negative electrodes. Since it is possible to procure, it is possible to easily achieve higher capacity and higher output of the battery.

Furthermore, due to the characteristics due to the capillary phenomenon, the penetration and diffusion speed of the electrolytic solution is also high in the battery assembly process, and the process can be shortened, so that there is an effect that the manufacturing cost can be reduced. Since it can be sufficiently distributed to each part of the electrode, it is possible to improve the uniformity regarding the charge / discharge performance, and it is possible to improve all battery performance including cycle, storage, and safety.
In addition, even when the positive electrode is charged 4.40 V or more with respect to the lithium reference electrode potential, it is possible to suppress the shortage of the electrolyte in the electrode due to the expansion of the electrode or the oxidative decomposition of the electrolyte. Therefore, an excellent effect that stable charge / discharge battery characteristics can be maintained is obtained.

  Hereinafter, the present invention will be described in more detail. However, the present invention is not limited to the following best modes, and can be appropriately modified and implemented without departing from the scope of the present invention.

[Production of positive electrode]
First, lithium cobaltate (hereinafter sometimes abbreviated as LCO) as a positive electrode active material, SP300 and acetylene black (hereinafter also abbreviated as AB) as a carbon conductive agent, and 92: 3: 2 A positive electrode mixture powder was prepared by mixing at a mass ratio. Next, after 200 g of the powder is filled into a mixing apparatus [for example, meso-fusion apparatus (AM-15F) manufactured by Hosokawa Micron], the mixing apparatus is operated at a rotation speed of 1500 rpm for 10 minutes to cause compression, impact, and shearing action. The mixed positive electrode active material mixture was prepared by mixing. Subsequently, both were mixed in an N-methyl-2-pyrrolidone (NMP) solvent so that the mass ratio of the mixed positive electrode active material mixture to the fluorine-based resin binder (PVDF) was 97: 3. After preparing the slurry, the positive electrode slurry was applied to both surfaces of the aluminum foil as the positive electrode current collector, and further dried and rolled to form a positive electrode.

(Production of negative electrode)
A negative electrode current collector was prepared by mixing a carbon material (graphite), CMC (carboxymethylcellulose sodium), and SBR (styrene butadiene rubber) in an aqueous solution at a mass ratio of 98: 1: 1 to prepare a negative electrode slurry. A negative electrode slurry was applied to both surfaces of a copper foil as a body, and further, dried and rolled to prepare a negative electrode.

(Preparation of non-aqueous electrolyte)
LiPF ₆ was mainly dissolved at a rate of 1.0 mol / liter in a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7. Note that the amount of the non-aqueous electrolyte was about 2.5 cc by including an excess electrolyte in addition to the electrolyte required for charging and discharging.

[Production of resin laminated separator]
As a separator, a polyamide (hereinafter abbreviated as PA) is formed on one surface of a separator body made of a microporous membrane (film thickness: 12 μm) made of polyethylene (hereinafter abbreviated as PE) constituting the separator body. In which a porous layer (thickness: 4 μm) is formed is used. The separator has a porosity of 50%.

Here, the porous layer made of PA was prepared as follows.
First, a PA raw material is dissolved in a water-soluble polar solvent (NMP solution), and low-temperature condensation polymerization is performed in the solution to prepare a polyamide dope solution. This was coated on one surface of a PE microporous membrane that became a substrate (separator body) and impregnated in an aqueous solution to extract a solvent, thereby producing a resin laminated separator. At the time of extraction of the solvent, the heat-resistant material (PA) does not dissolve in the aqueous solution, so that it can be precipitated and solidified on the substrate, thereby making it microporous. In this method, the number and size of the porous membranes can be adjusted by the solution concentration of the polyamide dope solution.

[Battery assembly]
A lead terminal is attached to each of the positive and negative electrodes, and a spiral wound electrode is pressed through a separator to produce a flattened electrode body, and then a storage space for an aluminum laminate film as a battery exterior body An electrode body was loaded therein, and a non-aqueous electrolyte was poured into the space, and then an aluminum laminate film was welded and sealed to prepare a battery.

  In the battery, the porous layer is disposed so as to be in contact with the negative electrode. Further, a part of the internal space of the battery housing made of the aluminum laminate film excluding the electrode body contains an excess electrolyte solution, and the excess electrolyte solution is in contact with at least a part of the porous layer. It has a structure like this. Furthermore, the design capacity of the battery is 780 mAh.

[Preliminary experiment 1]
We changed the injection conditions of the battery (without pressurization and pressure reduction after injection of the electrolyte), confirmed the electrolyte penetration of the winding electrode body, and evaluated the penetration and diffusion of the electrolyte in the actual battery The results are shown in Table 1.

(Battery used)
Here, in carrying out this experiment, the 18650 type cylindrical battery (the winding electrode body is not a flat type like a laminate battery but a cylindrical type, and the maximum height of the winding electrode body is 59. 5 mm) and a battery having the same structure as the battery shown in the best mode for carrying out the invention (hereinafter abbreviated as the best mode) except that the following positive electrode and separator are used. Was used. In addition, as both electrodes, the high filling type electrode mounted in the cylindrical battery currently marketed is used. Specifically, the coating amount of the positive electrode active material is 532 mg / 10 cm ² and the packing density of the positive electrode active material is 3.57 g / cc. The coating amount of the negative electrode active material is 225 mg / 10 cm ² , and the packing density of the negative electrode active material is 1.67 g / cc.

-Positive electrode It produced similarly to the best form except not using SP300 as a carbon electrically conductive agent, and having made LCO, AB, and PVDF into the mass ratio of 94: 3: 3.
Separator A PE microporous film (film thickness: 23 μm, porosity 48%) that is usually used was used.

(Details of the experiment)
[1] The battery in the middle of injection in the production process was disassembled, and the state of penetration of the electrolyte into the electrode was confirmed.
[2] Next, one end of the wound electrode body was immersed in an electrolytic solution (the liquid surface height of the electrolytic solution is 7 mm), and the state of penetration of the electrolytic solution was confirmed (the height of the sucked-up electrode) Comparison).
In carrying out the experiment [2], due to the battery configuration, the innermost peripheral portion and the outermost peripheral portion have a weak winding tension, and there is a gap, and it is difficult to determine the measured value by the electrolytic solution that passes through this gap. Therefore, after the battery was disassembled, the electrolyte uptake height at a position 20 cm from the end of the electrode on the outermost periphery (near the center in the length direction of the belt-like electrode) was measured and compared.

(Experimental result)
Experimental Results of [1] As shown in FIG. 1 (this figure is a developed view of the winding electrode body 4, in which A is the length direction and B is the width direction) In the body 4, the electrolyte 5 simultaneously penetrates from the upper and lower ends (winding up and down direction) in the width direction B into the inside of the winding electrode body 4 after the injection, and the center of the winding electrode body 4 is electrolyzed. It is recognized that the liquid non-penetrating part 6 exists. In addition, since the winding tension is weak at the outermost peripheral end portion 7 and the innermost peripheral end portion 8, some penetration and diffusion in the length direction A are seen, but this penetration and diffusion are not the main diffusion or the like.
Therefore, it is necessary for the winding electrode body 4 to ensure the permeability of the electrolyte solution in the width direction B.
In addition, although the same test was done also with the square-type battery or the laminate-type battery, the same tendency was observed.

2. Experimental results of [2] As is apparent from Table 1 and FIG. 2, although the height increases with time, it is 35.0 mm even after 180 minutes, and the height of the winding electrode body (59.5 mm). It can be seen that only about half of the electrolyte has penetrated, and the electrolyte penetration is quite slow.

  In the actual battery manufacturing process, it is possible to accelerate the penetration of the electrolytic solution into the winding electrode body by a technique such as pressure reduction or pressurization, so that the penetration and diffusion of the electrolytic solution is delayed. The problem is not a big problem. However, when a reaction that consumes the electrolytic solution occurs inside the winding electrode body during use of the battery, in addition to the electrolytic solution impregnated in the winding electrode body in the initial stage, the outside of the winding electrode body Therefore, it is necessary to supply a new electrolyte solution. In this case, the above-described methods such as depressurization and pressurization cannot be used, and based on the experimental results, it can be considered that the speed is very low, resulting in problems described later.

[Preliminary experiment 2]
Based on the results of permeation of the electrolyte solution of the cylindrical electrode body shown in the preliminary experiment 1, first, comparison of the electrolyte solution absorption state in the separator was performed for the purpose of permeation of the electrolyte solution and specification of the diffusion path. Specifically, the separator was evaluated for liquid absorbency and the air permeability of the separator was measured.

(Separator used)
In this experiment, PE separators (large pore type and small pore type), PP (polypropylene) / PE / PP laminated structure separator (PP membrane / PE membrane / PP membrane thermocompression bonded) In addition, a porous resin laminated separator (a separator similar to the separator shown in the best mode) in which a porous layer made of PA was formed on a PE separator was used. The separator was cut into a shape having a width of 1.5 cm and a length of 5.0 cm for evaluation.

(Details of the experiment)
[1] Measurement of air permeability of separator This measurement was performed according to JIS P8177, and a B-type Gurley densometer (manufactured by Toyo Seiki Co., Ltd.) was used as a measuring device.
Specifically, a sample piece is fastened to a circular hole (diameter 28.6 mm, area 645 mm ² ) of the inner cylinder (mass 567 g), and air (100 cc) in the outer cylinder is transmitted from the test tube circular hole portion to the outside of the cylinder. The time required for this was measured, and this was taken as the air permeability.

[2] Evaluation of Liquid Absorption of Separator Generally, there is a stretching process when manufacturing a separator, and there are MD (Machine Direction: machine direction) and TD (Transverse Direction: right angle direction) due to the manufacturing method. Usually, when winding a strip-shaped electrode body, the length direction of the separator coincides with MD, and the width direction coincides with TD. For this reason, when the winding electrode body is used for the battery, the penetration of the electrolytic solution from the upper and lower portions of the winding electrode body is the main because of the structure, and the separator needs to have high TD liquid absorption. It becomes.

For the purpose of evaluating the physical properties, as shown in FIG. 3, the end portion of the separator 3 was immersed in the electrolytic solution 5 used in the best mode, and the suction height of the electrolytic solution was compared after 10 minutes. In the battery assembly process, the cylindrical battery has a thickness reduction due to elongation due to the winding tension, and the square battery and the laminate battery have a thickness reduction by hot pressing in the rolling process. In simulating this situation, the press conditions are calculated from the measured values of the separator thickness change in the cylindrical battery and the separator thickness change in the square battery, and the situation of the separator in the actual battery is also simulated. The same evaluation test was performed on the post-press separator. The post-press separator used was a sheet having an area of 80 × 170 mm ² pressed under the following press conditions. Thereby, the separator of the conditions substantially the same as the separator in a square battery is reproducible.

・ Pressing conditions Pressure: 15 MPa
Temperature: 50 ° C
Time: 15 seconds (experimental result)

Experimental results of [1] As is apparent from Tables 2 and 3, in all the samples 1 to 6, the air permeability is lower after the press treatment than before the press treatment (air permeation time). In particular, it can be seen that Sample 1 to Sample 3 which are PE large pore size type separators have a very low air permeability.

Experimental results of [2] As is clear from Tables 2 and 3, in Samples 1 to 4, MD has a certain level of liquid absorbency, but TD has a low liquid absorbency (in Tables 2 and 3, It is recognized that the liquid absorption height of MD is somewhat large, but the liquid absorption height of TD is small. As shown in FIGS. 4 and 5, in the case of fibrous polyolefin (polyethylene), the olefin fiber has a structure that tends to extend in the MD due to stretching, and as a result, the polymer fibers tend to be arranged in the MD. For this reason, TD is considered to be because the fibrous polyolefin acts like a wall and prevents the penetration and diffusion of the electrolyte.

  Further, in the samples 1 to 4, the pores of the separator are reduced by pressing, so that the penetration and diffusion of the electrolytic solution are less likely to occur after pressing, and the TD absorbability is higher. Lower. In addition, it is thought that there is almost no dependence between the thickness of a separator and a liquid absorptivity.

  In contrast, sample 6 in which a porous layer made of polyamide resin is provided on the surface of the separator main body made of polyolefin microporous membrane has improved liquid absorbency in both MD and TD compared to samples 1 to 4. It is recognized that This is because, as shown in FIG. 6 (in FIG. 6, 3 is a separator, 31 is a separator main body, and 32 is a porous layer), the porous layer 32 has a non-oriented porous structure due to its manufacturing method. Therefore, regardless of the MD and TD, the permeation and diffusion of the electrolyte acts more preferentially than the separator body 31. In particular, the separator main body 31 can drastically improve the liquid absorbency at TD, which is inferior in liquid absorbency, so that the liquid absorbency of the electrolytic solution in the winding electrode body in which the winding direction and MD coincide with each other is dramatically increased. Improve.

In addition, since this type of resin has a high strength and is not easily crushed as compared with an olefin, the liquid absorption height of the electrolytic solution is hardly lowered even after pressing. Therefore, it can be considered effective to provide a porous layer in the separator main body and promote permeation and diffusion using the capillary phenomenon in order to improve the liquid absorption of the electrolytic solution.
In addition, it is recognized that sample 5 has low liquid absorbency in both MD and TD regardless of before and after pressing.

[Preliminary experiment 3]
In response to the result of the electrolyte solution permeation of the cylindrical electrode body shown in Preliminary Experiment 1, a comparison was made of the electrolyte solution absorption state in the electrodes for the purpose of permeating the electrolyte solution and specifying the diffusion path.

(Electrode used)
Electrodes (positive electrode and negative electrode, sample 11 and sample 12 in Table 4) similar to the electrode shown in the preliminary experiment 1 (electrode for 18650 cylindrical battery), and a porous layer on the surface of the negative electrode The formed electrodes (Sample 13 to Sample 15 in Table 4) were used. The electrode has a width of 1.5 cm and a length of 5.0 cm.
The porous layer was prepared by first mixing titania (TiO ₂ , average particle diameter 31 nm) and PVDF at a mass ratio of 95: 5, and then preparing a slurry whose viscosity was adjusted using NMP as a solvent, This slurry was applied to the surface of the negative electrode by the doctor blade method and further dried (Sample 13 in Table 4). The negative electrode thus produced had a thickness of 6 μm. Moreover, it replaced with titania (average particle diameter 31nm), and produced the negative electrode similarly to the above except having used titania (average particle diameter 500nm) or alumina (average particle diameter 200nm) (the former is a sample of Table 4). 14 and the thickness of the negative electrode is 40 μm, the latter is the sample 15 of Table 4 and the thickness of the negative electrode is 6 μm).

(Details of the experiment)
It was carried out in the same manner as the liquid absorption evaluation of [2] separator in Preliminary Experiment 1. Specifically, as shown in FIG. 7, an electrode (positive electrode and negative electrode) 13 having an active material layer 11 and a current collector 12 is immersed in the electrolytic solution used in the best mode, and the electrolytic solution 5 The suction height of each was checked every predetermined time. For samples 13 to 15, the porous layer 14 is formed on the surface of the active material layer 11.
(Experimental result)

As is apparent from Tables 2, 3 and 4 above, the results of the comparison with the separator show that the electrodes rather have the same level of absorption or higher.
Therefore, how the electrolyte solution permeates and diffuses into the electrode was examined, and the result will be described with reference to FIG.

  Specifically, the active material layer 11 infiltrated with the electrolytic solution 5 is subjected to a peeling operation by pressurizing the permeated portion of the electrolytic solution 5 in the active material layer 11 on the assumption that the active material layer 11 is easily peeled off from the current collector 12. In the portion immersed in the electrolytic solution 5 and in the vicinity thereof, it was confirmed that most of the active material layer 11 was peeled off from the current collector 12, but in the vicinity of the central portion (near the upper end of the portion where the electrolytic solution penetrated) Then, it was observed that the active material layer 11a on the surface peels off, but the active material layer 11b near the current collector 12 does not peel off. From this, it is considered that the electrolytic solution 5 does not permeate and diffuse from the inside of the electrode (active material layer 11) 13 but permeates and diffuses by a capillary phenomenon through a gap on the surface of the electrode 13.

  That is, the electrolytic solution 5 slowly permeates and diffuses in the electrode thickness direction (D direction in the figure) while permeating and diffusing the surface of the electrode 13 in the electrode height direction (C direction in the figure). The penetration height of the electrolyte solution 5 near the body 12 is considered to be smaller than the penetration height of the electrolyte solution 5 on the electrode surface. It has been confirmed that the wettability of the surface of the electrode 13 depends on the unevenness and gaps of the electrode plate.

  Further, as is clear from Table 4, when the positive electrode (sample 11) and the negative electrode (sample 12) are compared, it is recognized that the positive electrode tends to be superior in liquid absorbency. This is because, in general, the carbon particles that are the negative electrode active material are easy to be crushed rather than cracked, so the negative electrode is likely to be a mirror surface, and in that sense, there are few uneven surfaces, and capillary action is unlikely to occur. The positive electrode active materials such as lithium cobaltate, lithium manganate, lithium nickelate, and olivine-type lithium phosphate have a smaller particle size than the negative electrode active material, and when force is applied, the particles crack and disperse the stress. This is considered to be caused by the tendency that unevenness tends to remain relatively.

Furthermore, when the porous layer is provided on the surface of the electrode (negative electrode) (sample 13 to sample 15), the liquid absorbency is dramatically improved as compared with the case where the porous layer is not provided (sample 12). It is recognized that there is a tendency.
This is because of the capillary phenomenon, the electrolytic solution 5 rapidly penetrates and diffuses through the porous layer in the height direction of the electrode (C direction in the figure), and in the thickness direction of the electrode (D direction in the figure). This is thought to be due to the slow penetration and diffusion of water.

  In the above results, there is no particular difference in liquid absorbency due to differences in the type and size of the particles used and the thickness of the porous layer. From this result, it can be considered that if there is a gap in the porous layer, the effect of the present invention can be exhibited. If so, the material of the porous layer is limited to the above-mentioned alumina and titania. Any material can be used as long as it can form a porous layer. However, it must be electrically and chemically stable, such as not adversely affecting the charge / discharge reaction in the battery. In that sense, inorganic particles such as alumina, titania, zirconia, polyamide, polyimide, polyamide Organic particles such as imide or a porous body thereof is considered preferable. In some cases, active materials such as lithium cobaltate and carbon can also be targeted. However, alumina and titania are particularly preferable in view of cost.

  In this preliminary experiment 3, since a PVDF-based binder was used, the formation of a porous layer on the positive electrode was not examined. However, as shown in the fifth embodiment described later, the selection of the binder and the solvent is appropriate. If this is the case, it is presumed that an improvement in liquid absorbency due to capillary action can be expected on the positive electrode as well. Specifically, if the electrode active material layer is coated with an NMP-based solvent, the porous layer preferably uses an aqueous solvent, and if the electrode active material layer is coated with an aqueous solvent, the porous layer is preferably porous. It is preferable to use a solvent such as NMP for the quality layer. However, depending on the formation conditions of the porous layer, it is considered that the same solvent system can be used.

  Furthermore, as a method for forming the porous layer, techniques such as spray, gravure coating, die coating, ink jet, and dip coating are preferable, but other techniques may be used as long as a thin film can be formed. Further, the thickness of the porous layer is not particularly limited, but there is no problem as long as the capillary phenomenon can be effectively applied, and if the capacity of the battery is increased, it is 5 μm or less, preferably 3 μm or less. . Furthermore, although the filling rate of the porous layer depends on the particle size and type, any amount may be used as long as the permeability of the electrolytic solution is higher than that of the electrode serving as the base material under the experimental conditions.

[Preliminary experiment 4]
Based on the result of the preliminary experiment 3, the penetration rate of the electrolyte solution in the electrode internal direction (electrode thickness direction) was compared for the purpose of specifying the penetration of the electrolyte solution and the diffusion path.

(Electrode used)
An electrode similar to the electrode shown in the preliminary experiment 1 (electrode for 18650 cylindrical battery) was used.

(Details of the experiment)
The electrolytic solution was dropped on the electrode surface, and the disappearance time of the droplet was measured. The results are shown in Table 5. As the electrolytic solution, only the PC (3 μl) was used because the electrolytic solution shown in the best mode contains a highly volatile chain carbonate (DEC).
(Experimental result)

  As is clear from Table 5 above, as the packing density increases for both the positive and negative electrodes, the rate of penetration of the electrolyte into the electrode plate becomes slower. In particular, as described above, the surface of the negative electrode tends to become a mirror body. In addition, it is recognized that the liquid absorbency is extremely lowered when filling to a certain density or more. In this sense, it can be considered that the negative electrode generally has a lower liquid absorption rate than the positive electrode. Although this characteristic depends on the design concept and balance of the battery and may vary depending on the battery type, it is presumed that the positive electrode is superior in liquid absorbency at the level that is usually marketed.

(Summary of preliminary experiment 3 and preliminary experiment 4)
From Preliminary Experiment 3, the positive electrode has a higher permeation rate of the electrolyte solution in the electrode height direction, and the positive electrode has a faster permeation rate of the electrolyte solution in the electrode thickness direction. From this, it is considered that the positive electrode is more likely to have better electrolyte absorbability than the negative electrode.
Here, based on the results of the preliminary experiments 1 to 4, an actual battery was manufactured and the experiment was performed. The results are shown below.

[First embodiment]
Example 1
As Example 1, the battery shown in the best mode was used.
The battery thus produced is hereinafter referred to as the present invention battery A1.

(Example 2)
A battery was fabricated in the same manner as in Example 1 except that the porous layer formed on the surface of the separator body was disposed on the positive electrode side.
The battery thus produced is hereinafter referred to as the present invention battery A2.

(Comparative Example 1)
A battery was fabricated in the same manner as in Example 1 except that a separator composed of only a PE microporous film (thickness: 16 μm, porosity 50%) was used.
The battery thus manufactured is hereinafter referred to as a comparative battery Z1.

(Comparative Example 2)
A battery was fabricated in the same manner as in Example 1 except that a separator composed only of a PE microporous film (thickness: 12 μm, porosity 41%) was used.
The battery thus produced is hereinafter referred to as a comparative battery Z2.
The main configurations of the present invention batteries A1 and A2 and comparative batteries Z1 and Z2 are shown in Table 6 below.

(Experiment)
Since the cycle characteristics of the inventive batteries A1 and A2 and the comparative batteries Z1 and Z2 were examined, the results are shown in FIG. The charge / discharge conditions are as follows.

[Charging / discharging conditions]
-Charging conditions After constant current charging to a battery voltage of 4.20 V at a current of 1.0 It (750 mA), constant voltage charging is performed until the current value reaches 1/20 It (37.5 mA) at a voltage of 4.20 V. The condition to do.
-Discharge condition The condition that constant current discharge is performed up to a battery voltage of 2.75 V at a current of 1.0 It (750 mA).
The charge / discharge interval is 10 minutes, and the charge / discharge temperature is 60 ° C.

  As is clear from FIG. 8, the batteries A1 and A2 of the present invention are superior in cycle characteristics at 60 ° C. (hereinafter sometimes simply referred to as cycle characteristics) compared to the comparative batteries Z1 and Z2. Is recognized. Further, when the present invention battery A1 and the present invention battery A2 are compared, the present invention battery A1 has better cycle characteristics than the present invention battery A2, and further, when the comparison battery Z1 and the comparison battery Z2 are compared, It can be seen that the comparative battery Z1 has better cycle characteristics than the comparative battery Z2. These reasons will be described below separately for each item.

(1) Reason why the comparative batteries Z1 and Z2 are inferior to the cycle characteristics of the batteries A1 and A2 of the present invention. ・ The reason why the comparative batteries Z1 and Z2 are inferior in the cycle characteristics. Although it is in a state filled in the electrode and in the separator, if it is exposed to a condition where the consumption of the electrolytic solution is severe, such as a 60 ° C. cycle test or a storage test, the battery may be insufficient due to insufficient amount of electrolyte or deposition of reactants. The capacity tends to decrease. In particular, a decrease in battery capacity is greatly affected by a shortage of electrolyte.

  Here, as shown in the preliminary experiment 2, the separator has MD (Machine Direction: machine direction) and TD (Transverse Direction: right angle direction) due to the manufacturing method. When winding, the length direction of the separator coincides with MD, and the width direction coincides with TD. On the other hand, in a battery using a winding electrode body, the penetration of the electrolyte from the upper and lower portions of the winding electrode body is the main because of its structure, and the separator needs to have a high TD liquid absorption.

  However, in the comparative batteries Z1 and Z2 using the separator made of only PE, the PE fibers tend to extend in the MD due to the stretching, and as a result, the polymer fibers tend to be arranged in the MD. The fibrous polyolefin acts like a wall, preventing the electrolyte from penetrating and diffusing. As a result, although the comparative batteries Z1 and Z2 and the batteries A1 and A2 of the present invention have substantially the same amount of electrolyte filled in the batteries, the comparative batteries Z1 and Z2 are electrolyzed contained in the separator during discharge. The amount of the liquid decreases, and the positive and negative electrodes cannot be smoothly replenished with electrolyte, and the electrolyte is depleted in both the positive and negative electrodes, so that a so-called dry-out phenomenon occurs and cycle characteristics deteriorate.

  Specifically, a description will be given based on FIG. In FIG. 9, the concentrations are made different according to the amount of electrolyte in the positive and negative electrodes 1 and 2 and the separator 3 (in the case where the amount of electrolyte in the positive and negative electrodes 1 and 2 and the separator 3 is large, the concentration is high). When the amount of electrolyte in the positive and negative electrodes 1 and 2 and the separator 3 is small, it is drawn to be thin). Moreover, about discharge | release and osmosis | permeation of electrolyte solution, when performing smoothly, it shows with the normal arrow, and when not performing smoothly, it shows with the arrow of the broken line. These are the same in FIG. 10 shown later.

  First, at the initial stage of the injection, as shown in FIG. 5A, the electrolytic solution penetrates and diffuses to both corners of the positive and negative electrodes 1 and 2 by forced operation such as decompression and pressurization. Yes. Next, as shown in FIG. 4B, when the battery is charged, the positive and negative electrodes 1 and 2 expand (for example, about 1% by volume when LCO is used as the positive electrode, and when graphite is used as the negative electrode). Is expanded by about 10% by volume), and the electrolyte solution is released from the inside (particularly, a large amount of electrolyte solution is released from the inside of the negative electrode). In this case, the separator 3 absorbs the expansion (that is, the thickness of the separator 3 is reduced), and the electrolytic solution that cannot be held by the separator 3 is discharged out of the winding electrode body 20. Thereafter, when the positive and negative electrodes 1 and 2 are contracted by discharging, the electrolytic solution held in the separator 3 is supplied to the positive and negative electrodes 1 and 2 and the electrolysis discharged to the outside of the winding electrode body 20. The liquid is permeated and diffused into the separator 3 by the gap between the positive and negative electrodes 1 and 2 and the separator 3 and the penetration and diffusion of TD in the separator 3, and then supplied from the separator 3 to the positive and negative electrodes 1 and 2.

  However, as shown in FIG. 2C, the electrolyte solution discharged out of the winding electrode body 20 has a very slow penetration and diffusion rate into the separator. In the test where the consumption of the electrolyte is intense, the penetration and diffusion of the electrolyte may not catch up. For this reason, the electrolyte solution is insufficient in the positive and negative electrodes 1 and 2, and in particular, the electrolyte solution tends to be insufficient in the vicinity of the central portion 40. As a result, the so-called dry-out phenomenon occurs due to the depletion of the electrolyte in the positive and negative electrodes 1 and 2. Note that the rate at which the electrolyte discharged outside the winding electrode body 20 penetrates and diffuses from the ends of the positive and negative electrodes 1 and 2 is very slow as shown in the preliminary experiment 3, and thus cannot be expected.

-Reason why the present invention batteries A1 and A2 are excellent in cycle characteristics In the present invention batteries A1 and A2 using separators in which a porous layer is laminated, the porous layer acts as a liquid absorption path for the electrolytic solution. A sufficient amount of electrolytic solution permeates and diffuses into the separator, and the positive and negative electrodes can be smoothly replenished with the electrolytic solution. Therefore, it is possible to suppress the electrolyte from being depleted in both the positive and negative electrodes, and it is considered that the deterioration of the cycle characteristics due to the so-called dry-out phenomenon can be suppressed.

  Specifically, a description will be given based on FIG. First, at the initial stage of the injection, as shown in FIG. 5A, the electrolytic solution penetrates and diffuses to both corners of the positive and negative electrodes 1 and 2 by forced operation such as decompression and pressurization. In addition, as shown in FIG. 5B, when the battery is charged, the positive and negative electrodes 1 and 2 expand to discharge the electrolyte from the inside, and the separator 3 absorbs the expansion, The electrolyte solution that cannot be held by the separator 3 is released from the winding electrode body 20 in the same manner as the comparative batteries Z1 and Z2. In addition, when the positive and negative electrodes 1 and 2 contract due to discharge, the electrolyte held in the separator 3 is supplied to the positive and negative electrodes 1 and 2 in the same manner as the comparative batteries Z1 and Z2.

  However, as shown in FIG. 3C, the electrolytic solution discharged to the outside of the take-up electrode body 20 penetrates and diffuses into the porous layer 32, and then positive and negative electrodes 1 from the porous layer 32 and the separator main body 31. 2, but the electrolyte solution (including surplus electrolyte solution) discharged out of the take-up electrode body 20 penetrates into the porous layer 32 and has a very high diffusion rate. Even in tests that consume a lot of electrolyte, such as storage tests and storage tests, the electrolyte sufficiently penetrates and diffuses into both the positive and negative electrodes 1 and 2. For this reason, there is no shortage of electrolyte in the positive and negative electrodes 1 and 2, and it is possible to suppress the shortage of electrolyte even in the vicinity of the central portion. As a result, it is possible to suppress the so-called dry-out phenomenon due to the depletion of the electrolyte in the positive and negative electrodes 1 and 2. The rate at which the electrolyte discharged outside the take-up electrode body 20 penetrates and diffuses from the ends of the positive and negative electrodes 1 and 2 is very slow as shown in the preliminary experiment 3 and cannot be expected. Is the same as the comparative batteries Z1 and Z2.

(2) Reason why the comparative battery Z2 is inferior in cycle characteristics to the comparative battery Z1 The amount of the electrolyte contained in the separator is substantially proportional to the void volume calculated by the film thickness × the porosity. Here, when the film thickness of the separator becomes small, not only does the amount of electrolyte contained in the separator decrease, but also the porosity needs to be reduced to ensure strength, so it is further included in the separator. The amount of electrolyte decreases. As a result, the comparative battery Z2 in which the separator film thickness is small and the porosity must be reduced in order to ensure strength is the comparative battery in which the separator film thickness is large and the porosity can be increased to some extent. Cycle characteristics are degraded compared to Z1.
In addition, in a square battery and a laminate battery, since the winding electrode body pressing process is included, it is estimated that the void is smaller than the initial separator.

(3) Reason why the present invention battery A1 has better cycle characteristics than the present invention battery A2 The present invention battery A1 has a porous layer disposed on the negative electrode side, whereas the present invention battery A2 has a porous layer. This is probably due to the arrangement on the positive electrode side. Specifically, it is as follows.

  That is, when charging is performed at a high temperature as in a cycle characteristic test at 60 ° C., the frequency of decomposition of the electrolytic solution due to the oxidizing action of the positive electrode active material increases. As far as the results of high-temperature storage tests that have been carried out conventionally are seen, there is a strong tendency for the electrolyte to decompose and generate gas due to the positive electrode. As a result, the electrolytic solution is consumed inside the positive electrode. In this case, the excess electrolytic solution contained in the separator is smoothly replenished to the positive electrode, so that the amount of the electrolytic solution inside the positive electrode is secured. This is because, as shown in Preliminary Experiment 3, the positive electrode can absorb the electrolytic solution at a higher rate than the negative electrode, so that when the electrolytic solution is consumed at the positive electrode, there is a porous layer on the positive electrode side. This is because the excess electrolyte contained in the separator is smoothly supplied to the positive electrode even if it is not. However, this is a behavior in a battery having a charge end voltage of about 4.2 V, and if the battery has a charge end voltage exceeding that, the behavior will be as described later. In addition, it is estimated that the same reaction is occurring also in the negative electrode.

On the other hand, in a battery having a charge end voltage of about 4.2 V, the results of actual measurement of electrodes show that the rate of change in the thickness of the electrode plate before and after charge / discharge is within 2% for the positive electrode and about 10% for the negative electrode. I'm crazy. As described above, since the thickness of the positive electrode hardly changes due to charging / discharging, there is almost no change from the amount of the electrolytic solution initially injected into the electrode plate unless the electrolytic solution is consumed due to storage at a high temperature or charging / discharging cycle. Can be considered. On the other hand, since the negative electrode has a change of about 10%, the electrolyte is squeezed out from the inside of the electrode plate due to expansion due to charging, and the amount of electrolyte in the electrode plate is absorbed by the separator during discharge. It is thought that it supplements. The separator fulfills this buffering action, and the electrolytic solution in the separator exists mainly while interacting with the negative electrode.
Therefore, when the porous layer is disposed on the negative electrode side as in the present invention battery A1, the electrolyte can be smoothly supplied to the negative electrode, so that the cycle characteristics are excellent. On the other hand, as in the present invention battery A2, the porous layer is porous. When the porous layer is disposed on the positive electrode side, the negative electrode is gradually deficient in the electrolytic solution, and as a result, it is considered that the cycle characteristics are inferior due to non-uniform charge / discharge reactions and the like.

  In the case of the battery A2 of the present invention, it can also be considered that the electrolyte solution that has permeated the porous layer may be supplied to the negative electrode through the separator body. However, there is at least an electrolyte penetration resistance (barrier) on the pore contact surface at the interface between the PA resin constituting the porous layer and the PE constituting the separator main body. It is presumed that the electrolyte solution penetrating the layer is not necessarily supplied to the separator body. Therefore, in the battery A2 of the present invention, the negative electrode gradually becomes deficient in the electrolyte solution, resulting in deterioration of cycle characteristics.

  Thus, it is presumed that the cycle life can be improved by preferentially disposing the porous layer on the electrode surface that tends to be insufficient in the electrolytic solution. This is because, in the lithium cobaltate / graphite combination electrode, graphite has a larger volume change due to charge / discharge. Therefore, it is desirable to dispose the porous layer on an electrode that is large in expansion and contraction and large in and out of the electrolyte. Even when silicon or tin is used as the negative electrode active material, the volume change during charging and discharging is large, and it is considered preferable to dispose a porous layer on the negative electrode side in the same way as graphite (although depending on the mode of deterioration) From this result, it is considered desirable to form and dispose a porous layer on the negative electrode surface in the combination of lithium cobaltate and graphite.

(Second embodiment)
(Example)
As the separator, instead of the resin laminated separator, an inorganic fine particle laminated separator (a separator in which the porous layer is composed of inorganic fine particles and slurry) prepared as described below is used, and this porous layer is used as the separator. A battery was fabricated in the same manner as in Example 1 of the first example except that it was disposed on the positive electrode side and the negative electrode side of the main body (total thickness of both porous layers was 4 μm and one side was 2 μm).

Copolymer containing TiO ₂ (rutile type, particle size 0.38 μm, KR380 manufactured by Titanium Industrial Co., Ltd.), which is inorganic fine particles, in acetone as a solvent, 10 mass% with respect to acetone, and an acrylonitrile structure (unit) A coalescence (binder which is a rubber-like polymer) was mixed in an amount of 5% by mass with respect to TiO ₂ and mixed and dispersed using Special Mechanics Films to prepare a slurry in which TiO ₂ was dispersed. Next, after applying the slurry to both sides of the separator body (thickness 12 μm, porosity 41%) using the dip coating method, the solvent is dried and removed, and TiO ₂ ( A porous layer (inorganic fine particle layer, total thickness: 4 μm [one side 2 μm]) mainly composed of inorganic fine particles) was formed.
The battery thus produced is hereinafter referred to as the present invention battery B.
Table 7 below shows the main configurations of the present invention battery B and the comparison batteries Z1 and Z2 that are comparison objects of the present invention battery B.

(Experiment)
Since the cycle characteristics of the battery B of the present invention were examined, the results are shown in FIG. FIG. 11 also shows the cycle characteristics of the comparative batteries Z1 and Z2. The charge / discharge conditions are the same as those in the experiment of the first embodiment.

As is clear from FIG. 11, the battery B of the present invention in which the porous layer mainly composed of inorganic fine particles is arranged between the separator main body and the positive and negative electrodes is a comparative battery Z2 (separator) in which no porous layer is arranged. Thickness [same as the thickness of the separator body of the present invention B because the porous layer is not provided] and the comparative battery Z1 (separator thickness [the porous layer is provided. Therefore, it is recognized that the same as the thickness of the separator main body of the battery B of the present invention is superior in cycle characteristics. This is because the battery B of the present invention is similar to the batteries A1 and A2 of the present invention in which the porous layer is made of resin, and the penetration and diffusion rate of the electrolyte solution (including the excess electrolyte solution) outside the winding electrode body into the porous layer. This is considered to be due to the fact that the electrolyte sufficiently penetrates and diffuses into both the positive and negative electrodes even in a test where the consumption of the electrolyte is intense, such as a 60 ° C. cycle test and a storage test.
From the above results, it can be seen that even a porous layer mainly composed of inorganic fine particles exhibits the same effects as a porous layer made of resin.

(Third embodiment)
(Example)
A porous layer is formed on the positive electrode surface (the surface of the positive electrode active material layer), and a separator having a thickness of 23 μm and a porosity of 52% is used, and the battery shape is cylindrical (design capacity is A battery was fabricated in the same manner as in the second embodiment except that a 2100 mAh cylindrical battery) was used.
The porous layer on the positive electrode surface was produced as follows. First, NMP (N-methyl-2-pyrrolidone) as a solvent is mixed with TiO ₂ which is an inorganic fine particle [KR380 (rutile type) manufactured by Titanium Industry Co., Ltd., particle size 0.38 μm] with respect to NMP. 20 wt%, a copolymer containing acrylonitrile structures (units) (the rubber-polymer) was mixed 5 wt% with respect to the TiO _2, it performs mixing and dispersing treatment using a Tokushu Kika made Filmics, TiO ₂ is A dispersed slurry was prepared. Next, after applying the slurry to the surface of the positive electrode active material layer using the reverse method, the solvent is dried and removed, and the surface of the positive electrode active material layer is porous mainly composed of TiO ₂ (inorganic fine particles). A layer (inorganic fine particle layer, thickness: 4 μm) was formed.

Moreover, the manufacturing method of a cylindrical battery is as follows. First, the positive and negative electrodes and the separator are prepared in the same manner as in the laminate type battery, and then lead terminals are attached to both the positive and negative electrodes. Next, the positive and negative electrodes are wound in a spiral shape via a separator to produce a spiral electrode body. Next, this electrode body is put into a bottomed cylindrical battery outer can, and further an electrolyte is injected into the battery outer can. Finally, the sealing body was produced by sealing the opening of the battery outer can.
The battery thus produced is hereinafter referred to as the present invention battery C.

(Comparative example)
A battery was fabricated in the same manner as in the above example except that the porous layer was not provided on the surface of the positive electrode active material layer.
The battery thus produced is hereinafter referred to as comparative battery Y.
The main structures of the present invention battery C and comparative battery Y are shown in Table 8 below.

(Experiment)
Since the cycle characteristics of the battery C of the present invention and the comparative battery Y were examined, the results are shown in FIG. The charge / discharge conditions are as follows.

[Charging / discharging conditions]
-Charging conditions After constant current charging to a battery voltage of 4.20 V at a current of 1.0 It (2100 mA), constant voltage charging is performed until the current value reaches 1/50 It (42.0 mA) at a voltage of 4.20 V. The condition to do.
-Discharge conditions Conditions under which a constant current discharge is performed until the battery voltage reaches 2.75 V at a current of 1.0 It (2100 mA).
The charge / discharge interval is 10 minutes, and the charge / discharge temperature is 60 ° C.

As is clear from FIG. 12, the battery C of the present invention in which the porous layer mainly composed of inorganic fine particles is disposed between the separator and the positive electrode active material layer is compared with the comparative battery Y in which the porous layer is not disposed. Thus, it is recognized that the cycle characteristics are excellent.
This is considered to be due to the same reason as shown in the experiment of the second embodiment.
Moreover, this experiment shows that a porous layer is not limited to the structure formed in the surface of a separator (separator main-body part), You may form in the surface of a positive electrode (positive electrode active material layer).

(Assumptions for conducting experiments in the following fourth to seventh embodiments)
In general, since the end-of-charge voltage of the battery is 4.20V, in the first to third embodiments, the end-of-charge voltage of the battery is 4.20V. A lithium cobalt battery of lithium cobaltate / graphite based on 40V is also on the market. In this system, not only the electrolyte solution in the negative electrode is insufficient as described above, but also the charge potential of the positive electrode is increased so that the expansion / contraction rate of the positive electrode is increased and the charged state of the positive electrode is in a higher region. As a result of the oxidative decomposition of the electrolyte, the consumption of the electrolytic solution becomes very fast, and the shortage of the electrolytic solution at the positive electrode becomes serious. Therefore, the present inventors conducted experiments similar to those in the first to third embodiments with respect to batteries having a charge end voltage of 4.30 V or more.

(Fourth embodiment)
(Example)
The separator is designed to have a thickness of 16 μm, a porosity of 50%, and a battery design so that the end-of-charge voltage is 4.40 V (the positive electrode potential is 4.50 V with respect to the lithium reference electrode potential). Otherwise, a battery was fabricated in the same manner as in the second embodiment. In addition, when arrange | positioning a porous layer in the positive electrode side and the negative electrode side, the dip coating method was used.
The battery thus produced is hereinafter referred to as the present invention battery D.

(Comparative example)
A battery was fabricated in the same manner as in the above example except that a separator composed only of a PE microporous film (thickness: 16 μm, porosity 50%) was used.
The battery thus produced is hereinafter referred to as comparative battery X.
The main structures of the present invention battery D and comparative battery X are shown in Table 9 below.

(Experiment)
Since the cycle characteristics of the battery D of the present invention and the comparative battery X were examined, the results are shown in FIG. The charge / discharge conditions are as follows.

[Charging / discharging conditions]
-Charging conditions After constant current charging to a battery voltage of 4.40 V at a current of 1.0 It (750 mA), constant voltage charging is performed until the current value reaches 1/20 It (37.5 mA) at a voltage of 4.40 V. The condition to do.
-Discharge condition The condition that constant current discharge is performed up to a battery voltage of 2.75 V at a current of 1.0 It (750 mA).
The charge / discharge interval is 10 minutes, and the charge / discharge temperature is 45 ° C.

  As is clear from FIG. 13, the battery D of the present invention in which the porous layer mainly composed of inorganic fine particles is disposed between the separator main body, the positive electrode, and the negative electrode is a comparative battery X ( Compared to the thickness of the separator (the same as the thickness of the separator body of the battery D of the present invention is the same as the thickness of the separator body of the present invention D because no porous layer is provided), the cycle characteristics are excellent. Is recognized. In particular, the difference in cycle characteristics between the present invention battery D and the comparison battery X, both of which have a charge end voltage of 4.40 V, is the cycle between the present invention battery B and the comparison batteries Z1, Z2 both of which have a charge end voltage of 4.20 V. It is recognized that it is larger than the difference in characteristics.

  This is because, when the end-of-charge voltage is 4.40 V, the expansion and contraction of the electrode is further increased and the electrolyte in the separator is further insufficient and the positive electrode potential is higher than when the end-of-charge voltage is 4.20 V. Therefore, the electrolytic solution is easily oxidized and decomposed, and the electrolytic solution in the electrode is further insufficient. For this reason, in the comparative battery X in which the porous layer is not disposed, the electrolyte solution is remarkably insufficient in both positive and negative electrodes. On the other hand, in the battery D of the present invention in which the porous layer is disposed between the positive and negative electrodes and the separator, the penetration and diffusion rate of the electrolyte solution (including the excess electrolyte solution) outside the winding electrode body into the porous layer. This is considered to be because the electrolyte solution sufficiently penetrates and diffuses into both the positive and negative electrodes even in a test where the end-of-charge voltage is 4.40 V and the consumption of the electrolyte solution is severe.

Further, as described above, when the end-of-charge voltage is 4.40 V, not only the electrolyte in the negative electrode becomes insufficient, but also the positive electrode has a higher charging potential, which increases the expansion / contraction rate at the positive electrode and charges the positive electrode. Since the state is in a higher region, the consumption of the electrolytic solution becomes very fast due to the oxidative decomposition of the electrolytic solution, resulting in a serious shortage of the electrolytic solution at the positive electrode. Therefore, as in the present invention battery D, if a porous layer is disposed not only between the negative electrode and the separator but also between the positive electrode and the separator, the shortage of electrolyte in both the positive and negative electrodes can be resolved. It can also be understood that cycle characteristics can be obtained.
In order to support the increase in the expansion / contraction rate of the positive electrode because the charge potential of the positive electrode is increased, the end-of-charge voltage is 4.20 V (the positive electrode potential is 4.30 V with respect to the lithium reference electrode potential), and 4.30 V (lithium In the case of positive electrode potential with respect to reference electrode potential of 4.40V), 4.35V (positive electrode potential with respect to lithium reference electrode potential of 4.45V), 4.40V (positive electrode potential with respect to lithium reference electrode potential of 4.50V) The amount of expansion / contraction and the amount of expansion / contraction of the negative electrode were examined, and the results are shown in Table 10.

  As is clear from Table 10, the expansion and contraction amount is constant in the negative electrode regardless of the level of the end-of-charge voltage, whereas in the positive electrode, the expansion and contraction amount increases as the end-of-charge voltage increases. It is recognized that Therefore, the above is supported.

  In addition, when the end-of-charge voltage is 4.2 V, the battery temperature rarely rises to 60 ° C. in a normal use state. Therefore, experiments in the first to third examples (the end-of-charge voltage of 4. The cycle characteristic test at 2 V and a temperature of 60 ° C. has a strong meaning as an accelerated test under very severe conditions. On the other hand, when the end-of-charge voltage is 4.38 V or 4.40 V, the battery temperature may rise to about 45 ° C. in a normal use state. In the experiment in the seventh embodiment (cycle characteristic test at a charge end voltage of 4.38 V or 4.40 V and a temperature of 45 ° C.), the meaning is weak as an accelerated test under very severe conditions. Therefore, the experiments in the first to third examples are battery characteristic experiments in the case where the battery is used in a special environment, whereas this example and the fifth to seventh examples described later are used. It can be said that the experiment in the example is a battery characteristic experiment when the battery is used under a normal environment.

(5th Example)
Example 1
As the separator body, a separator having a thickness of 18 μm and a porosity of 50% is used, and a battery having a square shape (a square battery having a design capacity of 820 mAh) and a charge end voltage of 4.38 V are used. A battery was fabricated in the same manner as in the example of the fourth example except that the battery was designed so that the positive electrode potential with respect to the lithium reference electrode potential was 4.48 V. In addition, the manufacturing method of a square battery is as follows.

First, the positive and negative electrodes and the separator are prepared in the same manner as in the laminated battery, and then lead terminals are attached to the positive and negative electrodes, respectively. Next, after winding both the positive and negative electrodes in a spiral shape via a separator, this is pressed to produce a flat electrode body. Next, this electrode body is put into a battery outer can, and further an electrolyte is injected into the battery outer can. Finally, the sealing lid was produced by laser welding to the open end of the battery outer can.
The battery thus produced is hereinafter referred to as the present invention battery E1.

(Example 2)
A battery was fabricated in the same manner as in Example 1 except that a separator body having a thickness of 16 μm and a porosity of 46% was used.
The battery thus produced is hereinafter referred to as the present invention battery E2.

(Comparative Examples 1 and 2)
Batteries were prepared in the same manner as in Examples 1 and 2 except that the porous layer was not provided.
The batteries thus produced are hereinafter referred to as comparative batteries W1 and W2.

(Experiment)
Since the cycle characteristics of the inventive batteries E1 and E2 and the comparative batteries W1 and W2 were examined, the results are shown in Table 11. The charge / discharge conditions are as follows.

[Charging / discharging conditions]
-Charging conditions After constant current charging to a battery voltage of 4.38 V at a current of 1.0 It (800 mA), constant voltage charging is performed until the current value reaches 1/20 It (40.0 mA) at a voltage of 4.38 V. The condition to do.
-Discharge conditions Conditions under which a constant current discharge is performed up to a battery voltage of 2.75 V at a current of 1.0 It (800 mA).
The charge / discharge interval is 10 minutes, and the charge / discharge temperature is 45 ° C.

As is clear from Table 11, the batteries E1 and E2 of the present invention in which the porous layer mainly composed of inorganic fine particles is disposed between the separator main body and the positive and negative electrodes are comparative batteries in which the porous layer is not disposed. Compared to W1 and W2 (the thickness of the separator [the same as the thickness of the separator main body because no porous layer is provided] is the same as the thickness of the separator main body of the present invention batteries E1 and E2 respectively) It is recognized that the cycle characteristics are excellent.
This is considered to be due to the same reason as shown in the experiment of the fourth embodiment.
Further, this experiment shows that the present invention can be applied not only to a laminate type battery but also to a square type battery.

(Sixth embodiment)
(Example)
A porous layer is formed on the positive electrode surface (the surface of the positive electrode active material layer), and a separator having a thickness of 23 μm and a porosity of 52% is used, and the battery shape is a laminate type (design capacity is A battery was fabricated in the same manner as in Example 1 of the fifth example except that a 780 mAh laminate type battery) was used. The method for forming the porous layer on the positive electrode surface is the same as in the third embodiment.
The battery thus produced is hereinafter referred to as the present invention battery F.

(Comparative example)
A battery was fabricated in the same manner as in the above example except that the porous layer was not provided on the surface of the positive electrode active material layer.
The battery thus produced is hereinafter referred to as a comparative battery V.
The main configurations of the present invention battery F and comparative battery V are shown in Table 12 below.

(Experiment)
Since the cycle characteristics of the battery F of the present invention and the comparative battery V were examined, the results are shown in FIG. The charge / discharge conditions are the same as those in the experiment of the fourth embodiment.

As is clear from FIG. 14, the battery F of the present invention in which the porous layer mainly composed of inorganic fine particles is disposed between the separator and the positive electrode active material layer is compared with the comparative battery V in which the porous layer is not disposed. Thus, it is recognized that the cycle characteristics are excellent.
This is considered to be due to the same reason as shown in the experiment of the fourth embodiment.
Moreover, this experiment shows that a porous layer is not limited to the structure formed in the surface of a separator (separator main-body part), You may form in the surface of a positive electrode (positive electrode active material layer).

(Seventh embodiment)
(Example)
A battery was fabricated in the same manner as in Example 1 of the fifth example except that the porous layer was formed on the positive electrode surface (the surface of the positive electrode active material layer). The method for forming the porous layer on the positive electrode surface is the same as in the third embodiment.
The battery thus produced is hereinafter referred to as the present invention battery G.

(Comparative example)
A battery was fabricated in the same manner as in the above example except that the porous layer was not provided on the surface of the positive electrode active material layer.
The battery thus manufactured is hereinafter referred to as a comparative battery U.

(Experiment)
Since the cycle characteristics of the battery G of the present invention and the comparative battery U were examined, the results are shown in Table 13. The charge / discharge conditions are the same as those in the experiment of the fifth embodiment.

As is apparent from Table 13, the battery G of the present invention in which the porous layer mainly composed of inorganic fine particles is disposed between the separator and the positive electrode active material layer is compared with the comparative battery U in which the porous layer is not disposed. Thus, it is recognized that the cycle characteristics are excellent.
This is considered to be due to the same reason as shown in the experiment of the fourth embodiment.
Moreover, this experiment shows that a porous layer is not limited to the structure formed in the surface of a separator (separator main-body part), You may form in the surface of a positive electrode (positive electrode active material layer).

[Additional experiment]
Since the surplus space of the battery in the cylindrical battery, the square battery, and the laminate battery was calculated, the results are shown in Table 14. A 18650 cylindrical battery was used as the cylindrical battery, a 553450 rectangular battery and a 553436 rectangular battery were used as the rectangular batteries, and a 383562 laminated battery was used as the laminated battery.
First, the total volume in the battery can, the volume of the winding electrode body, and the volume of other members (spacers, tabs, etc.) are calculated. Then, the volume of the surplus space is calculated from the following formula 1, and the surplus is calculated from the following formula 2. The percentage of space was calculated.

  In the above battery, the results shown in Table 14 were obtained. However, when the ratio of the surplus space was calculated based on a battery that is generally commercially available, it is about 6 to 15% for a cylindrical battery and 10 to 20% for a prismatic battery. In the case of a laminate type battery, it was found to be about 1 to 8%, so that there is a lot of surplus space in the order shown by the following formula 3. In addition, in the lithium ion battery for HEV (hybrid) currently under examination, the surplus space tends to increase more than this, but the order of the space portion is the same.

Here, it is possible to fill the surplus space with surplus electrolyte, and by pouring the surplus electrolyte as in the present invention, the porous layer between the electrode and the separator body is formed. It is possible to supply the electrolytic solution into the electrode through. Therefore, the larger the surplus space, the larger the amount of surplus electrolyte solution filled, and the longer the cycle life of the battery. Therefore, the functions and effects of the present invention can be further demonstrated if the rectangular battery or the cylindrical battery has a large surplus space.
Since the laminated battery is a soft case, it can cope with a certain amount of battery shape change along with the expansion and contraction of the electrode, but the amount of electrolyte is controlled to some extent at the initial injection stage (the amount of excess electrolyte is excessive). The effect of the present invention is presumed to be smaller than that of a cylindrical or rectangular battery.

  However, by repeating the compression of the separator due to the electrode expansion during charging and the discharge of the electrolyte solution to the outside of the winding body, the electrolyte solution inside the electrode body seems to be insufficient due to diffusion control, Because the diffusion rate is high and the electrolyte released outside the system can penetrate and diffuse into the battery relatively quickly, even a battery with little excess electrolyte such as a laminate battery can exhibit sufficient advantages it is conceivable that.

  In addition, when a cylindrical battery is compared with a square battery and a laminate battery, the square battery does not have an intentionally provided space in the innermost peripheral portion of the battery, and a surplus electrolyte solution exists. Are concentrated on the upper and lower portions of the winding electrode body, the end surface of the porous layer is easily in contact with the excess electrolyte. On the other hand, in the cylindrical battery, as shown in FIG. 15, there is a space 50 for inserting and removing the winding jig in the center as shown in FIG. Since this space 50 is a surplus space where surplus electrolyte can exist, a considerable amount of electrolyte is required to contact the electrolyte with the upper and lower portions of the winding electrode body 52. Further, depending on the direction of the battery, the upper and lower portions of the winding electrode body 52 may be immersed in the electrolytic solution, but basically only a part or one side of the winding electrode body 52 is immersed in the electrolytic solution. The effect of sucking up the electrolyte is reduced. From such a point, the prismatic battery or the laminated battery can sufficiently exhibit the effects of the present invention rather than the cylindrical battery.

  However, even in the case of a cylindrical battery, it is not involved in the battery reaction as shown in FIG. 16 for the purpose of reducing the volume of the innermost peripheral part by reducing the diameter of the winding jig and reducing the volume. By inserting the substance 51 into the space 50 and reducing the surplus space, it is possible to achieve a configuration that can fully exhibit this effect.

  In addition, considering the above concept, it is desirable that the amount of electrolyte in the battery is large, but considering the increase in capacity and the risk of liquid leakage due to the presence of a large amount of electrolyte, it is currently marketed. Even when the maximum battery is taken into account, the total amount of the electrolyte is desirably 8.00 cc / Ah or less in the total amount inside the battery housing.

[Other matters]
(1) As described above, the effect of this effect varies depending on the shape of the battery. Further, as described above, the separator is inferior in the permeability and diffusibility of the electrolytic solution in TD, and the winding electrode body may be limited to the electrolytic solution penetrating path from the upper and lower portions of the winding. Penetration and diffusion are the worst battery systems.

  Here, at present, when the capacity is increased, the unevenness of the electrode surface is reduced due to an increase in the electrode packing density, and the penetration and diffusion of the electrolytic solution due to the capillary phenomenon tend not to occur. In addition, with high-power electrodes, the electrodes have a lower packing density than that for consumer batteries in order to ensure output, but batteries such as HEVs tend to be larger, with electrode widths and winding lengths being reduced. Due to the increase, the electrolytic solution tends to hardly penetrate and diffuse. Therefore, this configuration is considered to be particularly effective for a high capacity type battery having a high packing density and a high output type having a wide electrode width in a battery system using the winding electrode body as described above. Further, since the liquid absorption rate of the electrolytic solution and the penetration and diffusion rate of the electrolytic solution are remarkably improved, it is considered suitable for a battery for charging and discharging at a relatively high rate. Specifically, it is as follows.

  That is, when the results obtained in the various experiments described above are combined, the penetration and diffusion path of the electrolyte that travels through the space of the separator TD cannot be expected as much as in the preliminary experiment 2, and the penetration and diffusion paths that travel through the electrode surface are It cannot be expected as much as the effect from the preliminary experiment 3. Therefore, as shown in FIG. 17, the path through the gap between the positive and negative electrodes 1 and 2 and the separator 3 is the most promising for the penetration and diffusion path of the electrolyte into the electrode. By newly providing a porous layer 32 which is a permeation / diffusion path of the electrolyte, it is possible to dramatically improve the permeability and diffusion of the electrolyte into the positive and negative electrodes 1 and 2. Therefore, it is considered that the present invention is particularly effective for a high capacity type battery having a high filling density, a high output type battery having a wide electrode width, or a battery for charging / discharging at a relatively high rate.

  Further, the penetration and diffusion into the electrode are shown in FIG. 1, but when the situation is further analyzed in detail, FIG. 18 (in FIG. 18, the portion where the degree of penetration of the electrolytic solution is large is depicted to be darker). ). That is, the innermost peripheral portion 7 and the outermost peripheral portion 8 have a loose winding tension, and there is a step with the uncoated portion of the coated surface, so that the electrolyte easily penetrates and diffuses through the gap. Here, permeation and diffusion in the MD of the separator are added, and some of the electrolyte solution permeates. The other part is presumed to be the penetration and diffusion of the electrolyte in the route shown in FIG. Even when an actual battery is disassembled, color intensities are seen in the infiltrating portion of the electrolytic solution, so that the portion penetrating only the surface and the portion penetrating to the inside of the electrode can be clearly seen. This is considered to be consistent with the phenomenon seen in preliminary experiment 3.

(2) This effect is generally configured to promote penetration and diffusion in the width direction of the electrode, and is more effective when combined with a configuration that promotes penetration and diffusion in the back direction of the electrode. Can exert its functions. In particular, graphite, which is a negative electrode active material, tends to become a mirror body by rolling, and the electrode surface is difficult to permeate the electrolyte. Therefore, it is possible to assist in accelerating penetration and diffusion into the interior by performing treatments such as forming irregularities on the electrode surface or treatments using active materials with different particle sizes and shapes in the electrode layer. In combination with these, an improvement in electrolyte permeability can be expected.

(3) The method for producing the resin-made porous layer is not limited to the method shown in the best mode. As shown in FIGS. 19 (a) to 19 (c), the Rob-Srilleryan method and A similar method can also be used. Specifically, as shown in FIG. 1A, first, a casting liquid 70 containing a resin material made of polyamide or polyamideimide is applied to the surface of the separator main body 31 with a squeegee 71 or the like. As shown in the figure (b), this is immersed in the solution containing water. Then, the water 72 enters the casting liquid 70 and the inside of the membrane is separated into layers and solidified. At this time, in order to prevent the solvent concentration in water from greatly differing between the initial stage and the final stage, it is usually soaked in solutions (water + solvent) having different solvent concentrations, and the solvent is gradually removed. It is desirable to use a manufacturing method. Thereafter, as shown in FIG. 3C, the porous layer 32 is formed on the surface of the separator main body 31 by taking out from the water and then drying.
Further, the resin porous layer is not limited to the above polyamide, and other resin materials such as polyamideimide and polyimide may be used. The water-soluble polar solvent for producing the porous layer is not limited to N-methyl-2-pyrrolidone, and N, N-dimethylformamide, N, N-dimethylacetamide, etc. may be used. it can.

(4) The method for producing the porous layer made of inorganic fine particles to be formed on the separator is not limited to the die coating method and the dip coating method, and a gravure coating method, a transfer method, or a spray coating method may be adopted. good. Further, the method for producing the porous layer made of inorganic fine particles formed on the electrode is not limited to the reverse method, and may be the gravure coating method or the like.
Further, the porous layer made of inorganic fine particles is not limited to the above TiO ₂ but may be alumina, zirconia or the like.

(5) In the case of using a resin-made porous layer, there is an advantage that a battery with higher reliability can be produced because it has strength and adhesiveness that can withstand the processing steps of the battery. In the case of using the porous layer made of the product, the voids in the porous layer are increased, and the permeability of the electrolytic solution is further improved. Therefore, there is an advantage that the diffusion of the electrolytic solution into the electrode becomes smoother.

(6) In the above embodiment, the thickness of the separator (the separator body for the separator provided with the porous layer) is 12 to 23 μm. However, although it depends on the end-of-charge voltage, the thickness can be further reduced. Is possible.

(7) It is not limited to the structure in which the porous layer is formed on the separator as shown in the best mode, but as shown in the preliminary experiment 3 and the third example of the example, the electrode (positive electrode or negative electrode) Alternatively, it may be formed on the surface of the positive and negative electrodes), and may be formed separately from the positive and negative electrodes and the separator and disposed between the electrode and the separator. As a method for producing the resin porous layer separately from the positive and negative electrodes and the separator, in a method similar to the Rob-Srilleryan method, instead of forming a porous layer on the surface of the separator body, The method of forming a porous layer on the surface of glass and peeling this from glass can be illustrated.

In addition, when forming a porous layer in a separator main-body part, what is necessary is just to form in the single side | surface or both surfaces of a separator main-body part as mentioned above. However, if formed on both sides, the thickness of the separator increases, and the battery capacity may decrease. Therefore, it is formed on one side of the separator main body, or the thickness of the porous layer at a less necessary part. It is desirable to suppress a decrease in battery capacity by using a means such as reducing the battery capacity.
Moreover, when forming a porous layer in a separator main-body part, it is preferable that the width | variety of a separator is larger than the width | variety of a negative electrode. With such a configuration, since the contact area between the separator and the electrolyte existing in the excess space in the battery can increases, the penetration and diffusion from the upper and lower parts of the winding electrode body into the electrode are further promoted. This is because that. Considering the above, it is possible to expect the effect of the penetration and diffusion of the electrolytic solution by forming the porous layer on the separator rather than laminating the porous layer on the electrode (positive electrode or negative electrode). .

(8) In the above embodiment, the thickness of the porous layer (total thickness when two porous layers are provided) is 4 μm, but is not limited to this thickness. However, if the thickness of the porous layer is too small, the effects of electrolyte penetration and diffusion path are not sufficiently exhibited. On the other hand, if the thickness of the porous layer is too large, the occupied volume of the members that are not directly involved in power generation increases, the demand for higher capacity of the battery cannot be met, and the load characteristics of the battery are reduced and the energy is reduced. Incurs a decrease in density. Considering these matters, the total thickness of the porous layer is preferably regulated to 1 μm to 5 μm, particularly 1 μm to 3 μm. The total thickness of the porous layer means the thickness of the porous layer when the porous layer is disposed only between the separator and the positive electrode or between the separator and the negative electrode. When formed between, it means the total thickness of both porous layers.

(9) In the case of a porous layer made of inorganic fine particles, in order to increase the liquid absorbency of the electrolytic solution, the inorganic fine particles are appropriately bonded with a binder so that there is an excess space through which the electrolytic solution penetrates. It is desirable that For that purpose, the concentration of the binder with respect to the inorganic fine particles is preferably 30% by mass or less, particularly 20% by mass or less, and more preferably less than 10% by mass.

(10) In the above embodiment, the experiment was performed with the end-of-charge voltage being 4.38 V and 4.40 V, respectively (the positive electrode potential was 4.48 V and 4.50 V with respect to the lithium reference electrode potential). As a result, it is preferable to dispose a porous layer between the separator and the positive and negative electrodes if the end-of-charge voltage is 4.30 V or more, particularly 4.35 V or more, and in particular, if the voltage is 4.40 V or more, the separator It has been found that a porous layer is preferably present between the positive and negative electrodes.

(11) The positive electrode active material is not limited to the above lithium cobaltate, but may be olivine type lithium phosphate compound (LiFePO ₄ ), spinel type lithium manganate (LiMn ₂ O ₄ ), lithium nickelate (LiNiO ₂ ). Of course, a lithium nickel composite oxide, a lithium transition metal composite oxide represented by LiNi _x Co _y Mn _z O ₂ (x + y + z = 1), another olivine-type phosphate compound, or the like may be used. Moreover, you may use these mixtures.

(12) The method of mixing the positive electrode mixture is not limited to the above-mentioned mechano-fusion method, and a method of dry mixing while grinding with a rough method or a method of mixing / dispersing directly in a slurry in a wet manner, etc. It may be used.

(13) The negative electrode active material is not limited to the above graphite, and any material that can insert and desorb lithium ions, such as graphite, coke, tin oxide, metallic lithium, silicon, and a mixture thereof. Any type.

(14) The lithium salt of the electrolytic solution is not limited to the above LiPF ₆ , and LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiPF _6-X ( _{C n F 2n + 1) X} [ where, 1 <x <6, n = 1or2] may be such, or may be used as a mixture of two or more thereof. The concentration of the lithium salt is not particularly limited, but is preferably regulated to 0.8 to 1.5 mol per liter of the electrolyte. The solvent of the electrolytic solution is not limited to ethylene carbonate (EC) or diethyl carbonate (DEC), but propylene carbonate (PC), γ-butyrolactone (GBL), ethyl methyl carbonate (EMC), dimethyl carbonate. A carbonate-based solvent such as (DMC) is preferable, and a combination of a cyclic carbonate and a chain carbonate is more preferable.

(15) The present invention is not limited to a liquid battery, but can be applied to a gel polymer battery. Examples of the polymer material in this case include polyether solid polymer, polycarbonate solid polymer, polyacrylonitrile solid polymer, oxetane polymer, epoxy polymer, a copolymer composed of two or more of these, or a crosslinked polymer. A molecule or PVDF is exemplified, and a solid electrolyte in which this polymer material, a lithium salt, and an electrolyte are combined into a gel can be used.

  The present invention can be applied not only to a driving power source of a mobile information terminal such as a mobile phone, a notebook computer, and a PDA, but also to a large battery such as an in-vehicle power source of an electric vehicle or a hybrid vehicle.

It is explanatory drawing (electrode disassembly figure) which shows the osmosis | permeation state of the electrolyte solution in the middle of liquid injection of a cylindrical battery. It is a graph which shows a time-dependent change of the electrolyte solution suction height of a cylindrical battery. It is explanatory drawing which shows the state of the liquid absorption test of a separator. It is a schematic diagram of an olefin separator. It is a photograph when an olefin type separator is seen with an electron microscope. It is explanatory drawing which shows the electrolyte solution osmosis | permeation and the diffusion image of the separator which laminated | stacked the porous layer. It is explanatory drawing which shows the state of the liquid absorption test of an electrode. It is a graph which shows the cycle characteristics in this invention battery A1, A2 and comparative battery Z1, Z2. It is explanatory drawing which shows the motion of the electrolyte solution at the time of charging / discharging of a conventional battery. It is explanatory drawing which shows the motion of the electrolyte solution at the time of charging / discharging of this invention battery. It is a graph which shows the cycle characteristic in this invention battery B and comparative battery Z1, Z2. It is a graph which shows the cycle characteristic in this invention battery C and the comparison battery Y. 4 is a graph showing cycle characteristics of the present invention battery D and comparative battery X. It is a graph which shows the cycle characteristic in this invention battery F and the comparison battery V. FIG. It is a perspective view of the winding electrode body of a cylindrical battery. It is a perspective view of the improved winding electrode body of a cylindrical battery. It is explanatory drawing which shows the image of the osmosis | permeation of electrolyte solution, and a diffusion path. It is explanatory drawing which shows the image of the osmosis | permeation of the electrolyte solution inside an electrode, and a diffusion condition. It is process drawing which shows the preparation flow of the resin lamination separator by the Rob thrilleryan method. It is a graph which shows the relationship between the change of the crystal structure of lithium cobaltate, and electric potential.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 31 Separator main-body part 32 Porous layer

Claims (21)

An electrode body comprising a positive electrode having a positive electrode active material layer, a negative electrode having a negative electrode active material layer, and a separator interposed between the two electrodes, a nonaqueous electrolyte supplied to the electrode body, the electrode body, And the separator has two directions, MD and TD, which is less permeable to the non-aqueous electrolyte than MD. In the nonaqueous electrolyte battery in which the electrolyte is mainly supplied to the electrode body along the TD,
Between at least one of the positive and negative electrodes and the separator, at least a porous layer having better nonaqueous electrolyte permeability than the TD is disposed, and the electrode in the internal space of the battery housing is provided. A nonaqueous electrolyte battery characterized in that a surplus electrolyte solution is contained in at least a part of a portion excluding the body, and the surplus electrolyte solution is in contact with at least a part of the porous layer.   The non-aqueous electrolyte battery according to claim 1, wherein the electrode body is a wound electrode body in which the positive and negative electrodes and the separator are wound.   The nonaqueous electrolyte battery according to claim 2, wherein the battery housing is cylindrical or rectangular.   The nonaqueous electrolyte battery according to claim 1, wherein the porous layer is composed of at least one selected from a group of fine particles of inorganic material composed of alumina and titania and a binder.   The nonaqueous electrolyte battery according to claim 1, wherein the porous layer is composed of at least one selected from a resin-based material group consisting of polyamide and polyamideimide.   The nonaqueous electrolyte battery according to claim 1, wherein the positive electrode is charged until it becomes less than 4.40 V with respect to a lithium reference electrode potential.   The nonaqueous electrolyte battery according to claim 1, wherein the positive electrode is charged to 4.40 V or more with respect to a lithium reference electrode potential.   The nonaqueous electrolyte battery according to claim 1, wherein the positive electrode is charged to 4.45 V or more with respect to a lithium reference electrode potential.   The nonaqueous electrolyte battery according to claim 1, wherein the positive electrode is charged until it becomes 4.50 V or more with respect to a lithium reference electrode potential.   The nonaqueous electrolyte battery according to claim 6, wherein the porous layer is disposed between an electrode having a large volume change rate during charge and discharge and the separator.   The non-aqueous electrolyte battery according to claim 10, wherein the porous layer is formed on a surface of an electrode having a large volume change rate during charge and discharge.   The nonaqueous electrolyte battery according to claim 6, wherein the negative electrode active material is mainly composed of graphite, and the porous layer is disposed between the negative electrode and the separator.   The nonaqueous electrolyte battery according to claim 12, wherein the porous layer is formed on a surface of the negative electrode.   The nonaqueous electrolyte battery according to claim 7, wherein the porous layer is disposed between the negative electrode and the separator and between the positive electrode and the separator.   The non-aqueous solution according to claim 1, wherein the positive electrode active material contains at least lithium cobaltate in which aluminum or magnesium is dissolved, and zirconia is fixed to the surface of the lithium cobaltate. Electrolyte battery. There are two directions, MD and TD, which is inferior in permeability of the nonaqueous electrolyte than MD, and the nonaqueous electrolyte is mainly arranged so as to face the positive electrode through a separator that penetrates along the TD. In the negative electrode for water electrolyte batteries,
A negative electrode for a nonaqueous electrolyte battery, wherein a porous layer having a nonaqueous electrolyte permeability superior to that of the TD is formed on the surface.   The negative electrode for a non-aqueous electrolyte battery according to claim 16, wherein the porous layer is composed of at least one selected from a group of fine particles of inorganic material composed of alumina and titania and a binder. There are two directions, MD and TD, which is inferior to the permeability of the non-aqueous electrolyte than MD, and the non-aqueous electrolyte is disposed in a non-opposite manner facing the negative electrode through a separator that penetrates mainly along the TD. In the positive electrode for water electrolyte battery,
A positive electrode for a non-aqueous electrolyte battery, wherein a porous layer having a non-aqueous electrolyte permeability superior to that of the TD is formed on the surface.   The positive electrode for a non-aqueous electrolyte battery according to claim 18, wherein the porous layer is composed of at least one selected from a group of fine particles of inorganic material composed of alumina and titania and a binder. A first step of forming a negative electrode active material layer on the surface of the negative electrode current collector;
A second step of applying a slurry containing fine particles of an inorganic material to the surface of the negative electrode active material layer;
A third step of drying the slurry;
The manufacturing method of the negative electrode for nonaqueous electrolyte batteries characterized by having. A first step of forming a positive electrode active material layer on the surface of the positive electrode current collector;
A second step of applying a slurry containing fine particles of an inorganic material to the surface of the positive electrode active material layer;
A third step of drying the slurry;
The manufacturing method of the positive electrode for nonaqueous electrolyte batteries characterized by having.