JP2017162614A - Manganese oxide mixture, mixed positive electrode active material, and lithium secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new manganese oxide mixture capable of achieving both high energy density and low cost, a mixed positive electrode active material, and a high energy density lithium secondary battery using the same. A lithium-containing manganese composition represented by the general formula: Li(4/3)-(4X/5)Mn2/3O2-(2X/5) (where 0<X<1 is satisfied), A manganese oxide mixture containing a positive electrode material, containing a lithium-containing manganese composition represented by the general formula [Li2MnO3]1-E.[Li4Mn5O12]E (where 0<E<1 is satisfied) and a positive electrode material. A lithium secondary battery comprising a manganese oxide mixture, a mixed positive electrode active material containing the manganese oxide mixture, and a positive electrode containing the mixed positive electrode active material. [Selection diagram] None

Description

  The present invention relates to a manganese oxide mixture, a mixed positive electrode active material, and a lithium secondary battery using the same.

  Lithium secondary batteries have been widely used as storage batteries for portable terminals because they have higher energy density than other storage batteries. Recently, application to a large-sized application requiring a large capacity such as a stationary one and an in-vehicle one has been promoted.

  In applications that require large capacity, there is a strong demand for higher energy density, and the demand for cost reduction is particularly severe.

  As a positive electrode material of a lithium secondary battery currently being developed with the aim of increasing energy density, oxide materials containing a large amount of metal elements such as cobalt (Co) and nickel (Ni) are mainly studied. It is extremely difficult to reduce the cost of the positive electrode material containing a large amount of these rare elements. At present, there is no practical material that achieves both high energy density and low cost.

As an effort to realize a positive electrode material that achieves both high energy density and low cost, a mixed positive electrode active material of an oxide material containing a large amount of Co and Ni and a spinel type lithium manganate oxide material (LiMn ₂ O ₄ ) has been proposed, Some have been put to practical use. The reason why the manganese (Mn) -based material is selected is based on the fact that it is an element that has a large reserve and is inexpensive and is safer and less burdened on the environment than Co and Ni.

In Patent Document 1, lithium cobaltate (LiCoO ₂ ), in Patent Document 2, nickel / lithium manganate (LiNi _1/2 · Mn _1/2 O ₂ ), and in Patent Document 3 nickel / cobalt acid to which aluminum (Al) is added. Lithium (LiNi _0.8 Co _0.15 Al _0.05 O ₂ ; abbreviated NCA), in Patent Document 4, solid solution material (Li ₂ MnO ₃ —LiMeO ₂ , Me = Ni, Mn, Co; abbreviated / Li ₂ MnO ₃ -NMC) and mixed cathode active materials have been proposed.

However, since the practical capacity of LiMn ₂ O ₄ is as small as about 100 mAh / g, the mixing ratio is suppressed to such an extent that the characteristics of high energy density are not impaired, and there is a limit to cost reduction with the conventional mixed positive electrode active material. there were.

In addition, in-vehicle storage batteries for hybrid vehicles, plug-in hybrid vehicles, and electric vehicles, it is essential to increase the energy density for the purpose of reducing the weight and extending the cruising distance. Recently, LiMn ₂ O _{4 in} exchange for the economics of the storage battery. The use of a mixed positive electrode active material with a reduced mixing ratio has been made to increase the energy density.

Realization of a mixed positive electrode active material with a high-capacity Mn-based positive electrode material instead of LiMn ₂ O ₄ has been desired.

Japanese Patent No. 3754218 Japanese Patent Laid-Open No. 2003-168430 JP 2010-262914 A Special table 2013-520882 gazette

  An object of the present invention is to provide an unprecedented new manganese oxide mixture and mixed positive electrode active material that can achieve both high energy density and low cost, and furthermore, high energy that is excellent in economic efficiency using this as a positive electrode. A lithium secondary battery having a high density is provided.

The inventor has conducted extensive studies on a manganese oxide and a positive electrode active material that can achieve both high energy density and low cost. As a result, the lithium-containing manganese composition represented by the general formula Li _{(4/3)-(4X / 5)} Mn _2/3 O _{2- (2X / 5)} (where 0 <X <1 is satisfied). , Manganese based on a lithium-containing manganese composition represented by the general formula [Li ₂ MnO ₃ ] _1-E · [Li ₄ Mn ₅ O ₁₂ ] _E (where 0 <E <1 is satisfied) By using the oxide mixture as the positive electrode material of the mixed positive electrode active material, it becomes possible to charge and discharge at a very high capacity compared to the conventional mixed positive electrode active material using LiMn ₂ O _4. The present inventors have found that a lithium secondary battery having a high energy density and a low cost can be constructed by using it as a positive electrode of a secondary battery, and the present invention has been completed. That is, the present invention relates to lithium represented by the general formula Li _{(4/3)-(4X / 5)} Mn _2/3 O _{2- (2X / 5)} (where 0 <X <1 is satisfied). Manganese oxide mixture containing manganese composition and positive electrode material, general formula [Li ₂ MnO ₃ ] _1-E · [Li ₄ Mn ₅ O ₁₂ ] _E (where 0 <E <1 is satisfied). A lithium secondary battery comprising a lithium-containing manganese composition and a manganese oxide mixture containing a positive electrode material, a mixed positive electrode active material containing a manganese oxide mixture, and a positive electrode containing a mixed positive electrode active material.

  Hereinafter, the present invention will be described in more detail.

The manganese oxide mixture of the present invention is represented by the general formula Li _{(4/3)-(4X / 5)} Mn _2/3 O _{2- (2X / 5)} (where 0 <X <1 is satisfied). The lithium-containing manganese composition and the positive electrode material are contained.

Further, the manganese oxide mixture of the present invention has a general formula [Li ₂ MnO ₃ ] _1-E · [Li ₄ Mn ₅ O ₁₂ ] _E (where 0 <E <1 is satisfied). It contains a manganese composition and a positive electrode material.

The lithium-containing manganese composition contained in the manganese oxide mixture of the present invention has a higher capacity than LiMn ₂ O ₄ , and its capacity is 130 to 170 mAh / g. LiCoO ₂ , LiNi _1/2 · Mn _{1 /} Compared with ₂ O ₂ , NCA (lithium / nickel / cobalt / aluminum composite oxide) and NMC (lithium / nickel / manganese / cobalt composite oxide), it has the characteristics of high energy density regardless of the mixing ratio. There is no loss. For this reason, in the mixed positive electrode active material, both high energy density and low cost can be achieved.

The value of X in the general formula Li _{(4/3)-(4X / 5)} Mn _2/3 O _{2- (2X / 5)} , which is a lithium-containing manganese composition, is determined from the composition analysis of the lithium-containing manganese composition. be able to.

The value of E in the general formula [Li ₂ MnO ₃ ] _1-E · [Li ₄ Mn ₅ O ₁₂ ] _E , which is a lithium-containing manganese composition, can be determined from the composition analysis of the lithium-containing manganese composition.

  Examples of the method obtained from the composition analysis include dielectric coupling plasma emission analysis and atomic absorption analysis.

  The Mn valence of the lithium-containing manganese composition can be determined by a general transition metal valence evaluation method. For example, a method for estimating from each spectrum obtained by XPS measurement (X-ray photoelectron spectroscopy), XAFS measurement (X-ray adsorption fine structure), PES measurement (Photoelectron spectroscopy), JIS (Japanese Industrial Standard) Although the method etc. which combined the analysis method (G1311-1) and the manganese dioxide analysis method (K1467) as described in JIS are illustrated, it is not restricted to these.

  Since the lithium-containing manganese composition reversibly inserts and desorbs lithium, a two-phase coexistence state in which a layered rock salt type structure and a spinel type structure coexist is preferable. A twin structure in which a domain of a layered rock salt structure and a domain of a spinel structure are combined with a specific crystal plane or crystal axis in common in the same crystal solid is more preferable.

General formula Li _{(4/3)-(4X / 5)} Mn _2/3 O _{2- (2X / 5) which is} a lithium-containing manganese composition, general formula [Li ₂ MnO ₃ ] ₁ which is a lithium-containing manganese composition _-E. [Li ₄ Mn ₅ O ₁₂ ] _E is a molar ratio of the Mn source to the Li source (Li / Mn ratio) with 0.8 <Li / Mn ratio <2.0. Can be prepared by baking a solid phase, a liquid phase, or a combination of both. In order to make the valence of Mn +4, it is preferably fired at 300 to 800 ° C. in an air circulation or an atmosphere having an oxygen content higher than the air. Examples of the temperature increase and temperature decrease conditions during firing include, but are not limited to, temperature increase and decrease at a constant rate and stepwise temperature increase and decrease.

There is no particular limitation on the Mn raw material used in the production of the lithium-containing manganese composition, but in order to contain a layered rock salt type structure and a spinel type structure, a manganese raw material containing + 2-valent manganese and / or a monoclinic manganese raw material Is preferably used. Examples of manganese raw materials containing divalent manganese include manganese sulfate, manganese carbonate, manganese nitrate, manganese chloride, trimanganese tetraoxide (Mn ₃ O ₄ ), MnO, Mn (OH) ₂ , and acids of these manganese raw materials Although a processed material etc. are illustrated, it is not restrict | limited to these. Examples of the monoclinic manganese raw material include, but are not limited to, birnessite, hollandite, manganite, romanite, todokeite, manganese oxides having similar structures to these, and acid-treated products of these manganese raw materials. . The Li raw material used in the production of the lithium-containing manganese composition is not particularly limited, and examples include lithium carbonate, lithium hydroxide, lithium nitrate, lithium chloride, lithium iodide, lithium oxalate, lithium sulfate, and lithium oxide. However, it is not limited to these.

The positive electrode material contained in the manganese oxide mixture of the present invention is not particularly limited as long as it contains lithium and the lithium can be released by electrochemical oxidation. For example, NCA (lithium / nickel) Cobalt / aluminum composite oxide), NMC (lithium / nickel / manganese / cobalt composite oxide), lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium / nickel / manganese composite oxide (LiNi _{1) /} 2Mn _1/2 O ₂ ), lithium / nickel / manganese spinel composite oxide (LiNi _1/2 · Mn _3/2 O ₄ ), solid solution material, olivine type LiMnPO ₄ , olivine type LiFePO _{4 and the} like. .

  The manganese oxide mixture of the present invention can be produced by mixing a lithium-containing manganese composition and a positive electrode material.

  The mixing method is not limited as long as it can be uniformly mixed. For example, mixing with a mortar, mixing with a mixer, etc. are illustrated.

  By using the manganese oxide mixture of the present invention as a mixed cathode active material, it becomes possible to provide a high-capacity and low-cost lithium secondary battery that could not be obtained conventionally.

  By mixing the mixed positive electrode active material with a conductive additive, a binder, and the like, a positive electrode can be obtained.

The configuration of the lithium secondary battery other than the positive electrode is not particularly limited, but the negative electrode is a material that occludes and releases Li, for example, a carbon-based material, a tin oxide-based material, Li ₄ Ti ₅ O ₁₂ , SiO, Li, and the like. Examples of the material that forms an alloy include Li-based alloys, and examples of the material that forms an alloy with Li include silicon-based materials and aluminum-based materials. Examples of the electrolyte include an organic electrolytic solution in which a Li salt and various additives are dissolved in an organic solvent, a Li ion conductive solid electrolyte, and a combination thereof.

  The manganese oxide mixture and mixed positive electrode active material of the present invention can be charged / discharged at a very high capacity compared to the conventional mixed positive electrode active material, and can be used for a positive electrode of a lithium secondary battery to achieve high energy. It is possible to provide a lithium secondary battery that can achieve both density and low cost.

It is a powder X-ray-diffraction pattern of the lithium containing manganese composition used in Example 1 and Example 2. FIG. It is a powder X-ray-diffraction pattern of the lithium containing manganese composition used in Example 3 and Example 4. 3 is a powder X-ray diffraction pattern of NCA used in Example 1, Example 3, and Comparative Example 1. FIG. 3 is a powder X-ray diffraction pattern of NMC used in Example 2, Example 4, and Comparative Example 2. FIG. _{3 is} a powder X-ray diffraction pattern of LiMn ₂ O ₄ used in Comparative Example 1 and Comparative Example 2. FIG.

  Next, although this invention is demonstrated with a specific Example, this invention is not limited to these Examples.

<Production of battery>
The obtained manganese oxide mixture (mixed positive electrode active material) and conductive binder (trade name: TAB-2, manufactured by Hosen Co., Ltd.) were mixed at a weight ratio of 2: 1 using an agate mortar. A SUS mesh (SUS316) was uniaxially pressed at 1 ton / cm ² to form a pellet, and then dried under reduced pressure at 150 ° C. for 2 hours to obtain a positive electrode.

Metallic lithium for the negative electrode, 1 mol / dm ³ of LiPF ₆ dissolved in a 1: 2 volume ratio solvent of ethylene carbonate and dimethyl carbonate in the electrolyte, polyethylene sheet in the separator (trade name: Celgard, manufactured by Polypore Corporation) A 2032 type coin cell was prepared using

<Charge / discharge test>
Using the produced coin cell, the cell voltage is between 4.8 V and 2.0 V at a constant current of 10 mA / g under room temperature conditions (22 to 27 ° C.), and then discharged. Thereafter, charging and discharging are repeated, the charging capacity at the first cycle (mAh / g), the discharging capacity at the first cycle (mAh / g), the discharging capacity at the 10th cycle (mAh / g), the discharging capacity at the 50th cycle ( mAh / g) was measured.

<Composition analysis>
The composition of lithium and manganese in the prepared lithium-containing manganese composition was analyzed with a dielectric coupled plasma emission spectrometer (trade name: ICP-AES, manufactured by PerkinElmer Japan Co., Ltd.).

<Evaluation of crystallinity>
The crystal structure of the prepared lithium-containing manganese composition was identified with a powder X-ray diffraction measurement device (trade name: MXP3, manufactured by Mac Science).

  The measurement conditions were as follows.

Target: Cu
Output: 1.2kW (30mA-40kV)
Step scan: 0.04 ° (2θ / θ)
Measurement time: 3 seconds Example 1
Manganese carbonate 0.5 hydrate (special grade reagent) 12.35 g and lithium hydroxide monohydrate (special grade reagent) 6.66 g (Li / Mn ratio = 11/7) using a mortar 30 After dry-mixing for a minute, the mixture was pulverized until it passed through a mesh having a mesh size of 150 μm.

  2 g of the obtained mixed powder was put in a baking dish, subjected to a heat treatment at 400 ° C. for 32 hours under a 1-liter air aeration condition in a tubular furnace, cooled to room temperature, and a sample was taken out. The temperature increase rate and the temperature decrease rate were 50 ° C./hr and 100 ° C./hr, respectively. When the temperature was lowered, the furnace was cooled at 150 ° C. or lower.

From the composition analysis and crystallinity evaluation of the prepared sample, the obtained lithium-containing manganese composition had a layered rock salt structure and a spinel structure, and the Li / Mn ratio was 11/7. From this value, it was found that the value of X was 0.36, and a lithium-containing manganese composition of Li _1.05 Mn _2/3 O _1.86 was obtained. The value of E was 0.10, and it was found to be a lithium-containing manganese composition of [Li ₂ MnO ₃ ] _0.90 · [Li ₄ Mn ₅ O ₁₂ ] _0.10 .

The obtained lithium-containing manganese composition and the positive electrode material (NCA: LiNi _0.8 Co _0.15 Al _0.05 O ₂ , manufactured by Toshima Seisakusho Co., Ltd.) were mixed at a weight ratio of 1: 1 using an agate mortar. And a manganese oxide mixture (mixed cathode active material) was prepared.

The results of the charge / discharge test are shown in Table 1. From the result, it was found that the capacity was larger than that of the mixed positive electrode of LiMn ₂ O ₄ and NCA of Comparative Example 1, and the same performance as that of the case of only NCA was exhibited.

実施例２
正極材料として、ＮＭＣ（１１１）（ＬｉＮｉ_１／３Ｍｎ_１／３Ｃｏ_１／３Ｏ_２，株式会社豊島製作所製）を用いた以外は実施例１と同様にしてマンガン酸化物混合物（混合正極活物質）を調製した。

Example 2
A manganese oxide mixture (mixed positive electrode active material) was prepared in the same manner as in Example 1 except that NMC (111) (LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , manufactured by Toyoshima Seisakusho Co., Ltd.) was used as the positive electrode material. Material) was prepared.

The results of the charge / discharge test are shown in Table 1. From the result, it was found that the capacity was larger than that of the mixed positive electrode of LiMn ₂ O ₄ and NMC (111) of Comparative Example 2, and the same performance as that of NMC (111) alone was exhibited.

Example 3
Manganese tetraoxide <Chemical formula: Mn ₃ O ₄ > (trade name; CMO (registered trademark), manufactured by Tosoh Corporation) and 10.0 g of manganese dioxide (Mn content: 60.3 wt%) obtained by sulfuric acid treatment A lithium-containing manganese composition was prepared in the same manner as in Example 1 except that 4.66 g of monohydrate of lithium hydroxide (special grade reagent) was used.

From the composition analysis and crystallinity evaluation of the prepared sample, the obtained lithium-containing manganese composition had a layered rock salt structure and a spinel structure, and the Li / Mn ratio was 1/1. From this value, it was found that the value of X was 0.83, and a lithium-containing manganese composition of Li _0.67 Mn _2/3 O _1.67 was obtained. The value of E was 0.50, which was found to be a lithium-containing manganese composition having [Li ₂ MnO ₃ ] _0.50 · [Li ₄ Mn ₅ O ₁₂ ] _0.50 .

The obtained lithium-containing manganese composition and the positive electrode material (NCA: LiNi _0.8 Co _0.15 Al _0.05 O ₂ , manufactured by Toshima Seisakusho Co., Ltd.) were mixed at a weight ratio of 1: 1 using an agate mortar. And a manganese oxide mixture (mixed cathode active material) was prepared.

The results of the charge / discharge test are shown in Table 1. From the result, it was found that the capacity was larger than that of the mixed positive electrode of LiMn ₂ O ₄ and NCA of Comparative Example 1, and the same performance as that of the case of only NCA was exhibited.

Example 4
A manganese oxide mixture (mixed positive electrode active material) was used in the same manner as in Example 3 except that NMC (111) (LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , manufactured by Toyoshima Seisakusho Co., Ltd.) was used as the positive electrode material. Material) was prepared.

The results of the charge / discharge test are shown in Table 1. From the result, it was found that the capacity was larger than that of the mixed positive electrode of LiMn ₂ O ₄ and NMC (111) of Comparative Example 2, and the same performance as that of NMC (111) alone was exhibited.

Comparative Example 1
A lithium-containing manganese composition was prepared in the same manner as in Example 1 except that 2.12 g of lithium hydroxide monohydrate (special grade reagent) and the heat treatment temperature were 800 ° C. (Li / Mn ratio = 1 / 2).

From the composition analysis and crystallinity evaluation of the prepared sample, it was found that the obtained lithium-containing manganese composition had a spinel structure and was LiMn ₂ O ₄ .

A manganese oxide mixture (mixed cathode active material) was prepared in the same manner as in Example 1 except that the obtained LiMn ₂ O ₄ was used as the lithium-containing manganese composition.

  The results of the charge / discharge test are shown in Table 1. From the result, it was found that the capacity was smaller than the manganese oxide mixture of Example 1 and Example 3 (mixed positive electrode active material).

Comparative Example 2
A manganese oxide mixture (mixed positive electrode active material) was prepared in the same manner as in Example 2 except that LiMn ₂ O ₄ obtained in Comparative Example 1 was used as the lithium-containing manganese composition.

  The results of the charge / discharge test are shown in Table 1. From the result, it was found that the capacity was smaller than the manganese oxide mixture (mixed positive electrode active material) of Example 2 and Example 4.

  The manganese oxide mixture and mixed positive electrode active material of the present invention can be used for a positive electrode of a lithium secondary battery.

Claims (5)

Lithium-containing manganese composition and positive electrode represented by the general formula Li _{(4/3)-(4X / 5)} Mn _2/3 O _{2- (2X / 5)} (where 0 <X <1 is satisfied) A manganese oxide mixture comprising a material. A lithium-containing manganese composition represented by the general formula [Li ₂ MnO ₃ ] _1-E · [Li ₄ Mn ₅ O ₁₂ ] _E (where 0 <E <1 is satisfied) and a positive electrode material. Manganese oxide mixture characterized by The manganese oxide mixture according to claim 1 or 2, wherein the lithium-containing manganese composition has a layered rock salt structure and a spinel structure. A mixed cathode active material comprising the manganese oxide mixture according to any one of claims 1 to 3. A lithium secondary battery comprising a positive electrode containing the mixed positive electrode active material according to claim 4.

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