Lithium nickel manganese-based and lithium nickel iron manganese-based composite oxide-inorganic acid composite and production method of the same

Abstract

To provide a cobalt-free positive electrode material having a charge-discharge capacity being equivalent or more in comparison with that of existing NMC-based positive electrode materials and having a high average discharge voltage cycle retention rate.SOLUTION: A lithium nickel manganese-based or lithium nickel iron manganese-based composite oxide-inorganic acid composite is represented by the following general formula (1): Li1+x(NiyFezMn1-y-z)1-xO2 (1) [In the formula, x, y, and z respectively represent 0<x<1 / 3, 0.2≤y≤0.4, 0≤z≤0.2.] and has a monoclinic Li2MnO3-type layered rock salt structure, wherein the inorganic acid is phosphoric acid or silicic acid, and an R / (Ni+Fe+Mn) atomic ratio is 0.001≤R / (Ni+Fe+Mn)≤0.05 [In the formula, R is a phosphorus atom or silicon atom constituting the inorganic acid].SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a lithium nickel manganese-based and lithium nickel iron manganese-based composite oxide-inorganic acid complex and a method for producing the same.

Background Art

[0002] Lithium ion secondary batteries, which are useful as secondary batteries mounted on notebook personal computers and smartphones, etc., are also attracting attention as batteries for electric vehicles and plug-in hybrid vehicles, and as system configuration power sources for power load leveling systems, etc., and development is underway.

[0003] Lithium ion secondary batteries generally include a lithium transition metal composite oxide as a positive electrode, a carbon material as a negative electrode, and an organic electrolyte as components. The positive electrode material functions as a lithium supply source, and the product of the amount of lithium ion desorption and insertion in the positive electrode material and the amount of the positive electrode in a single cell determines the battery capacity of the single cell, and the operating voltage in the positive electrode material determines the single cell voltage. Therefore, it is one of the most important constituent members.

[0004] Currently, lithium nickel manganese cobalt oxide-based (NMC-based) positive electrode materials and lithium nickel oxide-based (high nickel-based) positive electrode materials are generally used as large-sized lithium ion secondary battery positive electrode materials. High nickel-based positive electrodes have a larger capacity per unit weight of the positive electrode material compared to NMC-based positive electrode materials, but there are problems with safety during charging. Therefore, NMC-based positive electrodes have been put into practical use for large-capacity prismatic batteries, while high nickel-based positive electrode materials have only been put into practical use for small-capacity cylindrical batteries.

[0005] On the other hand, both types of positive electrode materials contain cobalt elements that are highly unevenly distributed as resources and are rare. Considering the instability of cobalt raw material prices, the development of cobalt-free positive electrode materials with excellent charge and discharge characteristics is strongly demanded.

[0006] The inventor has clarified that a lithium nickel manganese composite oxide having a monoclinic Li2MnO3 layered rock salt structure (Patent Document 1) and a composite of a lithium iron nickel manganese composite oxide containing a different metal element (Patent Documents 2 and 3) exhibit excellent charge and discharge characteristics. However, among lithium nickel manganese composite oxides or lithium iron nickel manganese composite oxides, it remains unclear which materials should be combined to produce a secondary battery with excellent charge and discharge characteristics.

[0007] In particular, this material has been pointed out as a serious drawback for its discharge potential decline behavior in which the average discharge voltage gradually decreases as the charge and discharge cycles progress (Non-Patent Document 1), and the establishment of technology to overcome this is strongly required for practical application.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Non-Patent Documents

[0009]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] In view of the above circumstances, an object of the present invention is to provide a cobalt-free cathode material having a charge and discharge capacity equal to or higher than that of existing NMC-based or high-nickel-based cathode materials and a high average discharge voltage cycle maintenance rate.

Means for Solving the Problem

[0011] As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by complexing a lithium nickel manganese composite oxide with an inorganic acid compound by a predetermined method. Based on such findings, the present inventors have further conducted studies and completed the present invention.

[0012] That is, the present invention provides the following lithium nickel manganese-based and lithium nickel iron manganese-based composite oxide-inorganic acid composites, and a method for producing the same. Item 1. The following general formula (1): Li 1+x (Ni y Fe z Mn 1-y-z ) 1-x O2(1) 〔In the formula, x, y, and z each represent 0 < x < 1 / 3, 0.2 ≤ y ≤ 0.4, and 0 ≤ z ≤ 0.2.〕 A lithium nickel manganese-based or lithium nickel iron manganese-based composite oxide-inorganic acid composite represented by the formula and having a monoclinic Li2MnO3-type layered rock salt structure, wherein the inorganic acid is phosphoric acid or silicic acid, and the R / (Ni + Fe + Mn) atomic ratio is 0.001 ≤ R / (Ni + Fe + Mn) ≤ 0.05 (wherein R is a phosphorus atom or a silicon atom constituting the inorganic acid), a lithium nickel manganese-based or lithium nickel iron manganese-based composite oxide-inorganic acid composite. Item 2. The composite according to Item 1, wherein the inorganic acid is phosphoric acid and the P / (Ni + Fe + Mn) atomic ratio is 0.01 ≤ P / (Ni + Fe + Mn) ≤ 0.05. Item 3. The composite according to Item 1, wherein the inorganic acid is silicic acid and the Si / (Ni + Fe + Mn) atomic ratio is 0.001 ≤ Si / (Ni + Fe + Mn) ≤ 0.005. Item 4. Step 1: Mixing a lithium compound with a nickel manganese precursor or a nickel iron manganese precursor and performing heat treatment in an oxidizing atmosphere. Step 2: Heat-treating the product obtained in Step 1 under higher temperature conditions than those in Step 1 in an inert atmosphere, and Step 3: Adding an inorganic acid salt to the product obtained in Step 2 and then performing heat treatment under lower temperature conditions than those in Step 2 in an inert atmosphere. The method for producing the composite according to claim 1 includes these steps. Item 5. The nickel manganese precursor or nickel iron manganese precursor in Step 1 is obtained by dropping an aqueous solution of a nickel manganese metal salt or a nickel iron manganese metal salt into an alkaline solution and then performing wet oxidation treatment and water washing treatment. The method for producing the composite according to claim 4 is as described above.

Advantages of the Invention

[0013] According to the lithium nickel manganese-based or lithium nickel iron manganese-based composite oxide-inorganic acid composite according to the present invention formed as described above, it has a charge-discharge capacity equal to or higher than that of existing NMC-based or high-nickel-based cathode materials, and a cobalt-free cathode material with a high average discharge voltage cycle maintenance rate can be obtained.

Brief Description of the Drawings

[0014]

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Mode for Carrying Out the Invention

[0015] In this specification, "containing" is a concept that encompasses any of "comprise", "consist essentially of", and "consist of". Also, in this specification, when a numerical range is indicated as "A to B", it means A or more and B or less.

[0016] (1. Lithium nickel manganese-based or lithium nickel iron manganese-based composite oxide-inorganic acid complex) The lithium nickel manganese oxide or lithium nickel iron manganese oxide forming the positive electrode active material is represented by the following composition formula (1). Li 1+x (Ni y Fe z Mn 1-y-z ) 1-x O2(1) [In the formula, x, y, and z each represent 0 < x < 1 / 3, 0.2 ≤ y ≤ 0.4, and 0 ≤ z ≤ 0.2. ]

[0017] The crystal structure belongs to the following space group (a) described in the monoclinic Li2MnO3-type layered rock salt structure (P. Strobel et al., J. Solid State Chem., 75, 90-98, (1988)).

[0018]

Number

[0019] The monoclinic Li2MnO3-type layered rock salt structure has Li layers and transition metal-Li layers stacked alternately in the c-axis direction. This stacking state is similar to that of existing lithium cobaltate and lithium nickelate (hexagonal, space group (b) below), but the types of lattice positions in each layer of the Li layer and the transition metal-containing layer are different. In hexagonal LiCoO2 and LiNiO2, the lattice positions in each layer of the Li layer and the transition metal layer are each of one type (corresponding to the 3a and 3b positions), whereas in the monoclinic Li2MnO3 type, there are two types of lattice positions in each layer (the Li layer has 2c and 4h positions, and the transition metal-Li layer has 2b and 4g positions).

[0020]

Number

[0021] In the case of the present invention, the amount of transition metal present at the above four lattice positions tends to have 4g and 2b occupancies larger than the 2c and 4h position occupancies, but since the occupancy values themselves can take any value between 0 and 1, they are not particularly limited.

[0022] The amount of inorganic acid with respect to the lithium nickel manganese oxide positive electrode active material or the lithium nickel iron manganese oxide positive electrode active material that forms a composite is such that the R / (Ni + Fe + Mn) atomic ratio [wherein R is a phosphorus atom or a silicon atom constituting the inorganic acid] is 0.001 or more and 0.05 or less. When the R / (Ni + Fe + Mn) atomic ratio deviates from this numerical range, the effect of suppressing the decrease in the average discharge potential during desired cycles cannot be obtained.

[0023] Furthermore, when phosphoric acid is used as the inorganic acid, it is preferable that the atomic ratio of P / (Ni + Fe + Mn) satisfies 0.01 ≤ P / (Ni + Fe + Mn) ≤ 0.05, and more preferably 0.02 ≤ P / (Ni + Fe + Mn) ≤ 0.04. By setting the atomic ratio of P / (Ni + Mn) to be 0.01 or more and 0.05 or less, it is possible to suppress the decrease in charge-discharge capacity during P addition and to obtain a good effect of suppressing the decrease in the average discharge potential during cycling.

[0024] Also, when silicic acid is used as the inorganic acid, it is preferable that the atomic ratio of Si / (Ni + Fe + Mn) satisfies 0.001 ≤ Si / (Ni + Fe + Mn) ≤ 0.005, and more preferably 0.002 ≤ Si / (Ni + Fe + Mn) ≤ 0.004. By setting the atomic ratio of Si / (Ni + Fe + Mn) to be 0.001 or more and 0.005 or less, it is possible to obtain a good effect of suppressing the decrease in the average discharge potential during cycling.

[0025] In addition, the lithium nickel manganese-based or lithium nickel iron manganese-based composite oxide-inorganic acid composite of the present invention may contain other impurity phases (such as lithium carbonate, lithium hydroxide, manganese and nickel compounds, or their composite compounds, phosphoric acid and silicic acid compounds, etc.) within a range that does not significantly affect the charge-discharge characteristics (up to about 10% by mass ratio).

[0026] (2. Cathode active material for lithium ion secondary battery and lithium ion secondary battery) The lithium nickel manganese-based or lithium nickel iron manganese-based composite oxide-inorganic acid composite of the present invention can be suitably used as a cathode active material for a lithium ion secondary battery. It is also possible to manufacture a lithium ion secondary battery by a conventional method using the composite containing the lithium manganese-based composite oxide of the present invention.

[0027] Specifically, as the positive electrode material, the lithium nickel manganese composite oxide of the present invention is used, and as the negative electrode material, known metallic lithium, lithium titanate, silicon, silicon oxide, or carbon-based materials (graphite-based, hard carbon-based), etc. are used. As the electrolytic solution, an organic electrolytic solution in which a lithium salt such as lithium perchlorate or LiPF6 is dissolved in a solvent such as known ethylene carbonate or dimethyl carbonate, or a polymer electrolyte, a sulfide solid electrolyte, and other known battery components are used, and a lithium ion secondary battery can be assembled according to a conventional method.

[0028] (3. Method for producing lithium nickel manganese or lithium nickel iron manganese composite oxide - inorganic acid composite) The method for producing a composite containing a lithium nickel manganese or lithium nickel iron manganese composite oxide of the present invention comprises, for example, a step 1 of mixing a lithium compound and a nickel manganese precursor or a nickel iron manganese precursor and heat-treating in an oxidizing atmosphere, a step 2 of heat-treating the product obtained in step 1 at a temperature higher than that in step 1 in an inert atmosphere, and a step 3 of adding an inorganic acid salt to the product obtained in step 2 and heating at a temperature lower than that in step 2 in an inert atmosphere, in this order.

[0029] (3.1. Step 1) Step 1 is a step of mixing a lithium salt and a nickel manganese precursor or a nickel iron manganese precursor and heat-treating in an oxidizing atmosphere. As such a nickel manganese precursor, known ones can be widely adopted and there is no particular limitation. For example, Ni a Mn 1-a (OH) b(In the above formula, 0.2 ≦ a ≦ 0.4 and 1 ≦ c ≦ 4. It is more preferable that a is 0.25 or more and 0.35 or less, and it is even more preferable that a is 0.3.) can be exemplified. The b value can change according to the valences of nickel and manganese and to maintain charge neutrality according to the a value. As for the nickel manganese precursor or nickel iron manganese precursor, commercially available ones may be purchased, or they may be prepared by the methods as described later, or it is also preferable to prepare them by conventional methods. However, when using a commercially available nickel manganese precursor, spherical ones in the form of secondary particles suitable as the positive electrode material can be manufactured, and in terms of being able to produce samples on the kg order that are difficult to prepare in a laboratory system, it is preferable. The firing batch amount is not particularly limited, and it is preferably 0.05 to 1 mol / batch in terms of the sum of the molar amounts of the constituent transition metals, and more preferably 0.1 to 0.5 mol / batch.

[0030] As a method for preparing the above-mentioned nickel manganese precursor or nickel iron manganese precursor, a method can be exemplified in which an aqueous solution of a constituent transition metal salt composed of nickel, iron, and manganese is dropped into an alkali, followed by wet oxidation treatment, and the precursor is obtained by water washing treatment.

[0031] As the above-mentioned transition metal salt, known water-soluble ones can be widely adopted and there is no particular limitation. For example, chlorides, nitrates, acetates, sulfates, etc. can be used. Also, two or more kinds of salts may be mixed and used, and the valence of the constituent transition metal ions can be arbitrarily set as long as water solubility can be maintained. The metal salt charging batch amount is not particularly limited, and it is preferably 0.05 to 1 mol / batch in terms of the sum of the molar amounts of the constituent transition metals, and more preferably 0.1 to 0.5 mol / batch.

[0032] As the alkali source used for dropping the metal salt, lithium hydroxide, aqueous ammonia, sodium hydroxide, potassium hydroxide, etc. can be used. The molar amount of the alkali source needs to be larger than the molar amount of the metal salt in order to maintain the metal salt mixing ratio. Therefore, the (alkali molar amount) / (metal salt molar amount) ratio is preferably about 2 to 10. By setting the ratio to 10 or less, the amount of alkali does not become excessive and it is advantageous in terms of cost. Also, by setting the ratio to 2 or more, it becomes easier to maintain the metal salt mixing ratio. The batch molar amount of the charge is not particularly limited, and a range of 0.1 to 0.5 mol is desirable. As a method for mixing the alkali salt and the metal salt, a method of dropping the metal salt into the alkali source is preferable. Also, in order to stably obtain the precursor, it is preferable to keep the temperature of the alkali source constant in a thermostat or the like. The temperature to be maintained is preferably about -10°C to +60°C.

[0033] The alkaline aqueous solution containing the obtained precursor is preferably subjected to wet oxidation treatment while blowing oxygen or air. The oxidation time is not particularly limited, but is preferably from 1 hour to 4 days. The temperature for oxidation is preferably 5 to 40°C. After the oxidation treatment, the obtained precursor can be washed with water, filtered, and dried as necessary to obtain a nickel-manganese precursor or a nickel-iron-manganese precursor. By producing the nickel-manganese precursor or the nickel-iron-manganese precursor by this method, the metal mixing ratio can be freely set.

[0034] Regarding the lithium salt used in Step 1, it is not particularly limited, and in addition to general lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate, lithium chloride, and their hydrates can be used. These may be used alone or in combination of two or more.

[0035] The mixing ratio of the nickel-manganese precursor and / or the nickel-iron-manganese precursor and the lithium compound is preferably 1.0 ≦ Li / (Ni + Fe + Mn) ≦ 3.0 in terms of the Li / (Ni + Fe + Mn) molar ratio, and more preferably 1.5 ≦ Li / (Ni + Fe + Mn) ≦ 2.5.

[0036] Examples of the oxidizing atmosphere include the atmosphere or an oxygen stream. The heat treatment temperature is not particularly limited, and it is preferably 500 to 800°C. The heat treatment time is also not particularly limited, and for example, it can be 1 to 48 hours. When adopting the conditions in an oxygen stream as the oxidizing atmosphere, the oxygen gas flow rate is preferably 50 to 2000 ml / min. The powder after firing may be pulverized again as necessary for the next step.

[0037] As the heat treatment method, known heat treatment methods can be widely adopted without particular limitation. More specifically, firing treatment can be mentioned.

[0038] (3.2. Step 2) In Step 2, the product obtained in Step 1 is heat-treated in an inert atmosphere and at a temperature higher than that in Step 1. The reasons are to control the valence of the composition transition metal capable of achieving high capacity and to promote grain growth for improving cycle characteristics.

[0039] The inert atmosphere is not particularly limited, and examples include a nitrogen atmosphere and an argon atmosphere.

[0040] As the heat treatment method, known heat treatment methods can be widely adopted without particular limitation. More specifically, firing treatment can be mentioned. As the temperature condition, it is necessary to carry out the treatment at a temperature higher than that during the heat treatment in Step 1. Specifically, it is preferably 800 to 950°C, and more preferably 850 to 900°C. If the heat treatment temperature in Step 2 is not higher than the heat treatment temperature in Step 1, sufficient grain growth of the product necessary for obtaining stable charge and discharge characteristics cannot be achieved.

[0041] After the heat treatment and before carrying out Step 3, the product may be pulverized as necessary.

[0042] (3.3. Step 3) In Step 3, after adding an inorganic acid salt to the product obtained in Step 2, heat treatment is carried out under an inert atmosphere at a temperature lower than that in Step 2.

[0043] The inorganic acid salt to be used is not particularly limited, and for example, a phosphate or a silicate can be used.

[0044] As the phosphate, for example, ammonium dihydrogen phosphate, lithium phosphate, sodium phosphate, condensed phosphates, and phosphoric acid can be used. Among them, ammonium dihydrogen phosphate is preferable. These may be used alone or in combination of two or more.

[0045] As the silicate, sodium metasilicate, silicon oxide, water glass, sodium orthosilicate, condensed silicates, etc. can be used. Also, it is preferable to use sodium metasilicate. These may be used alone or in combination of two or more. Hydrates may also be used.

[0046] When using a phosphate or a silicate as the inorganic acid salt, the molar ratio of these inorganic acid salts to the positive electrode active material is preferably 0.01 to 0.05 in terms of the P / (Ni + Fe + Mn) molar ratio, and preferably 0.001 to 0.005 in terms of the Si / (Ni + Fe + Mn) molar ratio. As a method for adding the inorganic acid salt, it is preferable to dissolve the inorganic acid salt in water, then add the product obtained in Step 2, dry it, and pulverize it. Also, when using an insoluble inorganic acid salt, the product obtained in Step 2 and the inorganic acid salt may be dry pulverized and mixed.

[0047] Thereafter, a heat treatment step is carried out. As the heat treatment method, a known heat treatment method can be widely adopted and is not particularly limited. More specifically, a firing treatment can be mentioned.

[0048] As the temperature condition at this time, it is carried out at a lower temperature than the heat treatment in Step 2. Specifically, it is preferably 300 to 600°C, more preferably 400 to 550°C. If the heat treatment temperature in Step 3 is carried out at a temperature equal to or higher than the heat treatment temperature in Step 2, the inorganic acid will enter from the surface of the positive electrode active material into the interior and the desired effect cannot be obtained. Also, the heat treatment time is preferably 1 to 20 hours, more preferably 3 to 15 hours.

[0049] The heat treatment in Step 3 is preferably carried out in an inert atmosphere as in Step 2.

[0050] After the heat treatment in Step 3, the obtained lithium nickel manganese-based or lithium nickel iron manganese-based composite oxide-inorganic acid composite is preferably used after being pulverized. Also, after pulverization, it is also preferable to carry out a water washing treatment, a filtration treatment, and a drying treatment as necessary.

[0051] As described above, the embodiments of the present invention have been explained, but the present invention is not limited to such examples, and it goes without saying that the present invention can be implemented in various forms without departing from the gist of the present invention.

Examples

[0052] Hereinafter, based on examples, the embodiments of the present invention will be described more specifically, but the present invention is not limited thereto.

[0053] (Example 1) 1 / 4 mol of nickel-manganese precursor (Ni:Mn molar ratio = 3:7) and 1 / 4 mol of pre-ground lithium carbonate were thoroughly mixed in a mortar. The mixture was first fired in air at 650 °C for 5 hours. After grinding using a mortar, it was secondarily fired in a nitrogen stream at 850 °C for 3 hours. After the product was ground using a vibration mill, it was dispersed in a solution prepared by dissolving ammonium dihydrogen phosphate corresponding to a charging P / (Ni + Mn) molar ratio of 0.03 in 100 ml of distilled water. The active material-dispersed phosphoric acid solution was dried at 100 °C and then ground. It was placed in an electric furnace and tertiarily fired in a nitrogen stream at 400 °C for 5 hours. Thereafter, the powder was taken out of the electric furnace, ground in a mortar, washed with distilled water, filtered, and dried to obtain a lithium nickel manganese oxide-phosphate composite.

[0054] (Comparative Example 1) A lithium nickel manganese-based composite oxide was obtained in the same manner as in Example 1, except that no phosphate was added.

[0055] X-ray diffraction measurement The X-ray diffraction pattern of the sample of Example 1 is shown in Fig. 1. All peaks could be attributed only to the unit cell of the monoclinic Li2MnO3 described above. The lattice constant values obtained using the X-ray Rietveld analysis software RIETAN-FP (Izumi Fujio et al., Solid State Phenom. 130 (2007) 15-20.) were a = 4.9644(4) Å, b = 8.5702(6) Å, c = 5.0279(3) Å, β = 109.252(7)°, V = 202.0(5) Å for the sample of Example 1 3 and a = 4.9586(4) Å, b = 8.5645(5) Å, c = 5.0241(3) Å, β = 109.251(7)°, V = 201.4(5) Å for the sample of Comparative Example 1 3 for the sample of Comparative Example 1. The transition metal (virtual atom Ni 0.3 Mn 0.7When the occupancy rate was calculated assuming the isotropic thermal vibration parameter B to be 1, the results were as shown in Table 1 below. As described in the description of the crystal structure above, it is clear that the 4g and 2b positions, which contain a large amount of transition metals, have a higher transition metal occupancy rate than the 2c and 4h positions, which are lattice positions within the Li layer.

[0056]

Table 1

[0057] Chemical analysis Next, cation amount analysis was performed by elemental analysis. The results are shown in Table 2 below. As shown in Table 2, the x and y values in the composition formula of the lithium nickel manganate oxide of the samples of Example 1 and Comparative Example 1 were within the scope of the present invention. Also, P, which is a phosphoric acid constituent of the sample of Example 1, was detected as shown in Table 3 below and was within the scope of the present invention.

[0058]

Table 2

[0059]

Table 3

[0060] Charge-discharge characteristic evaluation After vacuum drying the sample of Example 1 or Comparative Example 1 at 120 °C overnight, 20 mg was weighed and used as the positive electrode active material. After mixing 5 mg of acetylene black in a mortar, 0.5 mg of polytetrafluoroethylene was added and bonded to prepare a positive electrode composite material. After crimping the composite material onto an aluminum mesh, it was again vacuum dried at 120 °C overnight, placed in a glove box with a dew point of -80 °C or lower, and left for one day. The obtained positive electrode composite material was set in an experimental lithium secondary battery container in the glove box, and a solution prepared by dissolving 1.5 M LiPF6 in a mixed solvent of ethylene carbonate + diethyl carbonate (volume fraction 7:3) was added as the electrolyte. After using a lithium metal foil as the negative electrode through a separator, the battery was sealed and fabricated. The battery was taken out of the glove box and set in a charge-discharge test device. Charging and discharging were performed at a constant current of 40 mA / g per gram of the positive electrode active material at the start of charging. The actual charging and discharging were carried out up to 34 cycles after the activation process by step charging (up to 5 cycles). The activation process by step charging was carried out in the potential range of 2.0 - 4.8 V. At the end of charging, first, charging was performed at a constant current / constant voltage up to 80 mAh / g, and then discharging to 2.0 V was taken as one cycle. Thereafter, the charging capacity was increased by 40 mAh / g each time, and the cycle was repeated up to 4 cycles (200 mAh / g charging). After charging to 4.8 V and discharging to 2.0 V in the fifth cycle, the activation was completed. From the sixth cycle onwards, charging was carried out at 4.6 V and discharging at 2.0 V for 34 cycles (equivalent to 30 cycles after activation).

[0061] The charge-discharge curves of the lithium secondary batteries using the obtained Samples of Example 1 and Comparative Example 1 as active materials are shown in FIGS. 2(a) and 2(b), respectively. The upward-sloping curve indicates charging c, and the downward-sloping curve indicates discharging d. It can be seen that both samples show similar charge-discharge curves and are high-capacity positive electrodes that maintain a capacity of 200 mAh / g or more (Table 4 below) even after 34 cycles. The cycle dependence of the discharge average voltage maintenance rate is shown in FIG. 3, and the measured values of the average discharge voltage are shown in Table 5. The discharge average voltage maintenance rate is obtained by dividing the average discharge voltage of each cycle by the average discharge voltage of the 5th cycle. As shown in Table 5 and FIG. 3, since the discharge average voltage maintenance rate of the Sample of Example 1 is higher than that of the Sample of Comparative Example 1, it is clear that the Sample of Example 1 exhibits more favorable charge-discharge characteristics than the Sample of Comparative Example 1.

[0062] (Example 2) Similar to Example 1, it was fired up to secondary firing. After the product was pulverized with a vibration mill, ammonium dihydrogen phosphate corresponding to a charge P / (Ni + Mn) molar ratio of 0.03 was dry-mixed. Thereafter, the same procedures as in Example 1, such as tertiary firing and water washing treatment, were performed to obtain the target positive electrode active material-phosphate composite.

[0063] X-ray diffraction measurement The X-ray diffraction pattern of the Sample of Example 2 is shown in FIG. 4. All the peaks could be assigned to the unit cell of the monoclinic Li2MnO3 described above and the peaks of lithium phosphate (Li3PO4). By comparing the peak heights of both crystal phases, it can be seen that the amount of the by-product lithium phosphate is small. The lattice constant values of the monoclinic Li2MnO3 phase obtained using the X-ray Rietveld analysis software RIETAN-FP (the literature mentioned above) were a = 4.9591(4) Å, b = 8.5647(5) Å, c = 5.0232(3) Å, β = 109.258(7)°, V = 201.4(5) Å 3 and were. At each lattice position, the transition metal (virtual atom Ni 0.3 Mn 0.7Assuming the occupancy rate is determined with the isotropic thermal vibration parameter B assumed to be 1, it became as shown in Table 1 above. As described in the description of the crystal structure above, it is clear that the transition metal occupancy rate is higher at the 4g and 2b positions containing a large amount of transition metal than at the 2c and 4h positions which are lattice positions within the Li layer.

[0064] Chemical analysis Next, cation amount analysis was performed by elemental analysis. The results are shown in Tables 2 and 3. As shown in Table 2, the x and y values in the composition formula of the lithium nickel manganate oxide of the sample of Example 2 were within the scope of the present invention. Also, P which is a phosphate constituent component of the same sample was detected as shown in Table 3 and was within the scope of the present invention.

[0065] Charge-discharge characteristic evaluation Charge-discharge curves of the lithium secondary battery using the sample of Example 2 prepared as an electrode composite material in the same manner as in Example 1 as the active material are shown in FIG. 5 respectively. The curve rising to the upper right indicates charge c, and the curve falling to the lower right indicates discharge d. It can be seen that it is a high-capacity positive electrode that maintains 200 mAh / g or more (Table 4) until 34 cycles of charge-discharge capacity have elapsed. The cycle dependence of the discharge average voltage maintenance rate is shown in FIG. 6, and the actually measured values of the average discharge voltage are shown in Table 5. As shown in Table 5 and FIG. 6, since the discharge average voltage maintenance rate is higher for the sample of Example 2 than for the sample of Comparative Example 1, it is clear that the sample of Example 2 shows preferable charge-discharge characteristics compared to the sample of Comparative Example 1.

[0066]

Table 4

[0067]

Table 5

[0068] (Example 3) Similar to Example 1, the process was carried out up to the secondary firing. After the product was pulverized in a vibration mill, it was dispersed in a solution prepared by dissolving sodium metasilicate nonahydrate corresponding to a molar ratio of Si / (Ni + Mn) of 0.03 in 100 ml of distilled water. The active material-dispersed silicic acid solution was dried at 100 °C and then pulverized. Thereafter, the same processes as in Example 1 such as the tertiary firing and the water washing treatment were carried out to obtain the target cathode active material-silicate composite.

[0069] X-ray diffraction measurement Fig. 7 shows the X-ray diffraction patterns of the samples of Example 3 and Comparative Example 1. All the peaks could be attributed only to the unit cell of the monoclinic Li2MnO3 described above. The lattice constant values of the monoclinic Li2MnO3 phase in the sample of Example 3 obtained using the X-ray Rietveld analysis software RIETAN-FP (the literature mentioned above) were a = 4.9611(4) Å, b = 8.5664(5) Å, c = 5.0233(2) Å, β = 109.259(6)°, V = 201.5(4) Å 3 and it was. Assuming the occupancy of the transition metal (assuming virtual atoms Ni 0.3 Mn 0.7 at each lattice position) and assuming the isotropic thermal vibration parameter B to be 1, the results were as shown in Table 1 above. As described in the description of the crystal structure above, it is clear that the 4g and 2b positions containing a large amount of transition metal have a larger transition metal occupancy than the 2c and 4h positions which are lattice positions within the Li layer.

[0070] Chemical analysis Next, cation amount analysis was carried out by elemental analysis. The results are shown in Tables 2 and 3. As shown in Table 2, the x and y values in the composition formula of the lithium nickel manganese oxide of the sample of Example 3 were within the scope of the present invention as in Comparative Example 1. Also, Si which is the silicate constituent component of the sample of Example 3 was detected as shown in Table 3 and was within the scope of the present invention.

[0071] Charge-discharge characteristic evaluation The charge-discharge curves of a lithium secondary battery using the sample of Example 3 prepared in the same manner as in Example 1 as the active material are shown in Fig. 8. The upward-sloping curve indicates charging c, and the downward-sloping curve indicates discharging d. It can be seen that it is a high-capacity positive electrode that maintains a capacity of 200 mAh / g or more (Table 4) until 34 cycles of charge and discharge have elapsed. The cycle dependence of the discharge average voltage maintenance rate is shown in Fig. 9, and the measured values of the average discharge voltage are shown in Table 5. As shown in Table 5 and Fig. 9, since the discharge average voltage maintenance rate of the sample of Example 3 is higher than that of the sample of Comparative Example 1, it is clear that the sample of Example 3 exhibits more favorable charge-discharge characteristics than the sample of Comparative Example 1.

[0072] (Example 4) Nickel(II) nitrate hexahydrate and manganese(II) chloride tetrahydrate were weighed so that the Ni:Mn molar ratio was 3:7 and the total molar amount was 1 / 4 mol, and then put into 500 ml of distilled water and completely dissolved. 50 g of sodium hydroxide was put into another container, 500 ml of distilled water was added and dissolved, and then it was put into a thermostat maintained at +20°C. After confirming that the sodium hydroxide solution was maintained at +20°C, the transition metal salt aqueous solution was dropped with a liquid delivery pump over 2-3 hours to prepare a nickel-manganese co-precipitate. The aqueous solution containing the co-precipitate was taken out of the thermostat, and while stirring the aqueous solution, oxygen gas was bubbled at a flow rate of about 4 L / min at 25°C for 2 days. The generated precursor was washed with water, and then lithium carbonate corresponding to a Li / (Ni+Mn) molar ratio of 2.00 (1 / 2 mol) was wet-mixed, dried at 50°C for 2 days, and then subjected to a primary firing in air at 550°C for 5 h. After the secondary firing, the sample was prepared in the same manner as in Example 1 to obtain the target lithium nickel manganese composite oxide-phosphate composite.

[0073] (Comparative Example 2) A lithium nickel manganese composite oxide was obtained by preparing it in the same manner as in Example 4 except that no phosphate was added.

[0074] X-ray diffraction measurement Figure 10 shows the X-ray diffraction patterns of the sample of Example 4 and the sample of Comparative Example 2. All peaks could be attributed mainly to the unit cell of monoclinic Li2MnO3 described above and only to the Li3PO4 phase as the secondary phase. The lattice constant values obtained using the X-ray Rietveld analysis software RIETAN-FP (Izumi Fujio et al., Solid State Phenom. 130 (2007) 15-20.) were a = 4.9598(4) Å, b = 8.5715(5) Å, c = 5.0239(3) Å, β = 109.224(7)°, V = 201.7(5) Å 3 for the sample of Example 4, and a = 4.9576(4) Å, b = 8.5701(5) Å, c = 5.0261(2) Å, β = 109.199(6)°, V = 201.7(4) Å 3 for the sample of Comparative Example 2. When the occupancy of the transition metal (assuming virtual atoms Ni 0.3 Mn 0.7 is assumed) at each lattice position was determined assuming the isotropic thermal vibration parameter B to be 1, it was as shown in Table 1 above. As described in the description of the crystal structure above, it is clear that the 4g and 2b positions, which contain a large amount of transition metal, have a larger transition metal occupancy than the 2c and 4h positions, which are lattice positions within the Li layer.

[0075] Chemical analysis Next, cation amount analysis was performed by elemental analysis. The results are shown in Tables 2 and 3. As shown in Table 2, the x and y values in the composition formula of the lithium nickel manganese oxide of the sample of Example 4 and the sample of Comparative Example 2 were within the scope of the present invention. Also, P, which is a phosphate constituent component of the sample of Example 4, was detected as shown in Table 3 and was within the scope of the present invention.

[0076] Charge-discharge characteristic evaluation Charge-discharge curves of lithium secondary batteries using the samples of Example 4 and Comparative Example 2 prepared with an electrode composite material in the same manner as in Example 1 as the active material are shown in FIGS. 11(a) and (b), respectively. The upward-sloping curve indicates charging c, and the downward-sloping curve indicates discharging d. It can be seen that the positive electrode has a high capacity that maintains 200 mAh / g or more (Table 4) until after 34 cycles of charge and discharge. The cycle dependence of the discharge average voltage maintenance rate is shown in FIG. 12, and the measured values of the average discharge voltage are shown in Table 5. As shown in Table 5 and FIG. 12, since the discharge average voltage maintenance rate of the sample of Example 4 is higher than that of the sample of Comparative Example 2, it is clear that the sample of Example 4, which is a phosphate composite, exhibits more favorable charge-discharge characteristics than the sample of Comparative Example 2.

[0077] (Example 5) After weighing iron(III) nitrate nonahydrate, nickel(II) nitrate hexahydrate, and manganese(II) chloride tetrahydrate so that the Fe:Ni:Mn molar ratio was 1:2:7 and the total molar amount was 1 / 4 mol, they were put into 500 ml of distilled water and completely dissolved. Thereafter, samples were prepared in the same manner as in Example 4 to obtain the target lithium nickel iron manganese-based composite oxide-phosphate composite.

[0078] (Comparative Example 3) A lithium nickel iron manganese-based composite oxide was obtained by preparing it in the same manner as in Example 5 except that no phosphate was added.

[0079] X-ray diffraction measurement The X-ray diffraction patterns of the samples of Example 5 and Comparative Example 3 are shown in FIG. 13. All peaks could be attributed only to the monoclinic Li2MnO3 and Li3PO4 unit cells described above. The lattice constant values of the monoclinic Li2MnO3 phase obtained using the X-ray Rietveld analysis software RIETAN-FP (Izumi Fujio et al., Solid State Phenom. 130 (2007) 15-20.) were a = 4.9640(3) Å, b = 8.5890(4) Å, c = 5.0342(2) Å, β = 109.278(5)°, V = 202.6(3) Å for the sample of Example 5 3where the sample of Comparative Example 3 had a = 4.9640(4) Å, b = 8.5901(4) Å, c = 5.0365(2) Å, β = 109.264(5)°, V = 202.7(4) Å 3 The occupancy of the transition metal (hypothetical atoms Fe 0.1 Ni 0.2 Mn 0.7 assumed) at each lattice position was determined assuming an isotropic thermal vibration parameter B of 1, and the results were as shown in Table 1 above. As described in the description of the crystal structure above, it is clear that the 4g and 2b positions, which contain a large amount of transition metal, have a higher transition metal occupancy than the 2c and 4h positions, which are lattice positions within the Li layer.

[0080] Chemical analysis Next, cation amount analysis was performed by elemental analysis. The results are shown in Tables 2 and 3. As shown in Table 2, the x, y, and z values in the composition formula of the lithium nickel iron manganese oxide of the sample of Example 5 and Comparative Example 3 were within the scope of the present invention. Also, P, which is a phosphate constituent component of the sample of Example 5, was detected as shown in Table 3 and was within the scope of the present invention.

[0081] Charge-discharge characteristic evaluation Charge-discharge curves of lithium secondary batteries using the samples of Example 5 and Comparative Example 3, prepared in the same manner as in Example 1, as active materials are shown in FIGS. 14(a) and (b), respectively. The upward-sloping curve indicates charging c, and the downward-sloping curve indicates discharging d. It can be seen that it is a high-capacity positive electrode that maintains a capacity of 200 mAh / g or more (Table 4) until 34 cycles of charge and discharge have elapsed. The cycle dependence of the discharge average voltage maintenance rate is shown in FIG. 15, and the measured values of the average discharge voltage are shown in Table 5. As shown in Table 5 and FIG. 15, since the discharge average voltage maintenance rate is higher for the sample of Example 5 than for the sample of Comparative Example 3, it is clear that the sample of Example 5, which is a phosphate composite, exhibits more favorable charge-discharge characteristics than the sample of Comparative Example 3.

[0082] From the above, the lithium nickel manganese-based or lithium nickel iron manganese-based composite oxide-inorganic acid complex of the present invention contains an appropriate amount of inorganic acid and has excellent charge and discharge characteristics compared to those not containing them, and is considered to be suitably used as a positive electrode material for large lithium ion secondary batteries such as in-vehicle use.

Industrial Applicability

[0083] The lithium nickel manganese-based or lithium nickel iron manganese-based composite oxide-inorganic acid complex of the present invention has an operating voltage and a charge and discharge amount equal to or greater than those of existing NMC-based positive electrode materials. Therefore, it can be suitably used for batteries for electric vehicles or plug-in hybrid vehicles, or stationary storage batteries.

Claims

1. The following general formula (1): Li １＋ｘ (Ni ｙ Fe z Mn １－ｙ－ｚ ) １－ｘ O ２ (1) [wherein, x, y, and z each represent 0 < x < 1 / 3, 0.2 ≤ y ≤ 0.4, and 0 ≤ z ≤ 0.2.] represented by monoclinic Li ２ MnO ３ a lithium nickel manganese-based or lithium nickel iron manganese-based composite oxide-inorganic acid complex having a layered rock salt structure of the type, The inorganic acid is phosphoric acid or silicic acid, A lithium nickel manganese-based or lithium nickel iron manganese-based composite oxide-inorganic acid composite, characterized in that the atomic ratio of R / (Ni + Fe + Mn) is 0.001 ≤ R / (Ni + Fe + Mn) ≤ 0.05 [wherein, R is a phosphorus atom or a silicon atom constituting the inorganic acid].

2. The composite according to Claim 1, wherein the inorganic acid is phosphoric acid and the atomic ratio of P / (Ni + Fe + Mn) is 0.01 ≤ P / (Ni + Fe + Mn) ≤ 0.

05.

3. The composite according to Claim 1, wherein the inorganic acid is silicic acid and the atomic ratio of Si / (Ni + Fe + Mn) is 0.001 ≤ Si / (Ni + Fe + Mn) ≤ 0.

005.

4. Step 1 of mixing a lithium compound with a nickel manganese precursor or a nickel iron manganese precursor and performing heat treatment in an oxidizing atmosphere, Step 2 of heat-treating the product obtained in Step 1 under higher temperature conditions than in Step 1 in an inert atmosphere, and A method for producing the composite according to Claim 1, comprising Step 3 of adding an inorganic acid salt to the product obtained in Step 2 and performing heat treatment under lower temperature conditions than in Step 2 in an inert atmosphere.

5. The method for producing the composite according to Claim 4, wherein the nickel manganese precursor or the nickel iron manganese precursor in Step 1 is obtained by dropping an aqueous solution of a nickel manganese metal salt or an aqueous solution of a nickel iron manganese metal salt into an alkaline solution, followed by wet oxidation treatment and washing treatment.

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