JP5177672B2 - Active material for lithium battery, method for producing the same, and lithium battery using the same - Google Patents

Description

  The present invention relates to an active material for a lithium battery, a method for producing the same, and a lithium battery including an electrode containing the active material as a constituent member.

  Currently, in Japan, lithium primary batteries are used as power sources for cameras and watches, and lithium secondary batteries are used as portable electronic devices such as mobile phones and laptop computers. Lithium batteries are one of the important storage batteries. It has become. In addition, lithium secondary batteries are expected to be put into practical use as large batteries such as hybrid cars and power load leveling systems in the future, and their importance is increasing.

  This lithium battery has a positive electrode and a negative electrode each containing a material capable of inserting and extracting lithium, and a separator or a solid electrolyte containing a non-aqueous electrolyte as main components.

Among these constituent elements, manganese dioxide (MnO ₂ ), lithium cobalt oxide (LiCoO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), lithium titanium oxide are considered as active materials for electrodes. Examples thereof include oxides such as products (Li ₄ Ti ₅ O ₁₂ ), metals such as lithium metal, lithium alloy and tin alloy, and carbon materials such as graphite and MCMB (mesocarbon microbeads).

  Regarding these materials, the voltage of the battery is determined by the difference in chemical potential in the lithium content in each active material, but it is a feature of the lithium battery that a large potential difference can be formed particularly by combination.

In particular, in the combination of lithium cobalt oxide LiCoO ₂ active material and carbon material as an electrode, a voltage close to 4V is possible, the charge / discharge capacity (the amount of lithium that can be desorbed and inserted from the electrode) is large, and the safety is also high. Due to its high cost, this combination of electrode materials is widely used in current lithium secondary batteries.

  In the future, chemical batteries such as lithium batteries and capacitors are expected to be large, long-life, such as automotive power supplies, large-capacity backup power supplies, and emergency power supplies. There has been a need for a higher performance (high capacity) electrode active material in combination with a material active material.

  Of these, titanium oxide active materials have a voltage of about 1 to 2 V when lithium metal is used for the counter electrode, so the possibility of materials having various crystal structures as electrode active materials is examined. Has been.

In particular, an electrode including a spinel-type lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ ) active material has a potential flat portion of about 1.5 V with respect to lithium, and a high capacity of about 175 mAh / g is obtained. Therefore, it is attracting attention and is mainly used for lithium secondary batteries.

Further, Na ₂ Ti ₆ O ₁₃ and K ₂ Ti ₆ O ₁₃ as alkali titanium oxides have been studied as electrode materials, and insertion capacities of about 150 mAh / g and 100 mAh / g have been reported, respectively. (See Non-Patent Documents 1 and 2)

The crystal structure taken by these compounds is a Na ₂ Ti ₆ O ₁₃ type tunnel structure, and is characterized by having a tunnel space in which two alkali elements can be occupied by a unit in which three TiO ₆ octahedrons are connected. The crystal structure is shown in FIG. In FIG. 1, an octahedron represents a TiO ₆ octahedron, and titanium is occupied in the center thereof. A sphere represents a position occupied by potassium, sodium, lithium, or hydrogen.

On the other hand, a layered structure sodium titanium oxide Na ₂ Ti ₃ O ₇ having a similar chemical composition, its proton exchanger H ₂ Ti ₃ O ₇ , and its lithium ion exchanger Li ₂ Ti ₃ O ₇ are also considered as active materials. And insertion capacities of 44 mAh / g, 174 mAh / g, and 147 mAh / g, respectively, have been reported. (See Patent Document 1 and Non-Patent Document 3)

  That is, it can be seen that the compound active material exchanged with lithium or proton, which has a smaller ion size than sodium, has a higher capacity compared to the starting sodium compound.

When this is applied to the A ₂ Ti ₆ O ₁₃ (A = K, Na, Li, H) system, the initial insertion capacity of the recently reported H ₂ Ti ₆ O ₁₃ is Since a high capacity of 283 mAh / g is obtained, the smaller the ion radius of the element A, the larger the empty space in the tunnel space, which is a characteristic of the crystal structure, which indicates that a high capacity is obtained. . (Patent Document 2)

  However, the proton exchanger has a problem in that it reacts with lithium in the electrolyte solution in the lithium battery, and generates water by decomposition, which is a problem as an electrode material active material.

On the other hand, regarding the composite titanium oxide having a chemical composition of Li ₂ Ti ₆ O ₁₃ in which A = Li in the A ₂ Ti ₆ O ₁₃ system, there has been no disclosure of application to an electrode active material.
JP 2007-234233 A Japanese Patent Application No. 2008-039820 R. Dominko, E .; Baudrin, P.M. Umek, D.M. Arcon, M.M. Gabersek, J. et al. Jamnik, Electrochemistry Communications, 8, 673-677 (2006) R. Dominko, L .; Dupont, M.M. Gabersek, J. et al. Jamnik, E .; Baudrin, Journal of Power Sources, 174, 1172-1176 (2007) K. Chiba, N .; Kijima, Y. et al. Takahashi, Y .; Idemoto, J .; Akimoto, Solid State Ionics, 178, 1725-1730 (2008)

The present invention solves the above-mentioned problems as described above, and a lithium titanium oxide active material having a Na ₂ Ti ₆ O ₁₃ type tunnel structure important as a lithium battery electrode material that can be expected to have a high capacity, and a method for producing the same, Another object of the present invention is to provide a lithium battery including an electrode containing the active material as a constituent member.

As a result of intensive studies, the present inventor has clarified the Na ₂ Ti ₆ O ₁₃ type tunnel structure composite titanium oxide Li ₂ Ti ₆ O ₁₃ active material as shown in FIG. 1 and the production method thereof, and contains the active material. The present invention was completed by producing a lithium battery including the prepared electrode as a constituent member and confirming a high insertion capacity.

That is, the present invention provides a lithium battery including, as constituent members, the following Na ₂ Ti ₆ O ₁₃ type tunnel structure composite titanium oxide Li ₂ Ti ₆ O ₁₃ active material, a method for producing the same, and an electrode containing the active material. I will provide a.
(1) Mainly a composite titanium oxide represented by the chemical formula Li ₂ Ti ₆ O ₁₃ (however, residual Na amount: Li amount = 0.13 to 0 (ie, below detection limit): 1.87 to 2)) An active material for lithium batteries as a component.
(2) The active material for a lithium battery according to (1), wherein the crystal structure is a monoclinic Na ₂ Ti ₆ O ₁₃ type tunnel structure.
(3) The monoclinic lattice constant is determined by the amount of residual sodium, the a-axis length is 1.507 to 1.545 nm, the b-axis length is 0.373 to 0.376 nm, and the c-axis length is 0.1. The active material for a lithium battery as described in (2), wherein the range is 911 to 0.916 nm and the β angle is in the range of 99.0 to 99.8 °.
(4) The lithium-titanium battery according to (1), which is synthesized by an ion exchange process using sodium titanium oxide Na ₂ Ti ₆ O ₁₃ generated from a sodium compound and titanium oxide as a starting material. A method for producing an active material.
(5) The method for producing an active material for a lithium battery according to (4), wherein the ion exchange step applies a lithium ion exchange reaction using a lithium molten salt.
(6) The method for producing an active material for a lithium battery according to (5), wherein the heat treatment temperature in the lithium ion exchange reaction using the lithium molten salt is in the range of 290 ° C. to 500 ° C.
(7) A lithium battery comprising two electrodes used as a positive electrode and a negative electrode and an electrolyte, wherein the electrode containing an active material according to any one of (1) to (3) is used as a constituent member.

According to the present invention, a composite titanium oxide Li ₂ Ti ₆ O ₁₃ active material having a Na ₂ Ti ₆ O ₁₃ type tunnel structure can be manufactured. By using this active material as an electrode material, a high insertion capacity can be obtained. A lithium battery having

The electrode material active material for a lithium battery of the present invention is a material mainly composed of a compound having a chemical composition of Li ₂ Ti ₆ O ₁₃ .
Further, the crystal structure is characterized by having a Na ₂ Ti ₆ O ₁₃ type tunnel structure.
Furthermore, the lattice constant of the composite titanium oxide Li ₂ Ti ₆ O ₁₃ is determined by the amount of sodium remaining from the starting material, and the a-axis length is 1.507 to 1.545 nm, The b-axis length is 0.373 to 0.376 nm, the c-axis length is 0.911 to 0.916 nm, and the β angle is 99.0 to 99.8 °.

Among the present inventions, the method for producing an active material for an electrode material for a lithium battery is synthesized by a step of ion-exchanging sodium to lithium using sodium titanium oxide generated from a sodium compound and titanium oxide as a starting material. It is a characteristic method.
In addition, a lithium battery using an electrode containing the composite titanium oxide active material of the present invention as a constituent member is a battery that can be expected to have a high capacity exceeding 200 mAh / g.

  The production method according to the present invention will be described in more detail.

(Production of starting material Na ₂ Ti ₆ O ₁₃ )
Among the present inventions, the Na ₂ Ti ₃ O ₇ polycrystal as a starting material has a chemical composition of Na ₂ Ti ₆ O ₁₃ with at least one sodium compound and at least one titanium compound as raw materials. Thus, it can be manufactured by weighing and mixing, and heating in an atmosphere containing oxygen gas such as air.

As the sodium raw material, at least one of sodium (metallic sodium) and a sodium compound is used. The sodium compound is not particularly limited as long as it contains sodium. For example, oxides such as Na ₂ O and Na ₂ O ₂ , salts such as Na ₂ CO ₃ and NaNO ₃ , hydroxides such as NaOH, etc. Is mentioned. Among these, Na ₂ CO ₃ is particularly preferable.

As the titanium raw material, at least one of titanium (metallic titanium) and a titanium compound is used. The titanium compound is not particularly limited as long as it contains titanium, and examples thereof include oxides such as TiO, Ti ₂ O ₃ and TiO ₂ , salts such as TiCl _{4 and the} like. Among these, TiO ₂ is particularly preferable.

First, a mixture containing these is prepared. The mixing ratio of sodium raw material and titanium material _is preferably mixed such that the chemical composition of Na ₂ Ti _{6 O 13.} In addition, since sodium easily volatilizes during heating, the amount of sodium should be slightly more excessive than 2 in the above chemical formula, and preferably in the range of 2.0 to 2.1. Moreover, a mixing method is not specifically limited as long as these can be mixed uniformly, For example, what is necessary is just to mix by a wet type or a dry type using well-known mixers, such as a mixer.

  The mixture is then fired. The firing temperature can be appropriately set depending on the raw material, but is usually about 600 ° C to 1200 ° C, preferably 700 ° C to 1050 ° C. Also, the firing atmosphere is not particularly limited, and it is usually performed in an oxidizing atmosphere or air. The firing time can be appropriately changed according to the firing temperature and the like. The cooling method is not particularly limited, but may be natural cooling (cooling in the furnace) or slow cooling.

  After firing, the fired product may be pulverized by a known method as necessary, and the above firing step may be further performed. That is, in the method of the present invention, it is preferable that the mixture is repeatedly fired, cooled and pulverized twice or more. Note that the degree of pulverization may be adjusted as appropriate according to the firing temperature and the like.

(Production of Lithium Exchanger Li ₂ Ti ₆ O ₁₃ Active Material)
Next, using Na ₂ Ti ₆ O ₁₃ obtained as described above as a starting material, by applying a lithium ion exchange reaction in a molten salt containing a lithium compound, almost all of the sodium in the starting material compound was exchanged for lithium. A lithium ion exchanger active material Li ₂ Ti ₆ O ₁₃ is obtained.

In this case, it is preferable to perform the ion exchange treatment while dispersing the pulverized Na ₂ Ti ₆ O ₁₃ in the molten salt containing the lithium compound. As the molten salt, a molten salt containing any one or more of salts that melt at a relatively low temperature such as lithium nitrate, lithium chloride, lithium bromide, and lithium iodide can be used. As a preferred method, a lithium salt is melted in advance, and Na ₂ Ti ₆ O ₁₃ powder is added thereto. The mixing ratio is usually 3 to 100, preferably 10 to 30, as a ratio of the weight of the entire lithium salt to the weight of Na ₂ Ti ₆ O ₁₃ .

  The temperature of the ion exchange treatment is in the range of 30 ° C to 500 ° C, preferably 200 ° C to 400 ° C. The treatment time is usually 2 to 72 hours, preferably 5 to 50 hours.

Furthermore, as a method of the lithium ion exchange treatment, a method of treating in an organic solvent or an aqueous solution in which a lithium compound is melted is also suitable. In this case, the pulverized Na ₂ Ti ₆ O ₁₃ raw material is put into an organic solvent or water in which a lithium compound is dissolved at a constant concentration, and the mixture is treated at a temperature not higher than the boiling point of the organic solvent or water. In order to avoid evaporation of the solvent, it is preferable to perform ion exchange while refluxing the solvent. The treatment temperature is usually 30 ° C to 300 ° C, preferably 50 ° C to 180 ° C. The treatment time is not particularly limited, but is usually 5 to 50 hours, preferably 10 to 20 hours.

  As the lithium compound used in the present invention, hydroxide, carbonate, acetate, nitrate, oxalate, halide, butyllithium and the like are preferable, and these are used alone or in combination of two or more as required. . As the organic solvent used in the present invention, higher alcohols such as hexanol and ethoxyethanol, ethers such as diethyl glycol monoethyl ether, or organic solvents having a boiling point of 140 ° C. or more have good workability. This is preferable. These may be used alone or in combination of two or more as required.

The density | concentration of the lithium compound in an organic solvent or aqueous solution is 3-10 mol% normally, Preferably it is 5-8 mol%. Further, the dispersion concentration of the Na ₂ Ti ₆ O ₁₃ raw material in the organic solvent or the aqueous solution is not particularly limited, but is preferably about 1 to 20% by weight from the viewpoint of operability and economy.

After the ion exchange treatment, the obtained product is washed with ethanol or the like and then dried to obtain a target lithium ion exchanger active material represented by the chemical formula Li ₂ Ti ₆ O ₁₃ . The washing method and the drying method are not particularly limited, and a normal method may be used, or natural drying in a desiccator or the like may be used.

The Li ₂ Ti ₆ O ₁₃ active material thus obtained can be obtained by changing the conditions for the exchange treatment so that the amount of sodium remaining from the starting material is reduced from the chemical composition leaving a significant amount to the wet state. It is possible to control the chemical composition below the detection limit of chemical analysis by the method.

(Lithium battery)
The lithium secondary battery of the present invention uses an electrode containing the Li ₂ Ti ₆ O ₁₃ as an active material as a constituent member. That is, a battery element of a known lithium battery (coin type, button type, cylindrical type, all solid type, etc.) can be used as it is, except that Li ₂ Ti ₆ O ₁₃ of the present invention is used as the electrode material active material. . FIG. 2 is a schematic view showing an example in which the lithium battery of the present invention is applied to a coin-type lithium secondary battery. The coin-type battery 1 includes a negative electrode terminal 2, a negative electrode 3, a (separator + electrolyte) 4, an insulating packing 5, a positive electrode 6, and a positive electrode can 7.

In the present invention, the Li ₂ Ti ₆ O ₁₃ active material of the present invention is mixed with a conductive agent, a binder or the like as necessary to adjust the electrode mixture, and this is crimped to the current collector. An electrode can be produced. As the current collector, a stainless mesh, aluminum foil or the like can be preferably used. As the conductive agent, acetylene black, ketjen black or the like can be preferably used. As the binder, tetrafluoroethylene, polyvinylidene fluoride, or the like can be preferably used.

The composition of the Li ₂ Ti ₆ O ₁₃ active material, the conductive agent, the binder and the like in the electrode mixture is not particularly limited, but usually the conductive agent is about 1 to 30% by weight (preferably 5 to 25% by weight). The binder may be 0 to 30% by weight (preferably 3 to 10% by weight), and the balance may be Li ₂ Ti ₆ O ₁₃ active material.

In the lithium battery of the present invention, as the counter electrode with respect to the electrode, for example, a known one that functions as a negative electrode and occludes lithium, such as metal lithium and a lithium alloy, can be adopted. Alternatively, as the counter electrode, a known one that functions as a positive electrode and occludes lithium, such as lithium cobalt oxide (LiCoO ₂ ) or spinel type lithium manganese oxide (LiMn ₂ O ₄ ), can also be used. . That is, the electrode containing the active material of the present invention can function as a positive electrode or a negative electrode depending on the electrode constituent material to be combined.

  In the lithium secondary battery of the present invention, a known battery element may be adopted for the separator, the battery container, and the like.

  Furthermore, known electrolyte solutions, solid electrolytes, and the like can be applied as the electrolyte. For example, as an electrolytic solution, an electrolyte such as lithium perchlorate or lithium hexafluorophosphate is used in a solvent such as ethylene carbonate (EC), dimethyl carbonate (DMC), propylene carbonate (PC), or diethyl carbonate (DEC). What was dissolved can be used.

  Hereinafter, examples will be shown to further clarify the features of the present invention. The present invention is not limited to these examples.

[Example 1]
(Production of starting material Na ₂ Ti ₆ O ₁₃ )
Sodium carbonate (Na ₂ CO ₃ ) powder with a purity of 99% or more and titanium dioxide (TiO ₂ ) powder with a purity of 99.99% or more were weighed so that the molar ratio was Na: Ti = 2.02: 6. After mixing these in a mortar, they were filled in a JIS standard platinum crucible and heated in an air at high temperature using an electric furnace. The firing temperature was 800 ° C. and the firing time was 20 hours. Then, after naturally cooling in an electric furnace, it was again pulverized and mixed in a mortar and refired at 800 ° C. for 20 hours to obtain a Na ₂ Ti ₆ O ₁₃ polycrystal as a starting material.

When the chemical composition of the obtained sample was analyzed by ICP emission analysis, Na: Ti = 2.0: 6 (analysis error of each element: within 0.04), and the chemical formula of Na ₂ Ti ₆ O ₁₃ It was reasonable. Furthermore, it was revealed by an X-ray powder diffractometer that the crystal has a monoclinic system and a single phase having a crystal structure of space group C2 / m having good crystallinity. The powder X-ray diffraction pattern of Na ₂ Ti ₆ O ₁₃ is shown in FIG. Further, when the lattice constant was determined by the least square method using each index and its surface spacing, the following values were obtained, which were in good agreement with the known Na ₂ Ti ₆ O ₁₃ value.
a = 1.5072 nm (error: within 0.0005 nm)
b = 0.3738 nm (error: within 0.0001 nm)
c = 0.9154 nm (error: within 0.0003 nm)
β = 99.00 ° (error: within 0.02 °)

When the particle shape of the Na ₂ Ti ₆ O ₁₃ polycrystal thus obtained was examined by a scanning electron microscope (SEM), the polycrystal was a primary having an isotropic shape of about 1 micron square. It was revealed that it was composed of particles.

(Production of Li ₂ Ti ₆ O ₁₃ active material)
Using the pulverized product of Na ₂ Ti ₆ O ₁₃ synthesized as described above as a starting material, anhydrous lithium nitrate (LiNO ₃ ) powder with a purity of 99% or more and Na ₂ Ti ₆ O ₁₃ : LiNO ₃ = by weight ratio = Weighed to be 1:20. These were mixed in a mortar, then filled in an alumina crucible, and held in air at 290 ° C. for 10 hours using an electric furnace to perform lithium ion exchange treatment. Thereafter, pure water, and it was washed well with ethanol, by air _drying, to obtain a Li ₂ Ti _{6 O 13} active material.

When the chemical composition of the obtained sample was analyzed by ICP emission spectrometry, Na: Li: Ti = 0.13: 1.87: 6 (analysis error of each element: within 0.04), significant Of residual sodium was observed. Furthermore, with an X-ray powder diffractometer, a single phase of Li ₂ Ti ₆ O ₁₃ having a monoclinic system, a space group C2 / m of a Na ₂ Ti ₆ O ₁₃ type tunnel structure having good crystallinity It became clear that there was. FIG. 4 shows a powder X-ray diffraction pattern of Li ₂ Ti ₆ O ₁₃ . Further, when the lattice constant was determined by the least square method using each index and its surface spacing, the following value was obtained, which was in good agreement with the value of the known Li ₂ Ti ₆ O ₁₃ , and the residual sodium amount was It became clear that there was almost no difference in the lattice constant.
a = 1.5310 nm (error: within 0.0004 nm)
b = 0.3746 nm (error: within 0.0001 nm)
c = 0.9142 nm (error: within 0.0002 nm)
β = 99.37 ° (error: within 0.02 °)

When the particle shape of the Li ₂ Ti ₆ O ₁₃ polycrystal obtained in this way was examined with a scanning electron microscope (SEM), the polycrystal had a shape of Na ₂ Ti ₆ O ₁₃ as a starting material. It was revealed that the particles were composed of primary particles having an isotropic shape of about 1 micron square.

(Lithium battery)
An electrode was prepared by using Li ₂ Ti ₆ O ₁₃ thus obtained as an active material, acetylene black as a conductive agent, and tetrafluoroethylene as a binder in a weight ratio of 10: 5: 1. Then, using lithium metal as a counter electrode, a 1M solution in which lithium hexafluorophosphate is dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio 1: 1) is used as an electrolytic solution. A lithium battery (coin-type lithium secondary battery) having the structure shown in FIG. 2 was prepared, and its electrochemical lithium insertion / extraction behavior was measured. The battery was produced according to a known cell configuration / assembly method.

The fabricated lithium secondary battery was subjected to an electrochemical lithium insertion test at a current density of 10 mA / g and a cut-off potential of 1.0 V under a temperature condition of 25 ° C. It has been found that a high voltage of 217 mAh / g is obtained with a voltage flat portion in the vicinity of 0.5 V. After that, when a lithium desorption / insertion test was performed at a cut-off potential of 3.0 to 1.0 V, the second and subsequent cycles showed a gentle voltage change at a potential near 1.8 V, while the capacity was changed. It was found that reversible lithium insertion / extraction was possible at about 90-100 mAh / g. FIG. 5 shows voltage changes associated with lithium insertion / extraction reactions. From the above, the Li ₂ Ti ₆ O ₁₃ active material of the present invention is useful as an electrode material for a high-capacity lithium primary battery having a lithium-based operating voltage of about 1.5 V and has a lithium-based operating voltage of about 1.8 V. It became clear that it was useful as a lithium secondary battery material.

[Example 2]
(Production of Li ₂ Ti ₆ O ₁₃ active material)
Using the pulverized Na ₂ Ti ₆ O ₁₃ polycrystal synthesized in Example 1 as a starting material, anhydrous lithium nitrate (LiNO ₃ ) powder having a purity of 99% or more and Na ₂ Ti ₆ O ₁₃ : LiNO in a weight ratio It measured so that it might become ₃ = 1: 20. These were mixed in a mortar, then filled in an alumina crucible, and held in air at 320 ° C. for 10 hours using an electric furnace to perform lithium ion exchange treatment. Thereafter, pure water, and it was washed well with ethanol, by air _drying, to obtain a Li ₂ Ti _{6 O 13} active material.

When the chemical composition of the obtained sample was analyzed by ICP emission analysis, it was Na: Li: Ti = 0.10: 1.90: 6 (analysis error of each element: within 0.04), significant The amount of residual sodium was confirmed, but when compared with Example 1, since the ion exchange treatment temperature was higher, the residual amount tended to decrease. Furthermore, with an X-ray powder diffractometer, a single phase of Li ₂ Ti ₆ O ₁₃ having a monoclinic system, a space group C2 / m of a Na ₂ Ti ₆ O ₁₃ type tunnel structure having good crystallinity It became clear that there was. The powder X-ray diffraction pattern of Li ₂ Ti ₆ O ₁₃ is shown in FIG. Further, when the lattice constant was determined by the least square method using each index and its surface spacing, the following values were obtained, which were in good agreement with the values of known Li ₂ Ti ₆ O ₁₃ .
a = 1.5324 nm (error: within 0.0004 nm)
b = 0.3750 nm (error: within 0.0001 nm)
c = 0.9146 nm (error: within 0.0002 nm)
β = 99.41 ° (error: within 0.01 °)

[Example 3]
(Production of Li ₂ Ti ₆ O ₁₃ active material)
Using the pulverized Na ₂ Ti ₆ O ₁₃ polycrystal synthesized in Example 1 as a starting material, anhydrous lithium nitrate (LiNO ₃ ) powder having a purity of 99% or more and Na ₂ Ti ₆ O ₁₃ : LiNO in a weight ratio It measured so that it might become ₃ = 1: 20. These were mixed in a mortar, then filled in an alumina crucible, and held in air at 350 ° C. for 10 hours using an electric furnace to perform lithium ion exchange treatment. Thereafter, pure water, and it was washed well with ethanol, by air _drying, to obtain a Li ₂ Ti _{6 O 13} active material.

When the chemical composition of the obtained sample was analyzed by ICP emission analysis, it was Na: Li: Ti = 0.06: 1.94: 6 (analysis error of each element: within 0.04), significant However, when the ion exchange treatment temperature was higher, the residual sodium amount tended to decrease as compared with Example 1 and Example 2. Furthermore, with an X-ray powder diffractometer, a single phase of Li ₂ Ti ₆ O ₁₃ having a monoclinic system, a space group C2 / m of a Na ₂ Ti ₆ O ₁₃ type tunnel structure having good crystallinity It became clear that there was. FIG. 7 shows a powder X-ray diffraction pattern of Li ₂ Ti ₆ O ₁₃ . Further, when the lattice constant was determined by the least square method using each index and its surface spacing, the following values were obtained, which were in good agreement with the values of known Li ₂ Ti ₆ O ₁₃ .
a = 1.5303 nm (error: within 0.0006 nm)
b = 0.3745 nm (error: within 0.0001 nm)
c = 0.9134 nm (error: within 0.0003 nm)
β = 99.40 ° (error: within 0.03 °)

When the particle shape of the Li ₂ Ti ₆ O ₁₃ polycrystal obtained in this way was examined with a scanning electron microscope (SEM), the polycrystal had a shape of Na ₂ Ti ₆ O ₁₃ as a starting material. It was revealed that the particles were composed of primary particles having an isotropic shape of about 1 micron square.

(Lithium battery)
Using the Li ₂ Ti ₆ O ₁₃ thus obtained as an active material, a lithium battery similar to that of Example 1 was produced, and the current density was 10 mA / g and the cutoff was 1.0 V under the temperature condition of 25 ° C. When an electrochemical lithium insertion test was conducted up to the potential, it was found that the initial insertion reaction had a voltage flat portion around a voltage of 1.5 V, and a high capacity of 215 mAh / g was obtained. After that, when a lithium desorption / insertion test was performed at a cut-off potential of 3.0 to 1.0 V, the second and subsequent cycles showed a gentle voltage change at a potential near 1.8 V, while the capacity was changed. It was found that reversible lithium insertion / extraction was possible at about 90-100 mAh / g. FIG. 8 shows voltage changes associated with lithium insertion / extraction reactions. From the above, the Li ₂ Ti ₆ O ₁₃ active material of the present invention is useful as an electrode material for a high-capacity lithium primary battery having a lithium-based operating voltage of about 1.5 V and has a lithium-based operating voltage of about 1.8 V. It became clear that it was useful as a lithium secondary battery material. Moreover, it became clear that the influence of the amount of residual sodium is not remarkable with respect to lithium insertion / extraction behavior compared with Example 1.

[Example 4]
(Production of Li ₂ Ti ₆ O ₁₃ active material)
Using the pulverized Na ₂ Ti ₆ O ₁₃ polycrystal synthesized in Example 1 as a starting material, anhydrous lithium nitrate (LiNO ₃ ) powder having a purity of 99% or more and Na ₂ Ti ₆ O ₁₃ : LiNO in a weight ratio It measured so that it might become ₃ = 1: 20. These were mixed in a mortar, then filled in an alumina crucible, and held in air at 380 ° C. for 10 hours using an electric furnace to perform lithium ion exchange treatment. Thereafter, pure water, and it was washed well with ethanol, by air _drying, to obtain a Li ₂ Ti _{6 O 13} active material.

When the chemical composition of the obtained sample was analyzed by ICP emission spectrometry, Na: Li: Ti = 0.03: 1.97: 6 (analysis error of each element: within 0.04) It was clarified that the amount of sodium to be contained is less than the analysis error and has a composition that does not contain sodium. Furthermore, with an X-ray powder diffractometer, a single phase of Li ₂ Ti ₆ O ₁₃ having a monoclinic system, a space group C2 / m of a Na ₂ Ti ₆ O ₁₃ type tunnel structure having good crystallinity It became clear that there was. FIG. 9 shows a powder X-ray diffraction pattern of Li ₂ Ti ₆ O ₁₃ . Further, when the lattice constant was determined by the least square method using each index and its surface spacing, the following values were obtained, which were in good agreement with the values of known Li ₂ Ti ₆ O ₁₃ .
a = 1.5334 nm (error: within 0.0003 nm)
b = 0.3751 nm (error: within 0.0001 nm)
c = 0.9148 nm (error: within 0.0002 nm)
β = 99.44 ° (error: within 0.01 °)

[Comparative Example 1]
Using the Na ₂ Ti ₆ O ₁₃ which is the starting material of the present invention synthesized in Example 1 as an active material, a lithium battery similar to that in Examples 1 and 3 was produced, and under a temperature condition of 25 ° C., a current density of 10 mA. When the electrochemical lithium insertion test was performed up to a cutoff potential of 1.0 V / g, 1.0 V, the initial insertion reaction had a voltage flat portion around 1.3 V and 1.1 V, and the capacity was 77 mAh / It was found that only about g was obtained. (See FIG. 10) After that, when a lithium desorption / insertion test was performed at a cut-off potential of 3.0 to 1.0 V, after the second cycle, the lithium desorption reaction was performed at about 1.3 V. At the time of the separation reaction, although having a potential flat portion in the vicinity of about 1.4 V, the capacity was about 60-50 mAh / g, and the capacity was remarkably small as compared with the past report (Non-Patent Document 3). This is thought to be because the amount of lithium that can be inserted / removed can be increased because past reports are characterized by nanoparticles. It is understood that this also suggests that the Li ₂ Ti ₆ O ₁₃ active material of the present invention may have a higher capacity by forming nanoparticles.

Since the composite titanium oxide Li ₂ Ti ₆ O ₁₃ active material has a Na ₂ Ti ₆ O ₁₃ type tunnel structure, the present invention can occlude a large amount of lithium, and as a high capacity lithium battery electrode material, It has a high practical value.

  Also, the manufacturing method does not require a special apparatus, and the raw material to be used is low in price, so that a high value-added material can be manufactured at a low cost.

Furthermore, a lithium battery in which the composite titanium oxide Li ₂ Ti ₆ O ₁₃ active material of the present invention is applied as an electrode material is a battery capable of high capacity.

Is a schematic diagram showing an _Na 2 _Ti 6 _{O 13} type tunnel structure having the _Li 2 _Ti 6 _{O 13} active material of the present invention. It is a schematic diagram which shows one example of a lithium battery. ₂ is an X-ray powder diffraction pattern of Na ₂ Ti ₆ O ₁₃ which is the starting material of the present invention obtained in Example 1. FIG. _{2 is} an X-ray powder diffraction pattern of the Li ₂ Ti ₆ O ₁₃ active material of the present invention obtained in Example 1 under conditions of an ion exchange treatment temperature of 290 ° C. FIG. It is a diagram illustrating a voltage change due to the lithium insertion-elimination reaction of the battery using the Li ₂ Ti ₆ O ₁₃ active material of the present invention obtained in the conditions of ion exchange treatment temperature 290 ° C. In Example 1 as an electrode. Is an X-ray powder diffraction pattern of _Li 2 _Ti 6 _{O 13} active material of the present invention obtained in the conditions of ion exchange treatment temperature 320 ° C. In Example 2. 4 is an X-ray powder diffraction pattern of the Li ₂ Ti ₆ O ₁₃ active material of the present invention obtained in Example 3 under conditions of an ion exchange treatment temperature of 350 ° C. FIG. It is a diagram illustrating a voltage change due to the lithium insertion-elimination reaction of the battery using the Li ₂ Ti ₆ O ₁₃ active material of the present invention obtained in the conditions of ion exchange treatment temperature 350 ° C. In Example 3 as electrodes. 4 is an X-ray powder diffraction pattern of the Li ₂ Ti ₆ O ₁₃ active material of the present invention obtained in Example 4 under conditions of an ion exchange treatment temperature of 380 ° C. FIG. In Comparative Example 1 is a diagram illustrating a voltage change due to the lithium insertion-elimination reaction of a battery using the produced electrode starting material Na ₂ Ti ₆ O ₁₃ as an active material of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Coin type lithium secondary battery 2 Negative electrode terminal 3 Negative electrode 4 Separator + Electrolyte 5 Insulation packing 6 Positive electrode 7 Positive electrode can

Claims (7)

Formula _Li 2 _Ti 6 _{O 13} (provided that residual Na amount: Li amount = 0.13 to 0: 1.87 to 2) active material for a lithium battery as a main component composite titanium oxide represented by. _{2. The} active material for a lithium battery according to claim 1, wherein the crystal structure is a monoclinic Na ₂ Ti ₆ O ₁₃ type tunnel structure.   The monoclinic lattice constant is determined by the amount of sodium remaining, the a-axis length is 1.507 to 1.545 nm, the b-axis length is 0.373 to 0.376 nm, and the c-axis length is 0.911 to 0. The active material for a lithium battery according to claim 2, which has a .916 nm and a β angle in the range of 99.0 to 99.8 °. _2. The lithium battery active material according to claim 1, which is synthesized by an ion exchange process using sodium titanium oxide Na ₂ Ti ₆ O ₁₃ generated from a sodium compound and titanium oxide as a starting material. Production method.   5. The method for producing an active material for a lithium battery according to claim 4, wherein the ion exchange step uses a lithium ion exchange reaction using a lithium molten salt. The method for producing an active material for a lithium battery according to claim 5, wherein the heat treatment temperature in the lithium ion exchange reaction using the lithium molten salt is in the range of 290 ° C to 500 ° C.   The lithium battery which uses the electrode containing the active material of any one of Claims 1 thru | or 3 as a structural member in the lithium battery which consists of two electrodes used as a positive electrode and a negative electrode, and electrolyte.