JP2009193701A - Lithium battery, positive electrode for lithium battery, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode for a lithium battery which is fabricated without using a large-scale device and is superior in adhesion with a current collection material, and is excellent in utilization rate, a lithium battery using the positive electrode for the lithium battery, and a method of manufacturing the positive electrode for the lithium battery. <P>SOLUTION: The method to form a thin film of lithium complex oxide on a metal substrate 1 includes a process in which the metal substrate is heated to a temperature in the range 250°C-500°C and a thin film containing lithium is vapor-deposited and an annealing process in which the metal substrate having the thin film vapor-deposited is heated to a temperature in the range 475°C-700°C. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a lithium battery, a positive electrode for a lithium battery, and a method for producing the same, and more specifically, a positive electrode for a lithium battery having good adhesion to the current collector and a high utilization rate, and a positive electrode for the lithium battery. The present invention relates to a lithium battery provided and a method for producing a positive electrode for a lithium battery.

In general, lithium batteries using a lithium-containing metal oxide (lithium composite oxide) for the positive electrode and metal lithium for the negative electrode are known. Since applications to portable electronic devices and cards are expected, research on positive electrode films has been actively conducted in order to improve battery characteristics and secure lithium ion mobility. For example, in order to form the positive electrode film on the current collecting base material with good adhesion, the deposition of the positive electrode film containing lithium and the ion beam irradiation to the current collecting base material are used in combination to form lithium on the current collecting base material. A method of forming a complex oxide has been proposed (Patent Document 1).
JP-A-8-236105

According to the above method for forming a positive electrode thin film, good adhesion between the current collecting base material and the positive electrode thin film may be obtained, but the following problems arise.
(1) Since vacuum deposition and ion beam irradiation are used in combination, the cost of manufacturing equipment increases.
(2) The deposited positive electrode thin film is charged by the influence of ion beam irradiation, and the performance of the positive electrode thin film may be deteriorated. That is, the positive electrode thin film is destroyed due to charging, or an oxidation-reduction reaction that does not require electrical neutrality inside the positive electrode thin film occurs, and the characteristics of the positive electrode thin film deteriorate.
(3) A thick mixed layer is formed at the interface between the current collecting substrate and the positive electrode thin film, the electric resistance of the positive electrode thin film is increased, and the utilization rate of the positive electrode thin film is decreased. Specifically, atoms of the material constituting the current collecting base material diffuse to the positive electrode thin film at a level of several μm. As a result, the crystallinity of the positive electrode thin film at the interface portion deteriorates and the electric resistance increases. Further, since the mixed layer formed at the interface portion has a thickness of several μm level, the effective film thickness of the positive electrode thin film is reduced, and the utilization factor of the positive electrode thin film is lowered.

  The present invention can be produced without using a large-scale apparatus, has excellent adhesion to the current collecting base material and has a high utilization rate, a lithium battery positive electrode using the lithium battery positive electrode, and the above-mentioned It aims at providing the manufacturing method of the positive electrode for lithium batteries.

  The manufacturing method of the positive electrode for lithium batteries of this invention is a method of producing the thin film of lithium complex oxide on a metal base material by vapor deposition. In this method, the metal substrate is heated to a temperature in the range of 250 ° C. to 500 ° C. to deposit a thin film containing lithium, and the metal substrate on which the thin film is deposited has a temperature in the range of 475 ° C. to 700 ° C. And an annealing step for heating.

  According to the above method, since the metal substrate is heated to 250 ° C. or higher in the thin film deposition step, sufficient diffusion from the metal substrate to the thin film occurs, and the thin film is sufficiently adhered to the metal substrate. You can gain power. When the heating is less than 250 ° C., the above adhesion is small, and the crystallization of the thin film (positive electrode) does not proceed, so that a thin film having a high defect density or a large defect (such as a crack) is formed. Further, when the metal substrate is heated to a temperature exceeding 500 ° C. in the thin film deposition process, the difference in thermal expansion between the metal substrate and the thin film becomes large, and the thin film is easily peeled off from the metal substrate due to internal stress. Further, by heating to 475 ° C. to 700 ° C. in the annealing step after film formation, it is possible to obtain good crystallinity while preparing oxygen and prevent excessive diffusion from the metal substrate to the thin film. . When the annealing temperature is less than 475 ° C., oxygen is not sufficiently introduced, the atomic arrangement still contains high-density defects, and good crystallinity cannot be obtained, and when it exceeds 700 ° C., the mixed layer increases. To do. As a result, a positive electrode having a high utilization rate is obtained, and cracks and peeling are prevented, so that the internal resistance of the lithium battery can be lowered.

After the annealing step, the thickness of the mixed layer formed by diffusing constituent elements of the metal substrate from the metal substrate to the thin film is preferably 0.5 μm or less. As a result, it is possible to prevent a significant decrease in the utilization rate while improving the adhesion of the positive electrode to the metal substrate. Electrical resistance can also be reduced. In order to ensure that the thickness of the mixed layer is 0.5 μm or less, the temperature of the annealing process is preferably in the range of 475 ° C. to 600 ° C., more preferably 475 ° C. to 555 ° C.

  In the vapor deposition of a thin film containing lithium, a thin film containing lithium and one or more of Co, Ni, and Mn can be deposited. Thereby, a positive electrode for a lithium battery excellent in battery characteristics such as discharge of a large current can be obtained.

  The positive electrode for a lithium battery of the present invention is a positive electrode that is formed on a metal substrate containing one or more of Cr, Fe, and Ni and is used for a lithium battery. This positive electrode is a lithium composite oxide containing one or more of Co, Ni and Mn and lithium, has a thickness in the range of 0.2 μm to 50 μm, and is formed by diffusion of atoms from a metal substrate The thickness of the layer is 0.5 μm or less.

According to said structure, the positive electrode for lithium batteries which is excellent in adhesiveness with a current collection base material, and has a high utilization factor can be obtained.

  A peeling prevention layer is not included between the metal base and the positive electrode, and no peeling can be provided between the metal base and the positive electrode. In a thin film positive electrode, since adhesion can be improved between a metal base material and a positive electrode film, measures such as interposing a sputtered vapor deposition layer for preventing peeling are taken to prevent peeling. However, although this anti-peeling measure that bothers sputter deposition layers is widely used at present, the process becomes complicated and the manufacturing cost increases. By manufacturing according to said method, since a mixed layer can be made thin and peeling can be eradicated, a positive electrode with high current collection performance can be obtained.

  It is possible to prevent cracks in cross-sectional observation at 10 or more positions of the positive electrode. Thereby, a positive electrode for lithium having excellent durability and high reliability can be obtained. The cross-sectional positions of 10 or more are preferably cross-sections such as positions separated at equal intervals when seen in a plan view, but may not be equal intervals. The number of cross-sections at 10 or more may be the number of observations for ensuring in practice that there are substantially no cracks, for example, 20 or the like.

  The lithium battery of the present invention is characterized by including a positive electrode produced by any one of the above-described methods for producing a positive electrode for a lithium battery, or any one of the above-described positive electrodes for a lithium battery. Thus, a highly reliable lithium battery having a large battery capacity and low internal resistance can be obtained.

  According to the present invention, a positive electrode for a lithium battery that can be manufactured without using a large-scale apparatus, has excellent adhesion to a current collecting base material, and has a high utilization rate, and a lithium battery using the positive electrode for a lithium battery And the manufacturing method of the said positive electrode for lithium batteries can be obtained.

FIG. 1 is a cross-sectional view showing a positive electrode 3 for a lithium battery according to an embodiment of the present invention. The positive electrode 3 in the present embodiment is formed by vapor deposition on the surface of a metal substrate (hereinafter abbreviated as “substrate”) 1, and is a lithium composite oxide containing lithium and one or more of Co, Ni, and Mn. It is a thin film. That is, it is a thin film such as LiMO ₂ or LiM ₂ O ₄ (M is Co, Ni, Mn and a mixture thereof). In the positive electrode 3, one or more kinds of atoms from the metal substrate 1 are diffused due to a thermal history during the production. Moreover, the constituent atoms of the positive electrode 3 have also penetrated from the positive electrode 3 by diffusion toward the base material 1 side. Since the ratio of these atoms diffusing to each other and entering the other side is small, the interface between the substrate 1 and the positive electrode 3 can be easily discriminated. The base material 1 may be a metal foil of various stainless steels containing Cr, Ni, Fe, Mn, etc., or a heat-resistant material such as ceramics coated with a metal layer containing Cr, Ni, Fe, Mn, etc. In short, it is only necessary that the thickness range in contact with the positive electrode 3 is conductive.

  In the present invention, the thickness d of the mixed layer 3a formed by diffusing and flowing into the positive electrode 3 from the substrate 1 is limited to 0.5 μm or less. When the thickness d of the mixed layer 3a is increased, the function of the positive electrode 3 cannot be sufficiently achieved in the mixed layer 3a, so that the utilization rate of the positive electrode 3 decreases. That is, although the positive electrode 3 is filled with a material sufficient to occupy a predetermined space, the positive electrode 3 cannot perform a function commensurate with it. For example, the battery capacity is reduced and the electric resistance is increased. From this viewpoint, the limit position of the mixed layer 3a in the positive electrode 3 is defined as a position where the ratio of atoms from the substrate 1 is 5% by weight in the positive electrode 3. When there are a plurality of types of atoms constituting the substrate, the total weight percent of the plurality of types of atoms is 2.5% by weight. Further, when there is a possibility that the positive electrode 3 and the base material 1 are common like Ni, Ni in the mixed layer 3a and Ni in the formal composition of the positive electrode (the composition of the positive electrode far enough from the interface) Regardless of the difference from the weight percent, it does not matter where Ni in the mixed layer 3a comes from. Mn is also an element contained in both the substrate 1 and the positive electrode 3, and the same can be said for Ni described above. This is because it can be considered that the amount of diffusion and outflow from the inside of the positive electrode 3 to the base material 1 is supplemented by the amount of diffusion and inflow from the inside of the base material 1 to the positive electrode 3 side, which does not lead to a decrease in the utilization rate.

  Further, in FIG. 1, no peeling occurs between the positive electrode 3 and the substrate 1 even if no peeling prevention layer is inserted between the positive electrode 3 and the substrate 1. Peeling can be detected by observing the cross section with an optical microscope. Further, if any peeling occurs, the electrical resistance increases and the current collecting performance is greatly deteriorated. For example, by using a tester to measure the electrical resistance between the substrate 1 and the positive electrode 3, the peeling is performed. The presence or absence of can be easily detected.

  FIG. 3 is a view showing a cross section of the positive electrode 3 when vapor deposition is performed at room temperature. It can be seen that the crack C is generated starting from the crystal grain boundary. As described above, when the deposition temperature is too high, the crack C generated in the positive electrode 3 starts from the crystal grain boundary. Cracks C often occur even when the deposition temperature is lower than the range of 250 ° C. to 500 ° C. as shown in FIG. When the deposition temperature is higher than 500 ° C., as described above, diffusion inflow of Ni or the like from the base material is promoted, the mixed layer is enlarged, and the utilization factor of the positive electrode is greatly reduced. When the deposition temperature is higher than 500 ° C., thermal expansion of the base material 1 further occurs, and a large stress is generated at the interface between the base material 1 and the positive electrode 3 when cooled to room temperature, and the positive electrode 3 is peeled off from the base material 1. Will increase. By setting the vapor deposition temperature within the range of 250 ° C. to 500 ° C., there can be obtained the positive electrode 3 that has no crack C, no peeling even if there is no peeling prevention layer, and suppresses the mixed layer.

  Next, the manufacturing method of the positive electrode 3 of this invention is demonstrated. Referring to FIG. 4, when depositing a thin film on substrate 1, substrate 1 is heated to an arbitrary temperature within the range of deposition temperature of 250 ° C. or lower and 500 ° C. or lower. Then, a thin film is formed on the substrate 1 using the amount of the vapor deposition source containing lithium as the vapor deposition source. FIG. 5 is a schematic diagram showing a vapor deposition apparatus used for vapor deposition. In FIG. 5, vapor deposition is performed in a vacuum chamber 30, and a raw material such as lithium or cobalt is charged into a crucible 21 that is a vapor deposition raw material container, and an electron beam, a laser beam, or resistance heating is performed as evaporation energy. By supplying the evaporation energy, the vapor 23 such as lithium or cobalt evaporates from the crucible 21 toward the base material 1 held by the substrate holder 29. It shuts off with a shutter (not shown) until the state of the vapor 23 is stabilized, and when the state of the vapor 23 is stabilized, the shutter is opened to form a lithium composite oxide vapor deposition layer on the substrate 1.

As a deposition material, lithium oxides such as LiCoO ₂ , LiMnO ₂ , and LiNiO ₂ can be used. Alternatively, a mixture of a substance containing lithium such as Li or Li ₂ O and a substance containing a metal such as Co, Mn, Ni, Co ₃ O ₄ , MnO ₂ , or NiO may be used. As an evaporation method, any evaporation method such as an electron beam evaporation method, a resistance heating evaporation method, a laser evaporation method, or a sputtering evaporation method can be used. The thickness of the positive electrode 3 is preferably an arbitrary thickness within a range of 0.2 μm or more and 50 μm or less.

  In FIG. 4, after depositing a thin film on the substrate 1 as described above, the thin film is annealed together with the substrate 1 by heating to an arbitrary temperature within the annealing temperature range of 475 ° C. to 700 ° C. The annealing atmosphere is preferably an air atmosphere or an oxygen atmosphere. When the annealing temperature is less than 475 ° C., the crystallinity and oxygen concentration of the lithium composite oxide are not sufficiently adjusted. On the other hand, when the annealing temperature exceeds 700 ° C., the thickness of the mixed layer 3a increases and the utilization rate of the positive electrode 3 decreases. To do. In addition, due to the difference in thermal expansion coefficient between the base material 1 and the positive electrode 3, a large internal stress is generated when it is cooled to room temperature, and it becomes easy to peel off.

  As described above, the thermal expansion coefficient of the thin film and the base material 1 is maintained while ensuring the adhesion of the thin film to the base material 1 by heating to a low temperature range of 250 ° C. or more and 500 ° C. or less in the thin film deposition step. The peeling of the thin film from the base material 1 due to the difference can be prevented, and the thickness growth of the mixed layer 3a can be suppressed. Further, in the annealing step, by heating to a temperature range of 475 ° C. or more and 700 ° C. or less, while adjusting the oxygen concentration of the lithium composite oxide, the crystallinity is improved, the adhesion is improved, and the mixed layer 3a is improved. The increase can be suppressed.

Test specimens of the present invention and two comparative examples were prepared by the following procedure. For the evaluation of these test specimens, the cross section of the substrate 1 / positive electrode 3 was observed with an optical microscope and a scanning electron microscope (SEM) to examine the presence or absence of cracks and the like. Moreover, the chemical composition was measured in the thickness direction of the cross section using XPS (X-ray photoelectron spectroscopy) and EDX (energy dispersion type) composition analysis, and the thickness of the mixed layer 3a was measured. Moreover, an all-solid lithium secondary battery incorporating the positive electrode of the test body was produced, and the discharge capacity was measured.
(Example of the present invention)
After charging a crucible with a deposition raw material mixed with lithium oxide (Li ₂ O) and cobalt oxide (Co ₃ O ₄ ), and confirming that the temperature of the substrate was 300 ° C. within the deposition temperature range, Vaporized by electron beam irradiation. When the vaporization stabilized, the shutter was opened, and vapor deposition was performed on a stainless steel substrate for 10 minutes. The deposited thin film was annealed together with the substrate at 500 ° C. for 3 hours in the air atmosphere. Thus, a positive electrode of lithium cobaltate (LiCoO ₂ ) having a thickness of 10 μm was produced on the substrate.
(Comparative Example 1)
An evaporation material mixed with lithium oxide (Li ₂ O) and cobalt oxide (Co ₃ O ₄ ) was placed in a crucible and vaporized by irradiation with an electron beam. When the vaporization stabilized, the shutter was opened, and vapor deposition was performed on a stainless steel substrate for 10 minutes. At this time, the temperature of the base material 1 was set to room temperature. The deposited thin film was annealed together with the substrate at 800 ° C. for 3 hours in the air atmosphere. Thus, a positive electrode of lithium cobaltate (LiCoO ₂ ) having a thickness of 10 μm was produced on the substrate.
(Comparative Example 2)
An evaporation material mixed with lithium oxide (Li ₂ O) and cobalt oxide (Co ₃ O ₄ ) was placed in a crucible and vaporized by irradiation with an electron beam. When the vaporization stabilized, the shutter was opened, and vapor deposition was performed on a stainless steel substrate for 10 minutes. At this time, the temperature of the base material 1 was set to room temperature. The deposited thin film was annealed together with the substrate at 500 ° C. for 3 hours in the air atmosphere. As a result, a positive electrode of lithium cobaltate (LiCoO2) having a thickness of 10 μm was produced on the substrate.

1. Form of the positive electrode The evaluation of the above-mentioned specimen was as follows. In Comparative Example 1, cracks occurred in the positive electrode 3. Moreover, the adhesiveness to the base material 1 of the positive electrode 3 was bad, and the location which peeled was recognized. In Comparative Example 1, use of the positive electrode for a lithium battery was stopped. In Comparative Example 2, since the deposition temperature was as low as room temperature, the crystallinity of LiCoO ₂ forming the positive electrode was not good. On the other hand, in the example of the present invention, the adhesion of the positive electrode 3 to the substrate 1 was good, and neither cracking nor peeling was observed. Moreover, the thickness of the mixed layer measured only about the example of this invention was 0.3 micrometer. Moreover, although it was recognized only in the examples of the present invention, LiCoO ₂ exhibited a layered crystal structure preferable as a positive electrode of a lithium battery.
2. Discharge capacity The discharge capacity measured by incorporating the positive electrode of Comparative Example 2 in a lithium battery was as low as 90 mAh / g. The discharge voltage was also low. On the other hand, in the present invention example, a desirable result was obtained with a discharge capacity of 140 mAh / g.

(Other embodiments)
(1) In the above-described embodiments and examples of the present invention, all-solid lithium secondary batteries are exemplified in the examples. However, the positive electrode for a lithium battery of the present invention can be used for any lithium battery. . For example, a lithium secondary battery and a lithium primary battery are included, and the electrolyte is most preferably a solid electrolyte, but may be a liquid phase electrolyte.

  Although the embodiments and examples of the present invention have been described above, the embodiments and examples of the present invention disclosed above are merely examples, and the scope of the present invention is the implementation of these inventions. It is not limited to the form. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

  According to the present invention, it is possible to easily obtain a positive electrode for a lithium battery having excellent adhesion and high utilization rate, which can contribute to the manufacture of an inexpensive and highly reliable lithium battery.

It is a figure which shows the positive electrode for lithium batteries in embodiment of this invention. It is a figure for demonstrating the mixed layer in the positive electrode of FIG. It is a figure for demonstrating a crack. It is a figure for demonstrating the manufacturing method of the positive electrode for lithium batteries of this invention. It is a schematic diagram of a vapor deposition apparatus.

Explanation of symbols

1 base material, 3 positive electrode, 3a mixed layer, 21 crucible, 23 steam, 29 substrate holder, 30 chamber.

Claims (7)

A method for producing a thin film of lithium composite oxide on a metal substrate by vapor deposition,
Heating the metal substrate to a temperature in the range of 250 ° C. to 500 ° C. to deposit a thin film containing lithium;
An annealing step of heating the metal substrate on which the thin film is deposited to a temperature in the range of 475 ° C to 700 ° C.   The mixed layer formed by diffusing constituent elements of the metal base material from the metal base material to the thin film after the annealing step has a thickness of 0.5 μm or less. The manufacturing method of the positive electrode for lithium batteries of description.   3. The method for producing a positive electrode for a lithium battery according to claim 1, wherein in the vapor deposition of the thin film containing lithium, a thin film containing lithium and one or more of Co, Ni, and Mn is vapor deposited. A positive electrode formed on a metal substrate containing one or more of Cr, Fe and Ni and used in a lithium battery,
A lithium composite oxide containing one or more of Co, Ni and Mn and lithium;
Having a thickness in the range of 0.2 μm to 50 μm,
A positive electrode for a lithium battery, wherein a thickness of a mixed layer formed by diffusion of atoms from the metal substrate is 0.5 μm or less.   5. The positive electrode for a lithium battery according to claim 4, wherein an exfoliation preventing layer is not included between the metal substrate and the positive electrode, and there is no exfoliation between the metal substrate and the positive electrode.   The positive electrode for a lithium battery according to claim 4 or 5, wherein there is no crack in cross-sectional observation at 10 or more locations of the positive electrode. It comprises the positive electrode produced with the manufacturing method of the positive electrode for lithium batteries as described in any one of Claims 1-3, or the positive electrode for lithium batteries as described in any one of Claims 4-6, A lithium battery.

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