JP2004323331A - Lithium-nickel-manganese compound oxide, its manufacturing method and its application - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium-nickel-manganese compound for improving the output characteristics which is a problem about LiNi<SB>0.5</SB>Mn<SB>0.5</SB>O<SB>2</SB>and to provide a lithium ion secondary cell using the compound. <P>SOLUTION: The lithium-nickel-manganese compound oxide is expressed by general formula of Li<SB>1+α-β</SB>A<SB>β</SB>Ni<SB>0.5</SB>Mn<SB>0.5</SB>O<SB>2</SB>(α≥0 and β>0) with α and β satisfying the relation of 1.00≤1+α≤1.25 and 0<β/(1+α)≤0.20, wherein A represents at least one element selected from alkali metals and alkaline earth metals. The compound has a layer rock salt structure in a single phase and has the ratio c/a of the c axis length to the a axis length in the range of ≥4.945 and ≤4.980 as the lattice constant attributed to the hexagonal system. In particular, the alkali metal or alkaline earth metal is at least one kind of metal selected from a group comprising sodium, potassium and magnesium. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

以上の結果から、比較例１のＬｉ_１．０１Ｎｉ_０．５Ｍｎ_０．５Ｏ_２の出力特性、充放電サイクル特性に比し、実施例１〜５のＮａ置換材料、Ｋ置換材料、およびＭｇ置換材料では出力特性、充放電サイクル特性が改善される傾向を示した。
【００３５】
【発明の効果】
本発明のリチウム−ニッケル−マンガン複合酸化物を用いることにより、Ｌｉ_１．０１Ｎｉ_０．５Ｍｎ_０．５Ｏ_２に比し高負荷での出力特性を改善したリチウム−ニッケル−マンガン複合酸化物およびこれを用いたリチウムイオン二次電池用正極活物質を提供可能である。
【図面の簡単な説明】
【図１】実施例１、２および比較例１、２、３、４に従って得られたリチウム−ニッケル−マンガン複合酸化物の粉末Ｘ線回折図を示す。
【図２】実施例１、２および比較例１に従って得られたリチウム−ニッケル−マンガン複合酸化物のＮａ置換量と六方晶で帰属された格子定数の比率ｃ／ａ値との相関図を示す。
【図３】実施例３に従って得られたＬｉ_１．１３Ｎａ_０．１０Ｎｉ_０．５０Ｍｎ_０．５０Ｏ_２の粉末Ｘ線回折図を示す。
【図４】実施例４に従って得られたＬｉ_０．９６Ｋ_０．０４Ｎｉ_０．５０Ｍｎ_０．５０Ｏ_２の粉末Ｘ線回折図を示す。
【図５】実施例５に従って得られたＬｉ_１．０１Ｍｇ_０．０５Ｎｉ_０．５０Ｍｎ_０．５０Ｏ_２の粉末Ｘ線回折図を示す。
【図６】比較例５に従って得られたＬｉ_１．３２Ｎａ_０．１６Ｎｉ_０．５０Ｍｎ_０．５０Ｏ_２の粉末Ｘ線回折図を示す。
【図７】比較例６に従って得られたＬｉ_０．７９Ｎａ_０．１７Ｎｉ_０．５０Ｍｎ_０．５０Ｏ_２の粉末Ｘ線回折図を示す。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a lithium-nickel-manganese composite oxide used as a positive electrode active material for a secondary battery, a method for producing the same, and uses thereof.
[0002]
[Prior art]
In recent years, the miniaturization and cordlessness of AV equipment, mobile phones, personal computers, and the like have been rapidly progressing.₂, LiNiO₂, LiMn₂O₄Etc. have been studied. However, none of these materials can be said to satisfy all of electrochemical capacity, safety and cost._0.5Mn_0.5O₂Li-Ni-Mn composite oxides are disclosed as materials satisfying high energy density, safety and cost (for example, Non-Patent Document 1). The LiNi_0.5Mn_0.5O₂Is a conventional LiNiO₂LiNi with Mn substituted for Ni_1-XMn_XO₂The idea is fundamentally different from system materials. That is, LiNiO₂And LiMnO₂It is disclosed that, instead of improving the properties possessed by Ni and Mn, a new function is exhibited by forming a solid solution by uniformly dispersing Ni and Mn (Patent Document 1). .
[0003]
However, we have found that LiNi_0.5Mn_0.5O₂As a result of detailed evaluation of the electrochemical characteristics of the positive electrode material using₂, LiNiO₂, LiMn₂O₄It became clear that there was a problem in the output characteristics as compared with the above. In addition, the LiNi_0.5Mn_0.5O₂According to the results of Rietveld analysis of the XRD pattern described above, there is a disclosure that cation mixing occurs (Non-Patent Document 2), and it is possible to think that these structural irregularities affect output characteristics and the like.
[0004]
In order to solve the above problems, the present invention provides LiNi_0.5Mn_0.5O₂Is a Li-Ni-Mn composite oxide obtained by substituting a part of the Li layer with a different element, an alkali metal or an alkaline earth metal, and the composition achieves improvement in output characteristics.
[0005]
Heretofore, there have been several inventions in which Li is replaced with a different element, but the composition is fundamentally different from that of the present invention, and no sufficient example is described. That is, a compound mainly composed of Co is disclosed (Patent Document 2), but there is no description of a Li-Ni-Mn compound in Examples. Further, substitution of an alkali metal for Li in a Li—Ni—Me compound (Me; Co, Mn, Al, Cr, Fe, V, Ti, Ga) is disclosed in the claims (Patent Documents 3 and 4). ), But in the description there are examples relating to the alkali metal substitution of Li and Li_1-XA_XNi_0.5Mn_0.5O₂No examples relating to the composition are given.
[0006]
[Patent Document 1] JP-A-2002-42813
[Patent Document 2] JP-A-5-74451
[Patent Document 3] JP-A-2001-85006
[Patent Document 4] JP-A-2001-243952
[Non-Patent Document 1] Proceedings of the 41st Battery Symposium on Battery (2000) 460-461
[Non-Patent Document 2] Nakano et al. Journal of the Ceramic Society of Japan 111 [1] 33-36 (2003)
[0007]
[Problems to be solved by the invention]
LiNi synthesized by the present inventors using a Ni-Mn composite hydroxide as a raw material_0.5Mn_0.5O₂As a result of examining the output characteristics of₂O₄, LiNi_0.5Mn_0.5O₂LiCoO with the same layered rock salt structure as₂, LiNiO₂It was found that the output characteristics were clearly lower than in the case of. Therefore, the problem to be solved by the present invention is LiNi_0.5Mn_0.5O₂, A novel lithium-nickel-manganese composite oxide having improved output characteristics while maintaining a structure in which transition metal layer (3b-site) contains equal amounts of Ni and Mn, and a composite oxide thereof An object of the present invention is to provide a lithium ion-based positive electrode active material, a method for producing the same, and a lithium ion secondary battery using the positive electrode active material.
[0008]
[Means for Solving the Problems]
The lithium-nickel-manganese composite oxide of the present invention for solving the above-mentioned problems has a general formula Li_{1+ α − β}A_βNi_0.5Mn_0.5O₂(Α ≧ 0, β> 0), wherein α and β satisfy the relational expressions of 1.00 ≦ 1 + α ≦ 1.25, 0 <β / (1 + α) ≦ 0.20, wherein A is an alkali At least one element selected from a metal and an alkaline earth metal, wherein a ratio c / a of a lattice constant, a-axis length, and c-axis length attributed in a hexagonal crystal is 4.945 or more and 4.980 or less. And a single-phase layered rock salt structure.
[0009]
Particularly, a lithium-nickel-manganese composite oxide in which the alkali metal or alkaline earth metal is at least one metal selected from the group consisting of sodium, potassium and magnesium is preferable.
[0010]
Hereinafter, the present invention will be described in detail.
[0011]
The lithium-nickel-manganese composite oxide of the present invention has the general formula Li_{1+ α − β}A_βNi_0.5Mn_0.5O₂(Α ≧ 0, β> 0), wherein α and β satisfy the relational expressions of 1.00 ≦ 1 + α ≦ 1.25, 0 <β / (1 + α) ≦ 0.20, wherein A is an alkali At least one element selected from metals and alkaline earth metals, wherein the lattice constant, a-axis length, and c-axis length ratio c / a attributed to hexagonal crystal satisfy 4.945 or more and 4.980 or less It is. Here, when α <0, the cation mixing, that is, the movement of Ni to the Li layer becomes remarkable, so that structural irregularities are caused and the electrochemical characteristics are reduced. Therefore, α ≧ 0 is essential. Although the β value depends on the type of the element A, the β-value is a single-phase layered rock salt structure, specifically, a single-phase structure having an R3m structure or a c2 / m structure, and a range in which the single-phase structure is maintained is essential. It is. Furthermore, the ratio c / a of the lattice constant, a-axis length, and c-axis length attributed to hexagonal crystal increases with the introduction of A. The c / a is LiNi_1/2Mn_1/2O₂C / a of 4.945 or more and 4.980 or less. Although the cause is not clear at present, the output characteristics tend to improve as c / a increases, that is, as the c-axis length is selectively extended. Further, the upper limit of c / a needs to be in a range where the layered rock salt structure is maintained.
[0012]
Further, the lithium-nickel-manganese composite oxide of the present invention has a general formula Li_{1+ α − β}A_βNi_0.5Mn_0.5O₂Α and β in the equation represented by β = 1 (NaNi_1/2Mn_1/2O₂), If α and β do not satisfy the relational expressions of 1.00 ≦ 1 + α ≦ 1.25 and 0 <β / (1 + α) ≦ 0.20, would a single-phase single-layered rock salt structure be obtained? Or, even if a single-phase single-layered rock salt structure is obtained, a desired initial output characteristic cannot be obtained due to a low initial discharge capacity or a low high-rate discharge ratio.
[0013]
The lithium-nickel-manganese composite oxide of the present invention has the general formula Li_{1+ α − β}A_βNi_0.5Mn_0.5O₂(Α ≧ 0, β> 0) A in the formula is an alkali metal or an alkaline earth metal, preferably at least one metal selected from the group consisting of sodium, potassium and magnesium, and more preferably sodium. . Because, Na⁺(1.16 angstroms) is Li among the alkali metals⁺(0.88 angstroms) and the closest ion radius, Li⁺This is because replacement with is easy.
[0014]
As the method for producing the lithium-nickel-manganese composite oxide of the present invention, various methods such as a neutralization coprecipitation method, a powder mixing method and a solid-liquid mixing method are possible. It can be produced from a step of mixing a manganese composite oxide, a lithium compound and a compound of an alkali metal or an alkaline earth metal, and then firing at a temperature of 750 ° C. or more and 1000 ° C. or less in an aerobic atmosphere.
[0015]
It is essential to set the firing temperature in the lower temperature range of 750 ° C. or more and 1000 ° C. or less. If it is lower than 750 ° C., crystallization is not sufficient, and if it exceeds 1000 ° C., structural irregularity tends to occur.
[0016]
In addition, hydroxides, acetates, carbonates, oxalates, nitrates, chlorides, sulfates, and the like can be used for the lithium compound, and hydroxides, acetates, and compounds of alkali metals or alkaline earth metals can also be used. Although carbonates, oxalates, nitrates, chlorides, sulfates, and the like can be used, it is preferable to use hydroxides or carbonates that have a low decomposition temperature and do not generate corrosive gas. Moreover, the ilmenite structure type nickel-manganese composite oxide used here has high reactivity with an alkali compound. The ilmenite structure type nickel-manganese composite oxide is obtained by calcining a nickel-manganese coprecipitate such as a nickel-manganese composite hydroxide, a nickel-manganese composite carbonate, and a nickel-manganese composite oxalate obtained by a coprecipitation operation. It is possible to obtain by doing. In this case, the nickel-manganese coprecipitate is preferably a uniform crystal phase in which nickel and manganese are dissolved. This is because nickel-manganese composite oxides that react with lithium compounds must maintain uniformity at the atomic level by the coprecipitation method, and operations such as powder mixing have high crystal perfection and high electrochemical properties. Tends to not be obtained.
[0017]
As a method of mixing the ilmenite structure nickel-manganese composite oxide with a lithium compound, an alkali metal compound and an alkaline earth metal compound, in addition to a dry mixing method, a lithium salt, an alkali metal and an alkaline earth salt are converted to water or alcohol or the like. It is also effective to use a wet slurry which is dispersed or dissolved, impregnated with the nickel-manganese composite oxide, dried and fired. The slurry may be sprayed and dried by a spray. In addition, an oxygen atmosphere is essential for the firing atmosphere. When calcined in an oxygen-free atmosphere such as nitrogen or argon, the reduction of oxides occurs, and the desired product cannot be obtained. Here, the aerobic atmosphere means an atmosphere having a higher oxygen partial pressure than air, such as air or pure oxygen.
[0018]
【Example】
Hereinafter, the present invention will be described with reference to the following specific examples, but the present invention is not limited by these examples.
(Preparation method of ilmenite structure type nickel-manganese oxide)
In Examples 1 to 5 and Comparative Examples 1 to 6, the ilmenite structure type nickel-manganese oxide obtained by the following method was used as a raw material.
[0019]
450 ml of an aqueous solution in which 0.20 mol of nickel sulfate and 0.20 mol of manganese sulfate are dissolved and 450 ml of an aqueous solution in which 0.80 mol of sodium hydroxide are dissolved are stirred into 800 ml of a 1.6 mol / L aqueous ammonium solution, and nitrogen is added. After simultaneous dropping while bubbling, the mixture was stirred and mixed at 25 ° C. overnight. Thereafter, while stirring 1.5 L of pure water, 50 ml of a 1.6 mol / L aqueous ammonium solution, 100 ml of 35% hydrogen peroxide solution and 100 ml of the obtained nickel-manganese coprecipitated slurry were added in the above order, and furthermore, Stirring was performed for 3 hours. Thereafter, the precipitate was separated by filtration, dried at 80 ° C. overnight, and calcined at 400 ° C. in an air stream for 2 hours.
(Charge / discharge cycle test and output characteristics test method)
Using the lithium-nickel-manganese composite oxide obtained in Examples 1 to 5 and Comparative Examples 1 to 6 as a cathode material of a battery, a mixture of polytetrafluoroethylene and acetylene black as conductive agents (trade name: TAB-2) ) 2: 1 by weight ratio, 1 ton / cm²After being formed into a pellet shape on a mesh (made of SUS316) at a pressure of 5 ° C., it was dried at 150 ° C. under reduced pressure to prepare a positive electrode for a battery. 1 mol / dm. Of lithium hexafluorophosphate in a mixed solvent of propylene carbonate and diethyl carbonate, and a negative electrode composed of the obtained battery positive electrode, a metal lithium foil (0.2 mm thick),³A battery was constructed using an electrolytic solution dissolved at a concentration of. The battery thus prepared was charged and discharged at 23 ° C. at a constant current and a battery voltage of 4.3 V to 2.5 V. Charging is 0.4mA · cm^-2And discharge is performed at a current density of 0.4 mA · cm.^-2And 2.5 mA · cm^-2At two constant currents. Change the high rate discharge ratio to the discharge capacity ratio (2.5 mA^-2/0.4mA·cm^-2). The above was the output characteristic test. Further, the current density is 0.4 mA · cm^-2The charge and discharge under the above conditions were repeated for 50 cycles.
[0020]
Example 1
The ilmenite structure type nickel-manganese oxide, lithium hydroxide monohydrate and sodium carbonate have an alkali metal (sodium + lithium) / transition metal (nickel + manganese) atomic ratio of 1.03, and a sodium / alkali metal (atomic ratio). ) Was adjusted to 0.067 with an automatic mortar for 1 hour. The obtained mixture was calcined in an air stream at 950 ° C. for 20 hours to obtain a lithium-sodium-nickel-manganese composite oxide. As a result of ICP composition analysis, Li_0.94Na_0.06Ni_0.50Mn_0.50O₂Met. The X-ray diffraction pattern was as shown in FIG. 1 and was an R3m structure containing no by-product phase or its related structure, that is, a single-phase layered rock salt structure. As a result of pattern fitting of the powder X-ray pattern by hexagonal crystal by the WPPD method developed by Toraya et al. (H. Toraya et al., J. Appl. Cryst. 19, 440 (1986)), as shown in FIG. The a-axis length is 2.901 angstroms, the c-axis length is 14.37 angstroms, and c / a is 4.953._1.01Ni_0.50Mn_0.50O₂The tendency of the c-axis length to selectively elongate compared to the lattice constant of was observed.
[0021]
When a discharge cycle test is performed, the initial discharge capacity (0.4 mA · cm^-2) 147 mAh / g, high rate discharge ratio was 85.9%, and capacity retention (%) was 93.0%.
[0022]
Example 2
The ilmenite structure type nickel-manganese oxide, lithium hydroxide monohydrate and sodium carbonate have an alkali metal (sodium + lithium) / transition metal (nickel + manganese) atomic ratio of 1.03, and a sodium / alkali metal (atomic ratio). ) Was adjusted to 0.017 with an automatic mortar for 1 hour. The obtained mixture was calcined in an air stream at 950 ° C. for 20 hours to obtain a lithium-sodium-nickel-manganese composite oxide. As a result of ICP composition analysis, Li_0.82Na_0.19Ni_0.50Mn_0.50O₂Met. The X-ray diffraction pattern was as shown in FIG. 1 and was an R3m structure containing no by-product phase or its related structure, that is, a single-phase layered rock salt structure. Further, as a result of fitting the X-ray diffraction pattern by the WPPD method, c / a was 4.973._0.50Mn_0.50O₂The tendency of the c-axis length to selectively elongate compared to the lattice constant of was observed. Further, as shown in FIG. 2, c / a tended to be proportional to the atomic ratio of Na / (Li + Na), that is, the Na substitution amount.
[0023]
Further, when this was used as a cathode material of a battery and an output characteristic test was performed in the same manner as in Example 1, the initial discharge capacity (0.4 mA · cm^-2) 149 mAh / g, high rate discharge ratio 92.4%. Further, as a result of performing a charge / discharge cycle test, the capacity retention ratio was 96.1%.
[0024]
Example 3
An ilmenite structure type nickel-manganese oxide, lithium hydroxide monohydrate and sodium carbonate have an alkali metal (sodium + lithium) / transition metal (nickel + manganese) atomic ratio of 1.25 and a sodium / alkali metal (atomic ratio). ) Was adjusted to 0.080 with an automatic mortar for 1 hour. The obtained mixture was calcined in an air stream at 950 ° C. for 20 hours to obtain a lithium-sodium-nickel-manganese composite oxide. As a result of ICP composition analysis, Li_1.13Na_0.10Ni_0.50Mn_0.50O₂Met. The X-ray diffraction pattern was as shown in FIG. 3 and showed an R3m structure containing no by-product phase or a related structure thereof, that is, a single-phase layered rock salt structure. As a result of fitting the X-ray diffraction pattern by the WPPD method, c / a was 4.952, and LiNi_0.50Mn_0.50O₂The tendency of the c-axis length to selectively elongate compared to the lattice constant of was observed. Further, when this was used as a cathode material for a battery and an output characteristic test similar to that in Example 1 was performed, the initial discharge capacity (0.4 mA · cm^-2) 142 mAh / g, high rate discharge ratio 98.0%. As a result of performing a charge / discharge cycle test, the capacity retention ratio was 97.9%.
[0025]
Example 4
The ilmenite type nickel-manganese oxide, lithium hydroxide monohydrate and potassium carbonate have an alkali metal (potassium + lithium) / transition metal (nickel + manganese) atomic ratio of 1.02, potassium / alkali metal (atomic ratio) ) Was 0.042 in an automatic mortar for 0.042. The obtained mixture was calcined in an air stream at 950 ° C. for 20 hours to obtain a lithium-potassium-nickel-manganese composite oxide. As a result of ICP composition analysis, Li_0.96K_0.04Ni_0.50Mn_0.50O₂Met. The X-ray diffraction pattern was as shown in FIG. 4 and showed an R3m structure containing no by-product phase or a related structure thereof, that is, a single-phase layered rock salt structure. Further, as a result of fitting the X-ray diffraction pattern by the WPPD method, c / a was 4.954._1.01Ni_0.50Mn_0.50O₂The tendency of the c-axis length to selectively elongate compared to the lattice constant of was observed. Further, when this was used as a cathode material for a battery and an output characteristic test similar to that in Example 1 was performed, the initial discharge capacity (0.4 mA · cm^-2) 146 mAh / g, high rate discharge ratio: 84.7%.
[0026]
Example 5
An ilmenite structure type nickel-manganese oxide, lithium hydroxide monohydrate and magnesium hydroxide have an alkali metal (magnesium + lithium) / transition metal (nickel + manganese) atomic ratio of 1.05, magnesium / alkali metal (atom) (Ratio) was 0.057 in an automatic mortar for 1 hour. The obtained mixture was calcined at 950 ° C. for 20 hours in an air stream to obtain a lithium-magnesium-nickel-manganese composite oxide. As a result of ICP composition analysis, Li_1.01Mg_0.05Ni_0.50Mn_0.50O₂Met. The X-ray diffraction pattern was as shown in FIG. 5 and showed a phase close to the R3m structure or its related structure, that is, a single-phase layered rock salt structure. Further, as a result of fitting the X-ray diffraction pattern by the WPPD method, c / a was 4.945._1.01Ni_0.50Mn_0.50O₂The tendency of the c-axis length to selectively elongate compared to the lattice constant of was observed. Further, when this was used as a cathode material for a battery and an output characteristic test similar to that in Example 1 was performed, the initial discharge capacity (0.4 mA · cm^-2) 145 mAh / g, high rate discharge ratio 83.6%.
[0027]
Comparative Example 1
The ilmenite structure-type nickel-manganese oxide and lithium hydroxide monohydrate were mixed in an automatic mortar for one hour so that the alkali metal / transition metal (nickel + manganese) atomic ratio was 1.02. The obtained mixture was calcined at 950 ° C. for 20 hours in an air stream to obtain a lithium-nickel-manganese composite oxide. As a result of ICP composition analysis, Li_1.01Ni_0.5Mn_0.5O₂Met. The X-ray diffraction pattern was as shown in FIG. 1 and showed an R3m structure or its related structure, that is, a single-phase layered rock salt structure. As a result of fitting the X-ray diffraction pattern by the WPPD method, as shown in FIG. 2, c / a was 4.941. Further, when this was used as a cathode material of a battery and an output characteristic test was performed in the same manner as in Example 1, the initial discharge capacity (0.4 mA · cm^-2) 145 mAh / g, high rate discharge ratio: 82.4%. Further, as a result of performing the same charge / discharge cycle test as in Example 1, the capacity retention ratio was 86.3%.
[0028]
Comparative Example 2
An ilmenite structure type nickel-manganese oxide, lithium hydroxide monohydrate and sodium carbonate have an alkali metal (sodium + lithium) / transition metal (nickel + manganese) atomic ratio of 1.01, sodium / alkali metal (atomic ratio) ) Was 0.30 with an automatic mortar for 1 hour. The obtained mixture was calcined in an air stream at 950 ° C. for 20 hours to obtain a lithium-sodium-nickel-manganese composite oxide. As a result of ICP composition analysis, Li_0.71Na_0.30Ni_0.50Mn_0.50O₂Met. The X-ray diffraction pattern was as shown in FIG. 1 and was a mixed phase having a layered rock salt structure. In addition, as a result of performing the same output characteristic test as in Example 1, the initial discharge capacity (0.4 mA · cm^-2) 95.5 mAh / g, high rate discharge ratio: 49.9%.
[0029]
Comparative Example 3
The ilmenite structure type nickel-manganese oxide, lithium hydroxide monohydrate and sodium carbonate have an alkali metal (sodium + lithium) / transition metal (nickel + manganese) atomic ratio of 1.02, and a sodium / alkali metal (atomic ratio). ) Was 0.50 in an automatic mortar for 0.5 hour. The obtained mixture was calcined in an air stream at 950 ° C. for 20 hours to obtain a lithium-sodium-nickel-manganese composite oxide. As a result of ICP composition analysis, Li_0.50Na_0.51Ni_0.50Mn_0.50O₂Met. The X-ray diffraction pattern was as shown in FIG. 1 and was a mixed phase having a layered rock salt structure. In addition, as a result of performing the same output characteristic test as in Example 1, the initial discharge capacity (0.4 mA · cm^-2) 80.7 mAh / g, high rate discharge ratio 48.3%.
[0030]
Comparative Example 4
The ilmenite structure type nickel-manganese oxide, lithium hydroxide monohydrate and sodium carbonate have an alkali metal (sodium + lithium) / transition metal (nickel + manganese) atomic ratio of 1.02, and a sodium / alkali metal (atomic ratio). ) Was adjusted to 0.670 with an automatic mortar for 1 hour. The obtained mixture was calcined in an air stream at 950 ° C. for 20 hours to obtain a lithium-sodium-nickel-manganese composite oxide. As a result of ICP composition analysis, Li_0.32Na_0.68Ni_0.50Mn_0.50O₂Met. The X-ray diffraction pattern was as shown in FIG. 1 and was a mixed phase having a layered rock salt structure. In addition, as a result of performing the same output characteristic test as in Example 1, the initial discharge capacity (0.4 mA · cm^-2) 29.0 mAh / g, high rate discharge ratio 51.1%.
[0031]
Comparative Example 5
The ilmenite structure type nickel-manganese oxide, lithium hydroxide monohydrate and sodium carbonate have an alkali metal (sodium + lithium) / transition metal (nickel + manganese) atomic ratio of 1.51, sodium / alkali metal (atomic ratio) ) Was 0.110 with an automatic mortar for 1 hour. The obtained mixture was calcined in an air stream at 950 ° C. for 20 hours to obtain a lithium-sodium-nickel-manganese composite oxide. As a result of ICP composition analysis, Li_1.32Na_0.16Ni_0.50Mn_0.50O₂Met. The X-ray diffraction pattern was as shown in FIG. 6, which was R3m containing some by-product phases or a related structure, that is, a single-phase layered rock salt structure. In addition, as a result of performing the same output characteristic test as in Example 1, the initial discharge capacity (0.4 mA · cm^-2) 118 mAh / g, high rate discharge ratio 93.8%.
[0032]
Comparative Example 6
The ilmenite structure type nickel-manganese oxide, lithium hydroxide monohydrate, and sodium carbonate have an alkali metal (sodium + lithium) / transition metal (nickel + manganese) atomic ratio of 0.970, and a sodium / alkali metal (atomic ratio). ) Was 0.180 with an automatic mortar for 1 hour. The obtained mixture was calcined in an air stream at 950 ° C. for 20 hours to obtain a lithium-sodium-nickel-manganese composite oxide. As a result of ICP composition analysis, Li_0.79Na_0.17Ni_0.50Mn_0.50O₂Met. The X-ray diffraction pattern was as shown in FIG. 7, which was R3m containing a by-product phase or an analogous structure thereof, that is, a single-phase layered rock salt structure. As a result of performing the same output characteristic test as in Example 1, the initial discharge capacity (0.4 mA · cm^-2) 111 mAh / g, high rate discharge ratio 40.9%.
[0033]
The chemical compositions of Examples 1 to 5 and Comparative Examples 1 to 6, 1 + α value, β / (1 + α) value, c / a, initial discharge capacity value, high-rate discharge ratio, and capacity retention ratio are shown in Table 1 below. .
[0034]
[Table 1]

From the above results, Li of Comparative Example 1_1.01Ni_0.5Mn_0.5O₂In comparison with the output characteristics and the charge / discharge cycle characteristics of Examples 1 to 5, the Na-substituted material, the K-substituted material and the Mg-substituted material of Examples 1 to 5 tended to have improved output characteristics and charge-discharge cycle characteristics.
[0035]
【The invention's effect】
By using the lithium-nickel-manganese composite oxide of the present invention, Li_1.01Ni_0.5Mn_0.5O₂It is possible to provide a lithium-nickel-manganese composite oxide having improved output characteristics under a high load as compared with the above, and a positive electrode active material for a lithium ion secondary battery using the same.
[Brief description of the drawings]
FIG. 1 shows a powder X-ray diffraction diagram of a lithium-nickel-manganese composite oxide obtained according to Examples 1 and 2 and Comparative Examples 1, 2, 3, and 4.
FIG. 2 shows a correlation diagram between the amount of Na substitution of the lithium-nickel-manganese composite oxide obtained according to Examples 1 and 2 and Comparative Example 1 and the ratio c / a of the lattice constant attributed to hexagonal. .
FIG. 3 shows Li obtained according to Example 3._1.13Na_0.10Ni_0.50Mn_0.50O₂1 shows a powder X-ray diffraction pattern of the sample.
FIG. 4 shows Li obtained according to Example 4._0.96K_0.04Ni_0.50Mn_0.50O₂1 shows a powder X-ray diffraction pattern of the sample.
FIG. 5 Li obtained according to Example 5_1.01Mg_0.05Ni_0.50Mn_0.50O₂1 shows a powder X-ray diffraction pattern of the sample.
FIG. 6 shows Li obtained according to Comparative Example 5._1.32Na_0.16Ni_0.50Mn_0.50O₂1 shows a powder X-ray diffraction pattern of the sample.
FIG. 7 shows Li obtained according to Comparative Example 6._0.79Na_0.17Ni_0.50Mn_0.50O₂1 shows a powder X-ray diffraction pattern of the sample.

Claims (5)

Formula _{Li 1+ α - β A β Ni} 0.5 Mn 0.5 O 2 (α ≧ 0, β> 0) is represented by, alpha and beta are 1.00 ≦ 1 + α ≦ 1.25,0 < β / (1 + α) ≦ 0.20, wherein A is at least one element selected from alkali metals and alkaline earth metals, and has a lattice constant assigned by hexagonal system, a-axis length, c A lithium-nickel-manganese composite oxide having an axis length ratio c / a of 4.945 or more and 4.980 or less and having a single-phase layered rock salt structure. The lithium-nickel-manganese composite oxide according to claim 1, wherein the alkali metal or alkaline earth metal is at least one metal selected from the group consisting of sodium, potassium, and magnesium. An ilmenite structure nickel-manganese composite oxide, a lithium compound and a compound of an alkali metal or an alkaline earth metal are mixed, and then calcined at a temperature of 750 ° C or more and 1000 ° C or less in an aerobic atmosphere. The method for producing a lithium-nickel-manganese composite oxide according to claim 1 or 2. A positive electrode active material for a lithium ion secondary battery, comprising the lithium-nickel-manganese composite oxide according to claim 1. A lithium ion secondary battery using the positive electrode active material according to claim 4.

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