JP4788579B2 - Lithium-nickel-manganese composite oxide, method for producing the same, and use thereof - Google Patents

Description

  The present invention relates to a lithium-nickel-manganese composite oxide used for a positive electrode active material for a lithium secondary battery, a production method thereof, and an application thereof.

Lithium ion secondary batteries (LIBs) are used as power sources for mobile phones, notebook computers, AV equipment, electric vehicles, and the like. LiCoO ₂ is mainly used as the positive electrode material of the secondary battery. However, LiCoO ₂ has a problem in terms of cost and resources because it contains Co, which is a rare element, as a main component. In addition, the effective capacity is up to about half of the theoretical capacity due to the phase transition accompanying Li desorption, and there is a limitation in terms of battery capacity. Furthermore, in terms of safety, it is easy to cause an oxidation reaction with respect to the organic electrolyte, and the thermal stability is poor.

In recent years, lithium ion secondary batteries with higher energy density and higher safety have been demanded along with an increase in power demand for portable devices or LIBs such as hybrid electric vehicles. Therefore, LiNi _0.5 Mn _0.5 O ₂ having a layered structure as a new positive electrode material has been proposed as a material that satisfies safety and high energy density (Non-patent Document 1). However, in the conventional LiNi _0.5 Mn _0.5 O ₂ , structural irregularities (replacement of Li and Ni between the 3a-3b sites) are remarkable, and the Ni seat occupancy of the Li main layer (3a-site) is large. It was up to about 10% (Non-Patent Document 2). Since structural irregularities inhibit the diffusion of Li ions, conventional LiNi _0.5 Mn _0.5 O ₂ has insufficient output characteristics.

  For this reason, the improvement by making it Li-Ni-Co-Mn complex oxide which added Co further is examined. The introduction of Co improves the structural irregularity and improves the output, but there are problems in cost and safety as described above.

In order to achieve particularly high output characteristics in a positive electrode material for LIB, it is advantageous that there is no crystal structure irregularity, no defect, and a smaller primary particle diameter, and this structural irregularity is suppressed. Therefore, synthesis of LiNi _0.5 Mn _0.5 O ₂ by Li ion exchange has been studied (Non-patent Document 3). In the report, it is reported that the Ni seat occupancy of the Li main layer (3a-site) is reduced to about 4% by Li ion exchange at a low temperature. However, the XRD pattern contains NiO which is an insulating layer as a by-product phase in addition to the main phase, and a complete single phase has not been obtained so far.

Regarding the Li ion exchange of NaNi _0.5 Mn _0.5 O ₂ , J. R. Although reported by Dahn et al., The crystallinity was still insufficient (Non-patent Document 4). Further, in the _report, but a solid solution composition of _{NaNi 0.5 Mn 0.5 O 2 -Na 0.67} Ni 0.33 Mn 0.67 O 2 has been studied, only at the end composition, respectively, O3, A P2 structure and a single phase were obtained, and only a mixed phase of O3 and P2 structure was obtained with an intermediate composition.

Proceedings of the 41st Battery Symposium (2000) 460-461 H. Kobayashi, et al. , Mater. , Chem. , 13, 590-595 (2003) K. Kang et al. , Science 311 977 (2006) J. et al. M.M. Paulsen and J.M. R. Dahn, J. et al. Electrochem. , Soc. , 147 (7) 2478 (2000)

  An object of the present invention is to provide a lithium-nickel-manganese composite oxide having high output characteristics, a method for producing the same, and a lithium ion secondary battery using the same as a positive electrode active material.

  As a result of intensive studies on a lithium-nickel-manganese composite oxide having both high energy density and safety, the present inventors have obtained a single component having a specific composition and crystal structure, and the structure The present inventors have found that irregularity is suppressed and that the battery has sufficient battery characteristics, and have completed the present invention.

  Hereinafter, the present invention will be described in detail.

  The lithium-nickel-manganese composite oxide (hereinafter referred to as “composite oxide”) of the present invention has a layered rock salt structure (O3 structure) that does not contain NiO as a byproduct phase, and Li / transition metal (molar ratio) is 0. 80 or more and 0.94 or less, containing at least Ni and Mn as transition metals, Mn / Ni molar ratio is larger than 1.08, and the occupation ratio of Ni atoms in the Li main layer is 0.0% or more. It is a composite oxide having a Na content of 0.2 wt% or less and 0% or less.

  The complex oxide of the present invention has a layered rock salt structure (O3 structure), and NiO appearing in the vicinity of 2θ (Cu-Kα) = 43 ° is not detected as a by-product phase in identification by powder X-ray diffraction method It is. When a NiO by-product phase appears, if a Li secondary battery using the composite oxide as a positive electrode active material is configured, the initial discharge capacity is low, and the discharge capacity is further rapidly reduced when the discharge cycle is repeated.

  The composite oxide of the present invention has a Li / transition metal (molar ratio) of 0.80 or more and 0.94 or less, contains at least Ni and Mn as the transition metal, and a Mn / Ni molar ratio of 1.08. The occupancy ratio of Ni atoms in the Li main layer is 6.0% or less, and the Na content is 0.2 wt% or less.

  When the Li / transition metal (molar ratio), Mn / Ni molar ratio, Ni atom occupancy in the Li main layer, and the Na content are out of this range, the Li secondary battery can be produced using the composite oxide as a positive electrode active material. This is because, when configured, the initial discharge capacity is low, and when the discharge cycle is repeated, the discharge capacity rapidly decreases.

  The composite oxide of the present invention preferably has a lattice constant a-axis length of 2.880 ≦ a ≦ 2.890 Å and a c-axis length of 14.29 ≦ c ≦ 14.32 場合 when attributed as hexagonal crystals. In particular, the range of 14.30 ≦ c ≦ 14.31 is more preferable in view of characteristics.

  When the lattice constant is out of this range, when a Li secondary battery using the composite oxide as a positive electrode active material is configured, the initial discharge capacity is high, but when the discharge cycle is repeated, the discharge capacity is also rapidly decreased.

The composite oxide of the present invention has a chemical composition of Li _{0.88 + x} Ni _{0.46 + y} Mn _0.54-y O ₂ (−0.08 ≦ x ≦ 0.06, −0.02 ≦ y ≦ 0.02). It is particularly preferable that it is composed of a crystal phase of a layered rock salt structure represented by the chemical formula of In such a crystal phase, a single crystal phase is obtained. In the chemical composition formula, the ranges of −0.02 ≦ x ≦ 0.02 and −0.02 ≦ y ≦ 0.02 preferable.

  Next, the method for producing the composite oxide of the present invention will be described.

  The composite oxide of the present invention is not based on a conventional solid-phase reaction method, a method of reacting a Ni-Mn precursor synthesized by coprecipitation or a sol-gel method with a Li compound, but a Ni, Mn raw material and an Na compound. And after obtaining Na—Ni—Mn composite oxide fired at 800 ° C. or higher and 1000 ° C. or lower, Li ion exchange can be performed.

The Ni raw material to be used is not particularly limited, and examples thereof include nickel hydroxide, nickel oxyhydroxide, nickel oxide, nickel carbonate, and nickel oxalate. Further, manganese oxide (MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ , MnO), manganese oxyhydroxide, manganese carbonate, manganese oxalate, or the like can be used as the Mn raw material.

  Similarly, examples of the Na compound include sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, sodium chloride, sodium nitrate, sodium sulfate and the like. Among the raw material groups, a combination of nickel hydroxide, manganese dioxide, and sodium hydroxide is particularly preferable from the viewpoint of cost.

  In order to obtain the composite oxide of the present invention, it is particularly preferable to refine the Ni and Mn raw materials, and the average particle size of the raw material components is 0.3 μm or less, more preferably 0.1 μm or less.

  When the average particle diameter of the raw material is large, the by-product phase NiO is easily generated, the charge / discharge characteristics tend to be polarized, and the loss of electricity associated with charge / discharge increases.

  The raw material can be mixed by either dry mixing or wet mixing, but a wet mixing method with high mixing properties is advantageous. For example, Ni and Mn raw materials are dispersed in water and refined with a wet ball mill, and then a water-soluble Na compound is added to obtain a mixed slurry. The slurry can be spray-dried with a spray dryer to obtain a highly uniform powder before firing.

  The Na—Ni—Mn composite oxide (hereinafter referred to as “precursor oxide”), which is a precursor of the composite oxide of the present invention, has a layered rock salt structure (O3 structure).

  When the precursor oxide is identified by a powder X-ray diffraction method, it is preferable to use a precursor in which NiO appearing in the vicinity of 2θ (Cu—Kα) = 43 ° is not detected as a by-product phase. The crystal structure is a layered rock salt structure (O3 structure) represented by the space group R-3m, a single phase that does not contain the P2 structure, and when assigned as a hexagonal crystal, the lattice constants a and c-axis lengths are 2.870 ≦ a ≦ 2.890Å, 14.30 ≦ c ≦ 14.31Å, more preferably composition: −0.02 ≦ x ≦ 0.02, −0.02 ≦ y ≦ 0.02. Lattice constants: 2.940 ≦ a ≦ 2.950 Å, 15.94 ≦ c ≦ 15.97 範 囲.

The chemical composition of the precursor oxide is expressed as Na _{0.92 + x} Ni _{0.46 + y} Mn _0.54-y O ₂ (−0.08 ≦ x ≦ 0.06, −0.02 ≦ y ≦ 0.02). It is possible. The firing is preferably performed in an oxygen-containing atmosphere. By firing in an inert atmosphere, it is difficult to obtain a good precursor oxide. The oxygen-containing atmosphere is most preferably in the air economically.

  The firing temperature is preferably in the range of 800 ° C. to 1000 ° C., particularly preferably 900 ° C. to 1000 ° C. The form of firing can be powder, pellets, or the like. In addition, since the substance has high hygroscopicity, it is preferable to suppress the reaction with moisture, for example, by passing dry air at least when the temperature is lowered or by rapidly cooling from the firing temperature to room temperature.

Li ion exchange of the precursor oxide can be performed with a Li molten salt, a eutectic salt, or a Li salt aqueous solution. LiNO ₃ For Li molten salt (mp 261 ° C.), LiCl (mp 605 ° C.), for eutectic _salt, LiNO ₃ -KNO 3 (melting point _{132 ℃), LiCl-LiNO 3} ( melting point 244 ° C.) a throat eutectic It is possible to control the ion exchange temperature by changing the salt composition. After ion exchange, it is washed with pure water, ethanol or the like and dried. The drying temperature is preferably 200 ° C. or lower.

  The Na content in the sample after ion exchange is preferably 0.2 wt% or less, and it is preferable to remove Na as close to zero as possible.

  The composite oxide of the present invention thus obtained is used as a positive electrode active material for a lithium ion secondary battery.

  As the negative electrode active material used in the Li secondary battery of the present invention, metallic lithium and lithium ions or materials capable of occluding and releasing lithium ions can be used. Examples include lithium metal, lithium / aluminum alloy, lithium / tin alloy, lithium / lead alloy, and carbon materials that can electrochemically insert and desorb lithium ions. A carbon material that can be desorbed is particularly preferable in terms of safety and battery characteristics.

  The electrolyte used in the lithium ion secondary battery of the present invention is not particularly limited. For example, a lithium salt dissolved in an organic solvent such as carbonates, sulfolanes, lactones, ether condyles, or lithium ion conductive A solid electrolyte can be used.

  Moreover, there is no restriction | limiting in particular as a separator used with the lithium ion secondary battery of this invention, For example, the microporous film etc. made from polyethylene or a polypropylene can be used.

  By using the composite oxide of the present invention for the positive electrode active material, it is possible to provide a lithium ion secondary battery having high output characteristics.

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

Example 1
Nickel hydroxide and manganese trioxide obtained by firing electrolytic manganese dioxide at 600 ° C. for 12 hours were weighed so that the molar ratio of Ni: Mn was 0.46: 0.54, and the solid content was 20 wt% in pure water. And were pulverized with a wet ball mill (grinding media: ZrO ₂ balls, 0.5 mmΦ) until the particle diameters of the Ni and Mn raw materials were 0.1 μm or less. In addition, the said particle diameter extracted 20 particles at random from SEM or a TEM image, and calculated | required the average particle diameter. The pulverized slurry was separated by filtration and dried at 150 ° C. Next, it was mixed with an appropriate amount of aqueous sodium hydroxide solution to make the Na / transition metal molar ratio 0.93. After drying this at 150 ° C., the mixture was fired in air at 900 ° C. for 24 hours, and then rapidly cooled to room temperature on a Cu metal plate.

  Powder X-ray diffraction measurement was performed on the obtained precursor oxide. As shown in FIG. 1, the XRD pattern showed a layered rock salt structure with an O3 structure. Further, as a result of refinement of the structure by Rietan-2000, a = 2.9470 mm and c = 15.941 mm.

  Next, Li ion exchange was performed on the precursor oxide. The precursor oxide powder was added to lithium nitrate melted in a liquid state at an ion exchange temperature of 275 ° C. and held for 10 hours. After ion exchange, the cooled solid was dissolved in pure water, filtered and separated, and dried at 150 ° C. This process consisting of ion exchange and filtration separation was repeated three times, and the finally obtained composite oxide powder was subjected to column washing with 1 L of ethanol per 10 g and dried at 150 ° C. for 1 hour.

As a result of chemical analysis by ICP method, the composition of the composite oxide was Li / (Ni + Mn) (molar ratio) = 0.88 and Mn / Ni (molar ratio) = 1.17. Further, Na content 0.1 wt%, the chemical composition _{was Li 0.88 Ni 0.46 Mn 0.54 O 2} .

  An X-ray diffraction pattern of the obtained composite oxide is shown in FIG. The obtained composite oxide has a layered rock salt structure (O3 structure), and NiO that has a main peak near 2θ (Cu-Kα) = 43 ° was not detected as a byproduct phase.

When the XRD pattern was refined and analyzed by the Rietveld method, it was composed of the crystal phase of the layered rock salt structure represented by the space group R-3m, and as shown in FIG. The length was 2.8873 mm, the c-axis length was 14.306 mm, and the Ni seat occupation ratio in the Li main layer was 5.0%. (Rwp 11.05%, Rp 7.17%, Re 9.44%) Therefore, the calculated composition formula is [Li _0.83 □ _0.12 Ni _0.05 ] _3a [Ni _0.41 Mn _0.54 Li _0.05 ] _3b [O ₂ ] _6c (□: vacancy).

  Next, the battery characteristic test as a positive electrode material of the obtained composite oxide was performed.

A mixture of a composite oxide, a conductive agent polytetrafluoroethylene and acetylene black (trade name: TAB-2) was mixed at a weight ratio of 4: 1, and meshed at a pressure of 1 ton / cm ² (manufactured by SUS316). ) After being molded into a pellet shape, it was dried under reduced pressure at 150 ° C. to produce a positive electrode for a battery. Electrolysis in which lithium hexafluorophosphate was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate at a concentration of 1 mol / dm ^{3 in} the obtained positive electrode for a battery, a negative electrode comprising a metal lithium foil (thickness 0.2 mm), and A battery was constructed using the liquid. Using the battery, the battery voltage was charged and discharged at a constant current between 4.5 V and 2.5 V at room temperature. The discharge capacities (mAh / g) when charging at 16 mA / g and discharging at ₁₆ , ₆₄ , ₄₀₀ , and ₈₀₀ mA / g are Q ₁₆ = 208, Q ₆₄ = 194, Q ₄₀₀ = 182, and Q _{800, respectively.} = 160 mAh / g.

  FIG. 4 shows the charge / discharge curve (initial cycle) at 16 mA / g, and FIG. 5 shows the results of repeating the charge / discharge cycle 30 times with the battery at a current density of 64 mA / g and an operating voltage of 2.5-4.5 V. It was.

Example 2
Nickel hydroxide and electrolytic manganese dioxide are weighed so that the Mn / Ni molar ratio is 1.27, dispersed in pure water so that the solid content is 20 wt%, and wet ball mill (grinding media: ZrO ₂ balls) , 0.5 mmΦ) until the particle size of the Ni and Mn raw materials is 0.3 μm or less. Next, the pulverized slurry is separated by filtration, dried at 150 ° C., mixed with an appropriate amount of sodium carbonate to obtain a Na / transition metal molar ratio of 0.92, and further dried at 150 ° C. It baked at 900 degreeC in the air for 24 hours, flowed in dry air, and cooled to room temperature at 100 degreeC / hour.

  The XRD pattern in the powder X-ray diffraction measurement of the obtained precursor oxide showed a layered rock salt structure having an O3 structure. Further, as a result of refinement of the structure by Rietan-2000, a = 2.9434 mm and c = 15.942 mm.

  Next, Li ion exchange of the precursor oxide was performed. The precursor oxide was added to lithium nitrate melted in a liquid state at an ion exchange temperature of 275 ° C. and held for 10 hours. After the ion exchange, the cooled solid was dissolved in pure water, separated by filtration, washed with a column with pure water, and dried at 150 ° C. This process consisting of ion exchange and filtration separation was repeated three times, and the finally obtained composite oxide was washed with 1 L of pure water per 10 g of column and dried at 150 ° C. for 1 hour.

As a result of chemical analysis by the ICP method, the composition is Li / (Ni + Mn) (molar ratio) = 0.81, Mn / Ni (molar ratio) = 1.27, the Na content is 0.2 wt%, and the chemical composition is Li _0.84 Ni _0.45 Mn _0.55 O ₂ .

  Next, when the X-ray diffraction pattern of the obtained composite oxide was measured, it was a layered rock salt structure (O3 structure), and NiO appearing in the vicinity of 2θ (Cu-Kα) = 43 ° as a byproduct phase. Not detected.

As a result of the refinement analysis of the structure of the XRD pattern by the Rietveld method, the a-axis length in the case of belonging to a hexagonal crystal as shown in FIG. 2.8860 mm, c-axis length was 14.315 mm, and the Ni seat occupancy ratio in the Li main layer was 2.5%. (Rwp 12.37%, Rp 8.59%, Re 8.39%) Therefore, in the calculation, the composition formula is [Li _0.81 □ _0.16 Ni _0.03 ] _3a [Ni _0.42 Mn _0.55 Li _0.03 ] _3b [O ₂ ] _6c (□: vacancy).

Next, the same battery characteristic test as in Example 1 was performed. As a result, Q ₁₆ = 201, Q ₆₄ = 183, Q ₄₀₀ = 165, and Q ₈₀₀ = 149. A charge / discharge curve (initial cycle) at 16 mA / g is shown in FIG.

Example 3
A sample was synthesized in the same manner as in Example 1 except that nickel hydroxide and electrolytic manganese dioxide were used, and the average particle diameter of Ni and Mn raw materials pulverized by a wet ball mill was 0.6 μm.

The obtained sodium-nickel-manganese composite oxide was subjected to powder X-ray diffraction measurement. The XRD pattern showed a layered rock salt structure with an O3 structure. Next, the XRD pattern of the sample after Li ion exchange was analyzed by the Rietveld method, and the structure was refined. As shown in FIG. 8, a = 2.8922 mm, c = 14.346 mm, and the Ni seat occupation ratio in the Li main layer was 4.3%. (Rwp 12.53%, Rp 8.29%, Re 8.25%) Therefore, in the calculation, the composition formula is [Li _0.76 □ _0.20 Ni _0.04 ] _3a [Ni _0.42 Mn _0.54 Li _0.04 ] _3b [O ₂ ] _6c (□: vacancy). As a result of chemical analysis by ICP method, the composition was Li / (Ni + Mn) (molar ratio) = 0.80 and Mn / Ni molar ratio = 1.17. Moreover, Na content rate was 0.1 wt%.

Next, the same battery characteristic test as in Example 1 was performed. As a result, Q ₁₆ = 204, Q ₆₄ = 149, Q ₄₀₀ = 133, and Q ₈₀₀ = 118. In addition, the charge curve (initial cycle) at 16 mA / g is shown in FIG. 9, and the polarization is larger than the charge / discharge curves of Examples 1 and 2 (FIGS. 4 and 7), and the electricity associated with charge / discharge Although the amount loss was relatively large, it could be used as a positive electrode active material for a Li secondary battery.

Comparative Example 1
Except for weighing nickel hydroxide and manganese trioxide obtained by firing electrolytic manganese dioxide at 600 ° C. for 12 hours so that the Mn / Ni molar ratio is 1.00 and the Na / (Ni + Mn) molar ratio is 1.00. Was synthesized in the same manner as in Example 1.

  Powder X-ray diffraction measurement was performed on the obtained precursor oxide. As shown in FIGS. 10 and 11, the XRD pattern has a layered rock salt structure having an O3 structure as a main phase, but a peak of byproduct NiO has appeared. A NiO phase also appeared in the XRD pattern of the composite oxide after Li ion exchange. As a result of chemical analysis by the ICP method, the composition of the composite oxide was Li / (Ni + Mn) (molar ratio) = 0.78 and Mn / Ni (molar ratio) = 1.00. Moreover, Na content rate was 0.2 wt%.

Next, the same battery characteristic test as in Example 1 was performed. As a result, Q ₁₆ = 168, Q ₆₄ = 150, Q ₄₀₀ = 132, and Q ₈₀₀ = 109.

Comparative Example 2
Except for weighing nickel hydroxide and manganese trioxide obtained by firing electrolytic manganese dioxide at 600 ° C. for 12 hours so that the Mn / Ni molar ratio is 1.50 and the Na / (Ni + Mn) molar ratio is 0.80. A sample was synthesized in the same manner as in Example 1.

  Powder X-ray diffraction measurement was performed on the obtained precursor oxide. As shown in FIGS. 10 and 11, the XRD pattern has a layered rock salt structure with an O3 structure as a main phase, but a peak derived from a P2 structure having a different stacking order from the O3 structure has appeared. The XRD pattern of the sample after Li ion exchange was not a single phase of a layered rock salt structure having an O3 structure, but a mixed phase. As a result of the chemical analysis by the ICP method, the composition of the composite oxide is Li / (Ni + Mn) (molar ratio) = 0.75, Mn / Ni (molar ratio) = 1.50, and the Na content is 0.2 wt%. there were.

As a result of conducting a battery characteristic test similar to that in Example 1, Q ₁₆ = 131, Q ₆₄ = 109, Q ₄₀₀ = 79, and Q ₈₀₀ = 54.

Comparative Example 3
A sample was synthesized in the same manner as in Example 1 except that the process consisting of ion exchange and filtration separation was performed twice.

When the obtained precursor oxide was subjected to powder X-ray diffraction measurement, the XRD pattern showed a layered rock salt structure having an O3 structure. Next, the structure of the XRD pattern of the sample after Li ion exchange was refined by the Rietveld method. As shown in FIG. 12, a = 2.8878 mm, c = 14.33 mm, and the Ni seat occupation ratio in the Li main layer was 5.0%. (Rwp 12.78%, Rp 8.85%, Re 9.50%) Therefore, in the calculation, the composition formula is [Li _0.81 □ _0.14 Ni _0.05 ] _3a [Ni _0.41 Mn _0.55 Li _0.05 ] _3b [O ₂ ] _6c (□: vacancy). As a result of chemical analysis by ICP method, the composition of the composite oxide was Li / (Ni + Mn) (molar ratio) = 0.86 and Mn / Ni molar ratio = 1.17. Moreover, Na content rate was 1.6 wt%.

  In the same battery system as in Example 1, the charge / discharge cycle was repeated 30 times at a current density of 64 mA / g and an operating voltage of 2.5-4.5 V. The results are shown in FIG. Compared with the charge / discharge cycle characteristics of Example 1 (FIG. 5), the characteristics were remarkably low, and the cycle characteristics decreased as Na remained.

Comparative Example 4
An appropriate amount of lithium hydroxide monohydrate, nickel hydroxide ground to an average particle size of 0.1 μm or less by a wet ball mill, and electrolytic manganese dioxide were dry mixed using a mortar. The obtained powder was fired at 900 ° C. for 12 hours in the air.

  As a result of chemical analysis by ICP method, the composition of the composite oxide was Li / (Ni + Mn) (molar ratio) = 0.92, and Mn / Ni molar ratio = 1.17. The XRD pattern of the obtained fired product is shown in FIG. The 10.8 and 11.0 diffraction peaks indicating the development of the layered rock salt structure are not separated, the 10.4 diffraction peak is also broad, and the 10.1, 00.6, and 10.2 diffraction peaks are also assigned. It was impossible. Therefore, the obtained crystal phase was a mixed phase.

  The discharge characteristics are shown in FIG.

Comparative Example 5
A sample was synthesized in the same manner as in Example 1 except that LiCl—KCl eutectic salt (molar ratio, 41:59) was used for ion exchange and the temperature was 365 ° C.

As shown in FIG. 15, the XRD pattern is a layered rock salt structure with an O3 structure, and when assigned as hexagonal crystals, the a-axis length was 2.8856 mm and the c-axis length was 14.312 mm. The seat occupancy rate was 8.4%. (Rwp 15.19%, Rp 10.35%, Re 8.62%) Therefore, in the calculation, the composition formula is [Li _0.84 □ _0.08 Ni _0.08 ] _3a [Ni _0.38 Mn _{0. 54} Li _0.08 ] _3b [O ₂ ] _6c (□: vacancy).

  Furthermore, a NiO phase also appeared in the XRD pattern of the composite oxide after Li ion exchange. As a result of the chemical analysis by the ICP method, the composition of the composite oxide was Li / (Ni + Mn) (molar ratio) = 0.92, Mn / Ni (molar ratio) = 1.17, and the Na content was 0.1 wt%. there were.

As a result of conducting a battery characteristic test similar to that of Example 1, Q ₁₆ = 185, Q ₆₄ = 166, Q ₄₀₀ = 135, and Q ₈₀₀ = 99.

  Table 1 below collectively shows the results in Examples 1 to 3 and Comparative Examples 1 to 4.

2 is a powder X-ray diffraction pattern (pattern fitting result by Rietveld analysis) of the precursor oxide (sodium-nickel-manganese composite oxide) obtained in Example 1. FIG. 2 is a powder X-ray diffraction pattern of the composite oxide (lithium-sodium-nickel-manganese composite oxide) obtained in Example 1. FIG. 2 is a powder X-ray diffraction pattern (pattern fitting result by Rietveld analysis) of the composite oxide (lithium-nickel-manganese composite oxide) obtained in Example 1. FIG. 2 is a charge / discharge curve of the composite oxide (lithium-nickel-manganese composite oxide) obtained in Example 1. FIG. (At the first cycle) 2 is a charge / discharge cycle characteristic of the composite oxide (lithium-nickel-manganese composite oxide) obtained in Example 1. FIG. 3 is a powder X-ray diffraction pattern (pattern fitting result by Rietveld analysis) of the composite oxide (lithium-nickel-manganese composite oxide) obtained in Example 2. FIG. 2 is a charge / discharge curve of the composite oxide (lithium-nickel-manganese composite oxide) obtained in Example 2. FIG. (At the first cycle) 4 is a powder X-ray diffraction pattern (pattern fitting result by Rietveld analysis) of the composite oxide (lithium-nickel-manganese composite oxide) obtained in Example 3. FIG. 3 is a charge / discharge curve of the composite oxide (lithium-nickel-manganese composite oxide) obtained in Example 3. FIG. (At the first cycle) 4 is a powder X-ray diffraction pattern of the precursor oxide (sodium-nickel-manganese composite oxide) obtained in Comparative Examples 1 and 2. FIG. 4 is a powder X-ray diffraction pattern of the precursor oxide (sodium-nickel-manganese composite oxide) obtained in Comparative Examples 1 and 2. FIG. FIG. 6 is a powder X-ray diffraction pattern (pattern fitting result by Rietveld analysis) of the composite oxide (lithium-nickel-manganese composite oxide) obtained in Comparative Example 3. 4 is a charge / discharge cycle characteristic of the composite oxide (lithium-nickel-manganese composite oxide) obtained in Comparative Example 3. 6 is a powder X-ray diffraction pattern of the composite oxide (lithium-nickel-manganese composite oxide) obtained in Comparative Example 4. FIG. 6 is a powder X-ray diffraction pattern (pattern fitting result by Rietveld analysis) of the composite oxide (lithium-nickel-manganese composite oxide) obtained in Comparative Example 5. FIG. It is the current density dependence of the discharge capacity of the composite oxide (lithium-nickel-manganese composite oxide) obtained in Examples 1 and 2 and Comparative Examples 1, 2, 3, and 5.

Claims (7)

It is a layered rock salt structure (O3 structure) that does not contain NiO as a by-product phase, Li / transition metal (molar ratio) is 0.80 or more and 0.94 or less, and contains at least Ni and Mn as transition metals, Lithium-nickel- having a Mn / Ni molar ratio of greater than 1.08, a Ni atom occupancy in the Li main layer of 0.0% to 6.0%, and a Na content of 0.2 wt% or less Manganese composite oxide. The lithium-nickel- of claim 1, wherein the lattice constant a-axis length in the case of hexagonal crystal is 2.880 ≦ a ≦ 2.890 and the c-axis length is 14.29 ≦ c ≦ 14.32 Manganese composite oxide. The chemical composition is represented by the chemical formula of Li _{0.88 + x} Ni _{0.46 + y} Mn _0.54-y O ₂ (−0.08 ≦ x ≦ 0.06, −0.02 ≦ y ≦ 0.02), and the space group 3. The lithium-nickel-manganese composite oxide according to claim 1, comprising a crystal phase having a layered rock salt structure represented by R-3m. The method for producing a lithium-nickel-manganese composite oxide according to claim 1, wherein the Na—Ni—Mn composite oxide calcined at 800 ° C. or more and 1000 ° C. or less is subjected to Li ion exchange. The Ni, Mn raw material and Na compound which were refined | miniaturized to the particle diameter of 0.3 micrometer or less are mixed, and after baking in air at 800 degreeC or more and 1000 degrees C or less, it synthesize | combines by performing Li ion exchange. A method for producing a lithium-nickel-manganese-composite oxide. A positive electrode active material for a lithium ion secondary battery comprising the lithium-nickel-manganese composite oxide according to claim 1. The lithium ion secondary battery formed using the positive electrode active material for lithium ion secondary batteries of Claim 6.

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