KR20030049290A - Method of Making Li4/3Ti5/3O4 Film Electrode for Use in Rechargeable Lithium Microbattery - Google Patents

Abstract

PURPOSE: Provided is a process for producing a Li4/3Ti5/3O4 thin film electrode for a lithium secondary microcell, wherein the Li4/3Ti5/3O4 thin film electrode is excellent in charging/discharging cycle life and charging/discharging rate capability. CONSTITUTION: The process for producing the Li4/3Ti5/3O4 thin film electrode contains the steps of: preparing a non-aqueous sol containing lithium ion and titanium ion by dissolving and stirring lithium salt and titanium salt in the molar ratio of 4:5-6:5 in a non-aqueous solvent comprising 1-butanol and acetic acid in the volume ratio of 3:1; spin-coating the non-aqueous sol on a current collector to form a thin film; drying the thin film; and annealing the thin film.

Description

Method of Making Li4 / 3Ti5 / 3O4 Thin Film Electrode for Lithium Secondary Micro Battery {Method of Making Li4 / 3T55 / 3O4 Film Electrode for Use in Rechargeable Lithium Microbattery}

The present invention relates to a method for manufacturing a Li _4/3 Ti _5/3 O ₄ thin film electrode for a lithium secondary micro battery, and more particularly, to a non-aqueous water containing lithium ion and titanium ion. A sol (non-aqueous sol) is prepared, uniformly coated on a metal current collector by spin-coating, and then heat treated to obtain pure Li _4/3 Ti _5/3. It relates to a method for producing an O ₄ thin film electrode.

In general, lithium secondary batteries use transition metal oxides such as LiMn ₂ O ₄ , LiCoO ₂ and LiNiO ₂ as cathode materials, and lithium metal and carbon as anode materials. It consists of an organic solvent containing lithium ions as electrolyte between two electrodes.

In the case of a microbattery, which has drastically reduced the size of a battery to utilize a lithium secondary battery as an energy source for microelectromechanical devices, it is composed of a solid electrolyte between a thin film anode and a cathode and two thin film electrodes. The thin film anode for the micro battery can use the transition metal oxide which is an existing anode material as it is, but the thin film cathode has not yet been selected for a suitable material and thin film manufacturing process other than lithium metal.

Among transition metal oxides known for easy thin film production and stable crystal structure, Li _4/3 Ti _5/3 O ₄ is a low voltage material that can be used as a cathode for lithium secondary micro batteries. However, the existing content of Li _4/3 Ti _5/3 O ₄ electrode is related to Li _4/3 Ti _5/3 O ₄ powder manufacturing method, which is not suitable for producing pure Li _4/3 Ti _5/3 O ₄ thin film electrode. It was the way.

The prior art associated with the present invention is Zero-Strain Insertion Material of Li [Li _1/3 Ti _5/3 ] O ₄ for Rechargeable Lithium Cells, T. Ohzuku, A. Ueda, N. Yamamoto, Journal of the Electrochemical Society, V. 142, p. 1431-1435 , 1995) of the study and U.S. Patent No. 5,766,796, U.S. Patent No. 6,083,644, U.S. Patent 6,153,336 and U.S. Patent No. 6,274,271 is to prepare a negative electrode Li _4/3 Ti _5/3 O ₄ After using this to configure a lithium secondary battery, but all of them are a composite electrode (composite electrode) was prepared by mixing Li _4/3 Ti _5/3 O ₄ powder with a conductive material (binder) There is a drawback that cannot be utilized in thin film electrodes or lithium secondary micro batteries.

See also Bach (Electrochemical Properties of Sol-Gel Li _4/3 Ti _5/3 O ₄ , S. Bach, JP Pereira-Ramos, N. Baffier, Journal of Power Sources, V. 81-82, p. 273-276, 1999) was related to the sol-gel method for preparing Li _4/3 Ti _5/3 O ₄ , but because it uses a water-soluble sol, it was not directly applied to the metal current collector, but was prepared in powder form. There is a disadvantage that a composite electrode must be prepared by mixing with a binder.

The present invention prepares a non-aqueous sol containing lithium and titanium ions simultaneously by dissolving and stirring lithium salt and titanium salt in a non-aqueous solvent, and uniformly applying the sol to the metal current collector by spin-coating uniformly. After the heat treatment, an object of the present invention is to manufacture a Li _4/3 Ti _5/3 O ₄ thin film electrode having excellent charge and discharge life cycle performance and rate capability.

1 is a flowchart schematically showing the whole process of the present invention.

FIG. 2 is an X-ray diffraction pattern of the Li _4/3 Ti _5/3 O ₄ thin film electrode prepared in Example 1. FIG.

3 is a Li / 1 M LiClO ₄ -PC / Li _4/3 Ti _5/3 O ₄ half-cell at 25 ℃ using the Li _4/3 Ti _5/3 O ₄ thin film electrode prepared in Example 2 (half charge / discharge curves obtained by applying a constant current of 20, 50, 100, 200 μA cm ^{−2 to} the cell).

4 is a Li / 1 M LiClO ₄ -PC / Li _4/3 by applying a constant current of 20 μA cm ^-2 at 25 ℃ using the Li _4/3 Ti _5/3 O ₄ thin film electrode prepared in Example 2 The change in the discharge capacity according to the number of charge and discharge cycles obtained by charging and discharging the Ti _5/3 O ₄ half cell 100 times is illustrated.

5 is a step of applying a constant current of 20,50, 100, 200 and 20 μA cm ⁻² at 25 ° C. using Li _4/3 Ti _5/3 O ₄ thin film electrode prepared in Example 2 and Li / 1 M LiClO ₄ -PC / Li _4/3 Ti _5/3 O _{4 This} shows the change in discharge capacity according to the number of charge and discharge cycles obtained by continuously charging and discharging the half cell 20 times.

Method for producing a Li _4/3 Ti _5/3 O ₄ thin film electrode for a lithium secondary micro battery of the present invention is dissolved in a non-aqueous solvent in a lithium salt: titanium salt in a molar ratio of 4: 5 to 6: 5 and Preparing a non-aqueous sol containing lithium ions and titanium ions by stirring;

Spin-coating a water-insoluble sol containing lithium ions and titanium ions onto a current collector to apply a thin film,

Drying the thin film coated on the current collector after spin coating;

And annealing the thin film applied on the current collector after drying.

In the present invention, a solvent is used to dissolve lithium salt and titanium to prepare a water-insoluble sol containing lithium ions and titanium ions. The water-insoluble solvent is 1-butanol (acetic acid). A solvent mixed in a volume ratio of 3: 1 is used. When the non-aqueous sol is prepared with the non-aqueous solvent mixed in the volume ratio, the wettability to platinum (Pt), which is the current collector, is excellent and uniform application is possible, and thus it is preferable to use the same value as above.

In the lithium salt and titanium salt, which are the most important constituents of the Li _4/3 Ti _5/3 O ₄ thin film electrode of the present invention, the lithium salt is lithium acetacetonate, Li [(CH ₃ COCH = (CO−) CH ₃ ]) can be used, and the titanium salt is titanium oxide acetylacetonate (OTi [CH ₃ COCH = (CO-) CH ₃ ]), titanium isopropoxide, Ti [OCH (CH ₃ ) ₂ ] ₄ ) or titanium diisopropoxide ([CH ₃ COCH = C (O−) CH ₃ ] ₂ Ti [OCH (CH ₃ ) ₂ ] ₂ ).

Meanwhile, in the present invention, the lithium salt and the titanium salt dissolve a lithium salt: titanium salt in a molar ratio of 4: 5 to 6: 5 in a non-aqueous solvent, in order to compensate the amount of vaporization of lithium having high vapor pressure during drying and annealing. A lithium salt of at least 4: 5 of lithium and titanium in the composite Li _4/3 Ti _5/3 O ₄ should be added to the non-aqueous solvent. However, if more than 6 moles of lithium salt is used with respect to 5 moles of titanium salt, there is a problem in that impurities of Li ₂ O exist in the final composite. Therefore, in the present invention, the lithium salt: titanium salt has a ratio of 4: 5 to 6: 5 in a molar ratio. It is good to dissolve in water-soluble solvent.

After dissolving lithium salt and titanium salt in a non-aqueous solvent and stirring to prepare a non-aqueous sol containing lithium ions and titanium ions, stirring is performed for 12 to 24 hours at room temperature for helium (He), neon (Ne), and argon (Ar). It is carried out in an inert gas atmosphere such as).

Since the water-insoluble sol reacts actively with water in the air to form inhomogeneous particles, it should be stirred under an inert gas atmosphere. In addition, in order to uniformly mix lithium and titanium in the non-aqueous solvent, stirring should be carried out for 12 hours or more, and if it is more than 24 hours, water and a non-aqueous sol present as trace impurities in the inert gas react to form non-uniform particles. There is a problem, and the stirring time is preferably carried out for 12 to 24 hours.

The non-aqueous sol containing lithium ions and titanium ions removes impurities using a filter and spin-coates at a rotational speed of 3000 to 5000 rpm on a current collector to apply a thin film.

Known filters such as polytetrafluoroethylene (PTFE) can be used to remove impurities of the water-insoluble sol.

The current collector may use a known current collector, which is not specific. Among the current collectors, platinum (Pt) having a thickness of 100 nm may be used in the present invention by a DC-sputtering method on an alumina (Al ₂ O ₃ ) substrate. ) Is prepared by depositing.

On the other hand, if spin-coating the water-insoluble sol on the current collector is less than 3000rpm, it is difficult to apply a uniform film.If the water-soluble sol is more than 5000rpm, the film thickness is too thin to control the water-soluble sol. When spin coating on the current collector, the rotation speed should be maintained at 3000 to 5000 rpm.

After coating the thin film by spin-coating a water-insoluble sol containing lithium ions and titanium ions on a current collector, drying the thin film at a temperature of 300 to 350 ° C. and a drying time of at least 10 minutes. It is good to remove. If the thin film is dried below 300 ℃, the solvent in the thin film cannot be removed completely. If the thin film is dried above 350 ℃, stress is caused by the difference in thermal expansion coefficient between the thin film and the substrate. Since there is a problem, it is preferable to perform the thin film drying at 300 ~ 350 ℃. In addition, in order to completely remove the solvent in the thin film in the above temperature range, it is preferable to perform at least 10 minutes during thin film drying.

After drying, the annealing time of the thin film coated on the current collector is performed at 700 to 800 ° C. for 1 to 6 hours. In order to crystallize the final composite Li _4/3 Ti _5/3 O ₄ into a tetragonal spinel structure, the annealing temperature should be 700 ° C or higher and the annealing time should be 1 hour or more. If the time is more than 6 hours, abnormal grain growth occurs and the electrochemical charge and discharge characteristics are deteriorated. Therefore, annealing of the thin film coated on the current collector is performed at 700 to 800 ° C. for 1 to 6 hours. It is good.

On the other hand, when it is necessary to adjust the thickness of the Li _4/3 Ti _5/3 O ₄ thin film electrode coated on the current collector in order to improve the excellent cycle life and rate capability (charge capability) The coating and drying may be repeated to obtain a Li _4/3 Ti _5/3 O ₄ thin film electrode having a desired thickness.

In the present invention, of various thicknesses Li _4/3 Ti _5/3 O ₄ hanba measuring the charge and discharge life and charge-discharge capacity of a thin film electrode Li _4/3 Ti _5/3 O ₄ when the thickness of the thin film electrode 100~300nm A Li _4/3 Ti _5/3 O ₄ thin film electrode having excellent charge and discharge life and charge and discharge rate capacity can be obtained.

Hereinafter, the present invention will be described by the following examples and test examples. However, these are examples for explaining the present invention and they do not limit the scope of the present invention.

<Example 1>

4 mol of lithium acetylacetone and 5 mol of titanium isopropoxide were dissolved in a non-aqueous solvent in which 1-butanol and acetic acid were mixed at a volume ratio of 3: 1, and stirred for 12 hours in an argon atmosphere to contain lithium ions and titanium ions. A water-insoluble sol was prepared.

After depositing platinum (Pt) having a thickness of 100 nm on the alumina substrate by using a pre-fabricated current collector prepared by depositing platinum (Pt) having a thickness of 100 nm, the spin-coating method was applied to the non-aqueous sol. Dried at ° C.

As mentioned above, the non-aqueous sol containing lithium ions and titanium ions on the platinum of the current collector was spin-coated and dried five times, followed by annealing for 1 hour at 700 ° C. for 100 nm. A thin Li _4/3 Ti _5/3 O ₄ thin film electrode was prepared.

<Example 2>

5 mol of lithium acetylacetone and 5 mol of titanium oxide acetylacetone were dissolved in a non-aqueous solvent in which 1-butanol and acetic acid were mixed at a volume ratio of 3: 1, and stirred under an argon atmosphere for 18 hours to contain lithium ions and titanium ions. A water-insoluble sol was prepared.

After depositing platinum (Pt) having a thickness of 100 nm on the alumina substrate by using a pre-fabricated current collector prepared by depositing platinum (Pt) having a thickness of 10 nm or more by using a spin-coating method, the spin-coating method was used for 10 minutes or more. Dried at ° C.

As mentioned above, the non-aqueous sol containing lithium ions and titanium ions on the platinum of the current collector was spin-coated 10 times, followed by annealing for 10 hours at 750 ° C. for 200 hours. A thin Li _4/3 Ti _5/3 O ₄ thin film electrode was prepared.

<Example 3>

6 mol of lithium acetylacetone with lithium salt and 5 mol of titanium isopropoxide with titanium salt were dissolved in a non-aqueous solvent in which 1-butanol and acetic acid were mixed at a volume ratio of 3: 1, and stirred under an argon atmosphere for 24 hours to carry out lithium ion. And a water-insoluble sol containing titanium ions was prepared.

Platinum (Pt) having a thickness of 100 nm was deposited on the alumina substrate by DC sputtering, and the non-aqueous sol prepared above was coated on the platinum of the current collector prepared in advance by spin-coating. Dried at ° C.

300 nm after annealing at 800 ℃ for 6 hours after spin-coating the water-insoluble sol containing lithium ions and titanium ions on the platinum of the current collector as described above. A thin Li _4/3 Ti _5/3 O ₄ thin film electrode was prepared.

Test Example 1 X-ray Diffraction Image of Li _4/3 Ti _5/3 O ₄ Thin Film Electrode

Li _4/3 Ti _5/3 O ₄ prepared in Example 1 using a Cu-K _α radiation ranging from 10 ^o to 70 ^o at a scanning rate of 3 ^o per minute The X-ray diffraction image of the thin film electrode was measured and the results are shown in FIG. 2.

The X-ray diffraction image of the Li _4/3 Ti _5/3 O ₄ thin film electrode of FIG. 2 showed a peak corresponding to the (111) plane of Li _4/3 Ti _5/3 O ₄ at 18.68 ^o . Peaks corresponding to the remaining (311), (331), and (440) planes also appeared at the same position as 2θ on the standard X-ray diffraction image for Li _4/3 Ti _5/3 O ₄ of the JCPDS card. X- ray diffraction was in Li _4/3 Ti _5/3 O ₄ and the platinum (Pt) electrode current collector, and an alumina (Al ₂ O _3), only the peak appeared pure by the substrate which is made thin Li _{4 / It} means that it _{consists of 3} Ti _5/3 O ₄ phase.

The peak of each X-ray diffraction image was analyzed by the cubic spinel crystal structure of the space group Fd3m. The lattice constant a of the prepared Li _4/3 Ti _5/3 O ₄ was analyzed. Was 8.367 nm and there was almost no change to 8.376 nm after 100 charge / discharge cycles. Therefore, the manufactured Li _4/3 Ti _5/3 O ₄ thin film electrode has a stable crystal structure and has excellent charge and discharge characteristics.

Test Example 2 Charge and Discharge Curves of a Li _4/3 Ti _5/3 O ₄ Thin Film Electrode

The result of charging and discharging in the range of 1.3 V _{Li / Li +} and 2.0 V _{Li / Li +} by applying a constant current to the Li _4/3 Ti _5/3 O ₄ thin film electrode prepared in Example 2 is shown in FIG. 3. The electrolyte used was a propylene carbonate (PC) solution in which 1 M of lithium perchlorate (LiClO ₄ ) was dissolved. The reference electrode and the counter electrode both had a purity of 99.99%. Lithium metal was used.

3 is a charge obtained by applying a constant current of 20, 50, 100, 200 μA cm ^-2 to a Li / 1 M LiClO ₄ -PC / Li _4/3 Ti _5/3 O ₄ half cell at 25 ℃ Discharge curve. In the charge / discharge curve, a large potential plateau region with a potential value of about 1.56 V _{Li / Li +} appears, and the length of the region determines the capacity of the battery.

The specific capacity of the battery was expressed based on the volume of the manufactured Li _4/3 Ti _5/3 O ₄ thin film electrode. The initial discharge capacity of the manufactured Li _4/3 Ti _5/3 O ₄ thin film electrode was found to be 587 mAh cm ^-3 when a constant current of 20 μA cm ^-2 was applied, which is the theoretical capacity of 608 mAh cm ^-3 The utilization rate was very good at about 97%.

The charge efficiency, expressed as the ratio of discharge capacity to charge capacity, was found to be 98% at initial charge and discharge. When the applied constant current was increased 10-fold to 200 μA cm ^-2 , the utilization rate was 88% and the charge efficiency was 96% at initial charge and discharge.

4 is a constant current of 20 μA cm ^-2 at 25 ℃ and the charge / discharge times obtained by charging and discharging 100 times Li / 1 M LiClO ₄ -PC / Li _4/3 Ti _5/3 O ₄ half cell The change in discharge capacity is shown. In this case, after 100 charge / discharge cycles, the discharge capacity was 584 mAh cm ^−3, and more than 99% of the initial discharge capacity was maintained.

Figure 5 is a continuous application of Li / 1 M LiClO ₄ -PC / Li _4/3 Ti _5/3 O ₄ half cell at 25 ℃ by applying a constant current of 20, 50, 100, 200 and 20 μA cm ^-2 stepwise The change in discharge capacity according to the number of charge and discharge cycles obtained by charging and discharging 20 times is shown.

Applied from 20 μA cm ^-2 to 50 μA cm ^-2 When the constant current is increased, the discharge capacity is more than 97% of the initial discharge capacity at 568 mAh cm ^-3 and again from 50 μA cm ^-2 to 100 μA cm ^-2 When the constant current is increased, the discharge capacity is 558 mAh cm ^-3 and above 95% of the initial discharge capacity, and 100 μA cm ^-2 to 200 μA cm ^-2 When the constant current is increased, the discharge capacity is 540 mAh cm ^-3 More than 92% of the initial discharge capacity was maintained.

In addition, when the applied constant current was lowered from 200 μA cm ⁻² to 20 μA cm ⁻² , the discharge capacity was 580 mAh cm ^−3, and more than 98% of the initial discharge capacity was recovered. From the above results, it can be seen that the Li _4/3 Ti _5/3 O ₄ thin film electrode manufactured by the present invention has a very good charge and discharge life and charge and discharge rate capacity compared to the conventional electrode.

The Li _4/3 Ti _5/3 O ₄ thin film electrode for lithium secondary micro batteries according to the present invention has an initial discharge capacity of 587 mAh cm ⁻³ and a discharge capacity of 584 after 100 charge / discharge cycles. It was found that mAh cm ^-3 has a very good charge / discharge life and charge / discharge rate capacity, which is maintained over 99% of the initial discharge capacity.

Claims (8)

Preparing a water-insoluble sol containing lithium ions and titanium ions by dissolving and stirring a lithium salt: titanium salt in a water-insoluble solvent in a molar ratio of 4: 5 to 6: 5, Spin coating a non-aqueous sol containing lithium ions and titanium ions onto a current collector to apply a thin film; Drying the thin film coated on the current collector after spin coating; A method of manufacturing a Li _4/3 Ti _5/3 O ₄ thin film electrode for a lithium secondary micro battery, comprising the step of annealing a thin film coated on a current collector after drying. The method of claim 1, wherein the water-insoluble solvent is 1-butanol: acetic acid 3: 1 volume ratio of the solvents for lithium secondary micro-cell Li _4/3 Ti _5/3 O _4, characterized in that the mixture to a method of manufacturing a thin film electrode. In a lithium salt is lithium acetylacetone characterized in that the lithium secondary micro-cell Li _4/3 Ti _5/3 O ₄ method of manufacturing a thin film electrode according to claim 1. In, Ti is titanium salt tatyum oxide acetylacetonate, titanium isopropoxide or titanium diisopropoxide Forsythe Forsythe characterized in that the lithium secondary micro-cell Li _4/3 Ti _5/3 O ₄ method of manufacturing a thin film electrode according to claim 1. The method of manufacturing a Li _4/3 Ti _5/3 O ₄ thin film electrode for a lithium secondary micro battery according to claim 1, wherein the stirring of the lithium salt and the titanium salt is performed for 12 to 24 hours in an inert gas atmosphere. The method of manufacturing a Li _4/3 Ti _5/3 O ₄ thin film electrode for a lithium secondary micro battery according to claim 1, wherein the thin film is dried at 300 to 350 ° C. for 10 minutes or more. The method for manufacturing a Li _4/3 Ti _5/3 O ₄ thin film electrode for a lithium secondary micro battery according to claim 1, wherein the thin film annealing is performed at 700 to 800 ° C. for 1 to 6 hours. The Li _4/3 Ti _5/3 O ₄ thin film electrode according to claim 1, wherein the thin film is maintained at 100 to 300 nm after repeated annealing by applying the thin film and drying. Method of preparation.