JP2004220898A - Positive active material for lithium secondary battery, its manufacturing method, and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive active material for a lithium secondary battery with high discharge capacity, high charge-discharge cycle characteristics, to provide its manufacturing method, and to provide the lithium secondary battery containing the positive active material. <P>SOLUTION: The positive active material for the lithium secondary battery contains a lithium-manganese composite oxide represented by composition formula Li<SB>1-x</SB>MnO<SB>2+y</SB>(0≤x<1, 0<y<1), and having O2 type layer structure. The manufacturing method of the positive active material for the lithium secondary battery has an ion exchange process in which a sodium-manganese composite oxide having P2 type layer structure is ion-exchanged in a solution containing lithium chloride. The lithium secondary battery contains the positive active material for the lithium secondary battery in a positive electrode. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
【Technical field】
The present invention relates to a positive electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery.
[0002]
[Prior art]
Conventionally, layered LiMnO ₂ Is LiMn having a spinel structure with a theoretical discharge capacity of 286 Ah / g. ₂ O ₄ Was considered to be an effective positive electrode active material for lithium secondary batteries.
LiMnO having the above layer structure ₂ Examples include the orthorhombic zigzag layered structure (Pmmn) and LiCoO ₂ And LiNiO ₂ A layered rock salt structure having the same crystal structure as that described above is known.
[0003]
Of these, LiMnO having a zigzag layered structure is used. ₂ Is, for example, LiOH and Mn ₂ O ₃ Are mixed at an atomic ratio of Li / Mn1 / 1.05 and fired in a vacuum at 600 to 800 ° C. for 12 hours (see Patent Document 1). However, this zigzag layered LiMnO ₂ Since the charge / discharge cycle maintenance rate at a capacity of 200 mAh / g was as short as about 30 cycles, it was difficult to put it into practical use as a positive electrode active material for a lithium secondary battery.
[0004]
On the other hand, LiMnO with the above-mentioned layered rock salt structure ₂ Although it has been considered that the above can be a good positive electrode active material for a lithium secondary battery as described above, there is a problem that its synthesis is difficult. Only recently, for example, among the above layered rock salt structures, LiMnO having an O3 type layered structure is obtained by the following three methods. ₂ Can be synthesized.
[0005]
The first method uses MnO as a manganese source. ₂ , Mn ₂ O ₃ , MnOOH, MnCO ₃ Inorganic salts such as manganese acetate, manganese butyrate, manganese oxalate, manganese citrate, etc .; ₃ , Li ₂ CO ₃ There is a method of synthesizing under a saturated vapor pressure of 100 to 300 ° C. using water or an organic solvent such as alcohol (see Patent Document 2).
[0006]
As a second method, KMnO ₄ Is used as a starting material, and through an ion exchange reaction, LiMnO ₄ There is a method of performing hydrothermal treatment at 160 ° C. for 3.5 days in a nitric acid acid atmosphere and then dehydrating (see Non-Patent Document 1).
As a third method, MnO ₂ And NaOH are reacted at 700 ° C. in an argon atmosphere to obtain NaMnO. ₂ Is synthesized by ion exchange with LiCl in a non-aqueous solvent (see Non-Patent Document 2).
[0007]
[Patent Document 1]
JP-A-8-37027
[Patent Document 2]
JP-A-10-3921
[Non-patent document 1]
"Journal of The Electrochemical Society", USA, 1997, 144, p. L64-L67
[Non-patent document 2]
"Nature", UK, 1996, 381, p. 499-500
[0008]
[Problem to be solved]
[0009]
However, LiMnO synthesized by the method disclosed in Patent Document 2 ₂ A secondary battery using as a positive electrode active material has a problem that, while the theoretical discharge capacity is 286 mAh / g, a very low discharge capacity of only 80 mAh / g can be obtained.
[0010]
The method disclosed in Non-Patent Document 1 is a multi-stage reaction, and in addition to the disadvantage in the production method that the precision of the solution adjustment in each step is required, the synthesized LiMnO ₂ A secondary battery using as a positive electrode active material obtained only a discharge capacity of 50% or less of the initial capacity after 10 cycles, and had extremely poor charge / discharge cycle characteristics.
[0011]
In the method disclosed in Non-Patent Document 2, the precursor NaMnO ₂ In addition to the necessity of synthesizing, a non-aqueous ion exchange reaction is required, which leads to an increase in cost. Furthermore, the synthesized LiMnO ₂ A secondary battery using as a positive electrode active material has a relatively high discharge capacity of 270 mAh / g, but has poor charge / discharge cycle characteristics, and can be reduced to 50% or less of the initial capacity in only 10 cycles. There was a problem.
[0012]
The present invention has been made in view of such conventional problems, and has a high discharge capacity and a positive electrode active material for a lithium secondary battery having excellent charge / discharge cycle characteristics, a method for producing the same, and a method for producing the same. To provide a rechargeable lithium secondary battery.
[0013]
[Means for solving the problem]
The first invention uses a composition formula Li _1-x MnO _{2 + y} (0 ≦ x <1, 0 <y <1) and comprising a lithium-manganese composite oxide having an O 2 -type layered structure, the positive electrode active material for a lithium secondary battery. (Claim 1).
[0014]
The positive electrode active material for a lithium secondary battery according to the first invention has a composition formula of Li _1-x MnO _{2 + y} (0 ≦ x <1, 0 <y <1) and contains a lithium-manganese composite oxide having an O2-type layered structure.
The O2-type layered lithium-manganese composite oxide has almost no change in crystal structure during charge and discharge. Therefore, the positive electrode active material for a lithium secondary battery has a high discharge capacity and excellent charge-discharge cycle characteristics.
[0015]
Hereinafter, the O2-type layered structure will be described with reference to FIG.
In FIG. 1 and FIG. 8, which will be described later, three oxygen atoms on the same plane in the crystal are connected by a line, and the plane on which the three oxygen atoms are present is indicated by a pattern. That is, the surfaces with the same pattern indicate the same surface or surfaces parallel to each other.
[0016]
FIG. 1 shows the crystal structure of the lithium-manganese composite oxide in the positive electrode active material for a lithium secondary battery of the present invention.
As can be seen from the figure, the lithium-manganese composite oxide has a hexagonal basic crystal structure, in which lithium atoms, manganese atoms, and oxygen atoms are regularly arranged. Each atom forms a lithium layer, a manganese layer, and an oxygen layer, and the lithium layer and the manganese layer are separated by oxygen.
[0017]
As shown in FIG. 1, the lithium-manganese composite oxide has a packing of ABCBAB... In the crystal thereof, and has a so-called O2-type layered structure. This O2 type layered structure is very stable, and there is almost no structural change in the crystal even after repeated charging and discharging. Therefore, the positive electrode active material for a lithium secondary battery containing the lithium-manganese composite oxide having the O2-type layered structure can maintain the high discharge capacity of the lithium-manganese composite oxide even after repeated charging and discharging. It can be maintained for a long time and has excellent charge-discharge cycle characteristics.
[0018]
On the other hand, as shown in FIG. 8, in the crystal structure of the above-mentioned conventional lithium-manganese composite oxide as the positive electrode active material, the packing of oxygen is ABCABC. That is, the overlap is the same as that of the spinel type, and the crystal structure is a so-called O3 type layered structure.
[0019]
When charging and discharging the lithium-manganese composite oxide having the O3 type layered structure, lithium is mixed into the manganese layer or manganese is mixed into the lithium layer. As a result, the O3-type layered structure lithium-manganese composite oxide is transformed into a more stable spinel structure. And, it is considered that the transition to the stable spinel structure causes an extreme decrease in the discharge capacity.
[0020]
As described above, according to the first aspect, a positive electrode active material for a lithium secondary battery having a high discharge capacity and excellent charge / discharge cycle characteristics can be provided.
[0021]
The second invention is based on the composition formula Li _1-x MnO _{2 + y} (0 ≦ x <1, 0 <y <1) and a method for producing a positive electrode active material for a lithium secondary battery, comprising a lithium-manganese composite oxide having an O 2 -type layered structure,
A lithium-manganese composite oxide having a P2-type layered structure in which a sodium-manganese composite oxide is ion-exchanged in a solution containing lithium chloride to replace sodium with lithium and convert it to an O3-type layered structure. There is provided a method for producing a positive electrode active material for a secondary battery (claim 6).
[0022]
The method for producing a positive electrode active material for a lithium secondary battery according to the second invention includes the above-described ion exchange step. Then, in this ion exchange step, sodium in the sodium-manganese composite oxide is exchanged for lithium in lithium chloride, and a lithium-manganese composite oxide is generated. Further, at this time, the crystal structure changes from the P2 type layered structure to the O2 type layered structure.
[0023]
Thus, the composition formula Li _1-x MnO _{2 + y} (0 ≦ x <1, 0 <y <1) and a lithium-manganese composite oxide having an O 2 -type layered structure can be easily synthesized. The positive electrode active material for a lithium secondary battery containing the lithium-manganese composite oxide is the same as that of the first invention, and has a high discharge capacity and excellent charge / discharge cycle characteristics. It becomes.
[0024]
A third invention is a lithium secondary battery comprising the positive electrode active material for a lithium secondary battery according to the first invention in a positive electrode (claim 11).
[0025]
The lithium secondary battery according to the third aspect of the present invention includes the positive electrode active material for a lithium secondary battery according to the first aspect of the present invention (claim 1) in a positive electrode.
Therefore, the lithium secondary battery has a high discharge capacity and excellent cycle characteristics by utilizing the excellent features of the positive electrode active material for a lithium secondary battery of the first invention.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
In the first invention (Invention 1), it is preferable that the lithium-manganese composite oxide is composed of flaky particles (Invention 2).
In this case, the initial discharge capacity of the positive electrode active material for a lithium secondary battery can be increased.
[0027]
It is preferable that the scale-like particles have a thickness of 0.05 to 5 μm and a maximum diameter of a surface substantially perpendicular to the thickness direction is 0.2 to 5 μm.
[0028]
The thickness of the scaly particles and the maximum diameter of a surface substantially perpendicular to the thickness direction can be measured by imaging the scaly particles using, for example, a scanning electron microscope. The thickness of the scaly particles refers to, for example, the width of a portion of the scaly particles sandwiched between substantially flat surfaces. The maximum diameter refers to, for example, the maximum distance between two points at the outer edge of the cross-sectional shape when the scale-like particles are cut along a plane substantially perpendicular to the thickness direction.
[0029]
If the thickness and the maximum diameter of the flake-shaped particles are outside the above ranges, it may be difficult to produce a positive electrode of a lithium secondary battery using the positive electrode active material.
[0030]
Further, it is preferable that the lithium-manganese composite oxide is composed of substantially spherical particles having a plurality of protrusions on the surface.
In this case, the positive electrode active material for a lithium secondary battery has a small change rate of the discharge capacity with respect to the discharge current density and has excellent stability.
[0031]
Preferably, the substantially spherical particles having the protruding portions have a diameter of 1 to 5 μm.
The diameter of the substantially spherical particles having the protruding portions can be measured by imaging the particles with, for example, a scanning electron microscope. Here, the diameter of the particle is the diameter of the entire substantially spherical particle including the protrusion.
If the diameter of the particles is outside the above range, it may be difficult to produce a positive electrode of a lithium secondary battery using the positive electrode active material.
[0032]
Next, in the second invention (claim 6), the sodium-manganese composite oxide having the P2-type layered structure is ion-exchanged in a solution containing lithium chloride.
Here, the state of the crystal structure of the sodium-manganese composite oxide having the P2 structure is shown in FIG.
As shown in FIG. 2, the basic crystal structure of the sodium-manganese composite oxide is hexagonal, and sodium atoms, manganese atoms, and oxygen atoms are regularly arranged. In the crystal, each atom forms a sodium layer, a manganese layer, and an oxygen layer, respectively, and the lithium layer and the manganese layer are separated by oxygen.
[0033]
As shown in FIG. 2, the packing of oxygen in this crystal structure is ABBAAB..., And the crystal structure is a so-called P2 type layered structure.
In FIG. 2, three oxygen atoms on the same plane in the crystal are connected by a line, and the plane on which the three oxygen atoms are present is indicated by a pattern. That is, the surfaces with the same pattern indicate the same surface or surfaces parallel to each other.
[0034]
Further, in the second invention, before the ion exchange step, KMnO ₄ A first hydrothermal step of heating the first solution containing to produce a potassium-manganese composite oxide having an O3-type layered structure;
A second hydrothermal step of heating the second solution containing the potassium-manganese composite oxide and sodium hydroxide obtained in the first hydrothermal step to produce the P2-type layered sodium-manganese composite oxide (Claim 7).
[0035]
In this case, the P2-type layered sodium-manganese composite oxide used in the ion exchange step can be easily produced by the first hydrothermal step and the second hydrothermal step.
Further, in this case, the lithium-manganese composite oxide obtained by the above-described series of steps is composed of substantially spherical particles having a plurality of protrusions on the surface. In this case, as described above, the rate of change of the discharge capacity with respect to the discharge current density of the positive electrode active material for a lithium secondary battery is small, and the stability is excellent.
Examples of the solvent used for the first solution and the second solution include water, glycols, and mixtures thereof.
[0036]
In the first hydrothermal step, it is preferable to further add KOH to the first solution.
In this case, the shape of the lithium-manganese composite oxide particles obtained by the above-described series of steps can be made scaly. In this case, as described above, the initial discharge capacity of the positive electrode active material for a lithium secondary battery can be increased.
[0037]
The heating in the first hydrothermal step and the second hydrothermal step is preferably performed at a temperature of 120 to 250 ° C. under substantially saturated steam pressure.
[0038]
If the temperature is lower than 120 ° C., the reaction does not proceed sufficiently and unreacted substances may remain. On the other hand, when the temperature exceeds 250, there is no difference in the product, but the saturated steam pressure is 40 kg / cm. ³ And it requires a special pressure vessel, which is not industrially suitable.
[0039]
The ion exchange step is preferably carried out in an alcohol, a non-aqueous organic solvent, or an aqueous solution at a reaction temperature of 50 ° C. to 150 ° C. (Claim 10).
In this case, since the reaction temperature is mild, an effect that ion exchange can be performed while maintaining the form can be obtained.
If the reaction temperature is lower than 50 ° C., ion exchange may not proceed sufficiently, and a desired lithium-manganese composite oxide may not be obtained. On the other hand, when the temperature exceeds 150 ° C., Li ₂ MnO ₃ To another Li compound.
[0040]
Next, in the third invention (claim 11), the lithium secondary battery is a lithium secondary battery including the positive electrode active material for a lithium secondary battery of the first invention in a positive electrode.
There are various types of the first positive electrode active material for a lithium secondary battery depending on the composition of the lithium-manganese composite oxide. In the lithium secondary battery of the third invention, one of these may be used for the positive electrode, or a mixture of two or more may be used. Further, a mixture of the positive electrode active material for a lithium secondary battery of the first invention and a known positive electrode active material can be used.
[0041]
The lithium secondary battery includes, for example, a positive electrode and a negative electrode that occlude and release lithium, a separator that is narrowly provided between the positive electrode and the negative electrode, and a nonaqueous electrolyte that transfers lithium between the positive electrode and the negative electrode. Can be configured as a main component.
[0042]
For the positive electrode, for example, a paste obtained by mixing a conductive material and a binder with the above-described positive electrode active material for a lithium secondary battery and adding an appropriate solvent to form a paste-like positive electrode mixture is made of a metal foil such as aluminum or stainless steel. It can be formed by coating and drying on the surface of the current collector and, if necessary, compressing it to increase the electrode density.
The conductive material is for ensuring the electrical conductivity of the positive electrode, and for example, one or a mixture of two or more of carbon material powders such as carbon black, acetylene black, and graphite can be used.
[0043]
The binder plays a role of binding the active material particles and the conductive material particles, and for example, a fluorine-containing resin such as polytetrafluoroethylene, polyvinylidene fluoride, or fluoro rubber, or a thermoplastic resin such as polypropylene or polyethylene. Can be used.
An organic solvent such as N-methyl-2-pyrrolidone can be used as a solvent for dispersing the active material, the conductive material, and the binder.
[0044]
The negative electrode can be formed, for example, by forming metal lithium as a negative electrode active material into a sheet, or by pressing the sheet into a current collector net made of nickel, stainless steel, or the like. As the negative electrode active material, a lithium alloy or Li instead of metallic lithium is used. ₄ Ti ₅ O ₁₂ And the like.
[0045]
As another form of the negative electrode, for example, the negative electrode can be formed by using a carbon material capable of inserting and extracting lithium ions as the negative electrode active material. Examples of the carbon substance that can be used include natural or artificial graphite, mesocarbon microbeans (MCMB), fired organic compounds such as phenolic resins, and powdered materials such as coke.
[0046]
In this case, for example, a binder is mixed with the above-mentioned negative electrode active material, an appropriate solvent is added thereto, and a paste-like negative electrode mixture is applied to the surface of a metal foil current collector such as copper, and dried. Can be formed by pressing. When a carbon material is used as the negative electrode active material, a fluorinated resin such as polyvinylidene fluoride or the like is used as the negative electrode binder and an organic solvent such as N-methyl-2-pyrrolidone is used as the solvent, similarly to the positive electrode. it can.
[0047]
The separator narrowed between the positive electrode and the negative electrode separates the positive electrode from the negative electrode and holds the electrolytic solution. For example, a thin microporous film such as polyethylene or polypropylene can be used.
[0048]
As the non-aqueous electrolyte, for example, a solution in which a lithium salt as an electrolyte is dissolved in an organic solvent can be used. In this case, the lithium salt is dissociated by dissolving in the organic solvent, and is present in the electrolyte as lithium ions. Examples of usable lithium salts include, for example, LiBF ₄ , LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ And the like. Each of these lithium salts may be used alone, or two or more thereof may be used in combination.
[0049]
As the organic solvent for dissolving the lithium salt, an aprotic organic solvent can be used. As such an organic solvent, for example, one or a mixture of two or more selected from cyclic carbonate, chain carbonate, cyclic ester, cyclic ether, chain ether and the like can be used.
[0050]
Here, examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and the like. Examples of the chain carbonate include dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Examples of the higher cyclic ester carbonate include gamma butyrolactone, gamma valerolactone, and the like. Examples of the cyclic ether include tetrahydrofuran and 2-methyltetrahydrofuran. Examples of the chain ether include dimethoxyethane and ethylene glycol dimethyl ether. Any one of these organic solvents can be used alone, or two or more of them can be used as a mixture.
[0051]
Also, instead of the above-described structure of the separator and the non-aqueous electrolyte, a high molecular weight polymer such as ₄ And LiN (CF ₃ SO ₂ ) ₂ A solid polymer electrolyte using a lithium salt such as described above can also be used. Further, a gel electrolyte in which the above non-aqueous electrolyte is trapped in a solid polymer matrix such as polyacrylonitrile can also be used.
[0052]
【Example】
(Example 1)
Next, an embodiment of the present invention will be described with reference to FIGS.
In this example, a positive electrode active material for a lithium secondary battery as an example of the present invention and a lithium secondary battery including the positive electrode active material for a lithium secondary battery in a positive electrode are manufactured.
[0053]
The positive electrode active material for a lithium secondary battery of the present example has a composition formula Li _1-x MnO _{2 + y} (0 ≦ x <1, 0 <y <1) and contains a lithium-manganese composite oxide having an O 2 -type layered structure as shown in FIG.
[0054]
The method for producing a positive electrode active material for a lithium secondary battery according to the present embodiment includes an ion exchange step of ion-exchanging a sodium-manganese composite oxide having a P2-type layered structure in a solution containing lithium chloride as shown in FIG. Have.
In this example, before the ion exchange step, KMnO was used. ₄ A first solution containing O.sub.3 to form a potassium-manganese composite oxide having an O3-type layered structure, and a potassium-manganese composite oxide obtained by the first hydrothermal process and sodium hydroxide And a second hydrothermal step of producing the sodium-manganese composite oxide having the P2-type layered structure.
[0055]
Hereinafter, a method for manufacturing the positive electrode active material for a lithium secondary battery of the present example will be described in detail.
First, KMnO ₄ (1.2 g) and KOH (28.1 g) are mixed, and 25 g of distilled water is added to prepare a slurry. This slurry was reacted at 200 ° C. for one day under saturated steam in an autoclave lined with Teflon (registered trademark) (first hydrothermal step). Then, the precipitate in the container is filtered, washed with water, and K _0.4 MnO ₂ ・ 0.5H ₂ O was obtained.
[0056]
This K _0.4 MnO ₂ ・ 0.5H ₂ O (0.6 g), NaOH (20 g) and water (25 g) were reacted again in a Teflon-lined autoclave under saturated steam at a temperature of 200 ° C. for one day (second water). Thermal process). Then, the precipitate in the container is filtered, washed with water, _0.75 MnO _2.6 (Sodium-manganese composite oxide) was obtained.
[0057]
Here, the crystal structure of the sodium-manganese composite oxide was examined with an X-ray diffractometer. As a result, the crystal structure was a P2 type layered structure. As shown in FIG. 2, in the P2-type layered structure, Na atoms, Mn atoms, and oxygen atoms are regularly arranged to form a lithium layer, a manganese layer, and an oxygen layer, respectively. The sodium layer and the manganese layer are separated by oxygen, and the packing of oxygen in the crystal is ABBAAB.
[0058]
Next, this Na _0.75 MnO _2.6 1 g was dispersed in a 1 M LiCl ethanol solution and reacted at 80 ° C. for one day (ion exchange step). Then, the precipitate in the container is filtered, washed with ethanol, _0.6 MnO _2.2 A positive electrode active material for a lithium secondary battery comprising (lithium-manganese composite oxide) was obtained. This is designated as Sample E1.
[0059]
Subsequently, the shape of the sample E1 was observed with a scanning electron microscope (SEM). The result is shown in FIG.
According to the SEM observation, the lithium-manganese composite oxide of sample E1 was composed of scale-like particles, the thickness of which was about 0.05 μm, and the maximum diameter of a plane substantially perpendicular to the thickness direction was 1 μm. It was about.
[0060]
Next, the X-ray diffraction pattern of the sample E1 was examined. The result is shown in FIG.
According to the X-ray diffraction measurement, all the peaks in the X-ray diffraction pattern of the sample E1 had an a-axis length of 2.85 ° and a c-axis length of 9.6 °, and had an O2 type layered LiMnO 2 layer structure. ₂ The unit cell of was able to index.
[0061]
Next, a coin-type lithium secondary battery was manufactured using the lithium-manganese composite oxide of Sample E1 as a positive electrode active material.
As shown in FIG. 5, the lithium secondary battery 1 includes a positive electrode 2 containing a positive electrode active material, a negative electrode 3 containing a negative electrode active material, and a separator narrowly disposed between the positive electrode 2 and the negative electrode 3. 4 in a coin-shaped battery case 11. A gasket 5 is disposed at an end in the battery case 11, and the battery case is sealed by a sealing plate 12.
[0062]
Next, a method of manufacturing the lithium secondary battery 1 will be described.
First, the positive electrode 2 was prepared as follows.
That is, first, 70 parts by weight of the positive electrode active material of Sample E1, 25 parts by weight of carbon black as a conductive material, and 5 parts by weight of Teflon (registered trademark) F104 (manufactured by Daikin Industries, Ltd.) as a binder were mixed. Thus, a positive electrode mixture was obtained. This positive electrode mixture was pressure-formed to produce a 13 mmφ pellet, and then the pellet was pressed onto a positive electrode current collector made of stainless steel mesh to obtain a positive electrode 2.
[0063]
Next, the negative electrode 3 was produced by punching a rolled sheet of metallic lithium into 15 mmφ and pressing the rolled sheet to a negative electrode current collector made of stainless steel mesh.
A microporous film made of polypropylene is used for the separator 4, and the nonaqueous electrolytic solution impregnated in the separator 4 is a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1. ₆ Was dissolved to obtain a concentration of 1M.
[0064]
Next, as shown in FIG. 5, the positive electrode 2 and the negative electrode 3 were arranged in the battery case 11 so as to be separated by the separator 4.
Then, the gasket 5 was disposed at an end in the battery case 11, and a suitable amount of a non-aqueous electrolyte was injected into the battery case 11 to be impregnated. Subsequently, the sealing plate 12 was arranged, and the end of the battery case 11 was caulked to seal the battery case 11 to produce a lithium secondary battery 1 (battery E1).
[0065]
(Example 2)
Next, in this example, a positive electrode active material for a lithium secondary battery containing a lithium-manganese composite oxide composed of substantially spherical particles having a plurality of projecting portions on the surface was prepared, and further, the lithium secondary battery was manufactured. A lithium secondary battery was manufactured using the positive electrode active material for a battery as a positive electrode.
Specifically, first, 0.3M KMnO ₄ The aqueous solution was reacted at 200 ° C. for one day under saturated steam in an autoclave lined with Teflon (registered trademark). Then, the precipitate in the container is filtered, washed with water, and K _0.33 MnO ₂ ・ 0.45H ₂ O was obtained.
[0066]
Next, this K _0.33 MnO ₂ ・ 0.45H ₂ O (0.6 g), NaOH (20 g), and 25 g of water were reacted again for one day at a temperature of 200 ° C. under saturated steam in an autoclave lined with Teflon (registered trademark) (second hydrothermal step). . Thereafter, the precipitate in the container was filtered and washed with water, and the same P2-type layered Na solution as in Example 1 was used. _0.75 MnO _2.6 (Sodium-manganese composite oxide) was obtained.
[0067]
Next, this Na _0.75 MnO _2.6 (1 g), an ion exchange step was performed in the same manner as in Example 1, the precipitate was filtered, washed, and Li _0.6 MnO _2.2 A positive electrode active material for lithium secondary batteries (sample E2) composed of (lithium-manganese composite oxide) was obtained.
[0068]
Subsequently, SEM observation and X-ray diffraction measurement were performed on the sample E2 in the same manner as in Example 1. Fig. 6 shows the result of SEM observation, and Fig. 6 shows the result of X-ray diffraction measurement.
FIG.
As is known from FIG. 6, the sample E2 was composed of substantially spherical particles having a plurality of protrusions on the surface. These particles consisted of strip particles having a width of about 0.1 μm and a length of about 0.5 μm, and constituted secondary particles having a diameter of 2 to 3 μm.
[0069]
As can be seen from FIG. 7, all the peaks of the X-ray diffraction pattern of the sample E2 obtained from the X-ray diffraction measurement have the a-axis length of 2.85 ° and c as in the case of the sample E1. LiMnO with O2 type layered structure with axis length of 9.6９ ₂ The unit cell of was able to index.
[0070]
Next, a lithium secondary battery was fabricated using the sample E2 as a positive electrode. The manufacturing method is the same as that of the battery E1 of the first embodiment.
Hereinafter, the lithium secondary battery obtained in this example is referred to as a battery E2.
[0071]
(Comparative example)
Next, in this example, in order to clarify the excellent characteristics of the samples E1 and E2, as a comparative example, a lithium secondary material containing an O3-type layered structure lithium-manganese composite oxide shown in FIG. A positive electrode active material for a battery was prepared, and a lithium secondary battery was prepared using the positive electrode active material for a lithium secondary battery as a positive electrode.
[0072]
First, a cathode active material for a lithium secondary battery comprising a lithium-manganese composite oxide having an O3-type layered structure was prepared as follows. The preparation method is described in “Nature”, UK, 1996, 381, p. This was performed in the same manner as described in 499-500.
[0073]
That is, first, MnO ₂ (1 g) and NaOH (0.46 g) in an argon atmosphere at 700 ° C. for 12 hours to react with NaMnO. ₂ Was prepared.
Next, the NaMnO obtained above was used. ₂ Was subjected to an ion exchange reaction in a 1 M LiCl ethanol solution at 80 ° C. for 24 hours.
In this way, the O3-type layered structure lithium-manganese composite oxide (LiMnO) ₂ ) Was obtained. This is designated as Sample C1.
[0074]
Next, a lithium secondary battery was manufactured using this sample C1 as a positive electrode. The manufacturing method is the same as that of the battery E1 of the first embodiment.
Hereinafter, the lithium secondary battery obtained in this example is referred to as a battery C1.
[0075]
(Experimental example)
In this example, a charge / discharge cycle test was performed on the batteries E1, E2, and C1 produced in Example 1, Example 2, and Comparative Example 1, respectively.
That is, using the batteries E1, E2 and C1, a constant current density of 0.5 mA / cm ² And left for 10 minutes at a constant current density of 0.5 to 4.0 mA / cm. ² , Discharge to 2.5 V and leave for 10 minutes. A cycle of 0 recharges was defined as one cycle, and charge and discharge were repeated up to 20 cycles at a temperature of 20 ° C., and the discharge capacity at each cycle was measured.
The result is shown in FIG. In the figure, the horizontal axis represents the number of cycles (times), and the vertical axis represents the discharge capacity (mAh / g).
[0076]
As is known from FIG. 9, in the battery C1, the discharge capacity is reduced to about 50 mAh / g after 10 cycles.
On the other hand, the batteries E1 and E2 maintained a very high discharge capacity of 150 mAh / g at the 10th cycle, and maintained a high discharge capacity of 60 mAh / g or more at the 20th cycle.
Further, the batteries E1 and E2 had a high initial discharge capacity exceeding 160 mAh / g.
As described above, the batteries E1 and E2 had a high discharge capacity and excellent charge / discharge cycle characteristics.
[0077]
In addition, comparing the battery E1 with the battery E2, the battery E1 containing the positive electrode active material composed of the flaky particles showed a higher discharge capacity than the battery E2. On the other hand, the battery E2 containing the positive electrode active material composed of the substantially spherical particles having the protruding portions had a smaller capacity change ratio with respect to the current density than the battery E1, and was excellent in stability.
[0078]
(Example 3)
This example is an example in which the same positive electrode active material for a lithium secondary battery as that of the above-mentioned sample E1 is manufactured by a simpler method than that of the first example. That is, in this example, the P2-type layered sodium-manganese composite oxide produced by the two steps of the first hydrothermal step and the second hydrothermal step in Example 1 was produced in one step. Then, using the sodium-manganese composite oxide, a lithium-manganese composite oxide having an O2-type layered structure was produced.
[0079]
Specifically, first, KMnO ₄ (1.2 g) and NaOH (28.1 g) are mixed, and 25 g of distilled water is added to prepare a slurry. This slurry was reacted for 1 day at a temperature of 200 ° C. under saturated steam in an autoclave lined with Teflon (registered trademark). Then, the precipitate in the container is filtered, washed with water, _0.75 MnO _2.05 Got.
[0080]
Next, this Na _0.75 MnO _2.05 (1 g) was dispersed in a 1 M LiCl ethanol solution and reacted at 80 ° C. for one day (ion exchange step). Then, the precipitate in the container is filtered, washed with ethanol, and the Li is used as the positive electrode active material for the lithium secondary battery. _0.6 MnO _2.2 (Lithium-manganese composite oxide) was obtained.
[0081]
All the peaks in the X-ray diffraction pattern of the lithium-manganese composite oxide of this example were LiMnO having an O2-type layered structure with an a-axis length of 2.85 ° and a c-axis length of 9.6 °. ₂ The unit cell of was able to index.
Thus, according to this example, the composition formula Li _1-x MnO _{2 + y} A positive electrode active material for a lithium secondary battery represented by (0 ≦ x <1, 0 <y <1) and containing a lithium-manganese composite oxide having an O2-type layered structure can be produced.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a crystal structure of a lithium-manganese composite oxide having an O2-type layered structure according to Example 1.
FIG. 2 is an explanatory view showing a crystal structure of a sodium-manganese composite oxide having a P2-type layered structure according to Example 1.
FIG. 3 is a view showing the result of observing the shape of the sample E1 according to Example 1 with a scanning electron microscope (SEM).
FIG. 4 is a view showing an X-ray diffraction pattern of the sample E1 according to Example 1.
FIG. 5 is an explanatory cross-sectional view of the lithium secondary battery according to the first embodiment.
FIG. 6 is a view showing the result of observing the shape of the sample E2 according to Example 2 with a scanning electron microscope (SEM).
FIG. 7 is a view showing an X-ray diffraction pattern of the sample E2 according to Example 2.
FIG. 8 is an explanatory diagram showing a crystal structure of a lithium-manganese composite oxide having an O3-type layered structure according to a comparative example.
FIG. 9 is an explanatory diagram showing a result of a charge / discharge cycle test according to an experimental example.
[Explanation of symbols]
1. . . Lithium secondary battery,
11. . . Battery case,
12. . . Sealing plate,
2. . . Positive electrode,
3. . . Negative electrode,
4. . . Separator,
5. . . gasket,

Claims (11)

A lithium-manganese composite oxide represented by a composition formula Li1 _- xMnO2 _{+ y} (0≤x <1,0 <y <1) and having an O2-type layered structure; Positive electrode active material for secondary batteries. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the lithium-manganese composite oxide is formed of scale-like particles. 3. The lithium battery according to claim 2, wherein the scale-like particles have a thickness of 0.05 to 5 μm, and a maximum diameter of a surface substantially perpendicular to the thickness direction is 0.2 to 5 μm. Positive electrode active material for secondary batteries. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the lithium-manganese composite oxide comprises substantially spherical particles having a plurality of protrusions on the surface. 5. The positive electrode active material for a lithium secondary battery according to claim 4, wherein the substantially spherical particles having the protruding portions have a diameter of 1 to 5 [mu] m. Positive electrode active material for a lithium secondary battery represented by a composition formula Li _1-x MnO _{2 + y} (0 ≦ x <1,0 <y <1) and containing a lithium-manganese composite oxide having an O2-type layered structure A method for producing a substance,
A lithium-manganese composite oxide having a P2-type layered structure, wherein the sodium-manganese composite oxide is ion-exchanged in a solution containing lithium chloride to replace sodium with lithium and convert it to an O3-type layered structure. Method for producing positive electrode active material for secondary battery. According to claim 6, prior to the ion exchange step, potassium first solution is heated to O3 type layered structure including KMnO ₄ - a first hydrothermal process to produce manganese composite oxide,
A second hydrothermal step of heating the second solution containing the potassium-manganese composite oxide and sodium hydroxide obtained in the first hydrothermal step to produce the P2-type layered sodium-manganese composite oxide And a method for producing a positive electrode active material for a lithium secondary battery. 8. The method according to claim 7, wherein in the first hydrothermal step, KOH is further added to the first solution. The positive electrode active material for a lithium secondary battery according to claim 7 or 8, wherein the heating in the first hydrothermal step and the second hydrothermal step is performed at a temperature of about 120 to 250 ° C under substantially saturated steam pressure. The method of manufacturing the substance. The lithium secondary battery according to any one of claims 6 to 9, wherein the ion exchange step is performed in an alcohol, a non-aqueous organic solvent, or an aqueous solution at a reaction temperature of 50C to 150C. Production method of positive electrode active material for use. A lithium secondary battery comprising the positive electrode active material for a lithium secondary battery according to claim 1 in a positive electrode.

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