JP3961514B2 - Method for producing Li-Ni-Ti composite oxide electrode material and battery using the electrode material - Google Patents

Description

  The present invention relates to a method for producing a Li—Ni—Ti composite oxide electrode material, and a battery including the Li—Ni—Ti composite oxide electrode material as a positive electrode active material.

  Batteries using a composite oxide of Li and a transition metal as a positive electrode active material are widely used mainly for applications for mobile phone power supplies because of their light weight and large capacity. However, the Li-Co composite oxide material that is most frequently used at present cannot use all of its theoretical specific capacity due to the change in crystal structure accompanying charge / discharge, and it is 150 mAh / g, which is half the theoretical value. It can only be used.

  Although the capacity of the battery has been improved by optimizing the filling method or the like, it has also reached its peak. Li-Ni composite oxide, Li-Mn composite oxide, etc. have been studied as a new composite oxide material system replacing Li-Co composite oxide, and those whose specific capacity exceeds 200 mAh / g have been reported. .

  However, even these materials have problems such as insufficient cycle characteristics, safety problems, and storage characteristics at high temperatures. Various methods have been reported to solve these problems by substituting a part of the transition metal with another transition metal or the like. However, the specific capacity is reduced, which is not sufficient for practical use.

On the other hand, in recent years, a material system such as LiNi _0.5 Mn _0.5 O ₂ typified by JP-A-2002-42813 has been reported as a composite oxide system of a plurality of transition metals. The feature of this system is that each of the two kinds of transition metals plays a different role, and it can be said that it is a completely new material system different from a normal partially substituted system. In the case of LiNi _0.5 Mn _0.5 O ₂ , Ni exhibits a function of an electrode material by an oxidation-reduction reaction of 2 + / 4 +, while Mn stably exists in a tetravalent state and provides a function of maintaining the structure. . This material system (or a compound having a composition corresponding thereto) is also reported in Japanese Patent Application Laid-Open Nos. 9-199127 and 2003-17060.

  The inventors paid attention to Li-Ni-Ti composite oxides whose properties and the like have not been reported in this material system, and have been studying to clarify the properties. It has been found that it is impossible to obtain a Li—Ni—Ti composite oxide exhibiting the performance of an electrode material by the methods described in JP-A-199127 and JP-A-2003-17060.

Specifically, according to the methods described in the published Japanese Patent Application Laid-Open Nos. 9-199127 and 2003-17060, a material having a crystal structure represented by the space group Fm3m was obtained. It is known that this crystal structure does not function as an electrode material (Yao, Ozawa, Lithium ion secondary battery-materials and applications-, Nikkan Kogyo Shimbun (1996)), and actually did not function. In order to function as an electrode material, it is necessary to obtain a crystal structure having a layered structure like LiNi _0.5 Mn _0.5 O ₂ .

In order to solve the above problems, the present inventors contain divalent Ni and tetravalent Ti in a ratio of approximately 1: 1, which was difficult to synthesize by the conventional firing method (solid phase method). A Li—Ni—Ti composite oxide having a layered structure and exhibiting the performance of an electrode material contains divalent Ni and tetravalent Ti in a ratio of approximately 1: 1, and has a layered structure Na— It has been found that synthesis is possible by ion exchange using Ni—Ti composite oxide as a precursor. That contains a divalent Ni and tetravalent Ti, formula _{Na b Ni y Ti 1-y} O 2-β (0.95 ≦ b ≦ 1.05,0.45 ≦ y ≦ 0.55, −0.1 ≦ β ≦ 0.1), and a Na—Ni—Ti composite oxide having a layered structure in which the crystal structure belongs to the space group R-3m is used as a raw material. This is a method of ion exchange.

LiNi _0.5 Mn _0.5 O ₂ described above is a material system having a structure similar to this system. In this material system, the closer the ratio of Ni and Mn is to 1, the better the performance as an electrode material. (Y. Makimura and T. Ohzuku, J. Power Sources, 119-121, 156 (2003); T. Ohzuku and Y. Makimura, Chemistry Lett. 744 (2001)). Similarly, in the above Li-Ni-Ti composite oxide, it is necessary for the ratio of Ni and Ti to be 1 in order to show high performance as an electrode material.

When synthesis is performed using a precursor as in this Li—Ni—Ti composite oxide system, the ratio of Ni and Ti needs to be 1 for the Na—Ni—Ti composite oxide that is the precursor. There is. However, it is not easy to set the ratio of Ni and Ti to 1 at the time of mixing raw materials due to problems of purity and weighing.
Kominato, Yoshizawa, Nagayama, JP 2002-42813 A Asaoka, Watanabe, Kobayashi, Japanese Patent Laid-Open No. 9-199127 Ansai, JP2003-17060A Yamazaki, Kimura, JP 10-87327 A Kanno, Electrochemistry, No. 9, 63 (1995) Yoshio, Ozawa, Lithium-ion secondary battery-Materials and applications-, Nikkan Kogyo Shimbun (1996) Y. Makimura and T.M. Ohzuku, J. et al. Power Sources, 119-121, 156 (2003) T.A. Ohzuku and Y.K. Makimura, Chemistry Lett. 744 (2001)

  An object of the present invention is to newly provide a battery having better performance by using a Li—Ni—Ti composite oxide electrode material having a ratio of Ni to Ti of 1.

  Further, as the means, a method for producing a Na—Ni—Ti composite oxide having a Ni / Ti ratio of 1 used as a precursor for synthesizing a Li—Ni—Ti composite oxide electrode material having a Ni / Ti ratio of 1 The object is to produce a Li—Ni—Ti composite oxide electrode material.

In order to achieve this object, a method for producing a Li—Ni—Ti composite oxide electrode material according to the present invention comprises a general formula Na _b Ni _y Ti _1-y O ₂ -β from Ni salt, Ti salt and Na salt. (0.95 ≦ b ≦ 1.05, 0.45 ≦ y ≦ 0.55, −0.1 ≦ β ≦ 0.1), the crystal structure belonging to the space group R-3m When the Na—Ni—Ti composite oxide having the structure is manufactured, Na and Li of the Na—Ni—Ti composite oxide manufactured using NiTiO ₃ as a raw material are ion-exchanged, and the general formula Li _a Ni _x Ti _The crystal structure represented by _1- xO _2-α (0.95 ≦ a ≦ 1.05, 0.45 ≦ x ≦ 0.55, −0.1 ≦ α ≦ 0.1) is a space group R A Li—Ni—Ti composite oxide having a layered structure belonging to −3 m is characterized.

The Na—Ni—Ti composite oxide is characterized by being produced by firing NiTiO ₃ and a Na salt in an inert atmosphere, and the sodium salt is preferably sodium carbonate. To do.

  Furthermore, in the method of the present invention, it is desirable that the Ni and Ti have the same amount (that is, X = 0.5). In order to obtain such a Li—Ni—Ti composite oxide, y is 0.5. It is characterized by being.

  In the present invention, when Na and Li of the produced Na—Ni—Ti composite oxide are ion-exchanged, the Na—Ni—Ti composite oxide and lithium nitrate are mixed, and at a temperature of 255 to 300 ° C. 1 to 24 hours by the molten salt method. The ion exchange is performed in an amount of lithium nitrate in which the Li / Na ratio is 5 to 10 times.

  Furthermore, the ion exchange is performed by the molten salt method by mixing the Na—Ni—Ti composite oxide and a plurality of lithium salts at a temperature of 200 to 300 ° C. for 1 to 24 hours, The lithium salt is lithium nitrate, lithium chloride, or lithium hydroxide. The ion exchange is performed in a mixed lithium salt in such an amount that the Li / Na ratio is 5 to 10 times.

  In addition, the battery of the present invention includes a positive electrode that includes the Li—Ni—Ti composite oxide manufactured by the above-described method as a positive electrode active material, and includes a material that can reversibly insert, desorb, occlude, and release lithium. It has a negative electrode, The lithium ion contains the substance which can perform the movement for an electrochemical reaction with the said positive electrode and the said negative electrode as an electrolyte substance, It is characterized by the above-mentioned.

  According to the production method of the present invention, it becomes possible to synthesize a Na—Ni—Ti composite oxide having a Ni / Ti ratio of 1, and by using this as a precursor, a Li / Ti ratio of 1 is obtained. -Ni-Ti composite oxide can be synthesized. As a result, by using the Li—Ni—Ti composite oxide produced by this method as a positive electrode active material, it is possible to realize a battery having excellent performance, including power supplies for various electronic devices, It has the advantage that it can be used in the field.

The present invention will be described in more detail. Ni salts, of Ti salts and Na salts of the general formula _{Na b Ni y Ti 1-y} O 2-β (0.95 ≦ b ≦ 1.05,0.45 ≦ y ≦ 0.55, -0.1 ≦ β ≦ 0.1), and when the Na—Ni—Ti composite oxide having a layered structure whose crystal structure belongs to the space group R-3m is produced, the NiTiO ₃ is used as a raw material. Na and Li of the Na—Ni—Ti composite oxide are ion-exchanged, and the general formula Li _a Ni _x Ti _1-x O _2-α (0.95 ≦ a ≦ 1.05, 0.45 ≦ x ≦ 0. 55, −0.1 ≦ α ≦ 0.1), and a Li—Ni—Ti composite oxide having a layered structure in which the crystal structure belongs to the space group R-3m.

As a result of earnest search for a method for producing a Li—Ni—Ti composite oxide electrode material having a Ni / Ti ratio of 1, the inventors have used Na— which is used as a precursor for synthesizing a Li—Ni—Ti composite oxide electrode material. It has been found that by synthesizing Ni—Ti composite oxide using NiTiO ₃ as a raw material, a Li—Ni—Ti composite oxide electrode material having a Ni / Ti ratio of 1 can be synthesized.

The inventors of the present invention contain divalent Ni and tetravalent Ti, which function as electrode materials, and have a general formula of Li _a Ni _x Ti _1-x O _2-α (0.95 ≦ a ≦ 1.05,. 45 ≦ x ≦ 0.55, −0.1 ≦ α ≦ 0.1), and a Li—Ni—Ti composite oxide having a layered structure in which the crystal structure belongs to the space group R-3m, In order to synthesize a Li-Ni-Ti composite oxide containing divalent Ni and tetravalent Ti in a ratio of approximately 1: 1 and having a layered structure, the conventional simple firing method cannot be used. As a new synthesis method, a Na-Ni-Ti composite oxide containing a divalent Ni and a tetravalent Ti in a ratio of approximately 1: 1 and having a layered structure was synthesized and used as a precursor. A method of performing ion exchange is provided.

  In this method, the ratio of Ni and Ti in the precursor Na—Ni—Ti composite oxide is reflected in the ratio of Ni and Ti in the Li—Ni—Ti composite oxide obtained by ion exchange thereafter. Therefore, in order to obtain a Li—Ni—Ti composite oxide having a Ni / Ti ratio of 1, it is necessary to obtain a Na—Ni—Ti composite oxide having a Ni / Ti ratio of 1.

This Na—Ni—Ti composite oxide can generally be obtained by a simple firing method. Specifically, Na salt, divalent Ni salt, and tetravalent Ti salt are mixed at a stoichiometric ratio (Na: Ni: Ti = 2: 1: 1) in an inert atmosphere (Ar, N ₂ Etc.) is preliminarily fired and main fired. Here, the inert atmosphere is used to prevent oxidation of Ni. The raw materials are not particularly limited as long as Ni divalent and Ti tetravalent salts are used, and it is shown that the combination of sodium carbonate, nickel hydroxide, and titanium oxide is simple because of availability and ease of handling. ing.

  However, in order to obtain a Li—Ni—Ti composite oxide having more excellent battery characteristics, it is necessary to use a raw material with a clear purity and to perform a strict weighing in order to make the ratio of Ni and Ti be 1. there were. Further, even when the ratio is 1 at the time of mixing raw materials, there is a problem of compositional deviation caused by the generation of impurities during the reaction. In order to solve these problems and to set the ratio of Ni and Ti to 1, a raw material whose ratio of Ni and Ti is originally 1 may be used.

An example of a raw material having a Ni / Ti ratio of 1 is NiTiO ₃ . By using this as a raw material, the ratio of Ni and Ti at the time of mixing raw materials can be made 1, and the ratio of Ni and Ti can also be made 1 in a Na—Ni—Ti composite oxide obtained by firing. As a result, even after ion exchange, it is possible to obtain a Li—Ni—Ti composite oxide having a Ni / Ti ratio of 1, and a battery having better performance can be realized.

In synthesizing the Na—Ni—Ti composite oxide using this NiTiO ₃ , the Na salt is not particularly limited, and sodium carbonate is convenient because it is easily available and easy to handle.

  It is preferable to use a molten salt method using a lithium salt for ion exchange of the obtained Na—Ni—Ti composite oxide. By this method, a sample with good crystallinity can be obtained in a short time. Also in this case, it is performed in an inert atmosphere in order to prevent oxidation of Ni.

  When lithium nitrate is used as the lithium salt, it may not melt when the temperature is lower than 255 ° C. When the treatment is performed at a temperature exceeding 300 ° C, the structure changes to a rock salt type structure, and the electrode performance is remarkably deteriorated. Therefore, attention is necessary. Basically, it is preferred that the temperature be as low as possible so that the lithium nitrate melts reliably. Therefore, it is most preferably around 270 ° C.

  In addition, since the ion exchange reaction occurs due to a difference in concentration, Li requires a considerable amount with respect to Na, and it is not realistic to make the Li salt excessive more than necessary for washing in the post-treatment. The Li / Na ratio is preferably 5 to 10 times.

  Furthermore, when the reaction time is short, the ion exchange reaction may not proceed sufficiently, but the Na—Ni—Ti composite oxide used in the production method of the present invention is a material that is easy to react. In addition, a long-time reaction is preferably 1 to 24 hours because there is a risk of structural change to a rock salt structure, and more preferably 1 to 5 hours because a sufficient sample can be obtained in a short time.

  From the above, it is most preferable to perform the treatment at about 270 ° C. for 3 to 5 hours in lithium nitrate having a Li / Na ratio of about 5 times. Wash excess lithium salt with a solvent such as water or methanol.

  When a plurality of lithium salts are mixed and used, the melting temperature of the salt decreases, so that treatment at a lower temperature is possible. Any salt can be used as long as the lithium salt satisfies the melting temperature condition, but the combination of lithium nitrate, lithium chloride, and lithium hydroxide is simple because it is easily available and easy to handle. . For example, a 88:12 mol% ratio salt of lithium nitrate and lithium chloride melts at about 244 ° C, and a 61:39 mol% ratio of lithium nitrate and lithium hydroxide melts at about 186 ° C. That's fine.

  Regarding the processing temperature, if the temperature is too low, the ion exchange reaction may not proceed sufficiently, and if the processing is performed at a temperature exceeding 300 ° C., a structural change to a rock salt type structure occurs and the electrode performance is remarkably improved. Since attention is required to lower the temperature, 200 to 300 ° C. is preferable. More preferably, it is 250-270 degreeC.

  For the reasons described above, the Li / Na ratio is preferably 5 to 10 times. Similarly, the reaction time is preferably 1 to 24 hours, more preferably 1 to 5 hours.

  From the above, it is most preferable to perform treatment at 250 to 270 ° C. for 3 to 5 hours in a plurality of lithium salts having a Li / Na ratio of about 5 times. Wash excess lithium salt with a solvent such as water or methanol.

  In order to form a battery positive electrode using a Li—Ni—Ti composite oxide synthesized by using the Na—Ni—Ti composite oxide produced by the production method of the present invention as a precursor, as a positive electrode active material, A mixture of the Li—Ni—Ti composite oxide powder produced in step 1 and a binder powder such as polytetrafluoroethylene is compression-molded on a support such as stainless steel. Alternatively, in order to impart conductivity to the active material powder, a conductive powder such as acetylene black is mixed, and a binder powder such as polytetrafluoroethylene is further added as necessary, and this mixture is added to a metal. It is formed by a means such as placing in a container, pressure forming on a support such as stainless steel, or dispersing in a solvent such as an organic solvent to form a slurry and applying it onto a metal substrate.

  A battery using the Li—Ni—Ti composite oxide as a positive electrode active material has a negative electrode containing a material capable of reversibly inserting / extracting lithium or inserting / extracting lithium, and lithium ions are electrically connected to the positive electrode and the negative electrode. By having a substance that can move for performing a chemical reaction as an electrolyte substance, a battery in which lithium ions travel between the positive electrode and the negative electrode is obtained. For example, as the negative electrode active material, conventionally known materials such as lithium metal, lithium-aluminum alloy, lithium-carbon compound, and lithium-containing nitride can be used.

  In a battery using the Li—Ni—Ti composite oxide as a positive electrode active material, for example, dimethoxyethane, diethoxyethane, 2-methyltetrahydrofuran, ethylene carbonate, propylene carbonate, methyl formate, dimethyl sulfoxide, acetonitrile, butyrolactone are used as the electrolyte. , Non-aqueous electrolyte solvents in which lithium salts are dissolved in organic solvents such as dimethylformamide, dimethyl carbonate, diethyl carbonate, sulfolane, ethyl methyl carbonate, or the like, or solid electrolytes, polymer electrolytes, polymer electrolytes carrying the organic solvents, etc. Can be used.

  In addition, the battery can be used as a secondary battery by repeatedly discharging and charging the battery.

  Furthermore, conventionally known various materials can be used for other elements such as a structural material such as a separator and a battery case, and there is no particular limitation.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

  FIG. 1 is a specific example of a battery using, as a positive electrode active material, a Li—Ni—Ti composite oxide synthesized by using a Na—Ni—Ti composite oxide produced by the production method according to the present invention as a precursor. 1 is a cross-sectional view of a coin-type battery, in which 1 is a sealing plate, 2 is a gasket, 3 is a positive electrode case, 4 is a negative electrode, 5 is a separator, and 6 is a positive electrode mixture pellet.

In Example 1, the sample a manufactured as follows was used. Na ₂ CO ₃ was used as the Na salt, mixed with NiTiO ₃ at a molar ratio of 1: 1, and baked in Ar at 950 ° C. for 36 hours to obtain a light green Na—Ni—Ti composite oxide powder. . Next, this Na—Ni—Ti composite oxide was used as a precursor and mixed with LiNO ₃ so that the Li / Na ratio was 5, and ion exchange treatment was performed in Ar at 270 ° C. for 3 hours. The obtained mixture was washed with distilled water to remove soluble components, and then dried in air at 90 ° C. to obtain a light green powder. The Li—Ni—Ti composite oxide sample thus obtained is designated as a.

  The powder of sample a was mixed with a conductive agent (acetylene black) and a binder (polytetrafluoroethylene) and roll-molded to form positive electrode mixture pellets 6 (thickness 0.3 mm, diameter 15 mm).

Next, a metal lithium negative electrode 4 placed under pressure on a stainless sealing plate 1 is inserted into a recess of a polypropylene gasket 2, and a polypropylene microporous separator 5 and a positive electrode mixture are formed on the negative electrode 4. The pellets 6 are arranged in this order, and after impregnating an appropriate amount of a 1N solution in which LiPF ₆ is dissolved in an equal volume mixed solvent of ethylene carbonate and dimethyl carbonate as an electrolytic solution, the stainless steel positive electrode case 3 is covered. By caulking, a coin-type battery having a thickness of 2 mm and a diameter of 23 mm was produced.

(Comparative Example 1)
In Comparative Example 1, a lithium battery was produced in the same manner as in Example 1 except that Sample A produced as follows was used. First, Na ₂ CO ₃ , Ni (OH) ₂ and TiO ₂ are mixed at a molar ratio of 1: 1: 1, fired in Ar at 950 ° C. for 36 hours, and light green Na—Ni—Ti composite oxide powder Got. Next, this Na—Ni—Ti composite oxide was used as a precursor and mixed with LiNO ₃ so that the Li / Na ratio was 5, and ion exchange treatment was performed in Ar at 270 ° C. for 3 hours. The obtained mixture was washed with distilled water to remove soluble components, and then dried in air at 90 ° C. to obtain a light green powder. The Li—Ni—Ti composite oxide sample thus obtained is designated as A.

  The structure and the valences of Ni and Ti were analyzed for the Na—Ni—Ti composite oxide and the Li—Ni—Ti composite oxide (sample a and sample A) obtained in Example 1 and Comparative Example 1. The composite oxide had a layered structure belonging to the space group R-3m, and Ni was bivalent and Ti was tetravalent.

  When the ratio of Ni and Ti was evaluated, Ni / Ti = 0.97 in sample A, but Ni / Ti = 1.00 in sample a.

Moreover, when these batteries were charged / discharged at a current density of 0.1 mA / cm ² and a voltage width of 2.0 to 4.3 V, they functioned as batteries. Further, when the capacity retention ratio was determined by the ratio of the discharge capacity at the nth cycle to the discharge capacity at the n-1th cycle, it was as shown in FIG. Compared to the battery of Comparative Example 1, the capacity retention rate of the battery of Example 1 was improved, and a battery having excellent battery characteristics could be realized.

  By using a Na—Ni—Ti composite oxide having a Ni / Ti ratio of 1 as a precursor, it becomes possible to synthesize a Li—Ni—Ti composite oxide having a Ni / Ti ratio of 1 as a result. Therefore, it is possible to realize a battery having more excellent battery characteristics.

Sectional drawing which shows the structural example of the coin-type battery in the Example of this invention. The figure which shows the capacity | capacitance retention of the battery of Example 1 and the comparative example 1 at the time of a charging / discharging test shown by ratio of the discharge capacity of the nth cycle with respect to the discharge capacity of the n-1 cycle.

Explanation of symbols

1 Sealing plate 2 Gasket 3 Positive electrode case 4 Negative electrode 5 Separator 6 Positive electrode mixture pellet

Claims (11)

Ni salts, of Ti salts and Na salts of the general formula _{Na b Ni y Ti 1-y} O 2-β (0.95 ≦ b ≦ 1.05,0.45 ≦ y ≦ 0.55, -0.1 ≦ β ≦ 0.1), and when the Na—Ni—Ti composite oxide having a layered structure whose crystal structure belongs to the space group R-3m is produced, the above-described NiTiO _{3 was} used as a raw material. Na and Li of the Na—Ni—Ti composite oxide are ion-exchanged, and the general formula Li _a Ni _x Ti _1-x O _2-α (0.95 ≦ a ≦ 1.05, 0.45 ≦ x ≦ 0. 55, −0.1 ≦ α ≦ 0.1), a Li—Ni—Ti composite oxide having a layered structure in which the crystal structure belongs to the space group R-3m. -Manufacturing method of Ni-Ti complex oxide electrode material. The method for producing a Li-Ni-Ti composite oxide electrode material according to claim 1, wherein the Na-Ni-Ti composite oxide is produced by firing NiTiO ₃ and a Na salt in an inert atmosphere. . The method for producing a Li-Ni-Ti composite oxide electrode material according to claim 1 or 2, wherein the Na salt is sodium carbonate. 4. The method for producing a Li—Ni—Ti composite oxide electrode material according to claim 1, wherein y is 0.5 in the general formula. 5. The method for producing a Li—Ni—Ti composite oxide electrode material according to claim 1, wherein x is 0.5 in the general formula. 6. The ion exchange according to claim 1, wherein the Na-Ni-Ti composite oxide and lithium nitrate are mixed and performed by a molten salt method at a temperature of 255 to 300 [deg.] C. for 1 to 24 hours. A method for producing a Li—Ni—Ti composite oxide electrode material according to claim 1. The said ion exchange is a manufacturing method of the Li-Ni-Ti complex oxide electrode material of Claim 6 performed in the quantity of lithium nitrate which becomes Li / Na ratio 5-10 times. 2. The ion exchange is performed by a molten salt method in which the Na—Ni—Ti composite oxide and a plurality of lithium salts are mixed and at a temperature of 200 to 300 ° C. for 1 to 24 hours. 6. A method for producing a Li—Ni—Ti composite oxide electrode material according to any one of items 1 to 5. The method for producing a Li—Ni—Ti composite oxide electrode material according to claim 8, wherein the lithium salt is lithium nitrate, lithium chloride, or lithium hydroxide. The method for producing a Li-Ni-Ti composite oxide electrode material according to claim 9, wherein the ion exchange is performed in a mixed lithium salt in an amount such that the Li / Na ratio is 5 to 10 times. A positive electrode containing the Li—Ni—Ti composite oxide produced in claim 1 as a positive electrode active material, a negative electrode containing a material capable of reversibly inserting / extracting lithium or inserting / extracting lithium, and a lithium ion A battery comprising an electrolyte substance containing a substance capable of performing an electrochemical reaction with the positive electrode and the negative electrode.

Images