JP2019114338A - Lithium ion secondary battery - Google Patents

Abstract

To provide a lithium ion secondary battery, which is required to achieve a high energy density, and which is highly safe while having a high capacity.SOLUTION: A lithium ion secondary battery according to the present invention comprises: a positive electrode containing a metal composite oxide containing lithium and nickel and a composite oxide containing a lithium and manganese; and a negative electrode. The metal composite oxide containing lithium and nickel includes nickel of 50 mol% or more in metal excluding lithium. In the case of a counter electrode of Li, the capacity ratio Q1/Q2 where Q1 is a single-pole positive electrode capacity of 3-4.3 V and Q2 is a single-pole positive electrode capacity of 3-5.0 V is 0.6 or larger.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lithium ion secondary battery.

  The lithium ion secondary battery has a higher energy density than an aqueous solution type secondary battery and is excellent in charge and discharge cycle characteristics. Therefore, lithium ion secondary batteries are being actively developed and improved for application to electric vehicles and electric power storage applications, and in these applications, high safety is required more than required for portable devices etc. ing.

  Generally, a lithium secondary battery comprises a positive electrode plate obtained by applying a positive electrode active material containing a lithium transition metal complex oxide to a positive electrode current collector such as an aluminum foil, and a negative electrode current collector such as copper foil with a negative electrode active material containing a carbon material. The negative electrode plate applied to the electrode plate is produced by housing the electrode plate group laminated or wound through the porous separator made of the insulating material in the battery case and injecting the non-aqueous electrolytic solution. Ru.

  The dimensions of a general wound lithium ion secondary battery used in portable devices and the like are 18 mm in diameter and 65 mm in height, and are called 18650 type batteries. The battery capacity of the 18650 type battery is approximately 1.0 to 3.5 Ah. On the other hand, lithium secondary batteries used for electric vehicles and power storage applications are required to have not only high capacity but also high output, long life, and cost reduction. In order to achieve high capacity and high output, it is common to increase the size of the wound electrode group or increase the number of turns of the wound electrode group.

  In recent years, further high energy density formation of a lithium ion secondary battery is calculated | required, and the positive electrode active material with a large capacity density is proposed. As such an active material, lithium manganese manganese cobaltate, lithium nickel cobalt aluminum aluminate, etc. in which the proportion of nickel is increased have been proposed (see, for example, Patent Document 1).

JP 2008-235147 A

  However, when a positive electrode active material in which the proportion of nickel such as nickel manganese cobaltate is increased is used for a lithium ion secondary battery, when the battery is overcharged, the battery is charged until the thermal runaway occurs. The amount may be large. This is because the theoretical capacity of the positive electrode active material in which the proportion of nickel is increased is large. When the battery is overcharged, if the amount of charge before the battery reaches thermal runaway is large, the possibility of causing the battery to ignite or rupture increases, and the battery safety decreases.

  This invention is made in view of this point, The objective is to provide a lithium ion secondary battery with high safety | security, although it is high capacity | capacitance.

  The present invention is a lithium ion secondary battery having a positive electrode containing a lithium nickel-containing metal composite oxide and a lithium manganese-containing composite oxide, and a negative electrode, wherein the lithium nickel-containing metal composite oxide is a metal other than lithium. When the single-electrode positive electrode capacity of 3 V-4.3 V and the single-electrode positive capacity of 3 V-5.0 V containing 50 mol% or more of nickel and the counter electrode as Li are Q1 and Q2, respectively, the capacity ratio of both Provided is a lithium ion secondary battery in which Q1 / Q2 is 0.6 or more. According to the present invention, a lithium ion secondary battery with high capacity and high safety can be provided.

  In the lithium ion secondary battery of the present invention, the positive electrode active material preferably contains a lithium manganese-containing composite oxide in a mass ratio of 50% or more to the total amount of the positive electrode active material. In the lithium ion secondary battery of the present invention, by setting the content ratio of the lithium manganese-containing composite oxide to 50% by mass or more, the safety of the battery can be sufficiently ensured.

The present invention further provides a lithium ion secondary battery in which the lithium nickel-containing metal composite oxide is represented by the following formula (I).
Li _a Ni _b Co _c M _d O _{(2 + e)} (I)
(Wherein M is at least one element selected from the group consisting of Al, Mn, Mg and Ca, and a, b, c, d and e each represent 0.2 ≦ a ≦ 1.2, 0.5 ≦ b ≦ 0.9, 0.1 ≦ c ≦ 0.4, 0 ≦ d ≦ 0.3, and −0.2 ≦ e ≦ 0.2 And b + c + d = 1.)

The present invention further provides a lithium ion secondary battery in which the lithium manganese-containing composite oxide is represented by the following formula (II).
Li _{(1 + η)} Mn _(2-λ) M ' _λ O ₄ (II)
In the formula (II), M ′ is at least one element selected from the group consisting of Mg, Ca, Sr, Al, Ga, Zn and Cu, and 0 ≦ 、 ≦ 0.2, 0 ≦ λ ≦ 0.1)

  According to the present invention, it is possible to provide a lithium ion battery having high capacity but high safety.

FIG. 1 is a cross-sectional view of a lithium ion battery showing an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings and the like. The following description shows specific examples of the content of the present invention, and the present invention is not limited to these descriptions, and various modifications by those skilled in the art can be made within the scope of the technical idea disclosed herein. Changes and modifications are possible.

  FIG. 1 is a cross-sectional view showing an embodiment of a lithium ion battery. As shown in the figure, the cylindrical lithium ion battery 20 includes a positive electrode in which a positive electrode active material is coated on a strip-like positive electrode current collector, and a negative electrode in which a negative electrode active material is coated on a strip-like negative electrode current collector. An electrode group 6 is used in which a strip-shaped laminate formed by laminating through a strip-shaped separator is wound in the longitudinal direction. The electrode group 6 is accommodated in the battery case 5, and at the same time, the electrolytic solution is accommodated in the battery case 5. A positive electrode current collection tab is connected to the positive electrode terminal, a negative electrode current collection tab is connected to the negative electrode terminal, and a cleavage valve 10 is attached to the battery lid 4 for sealing the battery container 5.

  The battery case 5 is selected so as not to cause deterioration of the material due to corrosion by the electrolytic solution or alloying with lithium ions. It is selected from materials such as aluminum, stainless steel, nickel plated steel and the like. The battery case 5 is placed in an electrically neutral state.

  As the shaft core, any known core can be used as long as it can support the electrode group 6. Even if there is no axis, as long as the shape of the electrode group can be maintained, the axis may not be used.

  The electrode group 6 can be applied as long as it is a wound shape such as a flat shape other than the cylindrical shape shown in FIG. The shape of the battery case 5 may be a cylindrical shape, a flat oval shape, a flat oval shape, or the like according to the shape of the electrode group 6.

<Positive electrode>
The positive electrode is composed of a positive electrode active material, a conductive agent, a binder and a current collector foil.
The present invention includes, as a positive electrode active material, a lithium nickel-containing metal complex oxide having lithium and nickel and having a proportion of nickel in metal excluding lithium of 50 mol% or more, and a lithium manganese-containing complex oxide It is characterized by including, and by using both complex oxides together, it is possible to provide a lithium ion secondary battery having high capacity and high safety.

The lithium-containing metal composite oxide containing lithium and nickel and having a ratio of nickel to metal excluding lithium of 50 mol% or more preferably contains a compound represented by the following formula (I).
Li _a Ni _b Co _c M _d O _{(2 + e)} (I)
(Wherein M is at least one element selected from the group consisting of Al, Mn, Mg and Ca, and a, b, c, d and e each represent 0.2 ≦ a ≦ 1.2, 0.5 ≦ b ≦ 0.9, 0.1 ≦ c ≦ 0.4, 0 ≦ d ≦ 0.3, and −0.2 ≦ e ≦ 0.2 And b + c + d = 1.)

  In the compound represented by the formula (I), the larger the proportion of Ni, the larger the capacity density of the positive electrode active material, and the smaller the proportion of Ni, the higher the thermodynamic stability of the positive electrode active material. is there. The ratio (b) of Ni is preferably 0.5 ≦ b ≦ 0.9 from the viewpoint of increasing the capacity of the battery and improving safety, and more preferably 0.55 ≦ b ≦ 0.85. Preferably, 0.6 ≦ b ≦ 0.8 is more preferable.

The lithium manganese-containing composite oxide contained in the present invention preferably contains a compound represented by the following formula (II).
Li _{(1 + η)} Mn _(2-λ) M ' _λ O ₄ (II)
(M ′ is at least one element selected from the group consisting of Mg, Ca, Sr, Al, Ga, Zn and Cu, and 0 ≦ η ≦ 0.2, 0 ≦ λ ≦ 0.1 Is)

The lithium ion battery of the present disclosure can use other than the positive electrode active material described above in combination. Other commonly used positive electrode active materials include LiCoO ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O _{2 and the} like.

  The lithium manganese-containing composite oxide represented by the above (II) is preferably contained in a mass ratio of 50% or more based on the total mass of the positive electrode active material used in the lithium ion secondary battery of the present invention. Thus, even in the case of using a lithium-nickel-containing metal composite oxide having a high lithium content to increase the capacity density of the positive electrode active material, safety can be reliably ensured.

  The particle size of the positive electrode active material is usually defined to be equal to or less than the thickness of the mixture layer formed on the positive electrode current collector foil by the positive electrode active material, the conductive agent and the binder. When the powder of the positive electrode active material contains coarse particles having a size equal to or larger than the mixture layer thickness, the coarse particles are preliminarily removed by sieve classification, air flow classification or the like, and sorted into particles smaller than the mixture layer thickness. Is preferred.

  In addition, since the positive electrode active material is generally oxide-based, it has high electrical resistance. Therefore, in order to compensate for the electrical conductivity, a conductive agent made of carbon powder is added to the positive electrode active material. Since both the positive electrode active material and the conductive agent are usually powders, the powders can be mixed with a binder to bond the powders together and simultaneously adhere to the coated positive electrode current collector.

As the positive electrode current collector, those commonly used in the field of energy devices can be used. Specifically, a sheet containing stainless steel, aluminum, titanium or the like, a foil or the like can be mentioned. Among these, a sheet or foil of aluminum is preferable from the electrochemical viewpoint and cost.
The average thickness of the sheet and the foil is not particularly limited, and is preferably, for example, 1 to 500 μm, more preferably 2 to 100 μm, and still more preferably 5 to 50 μm. In the present invention, any current collector foil can be used without being limited to the material, shape, manufacturing method and the like.

<Negative electrode>
The negative electrode is composed of a negative electrode active material, a binder and a current collector foil. A conductive aid is used as needed.
As the negative electrode active material, those commonly used in the field of energy devices can be used. Specifically, for example, metal lithium, lithium alloy, metal compound, carbon material, metal complex, and organic polymer compound can be mentioned. One type of negative electrode active material may be used alone, or two or more types may be used in combination.
Among these, as the negative electrode active material, a carbon material is preferable. Examples of carbon materials include natural graphite (scaly graphite etc.), graphite such as artificial graphite, acetylene black, ketjen black, channel black, furnace black, lamp black, carbon black such as thermal black, amorphous carbon, carbon fiber Etc.
The average particle diameter of the carbon material is preferably 0.1 to 60 μm, more preferably 0.3 to 45 μm, and still more preferably 0.5 to 30 μm.

  The binder is not particularly limited, but it is preferable to use, for example, polyvinylidene fluoride and a binder whose main skeleton is polyacrylonitrile. The heat treatment temperature in heat treatment to be described later can be lowered, and this is a preferable selection because the flexibility of the obtained electrode is excellent.

  As the negative electrode current collector used for the negative electrode, those commonly used in the field of energy devices can be used. Specifically, a sheet containing stainless steel, nickel, copper or the like, a foil, etc. may be mentioned. The average thickness of the sheet and the foil is not particularly limited, and is preferably, for example, 1 to 500 μm, more preferably 2 to 100 μm, and still more preferably 5 to 50 μm. In addition, porous materials, for example, porous metals containing copper (foam metal) can also be used.

<Electrolyte solution>
The electrolytic solution is composed of an electrolyte, a non-aqueous solvent and an additive. Representative examples of the electrolyte include LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (SO ₂ F) ₂ and LiN (C ₂ F ₅ SO ₂ ) ₂ , and LiPF ₆ , LiBF ₄ or LiN (CF ₃ SO ₂ ) ₂ , LiN (SO ₂ F) ₂ are preferred. One of these electrolytes may be used alone, or two or more of these electrolytes may be used in any combination and ratio.

  Examples of the non-aqueous solvent include linear and cyclic carbonates, linear and cyclic carboxylic acid esters, linear and cyclic ethers, phosphorus-containing organic solvents, sulfur-containing organic solvents, and boron-containing organic solvents. The non-aqueous electrolyte used in the lithium ion battery of the present invention may contain various additives as long as the effects of the present invention are not significantly impaired.

  As the above additives, conventionally known ones can be optionally used. The additives may be used alone or in any combination of two or more in any proportion. Examples of the additive include an overcharge inhibitor, an auxiliary agent for improving capacity retention characteristics after high-temperature storage and cycle characteristics, and a flame retardant which imparts flame retardancy to the electrolytic solution.

The electrolyte solution is not particularly limited as long as it can exhibit a function as a lithium ion secondary battery which is an energy device, for example. As the electrolytic solution, electrolytic solutions other than water, for example, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, carbonates such as methyl ethyl carbonate, lactones such as γ-butyrolactone, trimethoxymethane, 1, Organics such as ethers such as 2-dimethoxyethane, diethylether, 2-ethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, sulfoxides such as dimethyl sulfoxide, and sultones such as 1,3-propane sultone, 4-butane sultone, and naphtha sultone in a _{solvent, LiClO 4, LiBF 4, LiI} , LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiAlCl 4, LiCl, LiBr , Solutions in which electrolytes such as LiB (C ₂ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, Li [(CO ₂ ) ₂ ] ₂ B, etc. are dissolved Can be mentioned. Among these, an electrolyte in which LiPF ₆ is dissolved in carbonates is preferable.
The electrolytic solution is prepared, for example, by using an organic solvent and an electrolyte singly or in combination of two or more.

  The separator is not particularly limited as long as it has ion permeability while electrically insulating between the positive electrode and the negative electrode, and has resistance to oxidation on the positive electrode side and reducibility on the negative electrode side. Resin, an inorganic substance, etc. are used as a material (material) of the separator which satisfy | fills such a characteristic.

  As said resin, an olefin type polymer, a fluorine-type polymer, a cellulose type polymer, a polyimide, nylon etc. are used. Specifically, it is preferable to select from materials which are stable to the electrolytic solution and excellent in liquid retention, and it is preferable to use a porous sheet, non-woven fabric, etc., which are made of polyolefin such as polyethylene and polypropylene.

  As the inorganic substance, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, sulfates such as barium sulfate and calcium sulfate, glass and the like are used. For example, it is possible to use, as a separator, one in which the above-mentioned inorganic substance in the form of fibers or particles is attached to a thin film-shaped substrate such as a nonwoven fabric, a woven fabric or a microporous film.

  As a thin film-shaped substrate, one having an average pore diameter of 0.01 to 1 μm and an average thickness of 5 to 50 μm is suitably used. Also, for example, a composite porous layer using a binder resin and the above-mentioned inorganic material in the form of fibers or particles can be used as a separator. Furthermore, this composite porous layer may be formed on the surface of the positive electrode or the negative electrode, and may be used as a separator. Alternatively, the composite porous layer may be formed on the surface of another separator to be a multilayer separator. For example, an alumina particle having a 90% particle diameter (D90) of less than 1 μm may be formed on the surface of the positive electrode with a composite porous layer formed by binding a fluorine resin as a binder resin, as a separator.

  Hereinafter, the present embodiment will be described in more detail based on examples. The present invention is not limited by the following examples.

Example 1
[Production of positive electrode]
The preparation of the positive electrode was performed as follows. Lithium-manganese-containing composite oxide (LiMn ₂ O ₄ ) and lithium-nickel-containing metal composite oxide (LiNi _0.5 Co _0.2 Mn _0.3 O) having a nickel-cobalt-manganese ratio described in Table 1 below ₂ ) to a positive electrode active material blended with a mass ratio of 7: 3 by sequentially adding and mixing acetylene black (average particle diameter: 20 μm) as a conductive material and polyvinylidene fluoride as a binder A mixture of materials was obtained. The mass ratio in the positive electrode material was 90: 5: 5 positive electrode active material: conductive material: binder. Further, N-methyl-2-pyrrolidone (NMP), which is a dispersion solvent, was added to the above mixture and kneaded to form a slurry. A predetermined amount of the slurry was applied substantially uniformly and uniformly on both sides of a 20 μm thick aluminum foil as a current collector for a positive electrode. The aluminum foil had a rectangular shape with a short side (width) of 430 mm, and left an uncoated portion with a width of 50 mm along the long side on one side. Thereafter, it was subjected to a drying treatment, and compacted to a predetermined density by a press. Subsequently, the positive electrode plate of width 353 mm was obtained by cutting | judgement. Under the present circumstances, the notch was put in the said non-application part, and the notch remaining part was used as the lead piece. The width of the lead pieces was 10 mm, and the distance between adjacent lead pieces was 20 mm.

[Fabrication of negative electrode]
The preparation of the negative electrode was performed as follows. Graphitizable carbon was used as the negative electrode active material. Polyvinylidene fluoride was added to the graphitizable carbon as a binder. The mass ratio of these was: active material: binder = 92: 8. A dispersion solvent, N-methyl-2-pyrrolidone (NMP), was added thereto and kneaded to form a slurry. A predetermined amount of the slurry was applied substantially uniformly and uniformly on both sides of a 10 μm-thick rolled copper foil which is a current collector for a negative electrode. The rolled copper foil had a rectangular shape with a short side (width) of 430 mm, and left an uncoated portion with a width of 50 mm along the long side on one side. Thereafter, it was subjected to a drying treatment, and compacted to a predetermined density by a press. The negative electrode composite density was 1.1 g / cm ³ . Next, the resultant was cut to obtain a negative electrode plate having a width of 358 mm. Under the present circumstances, the notch was put in the said non-application part, and the notch remaining part was used as the lead piece. The width of the lead pieces was 10 mm, and the distance between adjacent lead pieces was 20 mm.

[Production of battery]
FIG. 1 shows a cross-sectional view of a lithium ion battery according to this example. The positive electrode and the negative electrode are wound with a 30 μm-thick polyethylene separator interposed therebetween so that they do not come into direct contact with each other. At this time, lead pieces of the positive electrode and lead pieces of the negative electrode are respectively positioned on opposite end surfaces of the winding group. Moreover, the length of the positive electrode, the negative electrode, and the separator was adjusted, and the winding group diameter was 65 ± 0.1 mm.

  Next, as shown in FIG. 1, the lead pieces 9 drawn from the positive electrode are deformed, and all of them are gathered near and in contact with the bottom of the flange portion 7 on the positive electrode side. The flange portion 7 on the positive electrode side is integrally formed so as to project from the periphery of the pole post (positive electrode external terminal 1) substantially on the extension of the axis of the winding group 6, and has a bottom portion and a side portion. Thereafter, the lead piece 9 is connected and fixed to the bottom of the collar 7 by ultrasonic welding. Similarly, the lead piece 9 'drawn out from the negative electrode plate and the bottom of the negative electrode side flange portion 7 are connected and fixed. The flange portion 7 on the negative electrode side is integrally formed so as to project from the periphery of the pole post (negative electrode external terminal 1 ') substantially on the extension of the axis of the winding group 6, and has a bottom portion and a side portion.

  Thereafter, using an adhesive tape, the side of the ridge 7 on the positive electrode external terminal 1 side and the side of the ridge 7 of the negative electrode external terminal 1 ′ were covered to form an insulation coating 8. Similarly, the insulating coating 8 was formed on the outer periphery of the winding group 6. For example, the pressure-sensitive adhesive tape extends from the side of the ridge 7 on the positive electrode external terminal 1 side to the outer peripheral surface of the winding group 6, and further, from the outer peripheral surface of the winding group 6 to the negative electrode external terminal 1 ' The insulation coating 8 is formed by winding several times over the side of 7. As the insulation coating (pressure-sensitive adhesive tape) 8, a pressure-sensitive adhesive tape in which a substrate is made of polyimide and a pressure-sensitive adhesive material made of hexamethacrylate is applied on one side thereof is used. The thickness (number of turns of adhesive tape) of the insulation coating 8 is adjusted so that the largest diameter portion of the winding group 6 is slightly smaller than the inner diameter of the stainless steel battery container 5. Inserted into The battery container 5 had an outer diameter of 67 mm and an inner diameter of 66 mm.

  Then, as shown in FIG. 1, the ceramic washer 3 'is fitted into the pole post whose tip constitutes the positive electrode external terminal 1 and the pole post whose tip constitutes the negative electrode external terminal 1'. The ceramic washer 3 ′ is made of alumina, and the thickness of the portion in contact with the back surface of the battery lid 4 is 2 mm, the inner diameter is 16 mm, and the outer diameter is 25 mm. Next, with the ceramic washer 3 mounted on the battery cover 4, the positive electrode external terminal 1 is passed through the ceramic washer 3, and the other ceramic washer 3 is mounted on the other battery cover 4. Pass 1 'through the other ceramic washer 3. The ceramic washer 3 is made of alumina, and is a flat plate having a thickness of 2 mm, an inner diameter of 16 mm, and an outer diameter of 28 mm.

Thereafter, the peripheral end face of the battery cover 4 is fitted into the opening of the battery case 5, and the entire area of both contact parts is laser welded. At this time, the positive electrode external terminal 1 and the negative electrode external terminal 1 'respectively protrude through the holes (holes) at the centers of the battery lids 4, 4' and protrude to the outside of the battery lids 4, 4 '. The battery cover 4 is provided with a cleavage valve 10 which is cleaved in response to the increase in internal pressure of the battery. The cleavage pressure of the cleavage valve 10 was 13 to 18 kg / cm ² .

  Next, as shown in FIG. 1, the metal washers 11 are fitted into the positive electrode external terminal 1 and the negative electrode external terminal 1 'respectively. Thereby, the metal washer 11 is disposed on the ceramic washer 3. The metal washer 11 is made of a material smoother than the bottom surface of the nut 2.

  Next, the metal nut 2 is screwed on the positive electrode external terminal 1 and the negative electrode external terminal 1 'respectively, and the battery lid 4, 4' is engaged with the collar 7 via the ceramic washer 3, metal washer 11 and ceramic washer 3 '. Secure by tightening between the nut 2. The tightening torque value at this time was 70 kgf · cm. The metal washer 11 did not rotate until the tightening operation was completed. In this state, the power generation element inside the battery case 5 is shielded from the outside air by the compression of the O-ring 12 made of rubber (EPDM) interposed between the back surface of the battery cover 4 or 4 'and the ridge portion 7. .

  Thereafter, an electrolytic solution is injected into the battery container 5 by a predetermined amount from the liquid injection port 13 provided in the battery lid 4 ′, and then the liquid injection port 13 is sealed to manufacture the cylindrical lithium ion battery 20.

As an electrolytic solution, 1.2 mol / L of lithium hexafluorophosphate (LiPF ₆ ) is dissolved in a mixed solution of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate mixed at a volume ratio of 2: 3: 2, respectively. Used. The cylindrical lithium ion battery 20 manufactured in the present embodiment is not provided with a current interrupting mechanism that operates to interrupt the current according to the increase in the internal pressure of the battery container 5.

  After producing the cylindrical lithium ion battery 20, the following initialization charge / discharge cycle, aging treatment and high temperature storage were performed to complete the manufacturing process.

[Initialization charge and discharge cycle]
The initialization charge-discharge cycle was performed in a temperature environment of 25 ° C. seven days after the completion of injection. The current value was 0.5 CA for both charging and discharging. The charge was constant current constant voltage (CCCV) charge with 4.2 V as the upper limit voltage, and the termination condition was 3 hours. The discharge was CC discharge, and the termination condition was 2.7V. Moreover, the pause for 30 minutes was put between charge and discharge. This was carried out for three cycles, and the discharge capacity at the third cycle was taken as the initial capacity.

[Aging process]
After the initialization charge-discharge cycle, charging was performed for 3 hours by constant current constant voltage (CCCV) charging with an upper limit voltage of 3.95V. Thereafter, the lithium ion battery was allowed to stand in a temperature environment of 25 ° C. for 21 days. After 21 days, after charging by constant current constant voltage (CCCV) charging with an upper limit voltage of 4.2 V and a termination condition of 3 hours, discharge was performed by CC discharge with a termination condition of 2.7 V. Moreover, the pause for 30 minutes was put between charge and discharge. The discharge capacity at this time was taken as the capacity after aging.
In addition, the process until implementing an aging treatment was the same in all the produced lithium ion batteries, and the average value of the capacity | capacitance (discharge capacity) after the aging was 84 Ah.

[Overcharge test]
The cell after the completion of the manufacturing process was adjusted to 2.7 V, and then the overcharge test was performed under a temperature environment of 25 ± 5 ° C. The overcharge test was performed at a current value of 225 A until the cell was thermally runaway.

The results of Examples and Comparative Examples are as shown in Table 1 below. In Table 1, "Ni: Co: Mn ratio" is the ratio of nickel, cobalt and manganese of the lithium nickel-containing metal composite oxide used.
"Capacity 3 V-4.3 V" and "Capacity 3 V-5.0 V" are single-pole capacities of lithium nickel cobalt manganese oxide when the counter electrode is Li, and the upper limit voltage is 4.3 V to the lower limit voltage, respectively. It is a discharge capacity up to 3 V and a discharge capacity up to 5 V from the upper limit voltage 3 V. "Capacity ratio" is a ratio of "Capacity 3 V-4.3 V" in "Capacity 3 V-5.0 V", and was calculated from the following equation (1).

Capacity ratio = positive electrode capacity 3V-4.3V / positive electrode capacity 3V-5.0V (1)

In Table 1, “limit SOC” is the charge amount at the time of thermal runaway of the cell, and the upper limit voltage and the lower limit voltage at cell operation are 4.2 V and 2.7 V, respectively, and the charge is from 2.7 V to 4.2 V The time is assumed to be 100% of the amount of charge (SOC: State Of Charge). Also, the “limit phenomenon” is a phenomenon that occurred when the cell ran out of heat. "White smoke" indicates that the gas discharge valve has been activated and the gas has spouted, and "rupture" indicates that the portion other than the gas discharge valve has been cleaved.

(Example 2)
Example 6 was carried out in the same manner as Example 1, except that the lithium nickel-containing metal complex oxide was changed to (LiNi _0.6 Co _0.2 Mn _0.2 O ₂ ). The results are shown in Table 1.

(Example 3)
The same procedure as in Example 1 was carried out except that the lithium nickel-containing metal composite oxide was changed to (LiNi _0.8 Co _0.1 Mn _0.1 O ₂ ). The results are shown in Table 1.

(Comparative example 1)
The same procedure as in Example 1 was carried out except that the lithium nickel-containing metal complex oxide was changed to (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ). The results are shown in Table 1.

(Comparative example 2)
The same lithium nickel-containing metal composite oxide (LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ) as in Example 1 without using lithium manganese-containing composite oxide (LiMn ₂ O ₄ ) as the positive electrode active material The same procedure as in Example 1 was carried out except that the above was used alone. The results are shown in Table 1.

As shown in Table 1, the limit time SOC of Examples 1 to 3 can be smaller than Comparative Examples 1 and 2. That is, the charge amount of the battery to thermal runaway at the time of overcharge can be reduced, and the phenomenon appearing at the time of the limit at the time of thermal runaway of the battery is only white smoke, and the safety is improved. On the other hand, Comparative Example 1 has a high SOC at the time of limit, and therefore, when the battery causes thermal runaway, it causes not only white smoke but also burst, and there is a problem in terms of safety. In Comparative Example 2, despite using the same lithium nickel-containing metal composite oxide as in Example 1 as a positive electrode active material _{(LiNi 0.5 Co 0.2 Mn 0.3 O} 2), containing lithium manganese Since the limit oxide was increased because the composite oxide was not used in combination, the rupture occurred and there was a serious problem in safety.

  As can be seen from the comparison between Examples 1 to 3 and Comparative Examples 1 and 2, it is necessary to set the Q1 / Q2 capacity ratio, which is a factor determining the safety of the battery, to 0.6 or more. It can be seen from Table 1 that the safety during thermal runaway can be effectively improved under the conditions.

  As described above, the present invention includes, as a positive electrode active material, a lithium-nickel-containing metal composite oxide and a lithium-manganese-containing composite oxide in which 50% by mole or more of nickel is contained in metal excluding lithium. By setting the capacity ratio Q1 / Q2 of the 3V-4.3V single-pole positive electrode capacity Q1 to the 3V-5.0V single-pole positive electrode capacity Q2 to be 0.6 or more, safety can be achieved despite the high capacity. A high lithium ion secondary battery can be provided.

DESCRIPTION OF SYMBOLS 1 Positive electrode external terminal 1 'Negative electrode external terminal 2 Nut 3, 3' Ceramic washer 4, 4 'Battery cover 5 Battery container 6 winding group or electrode group 7 ridge part 8 insulation coating 9, 9' lead piece 10 cleavage valve 11 metal Washer 12 O-ring 13 Injection port 20 Cylindrical lithium ion battery

Claims (4)

A lithium ion secondary battery having a positive electrode containing a lithium nickel-containing metal composite oxide and a lithium manganese-containing composite oxide, and a negative electrode,
The lithium nickel-containing metal composite oxide contains 50 mol% or more of nickel in the metal excluding lithium,
A lithium having a capacity ratio Q1 / Q2 of 0.6 or more, where Q1 and Q2 are 3V-4.3V single-pole positive electrode capacity and 3V-5.0V single-pole positive electrode capacity with Li as counter electrode respectively Ion secondary battery.   The lithium ion secondary battery according to claim 1, wherein the positive electrode active material contains a lithium manganese-containing composite oxide in a mass ratio of 50% or more with respect to the total amount of the positive electrode active material. The lithium ion secondary battery according to claim 1, wherein the lithium nickel-containing metal composite oxide is represented by the following formula (I).
Li _a Ni _b Co _c M _d O _{(2 + e)} (I)
(Wherein M is at least one element selected from the group consisting of Al, Mn, Mg and Ca, and a, b, c, d and e each represent 0.2 ≦ a ≦ 1.2, 0.5 ≦ b ≦ 0.9, 0.1 ≦ c ≦ 0.4, 0 ≦ d ≦ 0.3, and −0.2 ≦ e ≦ 0.2 And b + c + d = 1.) The lithium ion secondary battery according to claim 1, wherein the lithium manganese-containing composite oxide is represented by the following formula (II).
Li _{(1 + η)} Mn _(2-λ) M ' _λ O ₄ (II)
In the formula (II), M ′ is at least one element selected from the group consisting of Mg, Ca, Sr, Al, Ga, Zn and Cu, and 0 ≦≦≦ 0.2, 0 ≦ λ ≦ 0.1)

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