JP2018043889A - Manganese oxide, manganese oxide mixture, and lithium secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manganese oxide which is a novel manganese-based positive electrode material for a lithium secondary battery capable of achieving both a high energy density and a low cost, and to provide a lithium secondary battery with a high energy density using the manganese oxide as a positive electrode.SOLUTION: There are provided: a manganese oxide represented by general formula Li[LiMMn]O(where X+Y+Z=2, 0<X<1/3 and 5/3<Y+Z<2 are satisfied, and M is one or more elements selected from elements other than Li, Mn and O); a manganese oxide mixture containing the manganese oxide and a positive electrode material; a lithium secondary battery including a positive electrode containing the manganese oxide; and a lithium secondary battery including a positive electrode containing a mixed positive electrode active material.SELECTED DRAWING: None

Description

  The present invention relates to a manganese oxide, a manganese oxide mixture, and a lithium secondary battery using these.

  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 (for example, Patent Document 1).

  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.

However, since the practical capacity of LiMn ₂ O ₄ used in the past is as small as about 100 mAh / g, the mixing ratio can be suppressed to such an extent that the characteristics of high energy density are not impaired. There was a limit.

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.

Thus, realization of a high energy density Mn-based positive electrode material that replaces LiMn ₂ O ₄ is desired, and if high-energy density manganese-based positive electrode material can be put into practical use, it will be possible to achieve both cost and use in vehicles. The lithium secondary battery market is expected to expand dramatically.

JP 2015-72875 A

  An object of the present invention is to provide a manganese oxide, which is a novel positive electrode material for manganese-based lithium secondary batteries that can achieve both high energy density and low cost, and a manganese oxide mixture containing manganese oxide and a positive electrode material. Furthermore, the present invention provides a high energy density lithium secondary battery used for these positive electrodes.

The inventors of the present invention have made 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 general formula _{Li [Li X M Y Mn Z} ] O 4 ( here, meet the X + Y + Z = 2,0 < X <1 / 3,5 / 3 <Y + Z <2, M is Li, Mn, other than O It is possible to charge and discharge the manganese oxide and manganese oxide mixture characterized by the above in a higher capacity than conventional manganese-based positive electrode materials. Thus, the present inventors have found that a high energy density lithium secondary battery can be constructed by using it as a positive electrode of a lithium secondary battery, and the present invention has been completed. That is, the present invention is represented by the general formula _{Li [Li X M Y Mn Z} ] O 4 ( here, meet the X + Y + Z = 2,0 < X <1 / 3,5 / 3 <Y + Z <2, M is Li, Mn , One or more elements selected from elements other than O.), a manganese oxide mixture containing this manganese oxide and a positive electrode material, and these manganese oxides or manganese oxide mixtures. It is a lithium secondary battery provided for the positive electrode.

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

Manganese oxide of the present invention have the general formula _{Li [Li X M Y Mn Z} ] O 4 ( here, meet the X + Y + Z = 2,0 < X <1 / 3,5 / 3 <Y + Z <2, M is Li , One or more elements selected from elements other than Mn and O).

Manganese oxide of the present invention the general formula _{Li [Li X M Y Mn Z} ] O 4 of the X, Y, Z values, manganese oxide of the present invention the general formula general formula _Li [Li X _M Y Mn It can be determined from the composition analysis of _{Z 4} O ₄ . Examples of the method obtained from the composition analysis include dielectric coupling plasma emission analysis and atomic absorption analysis.

The M in the general formula _{Li [Li X M Y Mn Z} ] manganese oxide represented by _{O 4} of the present invention can be used Li, Mn, one or more elements selected from elements other than O. Examples of one or more elements selected from elements other than Li, Mn, and O include, for example, H, Na, K, Rb, Cs, Ib group element Cu, Ag, Au, and IIa group element Be, Mg, Ca, Sr, Ba, IIb group element Zn, Cd, IIIa group element Sc, Y, IIIb group element B, Al, Ge, In, Mn transition metals other than Mn, the first transition except Mn Series elements Ti, V, Cr, Fe, Co, Ni, second and third transition series elements Zr, Nb, Mo, Tc, Ru, Rh, Pd, Hf, Ta, W, Re, Os, Ir, Pt, Au, etc. are illustrated. In order to maintain the capacity per weight as the positive electrode, H, Na, K, Mg, Ca, Al, Zn, Ga, Ti, V, Cr, Fe, Co, and Ni are preferable. Therefore, it is preferable to have a spinel structure.

  Many of oxide materials containing a large amount of metal elements such as Co and Ni, which have been mainly studied so far, are compounds having a layered structure and have only a path for Li to diffuse two-dimensionally in the solid phase. On the other hand, in the spinel structure, Li has a movement path that can diffuse three-dimensionally in the solid phase and has excellent rate characteristics.

A general formula _{Li [Li X M Y Mn Z} ] manganese oxide represented by _{O 4 is, Li [Li 1/3 Mn 5/3]} O 4 and manganese oxide comprising LiMn ₂ O ₄ of the present invention Then, a part of Mn of either or both of Li [Li _1/3 Mn _5/3 ] O ₄ and LiMn ₂ O ₄ was replaced with at least one element selected from elements other than Li, Mn, and O Is.

Li [Li _1/3 Mn _5/3 ] O ₄ is obtained by replacing 1/3 Mn of the Mn layer of spinel type LiMn ₂ O ₄ with Li, and has the same spinel type structure as LiMn ₂ O ₄ . Furthermore, in order to reversibly insert and desorb lithium, a state where Li [Li _1/3 Mn _5/3 ] O ₄ ] and LiMn ₂ O ₄ coexist is preferable, and in order to express higher reversibility, A twin structure in which the domains of the spinel structure are bonded to each other with a specific crystal plane and a common crystal axis in the same crystal solid is more preferable.

Formula _{Li [Li X M Y Mn Z} ] O 4 is manganese oxide of the present invention, beyond the 1/2 (Mn + M) and Li molar ratio [Li / (Mn + M) molar ratio] 4/5 It can prepare by baking the raw material containing Mn, M, and Li so that it may become less.

  Firing is preferably performed at 400 to 600 ° C. in an oxygen content atmosphere in order to obtain a twin crystal structure. 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 restriction | limiting in particular in the Mn raw material used by manufacture of manganese oxide. For example, manganese sulfate, manganese carbonate, manganese nitrate, manganese chloride, trimanganese tetraoxide (Mn ₃ O ₄ ), MnO, Mn (OH) ₂ , Birnessite, Hollandite, Manganite, Romanite, Todorokite, and similar structures to these Manganese oxides and acid-treated products of these manganese raw materials are exemplified, but not limited thereto.

  There is no restriction | limiting in the M raw material used by manufacture of the manganese oxide of this invention. Examples of the element M include carbonates, nitrates, oxalates, chlorides and oxides, but are not limited thereto.

  In order to make the composition of the manganese oxide uniform, it is preferable to use a raw material containing Mn and M as the Mn raw material and the M raw material used in the manufacture of the manganese oxide. Examples include oxides containing Mn and M, oxyhydroxides, hydroxides, and mixtures containing one or more of these, but are not limited thereto.

  There is no particular limitation on the Li raw material used in the production of manganese oxide, for example, lithium carbonate, lithium hydroxide, lithium nitrate, lithium chloride, lithium iodide, lithium oxalate, lithium sulfate, lithium oxide, etc. It is not limited to these.

  By using the manganese oxide of the present invention for the positive electrode, it is possible to provide a high-capacity and low-cost lithium secondary battery that could not be obtained conventionally.

Manganese oxide mixtures of the present invention, the general formula _{Li [Li X M Y Mn Z} ] O 4 ( where, satisfies the X + Y + Z = 2,0 < X <1 / 3,5 / 3 <Y + Z <2, M is It contains one or more elements selected from elements other than Li, Mn, and O.) and a positive electrode material.

The manganese oxide 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 _1/2 O _2. Compared with NCA (lithium / nickel / cobalt / aluminum composite oxide) and NMC (lithium / nickel / manganese / cobalt composite oxide), the characteristics of high energy density are impaired regardless of the mixing ratio. There is no. For this reason, in the mixed positive electrode active material, both high energy density and low cost can be achieved.

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

2 is a powder X-ray diffraction pattern of manganese oxide of Example 1. FIG. 3 is a powder X-ray diffraction pattern of manganese oxide of Example 2. 3 is a powder X-ray diffraction pattern of NMC used in Examples 3 to 4 and Comparative Example 2. FIG. 2 is a powder X-ray diffraction pattern of manganese oxide of Comparative Example 1.

  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 or manganese oxide mixture (mixed positive electrode active material) and a conductive binder (trade name: TAB-2, manufactured by Hosen Co., Ltd.) were mixed at a weight ratio of 2: 1 using an agate mortar. After being uniaxially pressed into a 16 mmφ SUS mesh (SUS316) at 1 ton / cm ² to form a pellet, it was 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 were repeated, and the charge capacity (mAh / g) at the first cycle, the discharge capacity (mAh / g) at the first cycle, the discharge capacity (mAh / g) at the 10th cycle were measured, and the capacity retention rate ( The ratio (%) of the discharge capacity at the 10th cycle to the discharge capacity at the 1st cycle was determined.

<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 diffractometer (trade name: Ultimate IV, manufactured by Rigaku Corporation).

  The measurement conditions were as follows.

Target: Cu
Output: 1.6kW (40mA-40kV)
Step scan: 0.04 ° (2θ / θ)
Measurement time: 0.6 seconds Production Example Nickel sulfate and manganese sulfate are dissolved in pure water to obtain an aqueous solution containing 0.5 mol / L nickel sulfate and 1.5 mol / L manganese sulfate. (The total concentration of all metals in the aqueous metal solution was 2.0 mol / L).

  Further, 200 g of pure water was put into a reaction vessel having an internal volume of 1 L, and then this was heated to 80 ° C. and maintained.

The aqueous metal salt solution was added to the reaction vessel at a supply rate of 0.28 g / min. Further, air was bubbled into the reaction vessel at a supply rate of 1 L / min as an oxidant. A 2 mol / L sodium hydroxide aqueous solution (caustic soda aqueous solution) is intermittently added so that the pH becomes 10 when supplying the metal salt aqueous solution and air to obtain a mixed aqueous solution, and nickel-manganese in the mixed aqueous solution is obtained. A system composite oxyhydroxide was precipitated to obtain a slurry. The obtained slurry was filtered and washed, and then the wet cake after washing was air-dried in the air for 1 week, and then dried at 115 ° C. for 5 hours, thereby obtaining an oxyhydroxide containing Mn and Ni (Ni _0.245). Mn _0.755 OOH) was obtained (Mn: 45.3 wt%, Ni: 14.7 wt%).

Example 1
After dry-mixing 5.00 g of oxyhydroxide containing Mn and Ni obtained in the production example and 1.71 g of monohydrate of lithium hydroxide (special grade reagent) using a mortar for 30 minutes, the opening The whole amount was passed through a 150 μm mesh.

  1.13 g of the obtained mixed powder was put in a baking dish, subjected to heat treatment at 450 ° C. for 32 hours under an air aeration condition of 1 liter per minute 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 manganese oxide has a spinel structure, the Mn / Ni ratio is 3.304 / 1, and the Li / (Mn + Ni) ratio is 0.760. Met. From this value, X is 0.295, Y are 0.426, Z is _1.279, that of manganese oxide _{Li [Li 0.295 Ni 0.426 Mn 1.279} ] O 4 was obtained I understood.

The results of the charge / discharge test are shown in Table 1. From the result, it was found that the discharge capacity at the 10th cycle was larger than that of LiMn ₂ O ₄ of Comparative Example 1, and the cycle was stable from the first cycle.

実施例２
水酸化リチウムの１水和物（特級試薬）１．６２ｇとした以外は、実施例１と同様にしてマンガン酸化物を調製した。

Example 2
Manganese oxide was prepared in the same manner as in Example 1 except that 1.62 g of lithium hydroxide monohydrate (special grade reagent) was used.

From the composition analysis and crystallinity evaluation of the prepared sample, the obtained manganese oxide has a spinel structure, the Mn / Ni ratio is 3.304 / 1, and the Li / (Mn + Ni) ratio is 0.721. Met. From this value, X was 0.257, Y was 0.436, Z was 1.307, and a Li [Li _0.257 Ni _0.436 Mn _1.307 ] O ₄ manganese oxide was obtained. I understood.

The results of the charge / discharge test are shown in Table 1. From the result, it was found that the discharge capacity at the 10th cycle was larger than that of LiMn ₂ O ₄ of Comparative Example 1, and the cycle was stable from the first cycle.

Example 3
The agate mortar with the manganese oxide obtained in Example 1 and the positive electrode material (NMC (111) (LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , manufactured by Toshima Seisakusho Co., Ltd.) at a weight ratio of 1: 1. Mixing was carried out to prepare a manganese oxide mixture.

The results of the charge / discharge test are shown in Table 1. From the results, it was found that the discharge capacity at the 10th cycle was larger than that of the mixed positive electrode of LiMn ₂ O ₄ and NMC (111) in Comparative Example 2, and the cycle was stable from the first cycle.

Example 4
A manganese oxide mixture was prepared in the same manner as in Example 3 except that the manganese oxide obtained in Example 2 was used.

The results of the charge / discharge test are shown in Table 1. The discharge capacity at the 10th cycle was larger than that of the mixed positive electrode of LiMn ₂ O ₄ and NMC (111) in Comparative Example 2 and was found to cycle stably from the first cycle.

Comparative Example 1
Manganese carbonate 0.5 hydrate (special grade reagent) 12.35 g and lithium hydroxide monohydrate (special grade reagent) 2.12 g (Li / Mn ratio = 1/2) using a mortar 30 After dry-mixing for a minute, it was pulverized until it passed through a mesh with a mesh size of 150 μm.

  2 g of the obtained mixed powder was put in a baking dish, subjected to heat treatment at 800 ° C. for 32 hours under an air aeration condition of 1 liter per minute 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 of the prepared sample and the evaluation of crystallinity, it was found that the obtained manganese composition had a spinel structure and was LiMn ₂ O ₄ .

  The results of the charge / discharge test are shown in Table 1. From the results, it was found that although the initial capacity was larger than the manganese oxides of Examples 1 and 2, the capacity at the 10th cycle was small and the cycle deterioration was remarkable.

Comparative Example 2
A manganese oxide mixture was prepared in the same manner as in Example 3 except that LiMn ₂ O ₄ obtained in Comparative Example 1 was used for manganese oxide.

  The results of the charge / discharge test are shown in Table 1. From the results, it was found that although the initial capacity was larger than the manganese oxides of Examples 3 and 4, the capacity at the 10th cycle was small and the cycle deterioration was remarkable.

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

Claims (6)

In the general formula _{Li [Li X M Y Mn Z} ] O 4 ( where, satisfies the X + Y + Z = 2,0 < X <1 / 3,5 / 3 <Y + Z <2, M is Li, Mn, from elements other than O One or more selected elements)). The manganese oxide according to claim 1, which has a spinel structure. A manganese oxide mixture comprising the manganese oxide according to claim 1 or 2 and a positive electrode material. A mixed positive electrode active material comprising the manganese oxide mixture according to claim 3. A lithium secondary battery comprising a positive electrode containing the manganese oxide according to claim 1. A lithium secondary battery comprising a positive electrode containing the mixed positive electrode active material according to claim 4.

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