JP5036174B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery containing a lithium manganese composite oxide as a positive electrode active material.

Devices that use batteries as a power source, such as portable electronic devices such as mobile phones, laptop computers, and digital cameras, have become smaller and lighter and have advanced functions. As a result, batteries for power supplies used in these devices are required to be small, light and have a large battery capacity per volume.
Lithium ion batteries using positive electrode active materials and negative electrode active materials doped and dedoped with lithium ions are secondary batteries that have a larger energy density per volume or mass than conventional nickel metal hydride batteries. It is used as a power source for various devices.

As a positive electrode active material, a lithium manganese composite oxide typified by lithium manganate (LiMn ₂ O ₄ ) has a feature that safety during overcharge is larger than that of a lithium cobalt composite oxide.
On the other hand, when lithium manganate is repeatedly charged and discharged, the crystal structure is remarkably broken, resulting in a decrease in capacity.

Therefore, a non-aqueous electrolyte using a lithium manganese composite oxide in which the lithium site of lithium manganate or the lithium atom of the manganese site or part of the manganese atom is replaced with another element to improve the stability of the crystal as the positive electrode active material Secondary batteries have been proposed (for example, Patent Document 1). Here, as a substance in which Mn of LiMn ₂ O ₄ is replaced with Co, LiMn ₂ O ₄ and LiCoO ₂ solid solution, or Mn of LiMn ₂ O ₄ is replaced with V, Cr, Fe, Co, Ni, or Co. It has been proposed to use complex oxides.

  However, even when these composite oxides are used, when charging / discharging at a high temperature or when stored at a high temperature, the cycle life becomes insufficient, or a battery having excellent storage characteristics is obtained. Couldn't get.

In addition, by using a mixed cathode of lithium nickelate and spinel type lithium manganate, in which part of the nickel nickelate is replaced with cobalt and aluminum, a lithium-ion secondary battery with high capacity and excellent cycle characteristics can be obtained. The technique to provide is proposed (for example, patent document 2). However, the improvement of characteristics under high temperature storage was insufficient.

Further, a part of the manganese of the lithium manganate is an aluminum-substituted lithium manganate in which lithium and aluminum are substituted, and a cobalt-substituted lithium nickelate in which a part of the nickel in the nickel nickelate is substituted with cobalt, or cobalt A non-aqueous electrolyte secondary battery including cobalt-aluminum-substituted lithium nickelate substituted with aluminum has been proposed (for example, Patent Document 3).
However, complex oxides substituted with aluminum are effective in improving cycle characteristics when the depth of discharge is deep, but electric vehicles and stationary power sources that require long-term characteristics to be maintained over a wide range from low to high temperatures. However, it has not yet fully satisfied the characteristics required for large capacity batteries.
Japanese Patent Publication No. 7-34368 JP-A-11-54120 JP 2004-6094 A

An object of the present invention is to improve storage characteristics at high temperatures in a non-aqueous electrolyte secondary battery using a lithium manganese composite oxide as a positive electrode active material. It is an object to provide a liquid battery.

Object of the present invention is a nonaqueous electrolyte secondary battery, as a positive electrode active material, and a lithium-manganese composite oxide obtained by replacing a part of manganese with _{cobalt, Li 1 + x Co y Mn} 2-xy O 4 (Wherein x is 0.05 <x <0.07, y is 0.01 <y <0.04), and a nickel nickel composite in which a part of nickel is substituted with cobalt or cobalt and aluminum as the _{oxide, LiNi 1-x Co x O} 2 ( wherein, x is 0.1 <x <0.3) or _{LiNi 1-x Co x Al y} O 2 ( wherein, x is 0.1 <x <0.3, 0.02 <y <0.1), a lithium manganese composite oxide in which a part of the manganese is replaced with cobalt, and a part of the nickel is replaced with cobalt or cobalt and aluminum The weight ratio of the lithium-nickel composite oxide was 97 3 to 55: it can be solved by a non-aqueous electrolyte secondary battery which is 45.
In addition, the non-aqueous electrolyte secondary battery according to the present invention, wherein the negative electrode is a carbonaceous material that is doped or dedoped with lithium.

The sealed battery of the present invention includes, as a positive electrode active material, a lithium manganese composite oxide in which a part of manganese is replaced with cobalt, and a lithium nickel composite oxide in which a part of nickel is replaced with cobalt or cobalt and aluminum. Is used as the positive electrode active material, so that the high-temperature storage characteristics of the non-aqueous electrolyte secondary battery can be improved.

The positive electrode of the non-aqueous electrolyte secondary battery of the present invention has, as a positive electrode active material, a lithium manganese composite oxide in which a part of manganese is substituted with cobalt, and a part of nickel is substituted with cobalt or cobalt and aluminum. Li _{1 + x} Co _y Mn ₂₋ which is a lithium manganese cobalt composite oxide in which a part of manganese is replaced with lithium and cobalt, in particular, instead of lithium manganate. _xy O ₄ (wherein x is 0.05 <x <0.07, y is 0.01 <y <0.04), and a part of nickel of the lithium nickel composite oxide or lithium nickel composite oxide Cobalt aluminum substituted nickel substituted with aluminum, that is, lithium nickel composite oxide substituted with cobalt is LiNi _1-x Co _x O ₂ (wherein , X is, 0.1 <x <0.3), cobalt and lithium-nickel composite oxide obtained by substituting aluminum LiNi in _{1-x Co x Al y O} 2 ( wherein, x is 0.1 <x < It has been found that by using 0.02 <y <0.1 for 0.3 and y, an excellent effect can be obtained in terms of charge / discharge characteristics after high-temperature cycle and high-temperature storage.

The lithium manganese cobalt composite oxide in which a part of manganese of lithium manganate used as the positive electrode active material of the present invention is substituted with lithium and cobalt is preferably Li _{1 + x} Co _y Mn _2-xy O ₄ (wherein , X is 0.05 <x <0.07, y is 0.01 <y <0.04), and x representing the amount of substituted lithium is smaller than 0.05, or cobalt When y representing the amount of is less than 0.01, the effect of improving the high-temperature storage characteristics is small.

On the other hand, when x is larger than 0.07, the average valence of manganese is increased by substitution with lithium, and the capacity is significantly reduced, which is not practical.
Further, when y representing the amount of cobalt is larger than 0.04, even if x representing the amount of substituted lithium satisfies the relationship of 0.05 <x <0.07, it depends on the cobalt atom. Although the capacity drop is small, when charging / discharging, a flat portion called plateau appears around 3.3 V with respect to the lithium electrode in the charging / discharging curve. This plateau is due to oxygen deficiency and causes significant deterioration of charge / discharge cycle characteristics and storage characteristics.
Moreover, since a heterogeneous phase appears when the amount of cobalt increases, the amount of cobalt is preferably smaller than 0.04.

  A lithium manganese cobalt composite oxide in which manganese is replaced with lithium and cobalt can be produced by firing each material of a lithium source, a manganese source, and a cobalt source in an oxygen-containing atmosphere. Specifically, examples of the lithium source include lithium carbonate, lithium hydroxide, and lithium oxide. Examples of the manganese source include manganese oxides such as manganese dioxide, manganese carbonate, and the like. As the cobalt source, cobalt oxides such as tricobalt tetroxide, carbonates, oxides, and the like can be used.

Among these, lithium carbonate, manganese dioxide, and tricobalt tetroxide are preferable, and it is preferable to use fine particles in order to improve their reactivity, and lithium carbonate having an average particle diameter of 3 μm or less. It is preferable to use it. Further, it is preferable to use tricobalt tetroxide having an average particle diameter of 2 μm or less.
Further, manganese dioxide having a particle diameter of 5 to 20 μm is preferable from the viewpoints of ensuring reaction uniformity, ease of slurry production, safety, and the like.

The raw materials as described above are weighed and mixed so that the prepared lithium manganese cobalt composite oxide has a predetermined composition ratio. At this time, it is preferable that manganese and cobalt are mixed and fired in an oxygen-containing atmosphere to prepare a manganese-cobalt composite oxide, and then mixed with a lithium raw material and fired in a containing atmosphere.
The raw material is pulverized to a predetermined size and then uniformly mixed using a ball mill, jet mill, pin mill, etc., and then in the temperature range of 700 ° C. to 850 ° C. in the atmosphere, in oxygen, etc. Can be fired in an oxygen-containing atmosphere.

When the lithium nickel composite oxide used in combination with the lithium manganese cobalt composite oxide is cobalt-substituted lithium nickelate, the composition formula LiNi _1-x Co _x O ₂ (0.1 <x <0.3) The thing represented by these is preferable. When the amount of Co substitution x in the cobalt-substituted lithium nickelate is less than 0.1, the charge / discharge curve has many flat parts called plateaus that show phase transitions during charging and discharging. Cycle characteristics are significantly degraded. In addition, ensuring safety in mechanical destructive tests such as nail penetration tests and crush tests at 4.2 V to 4.3 V, which is the normal upper limit voltage of lithium ion secondary batteries using graphite or amorphous carbon as a negative electrode Becomes difficult. On the other hand, when x is larger than 0.3, the charge / discharge capacity decreases.

Cobalt-substituted lithium nickelate can be synthesized by firing in an oxygen-containing atmosphere using oxides, salts, hydroxides, and the like of cobalt, nickel, and lithium as raw materials.
Specifically, lithium carbonate, lithium hydroxide, nickel or cobalt hydroxide, oxide, carbonate, or nickel-cobalt composite hydroxide prepared in a predetermined composition of nickel and cobalt, composite carbonate, A composite hydroxide or the like can be used.

When the lithium nickel composite oxide uses cobalt-aluminum-substituted lithium nickelate in which a part of nickel is replaced with aluminum in addition to cobalt, the composition formula LiNi _1-xy Co _x Al _y O ₂ (0 0.1 <x <0.3, 0.02 <y <0.1) is preferred, and cobalt-aluminum-substituted lithium nickelate.
When this aluminum substitution amount increases, the initial charge / discharge efficiency is deteriorated, and therefore y is preferably smaller than 0.1. On the other hand, if the substitution amount is too small, the effect of improving the thermal stability cannot be seen, so the aluminum needs to be more than 0.02.

  Cobalt / aluminum-substituted lithium nickelate can be synthesized by firing in an oxygen-containing atmosphere using oxides, salts, hydroxides, and the like of cobalt, aluminum, nickel, and lithium as raw materials. Among them, it is preferable to use an oxide, carbonate, or hydroxide that does not generate a gas that needs to be treated during firing, and a composite oxide such as cobalt-substituted lithium nickelate may be used as a raw material. .

  In the present invention, lithium cobalt manganese composite oxide in which a part of manganese in lithium manganese composite oxide is replaced with cobalt, and substituted lithium nickel composite oxide in which a part of nickel in lithium nickel composite oxide is replaced with cobalt or cobalt and aluminum. It is preferable that the compounding ratio with the product is lithium cobalt manganese composite oxide: substituted lithium nickel composite oxide = 97: 3 to 55:45 by weight ratio in the composite oxide.

By using the positive electrode active material mixed at such a blending ratio, there is little deterioration in characteristics such as capacity reduction after high-temperature storage, and a highly reliable lithium secondary battery is obtained.
When the compounding ratio of the lithium cobalt manganese composite oxide in the composite oxide is greater than 97% by mass, the amount of manganese eluted from the lithium cobalt manganese composite oxide into the electrolyte solution increases, and the cycle characteristics deteriorate. Capacity storage characteristics are degraded.
Similarly, when the blending ratio of the lithium cobalt manganese composite oxide is less than 55% by mass, the safety is lowered and smoke may be generated even in the mechanical destructive test.
Mixing ratio, 70: 30 to 60: and more preferably a 4 0.

In the following examples, the non-aqueous electrolyte secondary battery of the present invention used metallic lithium as the negative electrode active material in order to clearly evaluate the characteristics of the composite oxide of the present invention as the positive electrode active material. A lithium ion secondary battery can be obtained by using a carbonaceous material such as graphite that is doped and dedoped with lithium ions and pyrolytic carbon.
Examples of the present invention will be described below to explain the present invention.

(Production of sample battery)
A positive electrode active material having the composition shown in Table 1 and carbon black were dry-mixed as a conductivity-imparting agent, and uniformly dispersed in N-methyl-2-pyrrolidone (NMP) in which polyvinylidene fluoride was dissolved to prepare a slurry.
The slurry was applied on an aluminum metal foil having a thickness of 20 μm, and then the solvent was evaporated to prepare a positive electrode sheet. The solid content ratio in the positive electrode was positive electrode active material: conductivity imparting agent: polyvinylidene fluoride = 85: 10: 5 by weight.

The obtained positive electrode sheet was punched out to a diameter of 12 mm and used as a positive electrode. Metal lithium with a diameter of 14 mm is used for the negative electrode, and the positive electrode and the negative electrode are laminated via a polypropylene porous membrane separator with a film thickness of 25 μm, and stored in a 2320 type coin cell container, and 1 mol / L LiPF ₆ is supported as a salt. A test battery was prepared by injecting an electrolyte solution composed of a mixed solvent of ethylene carbonate (EC): diethyl carbonate (DEC) = 30: 70 (volume ratio).

(Test method for capacity storage characteristics)
The battery was charged to 4.3 V at a current density of 0.1 mA / cm ² on the positive electrode side, then discharged to 3.0 V at the same current value, and the discharge capacity was measured.
Again, batteries charged to 4.3 V at a current density of 0.1 mA / cm ² on the positive electrode side were prepared and stored in a constant temperature bath at 60 ° C. for 2 weeks. After storage, the battery was discharged once to 3.0 V, and similarly, the discharge capacity up to 3.0 V after recharging to 4.3 V at 0.1 mA / cm ² was measured.

The ratio of the discharge capacity after storage to the initial discharge capacity of the battery after storage is shown in Table 1 as the capacity maintenance rate, that is, [discharge capacity after storage] / [initial discharge capacity].
Sample 1 or 2 using a composite oxide as a positive electrode active material in which manganese sites are replaced with lithium or cobalt, and a lithium manganese cobalt composite oxide in which manganese is replaced with both lithium and cobalt as a positive electrode Sample 3 as an active material was shown to have improved capacity retention after high temperature storage.
Further, in the sample 4 in which 20% by mass of the lithium nickel cobalt composite oxide which is LiNi _0.8 Co _0.2 O _{2 in} which a part of nickel of the lithium nickel composite oxide is substituted with cobalt is mixed in the positive electrode active material of the sample 1 As compared with Sample 1, an effect of improving the storage characteristics was observed.

Further, as compared with Sample 3 using lithium manganese cobalt composite oxide as the positive electrode active material, lithium nickel cobalt composite oxide of LiNi _0.8 Co _0.2 O _{2 in} which a part of nickel of lithium nickel composite oxide is replaced with cobalt. In sample 5 containing 20% by mass, the capacity retention rate was improved as compared with sample 3.
Furthermore, in the battery of sample 6 in which the blending ratio of the lithium nickel cobalt composite oxide of sample 5 was increased to 40% by mass, the capacity retention rate was further improved as compared with sample 5.
Further, in the battery of Sample 7 in which the lithium nickel cobalt composite oxide was LiNi _0.8 Co _0.15 Al _0.05 O ₂ , the capacity retention rate was improved as compared with the battery of Sample 5.

Table 1
Li _{1 + x} Co _y Mn _2-xy O ₄ LiNi _1-xy Co _x Al _y O ₂ Mixing capacity Capacity retention
xy xy (mass%) (%)
Sample 1 0.06---97.3
Sample 2-0.03--97.7
Sample 3 0.06 0.03--98.2
Sample 4 0.06-0.2 0 20 97.8
Sample 5 0.06 0.03 0.2 0 20 99.1
Sample 51 0.06 0.03 0.2 0 50 97.8
Sample 52 0.06 0.03 0.2 0 2 97.9
Sample 52 0.08 0.03 0.2 0 20 97.9
Sample 53 0.08 0.05 0.2 0 20 97.8
Sample 54 0.06 0.03 0.4 0 20 97.8
Sample 55 0.06 0.03 0.05 0 20 97.9
Sample 6 0.06 0.03 0.2 0 40 99.4
Sample 7 0.06 0.03 0.15 0.05 20 99.6
Sample 71 0.06 0.03 0.15 0.05 50 98.1
Sample 72 0.06 0.03 0.15 0.05 2 98.0
Sample 73 0.08 0.05 0.15 0.05 20 98.0
Sample 74 0.06 0.03 0.05 0.05 20 97.9
Sample 75 0.06 0.03 0.15 0.15 20 97.8

Non-aqueous electrolyte secondary battery of the present invention, as the positive electrode active material, a part of manganese as a lithium-manganese composite oxide was replaced with _{cobalt, Li 1 + x Co y Mn} 2-xy O 4 ( wherein , X is 0.05 <x <0.07, y is 0.01 <y <0.04), and a nickel-nickel composite oxide in which a part of nickel is substituted with cobalt or cobalt and aluminum _{, LiNi 1-x Co x O} 2 ( wherein, x is 0.1 <x <0.3) or _{LiNi 1-x Co x Al y} O 2 ( wherein, x is 0.1 <x <0. 3, 0.02 <y <0.1), a lithium-manganese composite oxide in which a part of the manganese is replaced by cobalt, and a lithium / a lithium in which a part of the nickel is replaced by cobalt or cobalt and aluminum The weight ratio of both nickel composite oxides is 97: 3-55: 4 Having a, it is possible to provide a non-aqueous electrolyte secondary battery with improved high-temperature storage characteristics.

Claims (2)

In the nonaqueous electrolyte secondary battery, as a cathode active material, a part of manganese as a lithium-manganese composite oxide was replaced with cobalt, in _{Li 1 + x Co y Mn 2} -xy O 4 ( wherein, x is , 0.05 <x <0.07, y is 0.01 <y <0.04) , and LiNi ₁ is a lithium nickel composite oxide in which a part of nickel is substituted with cobalt or cobalt and aluminum. _-x Co _x O ₂ (wherein, x is 0.1 <x <0.3) or _{LiNi 1-x Co x Al y} O 2 ( wherein, x is 0.1 <x <0.3, 0 0.02 <y <0.1), a lithium manganese composite oxide in which a part of the manganese is replaced by cobalt, and a lithium / nickel composite oxide in which a part of the nickel is replaced by cobalt or cobalt and aluminum The weight ratio between the two is 97: 3-55: 45 Non-aqueous electrolyte secondary battery, characterized in that there. The nonaqueous electrolyte secondary battery according to claim 1, wherein a carbonaceous material doped with lithium and dedoped is used as a negative electrode.