JP2005158623A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery realizing high output, high output especially under a low temperature environment and improving safety. <P>SOLUTION: A positive electrode is prepared by forming a positive mix layer by applying a positive mix containing a lithium-nickel-manganese-cobalt composite oxide having layered crystal structure and an average particle size of 5-20 μm, flake graphite, and PVDF to an aluminum foil. A positive electrode porosity is limited to 25-35%, and a negative electrode is prepared by forming a negative mix layer by applying a negative mix containing amorphous carbon having an average particle size of 5-20 μm, acetylene black, and PVDF to a rolled copper foil, and a negative electrode porosity is limited to 30-40%. The amount of a nonaqueous electrolyte penetrating into the positive and negative mix layers is made appropriate and the distribution of the nonaqueous electrolyte is made almost uniform. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and particularly includes a lithium transition metal composite oxide having a layered crystal structure and an average particle diameter of 5 to 20 μm, a conductive agent mainly composed of a graphite-based carbon material, and a binder. The present invention relates to a non-aqueous electrolyte secondary battery in which a positive electrode in which a positive electrode mixture is applied almost uniformly to a positive electrode current collector to form a positive electrode mixture layer and a negative electrode are infiltrated into the non-aqueous electrolyte.

  Conventionally, in the field of rechargeable secondary batteries, aqueous batteries such as lead batteries, nickel-cadmium batteries, and nickel-hydrogen batteries have been mainstream. However, attention has been paid to electric vehicles (EV) and hybrid vehicles (HEV) in which a part of driving is supported by electric motors due to problems of global warming and fuel depletion, and batteries used for these power sources have higher capacity and higher capacity. Output performance has been demanded. As a power source that meets such requirements, a non-aqueous electrolyte secondary battery having a high voltage has attracted attention.

  Generally, a lithium transition metal composite oxide is used for a positive electrode material of a non-aqueous electrolyte secondary battery, and lithium cobalt oxide is used in particular because of a balance of capacity and cycle characteristics. However, since cobalt is low in resources and high in cost, lithium transition metal composite oxides containing manganese typified by lithium manganate are promising as cathode materials for EV and HEV batteries, and development has been promoted. Yes. When the crystal structure of this lithium transition metal complex oxide is a spinel crystal structure, the diffusion path of lithium ions is three-dimensional, whereas when it is a layered crystal structure, it is two-dimensional. Therefore, the lithium transition metal composite oxide with a layered crystal structure has high lithium ion diffusibility and excellent output characteristics under normal temperature environment, but the crystal shrinks and the lithium ion diffusivity decreases under low temperature environment. Incurs a decrease in output.

  On the other hand, the negative electrode material is generally a carbon material of an amorphous carbon material obtained by firing natural graphite, artificial graphite such as scale or lump, graphite material such as mesophase pitch graphite, furan resin such as furfuryl alcohol, etc. Is used. Since amorphous carbon has a higher theoretical capacity value than graphite, it has excellent capacity and cycle characteristics, and has a slope in the voltage characteristics during charging and discharging, so the battery state can be easily and accurately measured simply by measuring the voltage. A non-aqueous electrolyte secondary battery can be obtained, but the irreversible capacity is larger than that of the graphite material, so it is difficult to increase the capacity of the battery, and the electronic conductivity is inferior to that of the graphite material. , There is a drawback. In contrast, graphite-based materials have a low irreversible capacity and flat voltage characteristics, so that a high-capacity, high-power non-aqueous electrolyte secondary battery can be obtained. Due to its large size, the electron conductivity cannot be maintained for a long period of time, resulting in an early life. In addition, when a large battery for an electric vehicle is assumed, charge acceptance at a large current density is inferior to that of amorphous carbon. There is a problem.

  The above-described EV and HEV batteries have a large current density in charge and discharge, and require a long life and high output characteristics. Therefore, a plurality of single cells are generally connected and used. Since fluctuations in the characteristics of single cells greatly affect the life characteristics and safety, it is usually possible to suppress fluctuations by monitoring and controlling the voltage, current, temperature, etc. of the single cells in combination with a control system. Yes. However, as described above, since the voltage characteristics of the graphite-based material are flat, it is difficult to accurately monitor the state of the battery from the voltage. To solve this, a highly accurate control system is required. Therefore, it is desirable that the negative electrode material of the battery for EV or HEV is mainly amorphous carbon, and use of a lithium transition metal composite oxide having a layered crystal structure as the positive electrode material to promote improvement in output. Is promising.

  In order to increase the output of the non-aqueous electrolyte secondary battery, it is necessary to improve the electron conductivity and lithium ion diffusibility in the positive and negative electrode mixture layers. In order to improve the electron conductivity, various improvements in resistance reduction have been made, such as adding a conductive agent or increasing the positive / negative electrode mixture density to ensure an electron conduction network. On the other hand, in order to improve the diffusibility of lithium ions, a space through which the nonaqueous electrolyte solution permeates is required in the positive and negative electrode mixture layers. For example, when lithium manganate having a spinel crystal structure is used, a technique for setting the porosity of the positive electrode mixture layer according to the thickness of the positive electrode mixture layer is disclosed (see Patent Document 1). Further, in a low temperature environment, the movement of lithium ions in the non-aqueous electrolyte solution becomes very slow, and the output characteristics change remarkably due to the distribution of the non-aqueous electrolyte solution in the positive and negative electrode mixture layers. In order to solve this, a technique for suppressing a decrease in lithium ion conductivity in a low temperature environment by using a mixed organic solvent in a nonaqueous electrolytic solution is disclosed (for example, see Patent Document 2).

JP 2001-325948 A JP 2001-155766 A

  However, in the technique of Patent Document 1, in the case of lithium manganate having a spinel crystal structure, a space through which a non-aqueous electrolyte permeates is ensured. However, as described above, a layered crystal structure in which crystal shrinkage occurs in a low temperature environment. In the case of a lithium transition metal composite oxide, it cannot be said that the space through which the nonaqueous electrolyte permeates is sufficient. Moreover, although the technique of patent document 2 suppresses the fall of lithium ion conductivity in a non-aqueous electrolyte, it is difficult to improve the diffusibility of the lithium ion in a positive / negative electrode mixture layer. Furthermore, increasing the positive and negative electrode mixture density improves the electron conductivity. However, as the positive and negative electrode mixture density increases, the amount of non-aqueous electrolyte that permeates into the positive and negative electrode mixture decreases and the lithium ion concentration increases. Since the diffusibility is lowered, a partial bias occurs in the electrode reaction. Therefore, when the battery is overcharged, an abrupt increase in internal pressure or temperature is caused.

  An object of the present invention is to provide a non-aqueous electrolyte secondary battery capable of improving safety while achieving high output, particularly high output in a low temperature environment.

  In order to solve the above problems, a first aspect of the present invention is a conductive agent and a binder mainly composed of a lithium transition metal composite oxide having a layered crystal structure and an average particle diameter of 5 to 20 μm, and a graphite-based carbon material. In a non-aqueous electrolyte secondary battery in which a non-aqueous electrolyte is infiltrated with a positive electrode in which a positive electrode mixture containing is applied to a positive electrode current collector almost uniformly to form a positive electrode mixture layer and a negative electrode. The ratio of the pore volume in the positive electrode mixture layer to the volume of the mixture layer is 25% or more and 35% or less.

  In the first aspect, when the ratio of the pore volume in the positive electrode mixture layer to the volume of the positive electrode mixture layer is less than 25%, the amount of the non-aqueous electrolyte that penetrates into the positive electrode mixture layer decreases. , Lithium ion diffusibility decreases. In particular, under the low temperature environment, the layered crystal of the lithium transition metal composite oxide contracts, so that the decrease in lithium ion diffusivity becomes significant. For this reason, since the electrode reaction between the lithium transition metal composite oxide having a layered crystal structure and an average particle diameter of 5 to 20 μm and the nonaqueous electrolytic solution hardly occurs, the output characteristics are deteriorated. In addition, non-uniform distribution of the non-aqueous electrolyte causes a partial bias in the electrode reaction, leading to a decrease in output and a shortened life in a normal state, and a decrease in safety if the battery is overcharged. Invite. On the other hand, when the proportion of the pore volume exceeds 35%, the proportion of the positive electrode mixture is reduced, leading to a decrease in output.

  According to the first aspect, since the ratio of the void volume in the positive electrode mixture layer to the volume of the positive electrode mixture layer is 25% or more and 35% or less, the amount of the non-aqueous electrolyte in the positive electrode mixture layer is Because it is optimized and the distribution of the non-aqueous electrolyte is almost uniform and the diffusivity and electronic conductivity of lithium ions are ensured, the electrode reaction is performed almost uniformly in a low-temperature environment, so the output characteristics are excellent, It is possible to obtain a nonaqueous electrolyte secondary battery that is excellent in safety during overcharge without partial concentration of electrode reactions.

  In order to solve the above problem, the second aspect of the present invention is that a negative electrode mixture containing amorphous carbon having an average particle diameter of 5 to 20 μm, a conductive agent and a binder is substantially equal to a negative electrode current collector. In a non-aqueous electrolyte secondary battery in which a negative electrode coated with a negative electrode mixture layer and a positive electrode are infiltrated into a non-aqueous electrolyte solution, the negative electrode mixture layer has a volume within the negative electrode mixture layer. The ratio of the pore volume is 30% or more and 40% or less.

  In the second aspect, when the ratio of the void volume in the negative electrode mixture layer to the volume of the negative electrode mixture layer is less than 30%, the amount of the nonaqueous electrolyte solution penetrating into the negative electrode mixture layer is reduced. Since the diffusibility of lithium ions is reduced, the electrode reaction between amorphous carbon having an average particle size of 5 to 20 μm and the non-aqueous electrolyte is less likely to occur, so that the output characteristics are reduced and the distribution of the non-aqueous electrolyte is reduced. Since it becomes non-uniform and a partial bias occurs in the electrode reaction, the output is reduced and the life is shortened in the normal state, and the safety is lowered when the battery is overcharged. On the other hand, when the ratio of the pore volume exceeds 40%, the ratio of the negative electrode mixture is decreased, leading to a decrease in output.

  According to the second aspect, since the ratio of the pore volume in the negative electrode mixture layer to the volume of the negative electrode mixture layer is set to 30% or more and 40% or less, the amount of the nonaqueous electrolytic solution in the negative electrode mixture layer is Because it is optimized and the distribution of the non-aqueous electrolyte is almost uniform and the diffusivity and electronic conductivity of lithium ions are ensured, the electrode reaction is performed almost uniformly in a low-temperature environment, so the output characteristics are excellent, It is possible to obtain a nonaqueous electrolyte secondary battery that is excellent in safety during overcharge without partial concentration of electrode reactions.

  The third aspect of the present invention is a positive electrode mixture comprising a lithium transition metal composite oxide having a layered crystal structure and an average particle diameter of 5 to 20 μm, a conductive agent mainly composed of a graphite-based carbon material, and a binder. A negative electrode current collector comprising: a positive electrode in which a positive electrode mixture layer is formed by being applied almost uniformly to the positive electrode current collector; and a negative electrode mixture comprising amorphous carbon having an average particle diameter of 5 to 20 μm, a conductive agent and a binder. In a non-aqueous electrolyte secondary battery in which a negative electrode formed by coating almost evenly on a non-aqueous electrolyte is infiltrated with a non-aqueous electrolyte, the inside of the positive electrode mixture layer with respect to the volume of the positive electrode mixture layer The ratio of the pore volume is 25% or more and 35% or less, and the ratio of the pore volume in the negative electrode mixture layer to the volume of the negative electrode mixture layer is 30% or more and 40% or less. And According to this aspect, since the positive electrode according to the first aspect and the negative electrode according to the second aspect are included, the effects of the first and second aspects can be achieved at the same time, and non-water excellent in output characteristics and safety. An electrolyte secondary battery can be obtained.

In the first and third embodiments, the lithium transition metal composite oxide used for the positive electrode has the chemical formula Li _a Ni _x Mn _y Co _1-xy O ₂ (0 <a <1.2, 0 <x <0 .50, 0 <y <0.50).

  According to the present invention, the ratio of the void volume in the positive electrode mixture layer to the volume of the positive electrode mixture layer is set to 25% or more and 35% or less, so that the amount of the non-aqueous electrolyte in the positive electrode mixture layer is optimized. As a result, the non-aqueous electrolyte distribution is almost uniform, and lithium ion diffusibility and electronic conductivity are ensured. Therefore, the electrode reaction is performed almost uniformly in a low-temperature environment. The effect that the non-aqueous-electrolyte secondary battery excellent in the safety | security at the time of an overcharge can be obtained without being concentrated partially can be acquired.

  Embodiments in which the present invention is applied to a cylindrical lithium ion secondary battery used for a power source for an electric vehicle will be described below.

(Positive electrode)
The positive electrode active material includes a lithium-nickel-manganese-cobalt composite oxide (LiNi _0.33 Mn _0.33 Co _0.33 O as a lithium transition metal composite oxide having a layered crystal structure and an average particle diameter of 5 to 20 μm. ₂ ) was used. To 100 parts by mass of the positive electrode active material, 10 parts by mass of flaky graphite as a conductive agent and 5 parts by mass of polyvinylidene fluoride (PVDF) as a binder are added, and N- Methylpyrrolidone was added and kneaded to obtain a slurry. This slurry was applied to both surfaces of an aluminum foil as a positive electrode current collector with a thickness of 20 μm by transfer by roll-to-roll, and dried to form a substantially uniform and homogeneous positive electrode mixture layer on the aluminum foil. . Thereafter, the positive electrode mixture layer is pressed at a predetermined pressing pressure with a roll press, so that the ratio of the pore volume in the positive electrode mixture layer to the total volume of the positive electrode mixture layer is in the range of 25 to 35% by volume. . After pressing, it was cut into a width of 80 mm to obtain a strip-shaped positive electrode. In addition, the ratio of the void | hole volume in a positive mix layer can be adjusted by changing a press pressure. Also, the X-ray diffraction method confirms that the lithium / nickel / manganese / cobalt composite oxide has a layered crystal structure, and confirms that the average particle size is 5 to 20 μm using a laser type particle size distribution analyzer. did.

(Negative electrode)
As the negative electrode active material, amorphous carbon powder having an average particle diameter of 5 to 20 μm was used. 5 parts by mass of acetylene black as a conductive agent and 10 parts by mass of PVDF as a binder are added to 100 parts by mass of the negative electrode active material, and N-methylpyrrolidone is added as a dispersion solvent thereto, and kneaded. To get a slurry. This slurry is applied to both surfaces of a rolled steel foil as a negative electrode current collector having a thickness of 10 μm by transfer by roll-to-roll, and dried to form a substantially uniform and homogeneous negative electrode mixture layer on the copper foil. did. Then, the ratio of the void | hole volume in the negative mix layer with respect to the volume of the whole negative mix layer was made into the range of 30-40 volume% by pressing a negative mix layer with a predetermined press pressure with a roll press machine. . After pressing, the strip was cut into a width of 85 mm to obtain a strip-shaped negative electrode. As with the positive electrode, the ratio of the pore volume in the negative electrode mixture layer can be adjusted by changing the press pressure.

(Battery assembly)
The produced positive and negative electrodes are wound together with a polyethylene separator having a thickness of 40 μm to produce an electrode group, the electrode group is inserted into a cylindrical battery container, a predetermined amount of nonaqueous electrolyte is injected, and the upper lid is caulked. The cylindrical lithium ion secondary battery was completed by sealing. As the non-aqueous electrolyte, a solution in which 1 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) was dissolved in a mixed solution of ethylene carbonate and dimethyl carbonate was used.

  Next, a battery of an example produced by changing the pore volume in the positive electrode mixture layer and the negative electrode mixture layer according to the present embodiment will be described. In addition, it describes together about the battery of the comparative example produced for the comparison.

(Example 1)
As shown in Table 1 below, in Example 1, the ratio of the pore volume in the positive electrode mixture layer to the total volume of the positive electrode mixture layer (hereinafter referred to as positive electrode porosity) is 25% by volume, and the negative electrode mixture. A battery was manufactured by setting the ratio of the pore volume in the negative electrode mixture layer to the volume of the entire layer (hereinafter referred to as negative electrode porosity) to 35 volume%. The positive electrode porosity and the negative electrode porosity were measured by peeling the mixture layer from the current collectors of the positive and negative electrodes, and the mercury intrusion method (the same applies to the following examples and comparative examples). The pore volume calculated from the true specific gravity, mass blending amount, and thickness of the positive and negative electrode plates after pressing in the positive and negative electrode mixture layers is very close to the measurement result by the mercury intrusion method. A value was obtained.

(Example 2 to Example 3)
As shown in Table 1, Examples 2 to 3 were the same as Example 1 except that the positive electrode porosity was changed. In Example 2, the positive electrode porosity was 30% by volume, and in Example 3, the positive electrode porosity was 35% by volume.

Example 4
As shown in Table 1, in Example 4, a battery was produced with a positive electrode porosity of 30% by volume and a negative electrode porosity of 30% by volume.

(Example 5 to Example 6)
As shown in Table 1, Examples 5 to 6 were the same as Example 4 except that the negative electrode porosity was changed. In Example 5, the negative electrode porosity was 35% by volume, and in Example 6, the negative electrode porosity was 40% by volume.

(Comparative Examples 1 to 2)
As shown in Table 1, Comparative Examples 1 and 2 were the same as Example 1 except that the positive electrode porosity was changed. In Comparative Example 1, the positive electrode porosity was 24% by volume, and in Comparative Example 2, the positive electrode porosity was 36% by volume.

(Comparative Example 3 to Comparative Example 4)
As shown in Table 1, in Comparative Examples 3 to 4, batteries were prepared with the positive electrode porosity and the negative electrode porosity being 24% by volume, 28% by volume, 36% by volume, and 41% by volume, respectively.

(Comparative Example 5 to Comparative Example 6)
As shown in Table 1, Comparative Examples 5 to 6 were the same as Example 4 except that the negative electrode porosity was changed. In Comparative Example 5, the negative electrode porosity was 28% by volume, and in Comparative Example 6, the negative electrode porosity was 41% by volume.

(test)
Next, the following tests were carried out on the batteries of Examples and Comparative Examples produced as described above.

  First, a constant-current / constant-voltage charge (set voltage 4.1 V) is performed for 5 hours at a 3-hour rate (0.33 C) in a room temperature (25 ° C.) atmosphere, and then a discharge end voltage is set at 1 hour rate (1 C) The battery was discharged to 2.7 V and charged again under the same conditions. Next, according to Japan Storage Battery Industry Association Standard SBA8503, discharge was performed at each current value of discharge currents 1, 3, and 6A, and the voltage at 5 seconds was measured. The initial output was obtained from the current-voltage characteristics.

  The battery whose initial output was measured was allowed to stand in a low temperature (−25 ° C.) constant temperature bath for 24 hours to cool the entire battery to −25 ° C. The output characteristics in a low temperature atmosphere were measured under the same conditions as the measurement.

  Next, in order to confirm the output deterioration due to the charge / discharge cycle, the sample was allowed to stand in a room temperature atmosphere for 24 hours, and then constant current and constant voltage charge (set voltage 4.1 V) at a room temperature atmosphere at a rate of 3 hours (0.33C) ) Was repeated for 5 hours, and the discharge until reaching the discharge end voltage of 2.7 V was repeated at a rate of 1 hour (1 C). The ratio of the output after 100 cycles to the initial output was obtained as a percentage and used as the maintenance rate.

  Moreover, the produced battery was continuously charged at a constant current of 10 A at room temperature to be in an overcharged state, the maximum temperature of the battery surface at that time was measured, and the phenomenon of the battery was observed (overcharge test).

  Table 2 below shows the test results of the output under room temperature atmosphere and low temperature atmosphere, the output maintenance rate after 100 cycles, and the maximum battery temperature and phenomenon in the overcharge test.

  As shown in Tables 1 and 2, in the batteries of Examples 1 to 3 in which the positive electrode porosity was 25% by volume or more and 35% by volume or less, the output in a low temperature atmosphere was secured at 320 W or more, An output of 85% or more of the initial output is maintained even after the charge / discharge cycle is repeated 100 times. Also in the overcharge test, the maximum temperature was 200 ° C. or less, and the battery was good without any abnormality.

  In contrast, in the batteries of Comparative Example 1 and Comparative Example 3 having a positive electrode porosity of less than 25% by volume, the decrease in output at a low temperature was remarkable, and in the overcharge test, the maximum temperature exceeded 240 ° C, Batteries are ruptured and the safety is significantly impaired. Since the phenomenon of the battery of Comparative Example 1 is the same as that of the batteries of Examples 1 to 3 even though the negative electrode porosity is the same, the non-aqueous electrolyte distribution in the positive electrode mixture layer is uneven. As a result, it is considered that the electrode reaction is concentrated on the portion where the non-aqueous electrolyte is present, and that portion has reached an overcharged state from an early stage. On the contrary, in the batteries of Comparative Example 2 and Comparative Example 4 in which the positive electrode porosity exceeds 35% by volume, the initial output at room temperature atmosphere is low, so that the electron conductivity in the positive electrode mixture layer decreases and the electrode The reaction is considered to be non-uniform. However, since the output characteristics were inferior from the beginning, it did not reach a rupture state.

  On the other hand, in the batteries of Examples 4 to 6 in which the negative electrode porosity was 30% by volume or more and 40% by volume or less, similarly to the positive electrode, an output at a low temperature of 300 W or more was secured, and the charge / discharge cycle was repeated 100 times. Even after this, an output of 88% or more of the initial output is maintained. Also in the overcharge test, the maximum temperature was 190 ° C. or less, and the battery was good without any abnormality.

  On the other hand, in the battery of Comparative Example 5 in which the negative electrode porosity was less than 30% by volume, the output at a low temperature was remarkably reduced, and in the overcharge test, the maximum temperature reached 250 ° C., and the battery burst. This significantly reduces safety. As in the case of the positive electrode, this is because the non-aqueous electrolyte distribution in the negative electrode mixture layer is non-uniform, and as a result, the electrode reaction concentrates on the portion where the non-aqueous electrolyte exists, and this portion is excessively exceeded from an early stage. It is considered that the battery has reached a state of charge. If the electrode reaction of the negative electrode is partially biased, lithium ions cannot be inserted between the active materials, and metallic lithium is deposited on the surface of the negative electrode mixture layer. For this reason, not only the output is significantly reduced, but also safety such as rupture is impaired. Conversely, even in the battery of Comparative Example 6 in which the negative electrode porosity exceeded 40% by volume, the initial output was significantly reduced.

  If the positive electrode porosity is less than 25%, the amount of the non-aqueous electrolyte that permeates into the positive electrode mixture layer decreases, and the diffusibility of lithium ions decreases. In particular, the diffusibility of lithium ions is further reduced because the layered crystal shrinks in a low temperature atmosphere. For this reason, since the electrode reaction between the lithium-nickel-manganese-cobalt composite oxide having a layered crystal structure and the non-aqueous electrolyte is difficult to occur, the output characteristics are deteriorated. Further, when the amount of the non-aqueous electrolyte in the positive electrode mixture layer is reduced, the distribution of the non-aqueous electrolyte becomes non-uniform, resulting in a partial bias in the electrode reaction. For this reason, the electrode reaction concentrates on the part where the non-aqueous electrolyte is present, leading to a decrease in output and shortening the life in a normal state, and incurring a rapid increase in battery internal pressure and temperature when falling into an overcharge state, Safety is reduced. On the other hand, when the positive electrode porosity exceeds 35%, the proportion of the positive electrode mixture decreases and the electron conductivity decreases, so that the electrode reaction becomes non-uniform and the output decreases.

  Further, if the negative electrode porosity is less than 30%, the amount of the nonaqueous electrolyte solution penetrating into the negative electrode mixture layer is reduced, as in the case where the positive electrode porosity is less than 25%. Since the diffusibility is lowered, the electrode reaction between the amorphous carbon and the non-aqueous electrolyte is less likely to occur, so that the output characteristics are lowered. In addition, the non-aqueous electrolyte distribution is non-uniform and the electrode reaction is partially biased. Therefore, the electrode reaction concentrates on the area where the non-aqueous electrolyte is present, reducing output and shortening the life under normal conditions. Inviting and falling into an overcharged state reduces safety. On the other hand, if the negative electrode porosity exceeds 40%, the proportion of the negative electrode mixture decreases and the electron conductivity decreases, so that the electrode reaction becomes non-uniform and the output decreases.

  As described above, for the positive electrode porosity and the negative electrode porosity, the amount of non-aqueous electrolyte that permeates into the positive and negative electrode mixture is optimized to maintain both good electron conductivity and lithium ion diffusibility. There is a possible range. In the cylindrical lithium ion secondary battery of this embodiment, the positive electrode has a positive electrode porosity in the range of 25% to 35% by volume, and the negative electrode has a negative electrode porosity in the range of 30% to 40% by volume. The presence of pores in the agent layer makes it possible to obtain a lithium ion secondary battery that can provide good output characteristics even in a low-temperature atmosphere and can ensure safety even in an overcharged state.

  In the present embodiment, the lithium-nickel-manganese-cobalt composite oxide of the positive electrode active material has a layered crystal structure. For this reason, since the diffusion path of lithium ions is two-dimensional, it is excellent in lithium ion diffusibility in a room temperature environment, so that excellent output characteristics can be obtained in a room temperature environment.

In this embodiment, LiNi _0.33 Mn _0.33 Co _0.33 O ₂ is used as the positive electrode active material, scaly graphite is used as the positive electrode conductive agent, PVDF is used as the binder, acetylene black is used as the negative electrode conductive agent, and nonaqueous electrolysis is used. Examples of the solution of lithium hexafluorophosphate dissolved in a mixed solution of ethylene carbonate and dimethyl carbonate in the liquid were exemplified, but as described in detail below, these are usually used in the above-mentioned claims. Either can be used.

The positive electrode active material exemplified in the present embodiment is a Li—Ni—Mn—Co composite oxide having a Ni / Mn / Co ratio of 1: 1: 1, but is limited to this ratio as long as it has a layered crystal structure. It is not something. The Li / (Ni + Mn + Co) ratio is 1.0 in the present embodiment, but is not limited to this value and may be excessive Li. Further, a lithium transition metal composite represented by the chemical formula Li _a Ni _x Mn _y Co _1-xy O ₂ (0 <a <1.2, 0 <x <0.50, 0 <y <0.50) An oxide may be used. Further, a composite oxide of Co or Ni, or a part of Mn, Co, or Ni, for example, Li, Co, Ni, Mn, Fe, Cu, Al, Cr, Mg, Zn, V, Ga, B, or F A lithium transition metal composite oxide or the like substituted or doped with at least one element may be used.

  In addition, examples of the binder that can be used in other embodiments include polytetrafluoroethylene (PTFE), polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, styrene / butadiene rubber, polysulfide rubber, nitrocellulose, and cyanoethyl cellulose. And various latexes, polymers such as acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, chloroprene fluoride, and mixtures thereof.

  Further, the positive electrode conductive agent that can be used in other than the present embodiment is not particularly limited as long as it is a graphite-based carbon material. For example, natural graphite, various artificial graphite materials, carbonaceous materials such as coke, and the like may be used, and any of particle shapes such as flaky, spherical, fibrous, and massive may be used. Moreover, there is no restriction | limiting in particular also in the negative electrode electrically conductive agent which can be used except this embodiment, For example, you may make it use amorphous carbon, such as ketjen black.

Furthermore, as the non-aqueous electrolyte, a non-aqueous electrolyte obtained by using a general lithium salt as an electrolyte and dissolving it in an organic solvent can be used. Further, the lithium salt and organic solvent used are not particularly limited. For example, as the electrolyte, in addition to this embodiment, LiC1O ₄ , LiAsF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, or a mixture thereof may be used. it can. Examples of organic solvents other than the present embodiment include propylene carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1 , 3-dioxolane, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propionitrile, or a mixed solvent of two or more of these. The mixing ratio is not limited.

  According to the non-aqueous electrolyte secondary battery according to the present invention, it is possible to improve safety while achieving high output, particularly high output in a low temperature environment, contributing to manufacturing, sales, etc. Industrially available.

Claims (4)

  A cathode mixture containing a lithium transition metal composite oxide having a layered crystal structure and an average particle diameter of 5 to 20 μm, a conductive material mainly composed of a graphite-based carbon material, and a binder is applied almost evenly to the cathode current collector. In the non-aqueous electrolyte secondary battery in which the positive electrode in which the positive electrode mixture layer is formed and the negative electrode are infiltrated into the non-aqueous electrolyte, the volume of pores in the positive electrode mixture layer with respect to the volume of the positive electrode mixture layer A non-aqueous electrolyte secondary battery, wherein the ratio is 25% or more and 35% or less.   A negative electrode in which a negative electrode mixture containing an amorphous carbon having an average particle size of 5 to 20 μm, a conductive agent, and a binder is applied almost evenly to the negative electrode current collector to form a negative electrode mixture layer and a positive electrode In the non-aqueous electrolyte secondary battery infiltrated with an aqueous electrolyte, the ratio of the pore volume in the negative electrode mixture layer to the volume of the negative electrode mixture layer is 30% or more and 40% or less. Non-aqueous electrolyte secondary battery.   A cathode mixture containing a lithium transition metal composite oxide having a layered crystal structure and an average particle diameter of 5 to 20 μm, a conductive material mainly composed of a graphite-based carbon material, and a binder is applied almost evenly to the cathode current collector. The negative electrode mixture obtained by forming a positive electrode mixture layer and a negative electrode mixture containing amorphous carbon having an average particle diameter of 5 to 20 μm, a conductive agent and a binder almost evenly on the negative electrode current collector In a non-aqueous electrolyte secondary battery in which a negative electrode having a layer formed is infiltrated with a non-aqueous electrolyte, a ratio of a void volume in the positive electrode mixture layer to a volume of the positive electrode mixture layer is 25% or more and 35 %, And the ratio of the void volume in the negative electrode mixture layer to the volume of the negative electrode mixture layer is 30% or more and 40% or less. The lithium transition metal composite oxide has the chemical formula Li _a Ni _x Mn _y Co _1-xy O ₂ (0 <a <1.2, 0 <x <0.50, 0 <y <0.50). The nonaqueous electrolyte secondary battery according to claim 1, wherein the nonaqueous electrolyte secondary battery is expressed by: