JP2009224305A - LITHIUM SECONDARY BATTERY WITH Li-Sn-Mn COMPOUND POSITIVE ELECTRODE THIN FILM, MANUFACTURING METHOD OF Li-Sn-Mn COMPOUND TARGET AND POSITIVE ELECTRODE THIN FILM DEPOSITION METHOD USING THIS - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery with a Li-Sn-Mn compound positive electrode thin film; a manufacturing method of a Li-Sn-Mn compound target; and a positive electrode thin film deposition method using this. <P>SOLUTION: The positive electrode thin film deposition method for the lithium secondary battery includes the steps of: forming mixed powder by mixing Li<SB>2</SB>CO<SB>3</SB>, MnO<SB>2</SB>, and SnO powder; conducting primary crushing of the mixed powder; calcinating the mixed powder after the primary crushing; conducting secondary crushing of the calcinated mixed powder; pressing the mixed powder after secondary crushing; manufacturing a target containing Li, Sn, Mn, and O by sintering the pressed mixture; and locally vapor depositing the positive electrode thin film containing Li, Sn, Mn, and O on a substrate by irradiating laser beams to the target. The discharge capacity and charge discharge reversibility can remarkably be enhanced by replacing a part of Mn with Sn. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a lithium secondary battery including a Li—Sn—Mn compound positive electrode thin film, a method for producing a Li—Sn—Mn compound target, and a method for forming a positive electrode thin film using the same.

Lithium cobalt oxide (LiCoO ₂ ), which has already been put into practical use as a positive electrode material for lithium secondary batteries, is expensive and has environmental and safety problems. Therefore, lithium manganese oxide is lithium nickel oxide. Along with (LiNiO ₂ ), many materials have been studied as an alternative material to solve these problems. Lithium cobalt oxide and lithium nickel oxide generate oxygen when overcharged and there is a danger of explosion. However, lithium manganese oxide does not generate oxygen even when overcharged, and it is relative to cobalt (Co). By using manganese (Mn), which is an abundant element, there is an advantage that the price is low.

However, the theoretical charge capacity (148 mAh / g) of lithium manganese oxide is smaller than the theoretical charge capacity (274 mAh / g) of lithium cobalt oxide, and the discharge capacity rapidly decreases as the charge / discharge cycle is repeated. It has the disadvantages. W. Liu et al. (J. Electronchem. Soc., Vol. 143, No. 11, pp. 3590-3596, 1996) and RJ Gummow et al. (Solid State Ionics, Vol. 69, No. pp. 59-67, 1994), when charge and discharge are repeated, the phase transition to tetragonal due to the formation of lithium manganese oxide (Li ₂ Mn ₂ O ₄ ) at the positive electrode by the insertion of lithium ions is the charge and discharge cycle. Explain that it is the cause of the defect.

Insertion of lithium ion reduces the average valence of manganese (Mn) ion to 3.5 or less, and strong Jahn-Teller deformation occurs (G. Pistoia et al., Solid State Ionics, Vol. 78, pp. 115- 122, 1995), the crystal structure changes from cubic to tetragonal, and as a result, further lithium desorption is difficult. That is, as the arrangement of trivalent manganese ions (t32g · e1g, high spin) changes in the spinel structure, the octahedron stretches strongly, and the c / a ratio increases by 16% per unit cell. It becomes impossible to maintain the structural equilibrium of the positive electrode during the repetition. Moreover, due to the change in the valence of Mn ³⁺ (3d4) that occurs while the average valence of manganese returns to 3.5 again when lithium leaves, the discharge becomes difficult and the charge / discharge capacity decreases rapidly. It is considered.

  An object of this invention is to provide the manufacturing method of a lithium secondary battery provided with a Li-Sn-Mn compound positive electrode thin film, a Li-Sn-Mn compound target, and a positive electrode thin film using the same.

The method of forming a thin film positive electrode for a lithium secondary battery according to the present invention includes a step of mixing Li ₂ CO ₃ , MnO ₂ and SnO powder to provide a mixed powder, a step of primary pulverizing the mixed powder, and a step of the primary A step of calcining the pulverized mixed powder, a step of secondary pulverizing the calcined mixed powder, a step of pressure-molding the secondary pulverized mixed powder, and the pressure-molded mixture A step of producing a target comprising Li, Sn, Mn, and O, and a step of locally depositing a positive electrode thin film comprising Li, Sn, Mn, and O on a substrate by irradiating the target with a laser. Prepare.

Moreover, the manufacturing method of the LiSn _{x / 2} Mn _2-x O ₄ (0 <x ≦ 0.05) target of the present invention includes a step of mixing Li ₂ CO ₃ , MnO ₂ and SnO powder to provide a mixed powder. A step of primary pulverizing the mixed powder, a step of calcining the primary pulverized mixed powder, a step of secondary pulverizing the calcined mixed powder, and the secondary pulverized mixed powder. And a step of sintering the pressure-molded mixture to produce a LiSn _{x / 2} Mn _2-x O ₄ (0 <x ≦ 0.05) target.

  The lithium secondary battery of the present invention includes a composition of a compound positive electrode of Li, Sn, Mn, and O.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings, but the present invention is not limited to these embodiments.

The lithium secondary battery positive electrode thin film of the present invention is formed by adding a small amount of a tin compound to lithium manganese oxide (LiMn ₂ O ₄ ) having a spinel structure, and has the following chemical formula (1).

LiSn _{x / 2} Mn _2-x O ₄ (1)
(Wherein x is 0 <x ≦ 0.05).

In an embodiment of the present invention, a target of LiSn _{x / 2} Mn _2-x O ₄ (0 <x ≦ 0.05) was manufactured, and a positive electrode thin film having a composition of target composition components was prepared using a laser local vapor deposition method. It can be formed easily.

First embodiment (target production)
For the production of LiSn _{x / 2} Mn _2-x O ₄ (x = 0, 0.025, 0.05) target, Li ₂ CO ₃ , MnO ₂ and SnO powder, each in weight percent, 19. Weigh accurately to be 0-19.1: 79.3-80.7: 0.3-1.6. Here, the weight percentage of Li ₂ CO ₃ is set to an amount that is about 10% larger than the appropriate amount in consideration of the loss of lithium during heat treatment. The weighed powder is ball-milled with anhydrous alcohol and yttria stabilized zirconia for 24 hours, then dried at 120 ° C. for 24 hours to prepare a mixed powder, and first ground in an alumina mortar And calcining at 400 ° C. to 800 ° C. for 1 to 5 hours in an air atmosphere. A part of the calcined powder is secondarily ground in an alumina mortar and mixed with a PVA (polyvinyl alcohol) binder, and then uniaxially pressed into a pellet at a pressure of 1 to 5 ton / cm ² . Sintering (final sintering) is carried out in the air atmosphere at 800 ° C. to 1200 ° C. for 1 to 24 hours together with the remaining non-press-molded powder in the calcined powder.

FIG. 1a shows the result of X-ray diffraction analysis of the powder after calcination and before sintering, and shows that there are impurity phases such as Li ₂ MnO ₃ , γ-Mn ₂ O ₃ and SnO ₂ . As shown in FIG. 1b, the X-ray diffraction analysis result of the powder after final sintering shows that only the LiMn ₂ O ₄ type spinel phase is shown. This means that the impurity phase disappeared after the final sintering, and in particular, the tin element was replaced by being dissolved in the spinel structure. Moreover, the density of the manufactured target is about 3.5 g / cm ³ , and this value is about 80% of the theoretical density (4.4 g / cm ³ ). Greater than the number.

Second Example (Manufacturing Thin Film by Laser Local Vapor Deposition)
The target manufactured by the first embodiment described above is fixed to the holder, and then the cleaned substrate is fixed to the substrate holder, and laser local vapor deposition is performed. At this time, a part of the substrate corresponding to the position of the electrode for measuring the electrochemical characteristics is divided with a mask. The distance between the substrate and the target is 3 to 5 cm. The basic pressure in the vacuum chamber is adjusted to 1 × 10 ⁻⁵ Torr or less. The temperature of the substrate is adjusted to 350 to 550 ° C., and the pressure of oxygen as the working gas is adjusted to 0.05 to 0.25 Torr. Using a KrF excimer laser with a wavelength range of 248 nm and a 20 ns duration, the laser beam size is ² to 5 mm ² , the PLD (pulsed laser deposition) output density is 1 to 4 J / cm ² , and the spot repetition rate Is set to 3 to 10 Hz and the irradiation time is set to 3 to 120 minutes, and LiSn _{x / 2} Mn _2-x O ₄ which is a component of the target is deposited on the substrate.

The lithium manganese oxide thin film partially substituted with tin of 0.1 to 1 μm thick obtained in Example 1 was used as the positive electrode, lithium as the negative electrode, and lithium hexafluorophosphate (LiPF ₆ ) as the electrolyte. A test battery using an electrolytic solution dissolved in an organic solvent of ethylene carbonate: diethyl carbonate = 1: 1 (volume ratio) was manufactured, and a charge / discharge experiment was performed on this battery.

The initial charge / discharge capacity of the LiSn _{x / 2} Mn _2-x O ₄ thin film was highest at x = 0.05. FIG. 2 shows the charge / discharge characteristics of LiSn _{x / 2} Mn _2-x O ₄ when the cut-off voltage is changed from 3.0 V to 4.5 V. The initial charge / discharge capacities are 97.9, 120.0, and 133.0 mAh / g in FIGS. 2A, 2B, and 2C, respectively, which are about 66%, 81%, and 90% of the theoretical capacity. In general, the amount of Mn ³⁺ ions that play a decisive role in the capacity of the spinel-type lithium manganese oxide positive electrode decreases with increasing x in LiSn _{x / 2} Mn _2−x O ₄ , and at the same time the initial charge / discharge capacity. Also decreases. However, in the present invention, the initial discharge capacity increased as the x value increased. This is because more lithium ions are desorbed into the positive electrode crystal structure due to the Mn deficient crystal structure of manganese. This is because it can be inserted. In addition, the electronic conductivity which is a decisive factor for the positive electrode capacity is improved by the addition of tin (Sn), and not only the charge / discharge efficiency but also the initial charge / discharge capacity is increased (GM Ehrlich et al. : Sens. Actuators A, Vol. 51, pp. 17-19, 1995, X. Wu et al .: Surf. Coat. Technol., Vol. 186, pp. 412-415 (2004), KS Park et al .: Solid State Commun Vol. 129, pp. 311-314, 2004).

FIG. 3 shows a change in discharge capacity depending on the number of times of charge / discharge when the interruption voltage is increased from 3.0V to 4.5V in a charge / discharge experiment in a test battery. While pure LiMn ₂ O ₄ exhibits an unstable discharge capacity, the charge / discharge efficiency characteristics of the battery _{comprising the} positive electrode thin film LiSn _0.0125 Mn _1.975 O ₄ formed according to the present invention are remarkably high. I understand. The capacity and charge / discharge efficiency of the LiSn _{x / 2} Mn _2-x O ₄ positive electrode thin film are improved for LiMn ₂ O ₄ based lithium secondary batteries doped and replaced by different elements produced by various existing thin film manufacturing methods. It is superior to the capacity and charge / discharge performance improvement value of the positive electrode thin film. Furthermore, even at a high current density (4C), excellent capacity and charge / discharge characteristics are exhibited.

（立方晶、ｎｏ．２２７）でスピネル構造を有することが示された。 As shown in FIG. 4, LiSn _0.0125 Mn _1.975 O ₄ and LiSn _0.025 Mn _1.95 O ₄ , which have an insufficient manganese composition, are similar to the LiMn ₂ O ₄ composition (111 ), (311) and (400) plane diffraction peaks respectively,

(Cubic crystal, no. 227) was shown to have a spinel structure.

As shown in FIG. 5, by analyzing the Raman spectrum result when the x value was changed in the LiSn _{x / 2} Mn _2-x O ₄ composition, manganese having a spinel structure partially substituted with tin (Mn It can be seen that the A1g peak (the main peak in the 630 to 650 cm ⁻¹ region) indicating the stretching vibration between oxygen) and oxygen (O) has shifted to a lower Raman shift value. This is because the distance between manganese-oxygen bonds has decreased, and phase change does not occur during charging / discharging, and more lithium ions can be inserted and removed into the vacant octahedron position, thereby improving the structural stability of the spinel. Means improved. It can be seen that the positive effect of tin substitution is limited to x = 0.05 or less, given that there is no change in the Raman peak between x = 0.025 and x = 0.05.

When the positive electrode thin film for a lithium secondary battery has a LiSn _{x / 2} Mn _2-x O ₄ (0 <x ≦ 0.05) composition with insufficient manganese, LiM _δ Mn _2-δ with insufficient manganese. Compared with the composition of O ₄ (“M” is a metal element), more lithium ions can be contained during charging / discharging, and the charge / discharge is larger than that of LiMn ₂ O ₄ of the original composition in which the metal element is not substituted. Indicates discharge capacity (RJ Gummow et al .: Solid State Ionics, Vol. 69, pp. 59-67, 1994, D. Singh et al .: Electrochem. Solid-State Letter, Vol. 5, Issue 9, pp. A198-A201, 2002). Further, the decrease in the manganese-oxygen bond distance acts as a path for lithium ions to be deinserted into the 8a tetrahedron position in the 4V region, and after all the lithium ions have been inserted into the 8a tetrahedron position, in the 3V region. The space of the octahedral position of spinel 16c into which lithium is inserted is further expanded (K. Kang et al .: Science, Vol. 311, pp. 977-980, 2006, K. Tateishi et al .: Appl. Phys. Letter, Vol. 84, Issue 4, pp. 529-531, 2004, JB Bates et al .: J. Electrochem. Soc., Vol. 142, Issue 9, pp. L149-L151, 1995). It means that the conductivity can be improved (S. Chitra et al .: J. Electrochem., Vol. 3, pp. 433-441, 1999, CM Julien et al .: Mater. Sci. Eng. B, Vol. 100, pp. 69-78, 2003).

  Those skilled in the art to which the present invention pertains can understand that the present invention has been implemented in other specific forms without setting the technical idea or essential features thereof. Accordingly, it should be understood that the embodiments described above are illustrative in all aspects and not limiting. The scope of the present invention is defined by the following claims rather than the above detailed description, and all the settings or modified forms derived from the meaning and scope of the claims and equivalents thereof are within the scope of the present invention. Must be interpreted as included.

[The invention's effect]
The present invention replaces manganese of lithium manganese oxide (LiMn ₂ O ₄ ) with a small amount of tin (Sn), thereby suppressing Jahn-Teller deformation, preventing phase transition, and averaging manganese (Mn) ions. The valence can be maintained at 3.5 or more, and the charge / discharge capacity can be increased.
The positive electrode thin film of the present invention has a higher charge / discharge capacity than a positive electrode thin film containing a pure lithium manganese oxide composition, can improve the life of a battery using the thin film, and has an excellent capacity and high current density. Because it exhibits charge / discharge cycle characteristics, it enables the realization of next-generation micro devices that have excellent stability and require high energy and high power density.

It is a graph which shows the X-ray-diffraction analysis result of the lithium tin manganese oxide powder for targets of the calcination state by the Example of this invention. It is a graph which shows the X-ray-diffraction analysis result of the lithium tin manganese oxide target manufactured by the Example of this invention. It is a graph showing changes in voltage due to charge and discharge experiment of the lithium-tin-manganese oxide _LiSn 0.0125 _{Mn 1.975} O ₄ thin film electrode according to an embodiment of the present invention (initial charge-discharge capacity: 97.9mAh / g). It is a graph showing changes in voltage due to charge and discharge experiment of the lithium-tin-manganese oxide _LiSn 0.0125 _{Mn 1.975} O ₄ thin film electrode according to an embodiment of the present invention (initial charge-discharge capacity: 120.0mAh / g). It is a graph showing changes in voltage due to charge and discharge experiment of the lithium-tin-manganese oxide _LiSn 0.0125 _{Mn 1.95} O ₄ thin film electrode according to an embodiment of the present invention (initial charge-discharge capacity: 133.0mAh / g). It is a graph which shows the change of the discharge capacity by charging / discharging of the lithium manganese oxide and lithium tin manganese oxide thin film electrode by the Example of this invention. It is a graph which shows the X-ray-diffraction analysis result of the lithium manganese oxide by the Example of this invention, and a lithium tin manganese oxide thin film electrode. It is a graph which shows the Raman spectrum result of the lithium manganese oxide by the Example of this invention and a lithium tin manganese oxide thin film electrode.

Claims (15)

A method for forming a lithium secondary battery positive electrode thin film,
a) mixing Li ₂ CO ₃ , MnO ₂ and SnO powder to provide a mixed powder;
b) primary pulverizing the mixed powder;
c) calcination of the primary pulverized mixed powder;
d) secondary pulverizing the calcined mixed powder;
e) pressure-molding the secondary pulverized mixed powder;
f) sintering the pressure-molded mixture to produce a target comprising Li, Sn, Mn and O;
g) irradiating the target with laser and locally depositing a positive electrode thin film comprising the Li, Sn, Mn and O on the substrate;
A method for forming a positive electrode thin film for a lithium secondary battery, comprising: _{2. The} method for forming a lithium secondary battery positive electrode thin film according to claim 1, wherein the positive electrode thin film is LiSn _{x / 2} Mn _2-x O ₄ (0 <x ≦ 0.05). The mixing ratio of Li ₂ CO ₃ , MnO ₂ and SnO powder in step a) is 19.0 to 19.1: 79.3 to 80.7: 0.3 to 1.6% by weight. 2. The method for forming a positive electrode thin film of a lithium secondary battery according to 1.   2. The method of forming a positive electrode thin film for a lithium secondary battery according to claim 1, wherein the step c) calcines the mixed powder at 400 ° C. to 800 ° C. for 1 to 5 hours in an air atmosphere.   2. The method of forming a positive electrode thin film for a lithium secondary battery according to claim 1, wherein the step e) press-molds the secondary pulverized mixed powder to form a pellet-shaped mixture.   The method of forming a positive electrode thin film for a lithium secondary battery according to claim 1, wherein the step f) sinters the pressure-molded mixture at 800 ° C to 1300 ° C for 1 to 24 hours in an air atmosphere. . In step g), the substrate temperature is 350 to 550 ° C., the distance between the substrate and the target is 3 to 5 cm, the oxygen partial pressure is 0.05 to 0.25 Torr, and the laser power density is 1 to 4 J / cm ^2. The thin film is locally deposited on the substrate by irradiating the target with a laser under the conditions of a laser beam area of ^{2 to 5} mm ² , a laser spot repetition rate of 3 to 10 Hz, and a laser irradiation time of 30 to 120 minutes. A method for forming a positive electrode thin film of a lithium secondary battery as described in 1. A method for producing a Li-Sn-Mn compound target,
a) mixing Li ₂ CO ₃ , MnO ₂ and SnO powder to provide a mixed powder;
b) primary pulverizing the mixed powder;
c) calcination of the primary pulverized mixed powder;
d) secondary pulverizing the calcined mixed powder;
e) pressure-molding the secondary pulverized mixed powder;
f) sintering the pressure-molded mixture to produce a LiSn _{x / 2} Mn _2-x O ₄ (0 <x ≦ 0.05) target;
A method for producing a Li—Sn—Mn compound target, comprising: The mixing ratio of Li ₂ CO ₃ , MnO ₂ and SnO powder in step a) is 19.0 to 19.1: 79.3 to 80.7: 0.3 to 1.6% by weight. The manufacturing method of the Li-Sn-Mn compound target of 8.   The method for producing a Li-Sn-Mn compound target according to claim 8, wherein the step c) calcines the mixed powder at 400C to 800C in an air atmosphere for 1 to 5 hours.   The Li-Sn-Mn compound target manufacturing method according to claim 8, wherein in step e), the secondary pulverized mixed powder is pressure-molded to form a pellet-shaped mixture.   The Li-Sn-Mn compound target production according to claim 8, wherein the step f) sinters the pressure-molded mixture at 800C-1300C for 1-24 hours in an air atmosphere. Method.   The Li-Sn according to any one of claims 8 to 11, wherein the target produced in step f) is used for a positive electrode active material target for bulk, thick film, or laser local vapor deposition. -Mn compound target manufacturing method.   A lithium secondary battery comprising a compound positive electrode composition of Li, Sn, Mn, and O, which is a lithium secondary battery. The lithium secondary battery according to claim 14, wherein the positive electrode composition is LiSn _{x / 2} Mn _2-x O ₄ (0 <x ≦ 0.05).

Images