JP2007087690A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery normally providing a function as the battery, such as cycle characteristics or storage characteristics in the nonaqueous electrolyte secondary battery having high capacity with a positive electrode and a negative electrode both highly densified. <P>SOLUTION: In the nonaqueous electrolyte secondary battery is quipped with a negative plate, a positive plate, and a separator or a lithium ion conductive layer, a porous insulation layer having a low compression deformation ratio is installed in at least one of an interface between the separator or the lithium ion conductive layer and the negative plate and an interface between the separator or the lithium ion conductive layer and the positive plate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery using lithium ions, and in particular, an insulating layer is provided on at least one of a separator or an interface between a lithium ion conductive layer and a positive electrode, or an interface between a separator or a lithium ion conductive layer and a negative electrode. The present invention relates to a non-aqueous electrolyte secondary battery having high capacity and excellent cycle life characteristics.

  In recent years, consumer electronic devices have become increasingly portable and cordless, and there is an increasing demand for small, lightweight, high energy density batteries that serve as power sources for driving these electronic devices. Non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, are batteries having a high voltage and a high energy density, and are therefore mainly used for notebook computers, mobile phones, AV devices and the like.

  The nonaqueous electrolyte secondary battery is required to have a higher capacity, a longer cycle life, and good discharge characteristics.

  Particularly in recent lithium ion secondary batteries, the positive electrode active material and the negative electrode active material have been increased in density in order to achieve higher capacity, and accordingly, the positive electrode active material in the space inside the battery case In addition, since the proportion of the negative electrode active material increases, the proportion of the non-aqueous electrolyte solution must be reduced.

  However, the electrode plate expands and contracts in the battery due to the charge / discharge cycle, and the separator is repeatedly compressed and returned to the original pressure due to the pressure from the electrode plate. Since the liquid moves from the pores in the separator and is reintroduced, the non-aqueous electrolyte becomes empty when the proportion of the non-aqueous electrolyte in the space in the battery case decreases. There is a possibility that a situation in which the non-aqueous electrolyte cannot fully return into the pores may occur during repeated discharge / reintroduction from the pores.

  In particular, the vicinity of the surface of the separator that is susceptible to pressure from the electrode plate is strongly compressed, so the distribution of the non-aqueous electrolyte tends to be non-uniform near the surface of the separator, and it is in contact with the area where the non-aqueous electrolyte is insufficient. The electrode plate is not able to sufficiently contribute to charging / discharging, the charge state becomes uneven in the electrode plate, and the deterioration of the active material is accelerated.

Therefore, recently, by providing a polyvinylidene fluoride resin layer with excellent liquid retention on the surface of the electrode plate, the liquid retention property of the surface of the electrode plate is improved, and the increase in the internal resistance of the battery during high temperature storage is reduced. Therefore, it has been proposed to suppress the capacity deterioration. (For example, see Patent Document 1)
However, in a situation where the nonaqueous electrolyte is repeatedly released and reintroduced from the pores of the separator every charge and discharge as in the cycle test, the liquid retention of the electrode plate surface is improved by providing a polyvinylidene fluoride resin layer. Is not enough, especially in recent high capacity non-aqueous electrolyte secondary batteries where the ratio of the non-aqueous electrolyte to the positive and negative electrode active materials has decreased, the non-aqueous electrolyte fully returns to the pores of the separator. An unsatisfactory situation occurs, and an appropriate distribution of the electrolyte cannot be ensured throughout the charge / discharge cycle, resulting in insufficient cycle life or deterioration of discharge characteristics.

As another example, improvement in cycle life performance and standing performance at high temperatures has been proposed by improving the liquid retention of the separator itself, but the ratio of the non-aqueous electrolyte to the positive and negative electrode active materials is still high. The recent high capacity non-aqueous electrolyte secondary battery that has been reduced cannot be sufficiently improved in liquid retention. (For example, see Patent Document 2)
JP 2001-176497 A JP 2002-367588 A

  In a conventional non-aqueous electrolyte secondary battery, in a situation where charge and discharge are repeated as in a cycle test, the liquid retention of the surface of the electrode plate is not sufficient, and the non-aqueous electrolyte solution is at the interface between the electrode plate and the separator. There has been a problem of non-uniform distribution. In particular, in the recent increase in capacity of non-electrolyte secondary batteries, the ratio of the non-aqueous electrolyte to the positive and negative electrode active materials is low, so that the distribution of the non-aqueous electrolyte is significantly reduced as the charge / discharge cycle progresses. As a result, there was a problem that the cycle life characteristics deteriorated.

  The present invention solves the above-mentioned conventional problems, suppresses capacity deterioration due to non-uniform distribution of the non-aqueous electrolyte accompanying charge / discharge cycles, and has high capacity and excellent cycle life characteristics. An object is to provide a liquid secondary battery.

  In order to achieve the above object, the present invention provides a nonaqueous electrolyte secondary battery comprising a negative electrode plate, a positive electrode plate, a separator or a lithium ion conductive layer, and a nonaqueous electrolyte solution, wherein the separator Alternatively, a porous insulating layer having a small compressive deformation rate is provided on at least one of the interface between the lithium ion conductive layer and the negative electrode plate, or the interface between the separator or lithium ion conductive layer and the positive electrode plate. It is a feature.

  According to the present invention, a uniform distribution of the non-aqueous electrolyte can be secured in the vicinity of the surface of the electrode plate through the charge / discharge cycle, so that a non-aqueous electrolyte secondary battery having a high capacity and excellent cycle life characteristics can be provided.

  In the present invention, a non-aqueous electrolyte secondary battery comprising a negative electrode plate, a positive electrode plate, a separator or a lithium ion conductive layer, and a non-aqueous electrolyte solution, the separator or the lithium ion conductive layer, A porous insulating layer having a small compressive deformation rate is provided on at least one of the interface with the negative electrode plate or the interface between the separator or the lithium ion conductive layer and the positive electrode plate.

  According to this configuration, a uniform distribution of the non-aqueous electrolyte can be ensured near the surface of the electrode plate through the charge / discharge cycle, so that a non-aqueous electrolyte secondary battery having high capacity and excellent cycle life characteristics can be obtained. Play.

  The porous insulating layer is preferably made of resin and organic compound filler, or resin and inorganic compound filler.

  According to this configuration, there is an effect that an insulating layer having a uniform porosity and a small compressive deformation rate can be formed relatively easily by using particulate fillers as a main structure and bonding them with a resinous binder.

Specific examples of the organic compound filler include epoxy resin, melamine resin, urea resin, phenol resin, polyimide resin, fluorine resin, polyamide resin, etc., which are polymerized until they are insoluble in organic solvent, or crosslinked fine particle type. The filler is mentioned. These may be used alone or in combination of two or more.

Specific examples of the inorganic compound filler are preferably inorganic oxide fillers, and examples thereof include alumina (Al ₂ O ₃ ), titania (TiO ₂ ), silicon (SiO ₂ ), zirconia, and magnesia. These may be used alone or in combination of two or more.

  Specific examples of the resin include amide resins such as aromatic polyamide, fluororesins such as polyvinylidene fluoride (hereinafter referred to as PVDF) and vinylidene fluoride-hexafluoropropylene copolymers, and rubbery polymers containing acrylonitrile units. It is done. These may be used alone or in combination of two or more. Among them, a polymer containing an acrylonitrile unit is most suitable because it has appropriate elasticity and binding properties.

  The porous insulating layer preferably has a thickness of 0.5 μm to 4.0 μm and a porosity of 20 to 80%.

  According to this configuration, it is possible to realize an appropriate lithium ion permeability and an appropriate non-aqueous electrolyte retention. As a result, there is an effect that a non-aqueous electrolyte secondary battery having a higher capacity and excellent cycle life characteristics can be obtained.

As the positive electrode active _{material, Li x Co 1-y M} y O 2 ( a 1.0 ≦ x ≦ 1.15,0.005 ≦ y ≦ 0.1, M is Mg, Al, Ti, Mn , Ni, Fe, Y, Zr, Mo, W) at least one selected from the group consisting of compounds represented by: Li _x Ni _y Co _z M _1-yz O ₂ (1.0 ≦ x ≦ 1.15, 0.1 ≦ y ≦ 0.85, 0.1 ≦ z ≦ 0.5, and M is Mg, Al, Ti, Mn, Fe, Y, Zr, It is preferable to mix and use at least one selected from the group consisting of compounds represented by at least one selected from Mo and W).

  According to this structure, the improvement effect of the cycle life characteristic by having the porous insulating layer of this invention can further be exhibited. The reason is as follows.

_{Li x Co 1-y M y} O 2 ( a 1.0 ≦ x ≦ 1.15,0.005 ≦ y ≦ 0.1, M is Mg, Al, Ti, Mn, Ni, Fe, Y, Zr , At least one selected from Mo and W) is excellent in electron conductivity, but has a small capacity per unit weight of the active material and is difficult to increase in capacity.

On the other hand, Li _x Ni _y Co _z M _1-yz O ₂ (1.0 ≦ x ≦ 1.15, 0.1 ≦ y ≦ 0.85, 0.1 ≦ z ≦ 0.5, and M is Mg , Al, Ti, Mn, Fe, Y, Zr, Mo, and W) have a large capacity per unit weight of the active material and are useful for increasing the capacity of the battery. However, there is a problem that the low-temperature discharge characteristics of the battery are lowered due to the poor electronic conductivity.

  Therefore, there is a possibility that a battery having higher capacity and excellent low-temperature discharge characteristics can be obtained by using a mixture of these compounds. However, when a battery is produced using this mixed positive electrode active material, a positive electrode plate having a significantly higher capacity than the conventional one is produced, and the negative electrode plate to be combined with it needs to be densified and stored in the battery case. The ratio of the non-aqueous electrolyte in the case is inevitably reduced.

  As a result, the non-aqueous electrolyte distribution in the vicinity of the surface of the electrode plate becomes non-uniform with the charge / discharge cycle, causing a problem that the cycle life characteristics are deteriorated.

  Therefore, the above problem is improved by providing the battery produced using this mixed positive electrode active material with the porous insulating layer of the present invention, which has a high capacity, excellent low-temperature discharge characteristics, and excellent cycle life characteristics. In addition, a non-aqueous electrolyte secondary battery can be realized.

If the compressive deformation rate when a load of 10 kg / cm ² is applied is 5% or less, the porous insulating layer is almost compressed even if it receives pressure due to expansion / contraction of the electrode plate due to charge / discharge. A porous insulating layer capable of maintaining the strength without deformation can be formed on the surface of the electrode plate.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  In addition, the figure shown here is an example of the battery of this invention, Comprising: If it has the structure represented to the claim of this invention, the same effect can be acquired.

<Example 1>
(Production of battery)
FIG. 1 is a partially cutaway perspective view showing an embodiment of the nonaqueous electrolyte secondary battery of the present invention, FIG. 2 is a schematic sectional view of an electrode plate group, and FIG. 2A is a porous insulating layer. FIG. 2B is a schematic cross-sectional view of an electrode plate group in which a porous insulating layer according to an embodiment of the present invention is provided on the surface of a positive electrode plate. FIG. 2 (c) is a schematic sectional view of an electrode plate group in which a porous insulating layer according to an embodiment of the present invention is provided on the surface of a negative electrode plate, and FIG. 2 (d) is an embodiment of the present invention. It is a schematic sectional drawing of the electrode group which provided the certain porous insulating layer on both surfaces of the positive / negative electrode board.

  As shown in FIG. 1, the electrode plate group 1 is configured by winding a belt-like positive electrode plate and a negative electrode plate in a spiral shape through a separator. An aluminum positive electrode lead 2 and a nickel negative electrode lead 3 are connected to the positive electrode plate and the negative electrode plate, respectively. It is accommodated in a battery case 4 made of aluminum. The other end of the positive electrode lead 2 is spot welded to the aluminum sealing plate 5, and the other end of the negative electrode lead 3 is spot welded to the lower part of the nickel negative electrode terminal 6 at the center of the sealing plate 5. The periphery of the opening of the battery case 4 and the sealing plate 5 are laser welded, and a predetermined amount of non-aqueous electrolyte is injected from the inlet 7. Finally, the inlet 7 is laser welded using an aluminum stopper to complete the battery.

(1) Production of Positive Electrode A mixture of LiCo _0.94 Mg _0.05 Al _0.01 O ₂ and LiNi _0.5 Co _0.4 Mn _0.1 O ₂ in a ratio of 5 to 5 was used as a positive electrode active material. An N-methylpyrrolidinone (NMP) solution of polyvinylidene fluoride is prepared and stirred so that 100 parts by weight of the mixed positive electrode active material is 3 parts by weight of acetylene black as a conductive material and 5 parts by weight of polyvinylidene fluoride as a binder. By mixing, a paste-like positive electrode mixture 13 was obtained.

  Next, an aluminum foil having a thickness of 20 μm is used as the positive electrode current collector 11, the paste-like positive electrode mixture 13 is applied to both surfaces thereof, dried and then rolled with a rolling roller, and cut into a predetermined size to obtain the positive electrode plate 8. did.

  The positive electrode conductive material may be any electron conductive material that is substantially chemically stable in the constructed battery. Examples include graphites, carbon blacks, conductive fibers, metal powders, conductive whiskers, organic conductive materials such as conductive metal oxides or polyphenylene derivatives, and these are used alone or as a mixture. Also good.

As the positive electrode binder, a thermoplastic resin, a thermosetting resin, or the like is used. For example, polytetrafluoroethylene (PTFE) is preferable in addition to polyvinylidene fluoride (PVDF).

  As the shape of the positive electrode current collector, a foil, a film, a sheet, a net, a punched one, a lath body, a porous body, a foamed body, a molded body of a fiber group, or the like can be used. The thickness is not particularly limited, but is preferably 1 to 500 μm.

(2) Production of negative electrode After mixing crushed and classified scaly graphite so that the average particle diameter is about 20 μm and 3 parts by weight of binder styrene / butadiene rubber, carboxymethyl cellulose becomes 1% with respect to graphite. Thus, a carboxymethyl cellulose aqueous solution was added and mixed by stirring to obtain a paste-like negative electrode mixture 14. Next, a copper foil having a thickness of 15 μm is used as the negative electrode current collector 12, a paste-like negative electrode mixture 14 is applied on both sides thereof, dried and then rolled using a rolling roller, and cut into a predetermined size to obtain a negative electrode plate It was set to 9.

  Examples of the negative electrode active material include pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke, etc.), graphites, and the like, which are mainly carbonaceous materials that can be doped and dedoped with lithium. , Glassy carbons, organic polymer compound fired bodies (phenol resins, furan resins, etc., fired at a suitable temperature and carbonized), carbon fibers, activated carbon, etc., and these may be used alone or in combination of two or more. It can be used by mixing. The average particle diameter of the negative electrode active material is not particularly limited, but is preferably 1 to 30 μm.

  The negative electrode conductive material is not particularly limited as long as it is an electron conductive material. For example, artificial graphite, acetylene black, and carbon fiber are preferable.

  Examples of the binder for the negative electrode include styrene butadiene rubber, polyvinylidene fluoride, ethylene-acrylic acid copolymer, or (Na +) ion-crosslinked product of the above material, ethylene-methacrylic acid copolymer, or (Na +) of the above material. An ionic cross-linked product, an ethylene-methyl acrylate copolymer, or a (Na +) ionic cross-linked product of the material, an ethylene-methyl methacrylate copolymer, or a (Na +) ionic cross-linked product of the material are preferable.

  As the negative electrode current collector, in addition to stainless steel, nickel, copper, titanium, carbon, conductive resin, etc., a composite material obtained by treating the surface of copper or stainless steel with carbon, nickel, or titanium is used. be able to. Among these, copper and copper alloys are particularly preferable, and the surfaces of these materials may be oxidized and used. Moreover, you may give an unevenness | corrugation to the collector surface by surface treatment. The shape and thickness are the same as those of the positive electrode current collector.

(3) Preparation of raw material paste of porous insulating layer As inorganic oxide filler, 950 g of alumina having a median diameter of 0.3 μm and BM-720H (containing acrylonitrile units) manufactured by Nippon Zeon Co., Ltd., which is a resin component 625 g of an NMP solution containing 8% by weight of a rubber-like polymer) and an appropriate amount of NMP were stirred with a double-arm kneader to prepare a raw material paste for the porous insulating layer 10.

(4) Preparation of non-aqueous electrolyte A solution prepared by dissolving 1.0 mol / l LiPF ₆ in a solvent prepared by adjusting ethylene carbonate and ethyl methyl carbonate at a volume ratio of 30:70 at 20 ° C. was used.

  The lithium ion conductive non-aqueous electrolyte of the present invention is composed of a solvent, a lithium salt and an additive dissolved in the solvent. Known materials can be used as the non-aqueous solvent.

(5) Battery assembly (Batteries A1 to A9 of Example 1)
The raw material paste for the porous insulating layer 10 prepared in the above (3) is gravure-coated on both surfaces of the positive electrode plate 8 prepared in the above (1), the coating film is dried with hot air, and the thickness is 1 on each surface. A positive electrode plate 8 having a porous insulating layer 10 having a thickness of 0.0 μm was produced.

  Then, the positive electrode plate 8 and the negative electrode plate 9 having the porous insulating layer 10 and a separator made of a microporous polyethylene resin having a thickness of 25 μm are spirally wound, and the non-water adjusted in (4) above is wound around this. The electrolyte was poured and sealed.

  The non-aqueous electrolyte injection weight was adjusted so that the ratio to the weight of the negative electrode active material was the value shown in (Table 1), and the battery thus produced was manufactured from the battery A1 of Example 1 of the present invention. A9.

(Batteries B1 to B9 of Example 1)
Batteries produced in the same manner as the batteries A1 to A9 except that they were applied to both surfaces of the negative electrode plate 9 were designated as batteries B1 to B9 of Example 1 of the present invention.

(Batteries C1 to C9 of Example 1)
Batteries produced in the same manner as the batteries A1 to A9 except that the positive electrode plate 8 and the negative electrode plate 9 were coated on both surfaces were designated as batteries C1 to C9 of Example 1 of the present invention.

(Comparison batteries D1 to D9)
Batteries produced in the same manner as in Example 1 except that the porous insulating layer 10 prepared in (3) was not applied were designated as batteries D1 to D9 of comparative examples.

(Cycle life characteristics evaluation)
Using the batteries D1 to D9 of Example 1 and Comparative Example, the charge / discharge cycle was performed 500 times at an environmental temperature of 20 ° C. The charging conditions were a constant voltage charge with a maximum current of 600 mA and a charge end voltage of 4.20 V for 2 hours. The discharge conditions were a constant current with a current value of 600 mA and a discharge end voltage of 3.0 V, the discharge capacity after 500 cycles had been measured, and the evaluation results were shown as a ratio to the initial capacity.

  Table 1 shows the capacity retention ratios after 500 cycles of the batteries A1 to A9, B1 to B9, C1 to C9 of Example 1, and the batteries D1 to D9 of Comparative Examples.

As can be seen from (Table 1), the weight ratio of the non-aqueous electrolyte to the weight of the negative electrode active material (the weight of the non-aqueous electrolyte (g) / the weight of the negative electrode active material (g)) is 500 under the same conditions. When comparing the capacity retention ratios after the cycle, the batteries D1 to D9 of the comparative examples that did not include the porous insulating layer 10 clearly show a decreasing tendency.

  Moreover, in batteries D1 to D9 of comparative examples, the weight ratio of the non-aqueous electrolyte to the weight of the negative electrode active material (weight of non-aqueous electrolyte (g) / weight of negative electrode active material (g)) was 0.9 or less. In the batteries D4 to D9, the capacity maintenance rate after 500 cycles shows a markedly decreasing tendency, and in particular, the batteries D7 to D9 having a ratio of 0.75 or less show a significant decrease.

  On the other hand, among the batteries A1 to A9, B1 to B9, and C1 to C9 of Example 1 including the porous insulating layer 10, the surface of one of the positive electrode plate 8 and the negative electrode plate 9 is porous. In the batteries A1 to A9 and B1 to B9 having the insulating layer 10, the weight ratio of the nonaqueous electrolyte to the weight of the negative electrode active material (weight of the nonaqueous electrolyte (g) / weight of the negative electrode active material (g The batteries A4 to A9 and the batteries B4 to B9 having a ratio of)) of 0.9 or less also show a relatively good capacity maintenance rate, and even when the ratio is 0.75 or less, no significant reduction in the maintenance rate is observed. .

  Furthermore, in the batteries C1 to C9 having the porous insulating layer 10 on both the positive electrode plate 8 and the negative electrode plate 9, a better capacity retention rate was obtained.

  As a result of disassembling and observing the comparative battery D9 having a large decrease in capacity retention after 500 cycles, a portion where the nonaqueous electrolyte was clearly depleted was observed at the interface between the separator and the electrode plate. When X-ray diffraction analysis of the positive electrode around such a part is performed, it is found that the crystal structure of the positive electrode active material is changed, the charge non-uniformity occurs, and the positive electrode active material is significantly deteriorated. It was. Further, in the negative electrode around such a part, lithium deposition was observed due to non-uniform charging.

  On the other hand, as a result of disassembling and observing the battery C9 after 500 cycles in which both the positive electrode plate 8 and the negative electrode plate 9 were provided with the porous insulating layer 10, the nonaqueous electrolytic solution was found at the interface between the separator and the electrode plate. There was no depleted site. Further, there was no significant change in the crystal structure of the positive electrode active material by X-ray diffraction analysis of the positive electrode, and no lithium deposition was observed in the negative electrode plate 9.

  From the above results, even in a battery in which the weight ratio of the non-aqueous electrolyte to the weight of the negative electrode active material (weight of the non-aqueous electrolyte (g) / weight of the negative electrode active material (g)) is 0.9 or less, the separator and By providing the porous insulating layer 10 at least one of the interface of the positive electrode plate 8 or the interface between the separator and the negative electrode plate 9, non-uniform distribution of the non-aqueous electrolyte in the charge / discharge cycle is suppressed, It has been clarified that since the reaction of the electrode plate accompanying the discharge is uniformly performed, the active material is not deteriorated and good cycle life characteristics can be obtained. In particular, a greater effect is obtained in a battery having a ratio of 0.75 or less.

  Moreover, although the improvement effect is recognized by providing the porous insulating layer 10 in either one of the interface between the separator and the positive electrode plate 8 or the interface between the separator and the negative electrode plate 9, the porous insulating layer is formed in both. By having 10, the larger effect is acquired.

<Example 2>
(Batteries E1 to E4 of Example 2 and batteries E5 to E7 of Comparative Examples)
As a raw material paste for the porous insulating layer 10, when the mixing ratio of the inorganic oxide filler and the resin component is adjusted to form a coating film, the compression deformation rate when a load of 10 kg / cm ² is applied (Table Batteries produced in the same manner as the battery A9 of Example 1 except that the paste having the values described in 2) were produced were designated as batteries E1 to E4 of Example 2 and batteries E5 to E7 of Comparative Examples.

(Batteries F1 to F4 of Example 2 and batteries F5 to F7 of Comparative Examples)
As a raw material paste for the porous insulating layer 10, when the mixing ratio of the inorganic oxide filler and the resin component is adjusted to form a coating film, the compression deformation rate when a load of 10 kg / cm ² is applied (Table The batteries produced in the same manner as the battery B9 of Example 1 except that the paste having the values described in 2) were produced were designated as batteries F1 to F4 of Example 2 and batteries F5 to F7 of Comparative Examples.

(Batteries G1 to G4 of Example 2 and batteries G5 to G7 of Comparative Examples)
As a raw material paste for the porous insulating layer 10, when the mixing ratio of the inorganic oxide filler and the resin component is adjusted to form a coating film, the compression deformation rate when a load of 10 kg / cm ² is applied (Table The batteries produced in the same manner as the battery C9 of Example 1 except that the paste having the values described in 2) were produced were designated as batteries G1 to G4 of Example 2 and batteries G5 to G7 of Comparative Examples.

  Table 2 shows the evaluation results of the capacity retention rate after 500 cycles.

The batteries E1 to E4, F1 to F4, and G1 to G4 of Example 2 each including the porous insulating layer 10 having a compressive deformation rate of 5% or less when a load of 10 kg / cm ² is applied are all good. The capacity retention rate after 500 cycles was shown, but in the batteries E5 to E7, F5 to F7, and G5 to G7 having a deformation rate of 6% or more, a decrease in the capacity retention rate was observed.

  This is because when the deformation rate is 6% or more, the change in the pore volume in the porous insulating layer 10 due to charge / discharge increases, and the discharged non-aqueous electrolyte is in the porous insulating layer 10. This is thought to be because the distribution of the non-aqueous electrolyte is not uniform because it cannot fully return to the pores.

From the above results, a load of 10 kg / cm ² was applied in order for the nonaqueous electrolytic solution released from the pores in the porous insulating layer 10 during the charge / discharge cycle to be reintroduced into the pores again. It can be said that it is preferable to provide the porous insulating layer 10 so that the compression deformation rate when added is 5% or less.

<Example 3>
(Batteries H3 to H6 of Example 3, batteries H1, H2, and H7 of comparative examples)
A battery produced in the same manner as the battery A9 of Example 1 except that the thickness of the porous insulating layer 10 was applied so as to have the value shown in (Table 3) was designated as batteries H3 to H6 of Example 3, and Comparative Example. Batteries H1, H2, and H7.

(Batteries I3 to I6 of Example 3 and batteries I1, I2, and I7 of Comparative Examples)
A battery produced in the same manner as the battery B9 of Example 1 except that the thickness of the porous insulating layer 10 was applied so as to have the value shown in Table 3 was obtained. Batteries I1, I2, and I7.

(Batteries J3 to J6 of Example 3, batteries J1, J2, and J7 of comparative examples)
A battery produced in the same manner as the battery C9 of Example 1 except that the thickness of the porous insulating layer 10 was applied so as to have the value shown in Table 3 was obtained. The batteries J1, J2, and J7 were used.

  Table 3 shows the evaluation results of the capacity retention rate after 500 cycles.

In the batteries H1, H2, I1, I2, J1, and J2 of comparative examples in which the thickness of the porous insulating layer 10 is 0.3 μm or less, a decrease in capacity retention rate after 500 cycles is recognized, and 0.3 μm In the following, it is considered that a sufficient thickness for holding the non-aqueous electrolyte is not obtained. On the other hand, in the batteries H7, I7, and J7 of comparative examples in which the thickness of the porous insulating layer 10 is 5.0 μm or more, the lithium ion permeability decreases because the porous insulating layer 10 is too thick. It is considered that the capacity maintenance rate after 500 cycles was lowered.

  From the above results, it can be said that the thickness of the porous insulating layer 10 is preferably 0.5 μm to 4.0 μm.

<Example 4>
(Batteries K3 to K6 of Example 4, batteries K1 and K2 of Comparative Examples)
As a raw material paste for the porous insulating layer 10, except that the median diameter of the inorganic oxide filler was adjusted to produce a paste having a porosity described in (Table 4) when used as a coating film. The batteries produced in the same manner as the battery A9 of Example 1 were designated as batteries K3 to K6 of Example 4 and batteries K1 and K2 of comparative examples.

(Batteries L3 to L6 of Example 4, batteries L1 and L2 of comparative examples)
As a raw material paste for the porous insulating layer 10, except that the median diameter of the inorganic oxide filler was adjusted to produce a paste having a porosity described in (Table 4) when used as a coating film. The batteries produced in the same manner as the battery B9 of Example 1 were designated as batteries L3 to L6 of Example 4 and batteries L1 and L2 of comparative examples.

(Batteries M3 to M6 of Example 4, batteries M1 and M2 of Comparative Examples)
As a raw material paste for the porous insulating layer 10, except that the median diameter of the inorganic oxide filler was adjusted to produce a paste having a porosity described in (Table 4) when used as a coating film. The batteries produced in the same manner as the battery C9 of Example 1 were designated as batteries M3 to M6 of Example 4 and batteries M1 and M2 of comparative examples.

  Table 4 shows the evaluation results of the capacity retention rate after 500 cycles.

In the batteries K1, K2, L1, L2, M1, and M2 of Example 4 in which the porosity of the porous insulating layer 10 was 15% or less, a decrease in capacity retention rate after 500 cycles was observed. This is because when the porosity is 15% or less, the amount of non-aqueous electrolyte for securing lithium ion permeability in the porous insulating layer 10 is not sufficient, and as a result, a good ion path cannot be obtained. it is conceivable that.

For the porous insulating layer 10 having a porosity of 85% or more, it was impossible to make the compression deformation rate 5% or less when a load of 10 kg / cm ² was applied, so that a battery was produced. Not done.

  From the above results, it can be said that the porosity of the porous insulating layer 10 is preferably 20% to 80%.

<Example 5>
(Batteries N1 to N8 of Example 5)
A battery manufactured in the same manner as the battery A9 of Example 1 except that LiCo _0.94 Mg _0.05 Al _0.01 O ₂ and LiNi _0.5 Co _0.4 Mn _0.1 O ₂ were mixed in the ratio shown in Table 5 as the positive electrode active material. 5 batteries N1 to N8.

(Batteries O1 to O8 of Example 5)
A battery manufactured in the same manner as the battery B9 of Example 1 except that LiCo _0.94 Mg _0.05 Al _0.01 O ₂ and LiNi _0.5 Co _0.4 Mn _0.1 O ₂ were mixed in the ratio shown in Table 5 as the positive electrode active material. 5 batteries O1 to O8.

(Batteries P1 to P8 of Example 5)
A battery produced in the same manner as the battery C9 of Example 1 except that LiCo _0.94 Mg _0.05 Al _0.01 O ₂ and LiNi _0.5 Co _0.4 Mn _0.1 O ₂ were mixed in the ratio shown in Table 5 as the positive electrode active material. No. 5 batteries P1 to P8.

(Comparison batteries Q1 to Q8)
Batteries produced in the same manner as in Example 5 except that the porous insulating layer 10 was not applied were designated as batteries Q1 to Q8 of comparative examples.

(Battery capacity evaluation)
The battery capacity was measured at an environmental temperature of 20 ° C. The charging conditions were a constant voltage charge with a maximum current of 600 mA and a charge end voltage of 4.20 V for 2 hours. The discharge conditions were a constant current with a current value of 600 mA and a discharge end voltage of 3.0 V, and the discharge capacity of each battery was measured.

  The battery capacity of the battery N1 of Example 5 was set to 100, and the battery capacity was compared by expressing the discharge capacity of each battery as a ratio.

(Discharge characteristic evaluation)
The battery capacity was measured at an environmental temperature of 20 ° C and 0 ° C. The charging conditions were a constant voltage charge with a maximum current of 600 mA and a charge end voltage of 4.20 V for 2 hours. The discharge conditions were a constant current with a current value of 600 mA and a discharge end voltage of 3.0 V, and the discharge capacity of each battery was measured.

  In each battery, the discharge capacity at 0 ° C. with respect to the discharge capacity at 20 ° C. was expressed as a ratio and compared.

  Table 5 shows the evaluation results of the battery capacity, discharge characteristics, and capacity retention rate after 500 cycles of the batteries N1 to N8, O1 to O8, P1 to P8 of Example 5 of the present invention, and the batteries Q1 to Q8 of Comparative Examples. Show.

Batteries N1 to N8, O1 to O8, P1 to P8 of Example 5 of the present invention, and battery Q of the comparative example
1 to Q8, the battery capacity increases as the ratio of LiNi _0.5 Co _0.4 Mn _0.1 O ₂ as the positive electrode active material increases, and LiNi _0.5 Co _0.4 Mn _0.1 O ₂ is a material suitable for increasing the capacity of the battery. It can be seen that it is. However, as the ratio of LiNi _0.5 Co _0.4 Mn _0.1 O ₂ increases, a decrease in discharge characteristics is observed, and the batteries N8, O8, P8 of Example 5 of the present invention using only LiNi _0.5 Co _0.4 Mn _0.1 O ₂ , In the battery Q8 of the comparative example, a significant decrease in discharge characteristics is observed.

On the other hand, the batteries N2 to N7 and O2 to O7 of Example 5 using the positive electrode active material in which LiCo _0.94 Mg _0.05 Al _0.01 O ₂ and LiNi _0.5 Co _0.4 Mn _0.1 O ₂ were mixed at a ratio of 95/5 to 5/95. , P2 to P7 and comparative batteries Q2 to Q7, a battery having a higher capacity and excellent discharge characteristics can be realized.

However, the batteries Q1 to Q8 of the comparative example not including the porous insulating layer 10 are compared with the batteries N1 to N8, O1 to O8, and P1 to P8 of Example 5 including the porous insulating layer 10. The capacity retention rate after 500 cycles has greatly decreased, and in particular, as the battery capacity is increased by increasing the ratio of LiNi _0.5 Co _0.4 Mn _0.1 O ₂ , the capacity retention ratio has decreased significantly.

In the batteries N1 to N8, O1 to O8, and P1 to P8 of Example 5 including the porous insulating layer 10, the ratio of LiNi _0.5 Co _0.4 Mn _0.1 O ₂ can be increased to increase the capacity of the battery. As with the results of Example 1, the porous insulating layer 10 is provided to suppress the non-uniform distribution of the non-aqueous electrolyte in the charge / discharge cycle, and charge / discharge is maintained. It is considered that the active material was not deteriorated because the reaction of the electrode plate accompanying the process was performed uniformly, and good cycle life characteristics were obtained.

From the above results, using the positive electrode active material in which LiCo _0.94 Mg _0.05 Al _0.01 O ₂ and LiNi _0.5 Co _0.4 Mn _0.1 O ₂ are mixed at a ratio of 95/5 to 5/95, the porous insulating layer of the present invention is used. It has been clarified that a high capacity, low temperature discharge characteristics and good cycle life characteristics can be obtained by providing the electrode plate on the surface.

<Example 6>
Using the batteries A9, B9, C9 of Example 1 of the present invention and the battery D9 of the comparative example, evaluation was performed by setting the charge end voltage in the cycle life characteristic evaluation to each voltage shown in Table 6.

  Table 6 shows the evaluation results of the capacity retention rate after 500 cycles.

In the battery D9 of the comparative example, the capacity maintenance rate greatly decreased as the charge end voltage was set higher, and charging and discharging became impossible before reaching 500 cycles at 4.40 V or higher.

  On the other hand, in the batteries A9, B9, C9 of Example 1, a good capacity maintenance rate is maintained even at a charge end voltage of 4.20V or higher, and the charge end voltage is set to 4.25 to 4.50V, which is higher than before. In the high voltage rechargeable battery whose capacity is increased by setting, the non-aqueous electrolyte solution 2 having higher capacity and excellent cycle life characteristics can be obtained by providing the porous insulating layer 10 according to the present invention. It became clear that a secondary battery would be feasible.

  However, when the end-of-charge voltage was set to 4.60V, a decrease in capacity maintenance rate was confirmed. This is probably because when the charge end voltage is set to 4.60 V, the crystal structure of the positive electrode active material itself has collapsed.

  From the above results, the porous insulating layer 10 of the present invention is also useful in a high-voltage rechargeable battery in which the end-of-charge voltage is set to 4.25 to 4.5 V, which is higher than the conventional one, and the capacity is increased. It was revealed that good cycle life characteristics can be obtained.

  In addition, although the porous insulating layer 10 of this invention was comprised by gravure coating, the same effect was acquired also by spray type coating.

Moreover, the same effect was acquired even if the separator of the Example of this invention was a lithium ion electroconductive layer. As a lithium ion conductive layer, an organic electrolyte composed of a polymer material consisting of a solvent and a lithium salt dissolved in the solvent is absorbed and held in the positive electrode mixture and the negative electrode mixture, and further the organic electrolyte is absorbed and held. A porous separator made of a polymer can be integrated with the positive electrode and the negative electrode. The polymer material is not particularly limited as long as it can absorb and retain the organic electrolyte, but vinylidene fluoride is particularly preferable.

  The nonaqueous electrolyte secondary battery according to the present invention is excellent in cycle characteristics, storage characteristics, etc. even in a nonaqueous electrolyte secondary battery with a high capacity due to a highly densified positive electrode and a negative electrode. It is useful as a liquid secondary battery.

The partially cutaway perspective view showing one embodiment of the nonaqueous electrolyte secondary battery of the present invention (A) Schematic sectional view of a comparative example showing an electrode plate group not provided with a porous insulating layer, (b) Electrode provided with a porous insulating layer according to an embodiment of the present invention on the surface of a positive electrode plate Schematic cross-sectional view of the plate group, (c) Schematic cross-sectional view of the electrode plate group provided with the porous insulating layer according to one embodiment of the present invention on the surface of the negative electrode plate, (d) In one embodiment of the present invention Schematic sectional view of an electrode plate group in which a certain porous insulating layer is provided on both surfaces of the positive and negative electrode plates

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrode plate group 2 Positive electrode lead 3 Negative electrode lead 4 Battery case 5 Sealing plate 6 Negative electrode terminal 7 Inlet 8 Positive electrode plate 9 Negative electrode plate 10 Porous insulating layer 11 Aluminum foil 12 Copper foil 13 Positive electrode mixture 14 Negative electrode mixture 15 Separator

Claims (5)

A nonaqueous electrolyte secondary battery comprising a negative electrode plate, a positive electrode plate, a separator or a lithium ion conductive layer, and a nonaqueous electrolyte solution,
A porous insulating layer having a low compressive deformation rate was provided at least one of the interface between the separator or lithium ion conductive layer and the negative electrode plate, or the interface between the separator or lithium ion conductive layer and the positive electrode plate. Non-aqueous electrolyte secondary battery.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the insulating layer is made of a resin and an organic compound filler.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the insulating layer is made of a resin and an inorganic compound filler.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the insulating layer has a thickness of 0.5 μm to 4.0 μm and a porosity of 20% to 80%. As the active material of the positive electrode _{plate, Li x Co 1-y M} y O 2 ( a 1.0 ≦ x ≦ 1.15,0.005 ≦ y ≦ 0.1, M is Mg, Al, Ti, Mn At least one selected from the group consisting of compounds represented by: at least one selected from Ni, Fe, Y, Zr, Mo, W),
Li _x Ni _y Co _z M _1-yz O ₂ (1.0 ≦ x ≦ 1.15, 0.1 ≦ y ≦ 0.85, 0.1 ≦ z ≦ 0.5, M is Mg, Al , Ti, Mn, Fe, Y, Zr, Mo, and W) are used in a mixture of at least one selected from the group consisting of compounds represented by: Non-aqueous electrolyte secondary battery.