JP5670262B2 - Thin-film lithium secondary battery manufacturing method and thin-film lithium secondary battery - Google Patents

Description

The present invention, lithium cobaltate: a method of manufacturing a thin film lithium secondary battery having a positive electrode layer made of (LiCoO 2 _LCO), a thin film lithium secondary battery produced by 及 beauty the production method.

In recent years, as portable electronic devices such as notebook computers and mobile phones have been reduced in size and performance, not only these devices themselves but also secondary batteries used as power sources have been required to be reduced in size and performance. Therefore, lithium secondary batteries having many advantages such as high energy density, large theoretical capacity, and good cycle characteristics are attracting attention as compared with other types of batteries. Among these, as described in Patent Document 1, for example, a thin film lithium secondary battery using a lithium nitride phosphate (Li _x PO _y N _z : LiPON) solid as an electrolyte uses a flammable organic solvent as an electrolyte. It has higher safety than lithium secondary batteries. For this reason, development of technologies relating to miniaturization and high performance of thin film lithium secondary batteries and mass production of thin film lithium secondary batteries has been actively conducted. Such a thin film lithium secondary battery will be described below with reference to FIG.

  As shown in FIG. 7, the positive electrode current collector layer 42 and the negative electrode current collector layer 43 are disposed at positions separated from each other on the upper surface of a substrate 41 made of, for example, glass, which is a base of the thin film lithium secondary battery 40. Are stacked. A positive electrode layer 44 is laminated on a part of the positive electrode current collector layer 42, and a portion of the surface of the positive electrode layer 44 exposed on the positive electrode current collector layer 42 covers the entire part. The solid electrolyte layer 45 is laminated so as to extend onto the negative electrode current collector layer 43. A negative electrode layer 46 covering the upper surface of the solid electrolyte layer 45 is laminated so as to extend to the negative electrode current collector layer 43. A protective layer 47 made of, for example, a resin is formed on the whole of the negative electrode layer 46, the solid electrolyte layer 45, and the positive electrode layer 44 exposed on the substrate 41, and the end portion of the positive electrode current collector layer 42 and the negative electrode current collector. The body layer 43 is laminated so that the end of the body layer 43 is exposed.

  The positive electrode current collector layer 42, the positive electrode layer 44, the solid electrolyte layer 45, the negative electrode layer 46, and the negative electrode current collector layer 43 are embodied as, for example, PtTi, LCO, LiPON, Li, and NiCr in this order.

  Among such thin-film lithium secondary batteries 40, the positive electrode layer 44 that affects the capacity is formed by the following method described in Patent Document 2, for example. That is, an amorphous LCO layer is first formed by a known film formation method, for example, a sputtering method in which a lithium cobalt oxide target is sputtered with an inert gas. The deposited LCO layer is crystallized by rapid annealing (Rapid Thermal Anneal: RTA), whereby the positive electrode layer 44 is formed. By performing such crystallization, the positive electrode layer 44 capable of increasing the capacity of the thin film lithium secondary battery 40 can be formed.

US Pat. No. 5,597,660 Special table 2008-523567 gazette

  As described above, by crystallization of the LCO layer that is the positive electrode layer 44 by RTA, it is possible to increase the capacity of the thin-film lithium secondary battery 40 and shorten the time required for forming the positive electrode layer 44. However, if RTA is performed on the LCO layer under the conditions of increasing the capacity and reducing the time as described above, the LCO layer breaks during RTA and peels off from the substrate 41, or the LCO layer cracks at the end of RTA. Even if not, the LCO layer is often broken and peeled off from the substrate 41 during use of the thin film lithium secondary battery 40.

  If the LCO layer, which is the positive electrode layer 44, is peeled off from the substrate 41, the discharge function of the thin film lithium secondary battery 40 is impaired. Therefore, the above-mentioned peeling of the LCO layer is caused by the yield of the thin film lithium secondary battery 40. And is a factor that reduces durability. By the way, according to the experiments of the present inventors, although it was recognized that the annealing temperature at the time of RTA was lowered to suppress the peeling of the LCO layer, the capacity of the thin film lithium secondary battery is reduced. It becomes difficult to obtain a thin film lithium secondary battery 40 having a high capacity.

  These problems are not limited to the case where the LCO layer is heated using the RTA, but even when the LCO layer is heated by other methods such as induction heating using electromagnetic waves, heating using an electric furnace, and heating using laser irradiation. It is almost common. Such a problem is not limited to the case where the material for forming the solid electrolyte layer 45 on which the positive electrode layer 44 is laminated is LiPON, but is generally common when the material is formed of a material other than LiPON. Further, such peeling due to the film stress of the positive electrode layer 44 is generally common between the positive electrode layer 44 and the positive electrode current collector layer 42, and even if the laminated structure is different from the above-described structure, As long as the layer 44 is included, it is generally recognized between any of the layers.

The present invention has been made in view of the above conventional circumstances, and an object while suppressing a reduction in capacity, a method of manufacturing a thin film lithium secondary battery capable of enhancing the yield,及 Beauty thin film lithium secondary battery Is to provide.

Hereinafter, means for solving the above-described problems and the effects thereof will be described.
The invention according to claim 1 is a thin film comprising a film forming step of forming a positive electrode layer made of lithium cobalt oxide on a substrate, and a crystallization step of heating the positive electrode layer to promote crystallization of lithium cobalt oxide. A method for manufacturing a lithium secondary battery, wherein the crystallization step is configured to promote crystallization of low-temperature phase lithium cobalt oxide in a part of the positive electrode layer by maintaining the temperature of the positive electrode layer at a first temperature. A first heating step, and a second temperature after the first heating step to maintain the temperature of the positive electrode layer at a second temperature higher than the first temperature. A heating step , wherein the first temperature is not lower than 400 ° C. and not higher than 500 ° C., the second temperature is not higher than 660 ° C., and the period of the second heating step is longer than the period of the first heating step. to be as high as summary

  It is known that lithium cobaltate crystallizes as low-temperature phase lithium cobaltate by heating at a relatively low temperature, and crystallizes as high-temperature phase lithium cobaltate by heating at a relatively high temperature. It has been.

In the invention according to claim 1, when heating the positive electrode layer, first, by maintaining the heating temperature at the first temperature, after the crystallization of the low-temperature phase lithium cobalt oxide in a part of the positive electrode layer, By maintaining the heating temperature at a second temperature higher than the first temperature, crystallization of the high-temperature phase lithium cobalt oxide is advanced in the positive electrode layer. Therefore, the film stress generated in the positive electrode layer can be reduced as compared with heating in which all of the positive electrode layer is crystallized into high-temperature phase lithium cobalt oxide at a time. Therefore, it is possible to prevent the positive electrode layer from being peeled off from the substrate. Moreover, the capacity | capacitance of the thin film lithium secondary battery which has a positive electrode layer can be raised compared with the case where it heats only by 1st temperature. Therefore, according to the first aspect of the present invention, it is possible to increase the production yield of the thin film lithium secondary battery while suppressing a decrease in the capacity of the thin film lithium secondary battery.
In the first aspect of the invention, since the first temperature is set to 400 ° C. or more and 500 ° C. or less, crystallization of the high-temperature phase lithium cobaltate is difficult to proceed in the first heating step. Some become easier to crystallize as lower temperature phase lithium cobaltate. Therefore, it is possible to further suppress the positive electrode layer from being peeled off from the substrate.
Furthermore, since the second temperature is 660 ° C. or lower, the deformation of the substrate can be suppressed. In addition, since the first heating process is performed at 400 ° C. or more and 500 ° C. or less in a shorter time than the second heating process, the low temperature phase cobalt is formed while forming the low temperature phase lithium cobaltate in the positive electrode layer. It can be suppressed that lithium acid becomes dominant in the crystal forming the positive electrode layer. Therefore, it can suppress that a positive electrode layer peels from a board | substrate and the capacity | capacitance of a thin film lithium secondary battery falls.

  According to a second aspect of the present invention, in the method for manufacturing a thin film lithium secondary battery according to the first aspect, the crystallization step is performed at a temperature higher than the ratio of the low-temperature phase lithium cobaltate in the positive electrode layer. The gist is to increase the proportion of lithium cobalt oxide in the positive electrode layer.

  In the positive electrode layer made of lithium cobaltate, the capacity of the thin film lithium secondary battery decreases as the proportion of the low-temperature phase lithium cobaltate in the positive electrode layer increases. In addition, once lithium cobaltate is crystallized as low-temperature phase lithium cobaltate, it is less likely to be a crystal of high-temperature phase lithium cobaltate than when it is crystallized from an amorphous state as high-temperature phase lithium cobaltate.

  Therefore, in the invention according to claim 2, in heating the positive electrode layer at the first temperature and the second temperature, the high-temperature phase lithium cobalt oxide occupies the positive electrode layer rather than the low-temperature phase lithium cobalt oxide. Increase the ratio. Therefore, by forming the low-temperature phase lithium cobalt oxide, it is possible to suppress the decrease in the capacity of the thin-film lithium secondary battery by the high-temperature phase lithium cobalt oxide while reducing the film stress generated in the positive electrode layer.

The invention according to claim 3 is formed by a film forming step of forming a positive electrode layer made of lithium cobalt oxide on a substrate and a crystallization step of heating the positive electrode layer to promote crystallization of lithium cobalt oxide. A thin film lithium secondary battery having a positive electrode layer, wherein in the crystallization step, the temperature of the positive electrode layer is maintained at a first temperature to crystallize a low-temperature phase lithium cobalt oxide in a part of the positive electrode layer. A first heating step in which the high temperature phase lithium cobalt oxide is crystallized by maintaining the temperature of the positive electrode layer at a second temperature higher than the first temperature after the first heating step. And the second temperature is 400 ° C. or more and 500 ° C. or less, the second temperature is 660 ° C. or less, and the period of the second heating step is the first heating step. Greater than the duration of the heating process Decoction can be summarized as.

In the invention according to claim 3 , the positive electrode layer of the thin film lithium secondary battery is maintained after the heating temperature is maintained at the first temperature, so that the low-temperature phase lithium cobalt oxide is crystallized in a part of the positive electrode layer. By maintaining the heating temperature at a second temperature higher than the first temperature, the high-temperature phase lithium cobalt oxide is crystallized in the positive electrode layer. Therefore, in the positive electrode layer, the film stress is reduced as compared with the case where all of the positive electrode layer is heated so as to be crystallized into high-temperature phase lithium cobalt oxide at a time. Therefore, it is possible to prevent the positive electrode layer from being peeled off from the substrate. Moreover, the capacity | capacitance of the thin film lithium secondary battery which has a positive electrode layer can be raised compared with the case where it heats only by 1st temperature. Therefore, according to the third aspect of the invention, the yield of manufacturing the thin film lithium secondary battery can be increased while suppressing the decrease in the capacity of the thin film lithium secondary battery.

Schematic which shows the whole structure of the sputtering device used in one Embodiment in the manufacturing method of the thin film lithium secondary battery of this invention. Schematic diagram showing the overall structure of a heating apparatus according to an embodiment of the board processor. The timing chart which shows the supply aspect of the nitrogen gas when heating an LCO layer, the aspect of ON / OFF of a lamp heater, and the aspect of a change of a substrate temperature. (A) (b) (c) SEM photograph which image | photographed the cross-section of an LCO layer. (A) (b) (c) Photographs taken of the surface of the LCO layer. (A) (b) (c) The graph which shows the charging / discharging characteristic of a thin film lithium secondary battery. Sectional drawing which shows the cross-section of a thin film lithium secondary battery.

Hereinafter, an embodiment of a method of manufacturing a thin film lithium secondary battery of the present invention, high-speed annealing (RTA) apparatus as an embodiment of the base plate processing apparatus, and, an embodiment of a thin film lithium secondary battery of the present invention A description will be given with reference to FIGS.
[Sputtering equipment]
First, a sputtering apparatus for forming a lithium cobaltate (LCO) layer, which is a positive electrode layer of a thin film lithium secondary battery, used for manufacturing a thin film lithium secondary battery will be described with reference to FIG. To do. As shown in FIG. 1, a cylindrical substrate stage 12 on which a substrate S as a processing target can be placed is disposed in a bottomed cylindrical vacuum chamber 11 of the sputtering apparatus 10. While the vacuum chamber 11 is connected to the ground potential, the substrate stage 12 is set to the floating potential. Therefore, the substrate S placed on the substrate stage 12 is also set to the floating potential. The substrate S placed on the substrate stage 12 is obtained by sequentially laminating a titanium layer and a platinum layer, which are a positive electrode current collector layer and a negative electrode current collector layer, on a square plate-like glass substrate.

  Above the substrate stage 12, a target 14 made of LCO is installed to face the substrate S via a backing plate 13 that seals the vacuum chamber 11. The diameter of the target 14 is, for example, 300 mm, and the TS distance that is the distance between the target 14 and the substrate is, for example, 60 mm.

  A high frequency power source RF that supplies high frequency power to the target 14 is connected to the backing plate 13 via a matching box M that matches the output impedance of the high frequency power source RF with the input impedance of the load. A DC power source DC that supplies DC power to the target 14 is connected to the backing plate 13 via an LC filter F. The high frequency power source RF and the direct current power source DC are connected in parallel to the backing plate 13. The high frequency power supply RF outputs high frequency power having a frequency of, for example, 13.56 MHz to the backing plate 13, while the direct current power source DC applies a negative voltage to the backing plate 13. A magnet 15 that forms a vertical magnetic field on the surface of the target 14 is mounted on the backing plate 13 opposite to the target 14.

  An exhaust port 16 for exhausting the fluid in the vacuum chamber 11 to the outside of the vacuum chamber 11 is connected to the exhaust port 11 a formed through the vacuum chamber 11. The exhaust unit 16 includes, for example, a valve that adjusts the pressure in the vacuum chamber 11 and a vacuum pump such as a turbo molecular pump and a dry pump.

Similarly, a sputter gas supply unit 17 that supplies, for example, argon gas, which is a sputter gas, is connected to the gas supply port 11 b formed through the vacuum tank 11. The sputter gas supply unit 17 is a mass flow controller connected to a cylinder in which argon gas is stored, and adjusts the flow rate of argon gas supplied to the vacuum chamber 11.
[Operation of sputtering equipment]
When the LCO layer is stacked on the substrate S as a film forming process in the sputtering apparatus 10, first, the exhaust unit 16 exhausts the fluid in the vacuum chamber 11, so that the pressure in the vacuum chamber 11 becomes a predetermined pressure. The pressure is reduced to. When the substrate S is carried into the vacuum chamber 11 from a carry-in / out port (not shown), the substrate S is placed on the substrate stage 12.

  When the substrate S is placed on the substrate stage 12, the sputtering gas supply unit 17 supplies argon gas into the vacuum chamber 11 at a flow rate of, for example, 49 sccm. Thereby, the pressure in the vacuum chamber 11 is set to, for example, 0.8 Pa by the gas supply amount of the sputtering gas supply unit 17 and the exhaust flow rate of the exhaust unit 16.

  When argon gas is supplied into the vacuum chamber 11, the high frequency power supply RF supplies high frequency power of 400 W, for example, to the backing plate 13, and the direct current power source DC supplies DC power of, for example, 2300 W to the backing plate 13. Supply. As a result, plasma is generated from the argon gas around the target 14, and argon ions contained in the plasma collide with the surface of the target 14, so that LCO particles are ejected from the target 14. When the LCO particles reach the surface of the substrate S, an LCO layer having a thickness of, for example, 3 μm is laminated on the substrate S.

  At this time, since a voltage obtained by superimposing a DC voltage on a high frequency voltage is applied to the target 14, the potential of the target 14 tends to be negative with respect to the vacuum chamber 11 that is the ground potential. Thereby, it is possible to prevent the argon ions from colliding with the vacuum chamber 11 instead of the target 14. In addition, since the substrate stage 12 and the substrate S are at a floating potential, the argon ions are less likely to be attracted to the substrate S side, so that the LCO layer formed on the substrate S can be prevented from being sputtered.

Further, when electric power is supplied to the target 14 to form the LCO layer, the temperature of the substrate S is not adjusted. Therefore, since the temperature of the substrate S is room temperature, most of the LCO layer laminated on the substrate S is amorphous. The room temperature is the standard temperature at the test site in the standard condition at the test site defined by JIS z 8703. Further, during the formation of the LCO layer by sputtering, the temperature of the substrate S may be higher than the environment where the sputtering apparatus 10 is installed due to the collision of the sputtered particles with the substrate S. In the present embodiment, the film formation with the temperature of the substrate S being room temperature means that the temperature of the environment where the sputtering apparatus 10 is installed is maintained in the above temperature range during the formation of the LCO layer. say. Further, most of the LCO layer formed in this way may be a crystallized LCO layer although it is amorphous as described above.
[RTA equipment]
Next, an RTA apparatus for heating an LCO layer laminated on a substrate, which is a substrate processing apparatus used for manufacturing a thin film lithium secondary battery, will be described with reference to FIG. As shown in FIG. 2, the bottomed cylindrical vacuum chamber 21 of the RTA apparatus 20 is provided with a reflector 22 along the inner wall surface of the vacuum chamber 21. On the reflection plate 22 and in a space surrounded by the reflection plate 22, a placement unit 23 that holds the substrate S on which the LCO layer is laminated by the sputtering apparatus 10 is installed.

  Above the vacuum chamber 21, a heater tank 24 is mounted that seals the opening of the vacuum chamber 21 with a cylindrical shape whose upper and lower surfaces are sealed. A glass window 25 that is concentric with the cross section of the reflection plate 22 and has the same size as a disk is fitted on the lower surface of the heater tank 24. A lamp heater 26 as a heating unit having a plurality of infrared lamps 26 b covered with a reflective cover 26 a is mounted above the glass window 25 in the heater tank 24. A part of infrared rays emitted from the infrared lamp 26 b reaches the inside of the vacuum chamber 11 through the glass window 25 and is then absorbed by the substrate S placed on the placement unit 23. Alternatively, a part of the infrared rays is reflected by the reflection plate 22 in the vacuum chamber 11 and then absorbed by the substrate S. As a result, the substrate S is heated to a predetermined temperature.

  An exhaust unit 27 that exhausts the fluid in the vacuum chamber 21 is connected to the exhaust port 21 a formed through the vacuum chamber 21. The exhaust unit 27 includes a pressure adjustment valve that adjusts the pressure in the vacuum chamber 21 to a predetermined pressure, and vacuum pumps such as a turbo molecular pump and a dry pump, as in the exhaust unit 16 included in the sputtering apparatus 10.

A heating gas supply unit 28 for supplying a heating gas, which is a gas supplied when the substrate S is heated in the vacuum chamber 21, is connected to the gas supply port 21 b formed through the vacuum chamber 21. Yes. The heating gas supply unit 28 is a mass flow controller connected to a cylinder that stores nitrogen gas, which is heating gas, and supplies the nitrogen gas to the vacuum chamber 21 at a predetermined flow rate. By heating the substrate S in a nitrogen gas environment, the adhesion between the LCO formed on the substrate S and the LIPON stacked on the LCO can be enhanced.
[Operation of RTA device]
Of the operations performed by the RTA apparatus 20, a heating operation for heating the substrate S and its action will be described below with reference to FIGS. When the substrate S having the LCO layer is heated by the RTA apparatus 20, first, exhaust in the vacuum chamber 21 is performed by the exhaust unit 27, so that the pressure in the vacuum chamber 21 is, for example, 1 × 10 ⁻⁶ Pa. The pressure is reduced to 1 × 10 ⁻⁵ Pa or less.

  When the inside of the vacuum chamber 21 is depressurized, as shown in FIG. 3, at timing t0, the substrate S is carried into the vacuum chamber 21 from a carry-in / out port (not shown), and the substrate S is placed on the placement unit 23. Placed on. When the substrate S is carried into the vacuum chamber 21, the heated gas supply unit 28 is brought into a temperature state at timing t1, so that nitrogen gas is supplied from the heated gas supply unit 28 to the vacuum chamber 21. As a result, the pressure in the vacuum chamber 21 rises to, for example, 1 atm, which is atmospheric pressure.

  When the pressure in the vacuum chamber 21 rises, the lamp heater 26 is turned on at timing t2 while supplying nitrogen gas at a flow rate of 500 sccm. Then, the output of the lamp heater 26 is increased by the timing t3. As a result, the temperature of the substrate S rises to a predetermined temperature of 400 ° C. or more and 500 ° C. or less, which is the first temperature, for example, 400 ° C., for example, in 2 minutes, which is the first rising period from timing t2 to timing t3. . The first temperature is a temperature at which crystallization from the amorphous LCO to the low temperature phase LCO proceeds in the LCO layer, and a temperature at which the crystallization from the amorphous LCO to the high temperature phase LCO does not proceed. The same temperature is also a temperature at which the LCO layer does not peel off even if the LCO layer is heated for a period of time during which the entire LCO layer is crystallized from the amorphous LCO to the low-temperature phase LCO.

  When the temperature of the substrate S reaches 400 ° C., the output of the lamp heater 26 is maintained in a constant state over a period from the timing t3 to the timing t4 as the first heating process, for example, for 1 minute. The temperature is maintained at 400 ° C.

Here, as described above, most of the LCO layer of the substrate S is laminated on the current collector layer in an amorphous state. Amorphous LCO may be crystallized by being heated to a predetermined temperature, and the crystal structure when crystallized by the temperature at the time of heating may be either a low temperature phase LCO or a high temperature phase LCO. Are known. The low-temperature phase LCO is a crystal phase obtained by heating an amorphous LCO layer at a relatively low temperature, and is a crystal similar to a spinel type or a cubic crystal. On the other hand, the high-temperature phase LCO is a crystal phase obtained by heating an amorphous LCO layer at a relatively high temperature, and specifically, a layered rock salt type (α-NaFeO ₂ type) or rhombohedral crystal. It is a crystal called. In the LCO layer, the portion once crystallized as the low temperature phase LCO can be the high temperature phase LCO, but the transition from the low temperature phase LCO to the high temperature phase LCO is the transition from the amorphous LCO to the low temperature phase LCO. Greater thermal energy is required than the transition from amorphous LCO to high temperature phase LCO.

  Many electrochemical properties of the low-temperature phase LCO and the high-temperature phase LCO have been reported so far. For example, J. et al. Electrochem. Soc. , Vol. 140, no. 3, March 1993 reports that the low temperature phase LCO has a lower discharge potential and a lower discharge capacity than the high temperature phase LCO. When the low temperature phase LCO is used as the positive electrode layer of the thin film lithium secondary battery, the high temperature phase LCO is used as the positive electrode layer in terms of electrochemical characteristics such as charge / discharge stability, cycle characteristics, or discharge capacity. It is said to be inferior to a thin film lithium secondary battery.

  When the amorphous LCO layer is heated at the first temperature, the crystallization of the low-temperature phase LCO proceeds while the crystallization of the high-temperature phase LCO does not proceed. Further, the period during which the first heating step is performed is appropriately selected according to the capacity required for the thin film lithium secondary battery, and is a period in which the crystallization of the low-temperature phase LCO proceeds, and This is a period during which amorphous LCO remains.

  The period from the timing t2 to the timing t3, which is the period from the start of heating the LCO layer to just before the first heating process, and the temperature increase rate are appropriately selected by the RTA apparatus. Even if the temperature of the substrate S during heating overshoots, it is preferable that the temperature and the heating rate be within a period not exceeding the first temperature.

  After the temperature of the substrate S is maintained at 400 ° C., the temperature of the substrate S is increased again by increasing the output of the lamp heater 26 at timing t4. Accordingly, the temperature of the substrate S is a second temperature, for example, 1 minute, which is a second rising period from timing t4 to timing t5, and is a predetermined temperature that is higher than the first temperature and not higher than 660 ° C. For example, the temperature rises to 580 ° C. The second temperature is a temperature at which crystallization from the amorphous LCO to the high temperature phase LCO proceeds in the LCO layer, and a temperature at which the crystallization from the low temperature phase LCO to the high temperature phase LCO does not proceed. The temperature is also a temperature at which the LCO layer does not peel even if the LCO layer is heated for a period of time during which the amorphous LCO remaining in the LCO layer is crystallized into the high-temperature phase LCO.

  When the temperature of the substrate S reaches 580 ° C., the output of the lamp heater 26 is kept constant over a period from the timing t5 to the timing t6 as the second heating process, for example, for 3 minutes, so that the temperature of the substrate S is increased. Maintained at 580 ° C. The second heating period is appropriately selected according to the capacity required for the thin film lithium secondary battery, and is preferably a period in which the progress of crystallization of the high-temperature phase LCO is saturated.

  When the LCO layer is heated at the second temperature, crystallization of the high-temperature phase LCO proceeds. Since the LCO layer is placed under a temperature at which crystallization of the high-temperature phase LCO proceeds, crystallization into the high-temperature phase LCO that is relatively stable at the temperature is more preferential than crystallization into the low-temperature phase LCO. Proceed to. Even when the second temperature is higher than the first temperature, the transition to the high-temperature phase LCO occurs at the same time as long as the transition to the high-temperature phase LCO occurs in the range where the second temperature is 500 ° C. or less. Will do. As described above, since the high-temperature phase LCO is electrochemically superior to the low-temperature phase LCO, the proportion of the low-temperature phase LCO in the entire LCO layer is small from the viewpoint of electrochemical characteristics. Is preferred. Therefore, the second temperature is preferably higher than the first temperature and higher than 500 ° C. at which the transition of the high-temperature phase LCO is superior to the degree of transition of the low-temperature phase LCO. .

  From the viewpoint of transferring the amorphous LCO to the high-temperature phase LCO, it is preferable that the heating temperature in the second heating step is higher. However, the substrate on which the current collector layer and the LCO layer are formed on the substrate S is a glass substrate having a strain point of about 660 ° C. Therefore, by setting the second temperature to 580 ° C., a margin is provided between the heating temperature of the substrate S and the strain point of the substrate S, so that the LCO layer causes the transition from the amorphous LCO to the high-temperature phase LCO. While proceeding, the deformation of the glass substrate can be more reliably suppressed.

  It should be noted that the period from the timing t4 to the timing t5 and the rate of temperature increase, which are periods in which the temperature is increased from the first temperature to the second temperature, are the same as the period from the timing t2 to the timing t3 and the temperature increase rate. It is preferable that the period and the rate of temperature increase should not exceed the second temperature even if the temperature of the substrate S during heating overshoots.

  When the temperature of the substrate S is maintained at 580 ° C., the lamp heater 26 is turned off at timing t6. At this time, since the supply of nitrogen gas from the heating gas supply unit 28 to the vacuum chamber 21 is maintained, the substrate S radiates heat in the vacuum chamber 21 maintained at atmospheric pressure by the nitrogen gas. Since the substrate S is cooled in the vacuum chamber 21 maintained at the atmospheric pressure, heat exchange occurs between the substrate S and the nitrogen gas in contact therewith. The substrate S can be cooled at a speed.

  When the temperature of the substrate S is lowered to a predetermined temperature, for example, a predetermined temperature of 20 ° C. or higher and 30 ° C. or lower due to heat dissipation of the substrate S, the heating gas supply unit 28 is turned off, so that the vacuum chamber 21 is turned off. The supply of nitrogen gas is stopped, and thereby the inside of the vacuum chamber 21 is reduced to a pressure before the timing t1. Thereafter, the substrate S is unloaded from the RTA apparatus 20 and then transferred to an apparatus for forming a solid electrolyte layer, for example.

  As described above, the LCO layer crystallized by performing in this order the first heating step for crystallization of the low-temperature phase LCO and the second step for crystallization of the high-temperature phase LCO will be described with reference to FIG. I will explain. In the LCO layer 33A laminated on the current collector layer 32 on the glass substrate 31, it was recognized that the cross section had a structure as shown in FIG. That is, it was recognized that the LCO layer 33A was formed by columnar particles extending in a direction substantially perpendicular to the stacking direction of the LCO layer 33A. In contrast, in the LLCO layer that was not heated after film formation by sputtering, a cross-sectional structure of the LCO layer 33B as shown in FIG. 4B was observed. When the cross-sectional structures of the LCO layer 33A and the LCO layer 33B are compared, the columnar particles are regularly arranged in the LCO layer 33B, whereas the above-described first heating step and second heating step are performed. In the LCO layer 33A thus formed, it can be seen that the columnar particles remain while the collapse of the columnar particles is observed.

  On the other hand, in the LCO layer subjected only to heating at a temperature at which the crystallization of the high-temperature phase LCO proceeds, for example, 580 ° C., the cross-sectional structure of the LCO layer 33C as shown in FIG. When the cross-sectional structures of the LCO layer 33C and the LCO layer 33A are compared, it can be seen that the columnar particles are significantly collapsed in the LCO layer 33C.

  Thus, as shown by the shape of the columnar particles in the LCO layers 33A, 33B, and 33C, in the crystallization from the amorphous state to the low-temperature phase LCO, the collapse of the columnar particles is hardly observed. On the other hand, in the crystallization from the amorphous state to the high-temperature phase LCO, it is recognized that the collapse of the columnar particles is remarkable. Therefore, it can be seen that the collapse of the columnar particles is alleviated by proceeding the crystallization of the high temperature phase LCO after the crystallization of the low temperature phase LCO in the LCO layer.

  As described above, according to the crystallization process in which the crystallization of the high-temperature phase lithium cobalt oxide is performed in the LCO layer after the crystallization of the low-temperature phase lithium cobalt oxide is performed in a part of the LCO layer, all of the LCO layer is formed at once. Compared with heating that crystallizes into the high-temperature phase LCO, the film stress generated in the LCO layer can be reduced by the amount of the low-temperature phase LCO. Therefore, the second temperature is adopted even when the amorphous LCO is crystallized in a single heating process, even if the temperature causes the LCO layer to peel off due to cracking of the LCO layer. Will be able to. Accordingly, the discharge capacity of the thin-film lithium secondary battery having the LCO layer is increased as compared with the case where the LCO layer is heated only at a temperature that can suppress the peeling of the LCO layer while suppressing the peeling in the LCO layer. Can do.

In addition, the first temperature is set to 400 ° C., and the second temperature is set to 580 ° C., and the period for performing the second heating step is set longer than the period for performing the first heating step. Therefore, while the low temperature phase lithium cobalt oxide is formed in the LCO layer, the low temperature phase lithium cobalt oxide can be suppressed from becoming dominant in the crystal forming the LCO layer. In this embodiment, the capacity of the thin film lithium secondary battery having the LCO layer formed through the first temperature, the first heating period, the second temperature, and the second heating period is LCO theory. It is set so as to satisfy 70% or more of the capacity of 137 mAh / g.
[Cluster device]
The sputtering apparatus 10 and the RTA apparatus 20 constitute a so-called cluster apparatus connected via a transfer chamber whose pressure is reduced to the same level as these apparatuses. Therefore, after the amorphous LCO having high reactivity with water is laminated on the substrate S by the sputtering apparatus 10, the amorphous LCO is conveyed to the RTA apparatus 20 without being exposed to the atmosphere. In addition to the sputtering apparatus 10 and the RTA apparatus 20, the cluster apparatus forms a film forming apparatus for forming each current collector layer of a thin film lithium secondary battery, a film forming apparatus for forming a negative electrode, and a solid electrolyte layer. An apparatus capable of reducing the pressure to the same level as the apparatuses 10 and 20 such as a film forming apparatus may be connected to the transfer chamber.
[Example]
On a substrate in which a titanium layer having a thickness of 20 nm and a platinum layer having a thickness of 200 mm are laminated in this order on a glass substrate having a side of 140 mm and a thickness of 0.5 mm In addition, an LCO layer was formed under the following conditions using the sputtering apparatus.
○ Film formation conditions ・ Diameter of LCoO ₂ target 300mm
・ Distance between target and substrate 60mm
・ Supply power to target DC2300W AC400W
-Argon gas flow rate 49sccm
・ Pressure inside the vacuum chamber 0.8 Pa
-Substrate temperature Room temperature And the board | substrate with which the LCO layer was formed was heated on condition of the following with the said RTA apparatus.
○ Heating conditions ・ First temperature 400 ℃
・ Second temperature 580 ℃
・ First rising period 2 minutes ・ Second rising period 1 minute ・ First heating process 1 minute ・ Second heating process 3 minutes ・ Nitrogen gas flow rate 500 sccm
・ Pressure inside the vacuum chamber: 1 atm
When heated under the above conditions, as shown in FIG. 5A, dense cracks having a diameter of about 30 μm were formed over substantially the entire LCO layer 33A. In the LCO layer 33A in which such dense cracks were formed, the LCO layer did not peel from the current collector layer.

FIG. 6A shows the charge / discharge characteristics of the thin film lithium secondary battery having the LCO layer 33A. The environmental temperature when measuring the charge / discharge characteristics was room temperature, and the charge rate and discharge rate were 1C. In addition, the percentage of the discharge capacity with respect to the theoretical capacity was calculated assuming that the LCO layer 33A was contained in an amount of 5.5 mg per cell. As shown in FIG. 6A, the capacity at the first and second discharges was 0.594 mAh. Since the theoretical capacity of LCO was 137 mAh / g, it was confirmed that the thin-film lithium secondary battery having the LCO layer showed a discharge capacity of 79% with respect to the theoretical capacity. Since the first and second discharge characteristic profiles are the same, in FIG. 6A, the first discharge characteristic profile indicated by the solid line and the second discharge characteristic indicated by the alternate long and short dash line overlap. As shown.
[Comparative Example 1]
An LCO layer was formed on the same substrate as in the above example using the same sputtering apparatus and film formation conditions as in the example. And the board | substrate with which the LCO layer was formed was heated on condition of the following using the RTA apparatus same as an Example.
○ Heating conditions / heating temperature 540 ℃
・ Rising period 3.5 minutes ・ Heating process 10 minutes ・ Flow rate of nitrogen gas 500 sccm
・ Pressure inside the vacuum chamber: 1 atm
When heated under the above conditions, as shown in FIG. 5B, a dense crack having a diameter of about 30 μm was formed over substantially the entire LCO layer 33B, as in the above example. Therefore, the LCO layer 33B heated under the conditions of Comparative Example 1 did not peel off the LCO layer 33B from the current collector layer.

The charge / discharge characteristics of the thin film lithium secondary battery having the LCO layer 33B were measured under the same conditions as in the above examples. As shown in FIG. 6B, the capacity at the first and second discharges was 0.423 mAh, and it was confirmed that the discharge capacity was 56% with respect to the theoretical capacity of LCO. Since the first and second discharge characteristic profiles are the same as in the above embodiment, the first discharge characteristic profile and the second discharge characteristic profile overlap in FIG. 6B as well. It is shown.
[Comparative Example 2]
An LCO layer was formed on the same substrate as in the above example using the same sputtering apparatus and film formation conditions as in the example. And the board | substrate with which the LCO layer was formed was heated on condition of the following using the RTA apparatus same as an Example.
○ Heating conditions / heating temperature 580 ° C
・ Rising period 3.5 minutes ・ Heating process 10 minutes ・ Flow rate of nitrogen gas 500 sccm
・ Pressure inside the vacuum chamber: 1 atm
When heated under the above conditions, as shown in FIG. 5 (c), cracks having a diameter of about 2 to 10 times that of the LCO layers 33A and 33B of the examples and comparative example 1 While formed by a part of 33C, cracks equivalent to those of Example and Comparative Example 1 were formed in the other parts. Then, the LCO layer 33C was peeled from the current collector layer in a region where a large crack was generated to the extent that it was not formed in Example and Comparative Example 1. In addition, among the LCO layers 33C heated under the conditions of Comparative Example 2, such peeling occurred in 80% or more of the LCO layers 33C.

  Further, the charge / discharge characteristics of the thin film lithium secondary battery having the LCO layer 33C in which peeling did not occur were measured under the same conditions as in the above examples. As shown in FIG. 6C, the capacity at the first and second discharge values was 0.622 mAh, and it was found that the discharge capacity was 83% with respect to the theoretical capacity of LCO. Since the first and second discharge characteristic profiles are the same as in the above embodiment, the first discharge characteristic profile and the second discharge characteristic profile overlap in FIG. 6C as well. It is shown.

  Thus, according to the above-described embodiment, it is possible to achieve both suppression of the LCO layer from peeling from the current collector layer and the discharge capacity of the thin film lithium secondary battery being 70% or more of the theoretical capacity. It was.

As described above, according to the embodiment, the effects listed below can be obtained.
(1) When heating the LCO layer, first, by maintaining the heating temperature at the first temperature, crystallization of the low-temperature phase LCO was advanced in a part of the LCO layer that is the positive electrode layer of the thin film lithium secondary battery. Later, by maintaining the heating temperature at a second temperature higher than the first temperature, the crystallization of the high-temperature phase LCO proceeds in the LCO layer. Therefore, the film stress generated in the LCO layer can be reduced as compared with heating that crystallizes all of the LCO layer at once into a high-temperature phase LCO. Therefore, it is possible to prevent the positive electrode layer from being peeled off from the substrate. Moreover, the capacity | capacitance of the thin film lithium secondary battery which has an LCO layer can be raised compared with the case where it heats only at 1st temperature. Therefore, it is possible to increase the production yield of the thin film lithium secondary battery while suppressing a decrease in the capacity of the thin film lithium secondary battery.

  (2) In heating the LCO layer at the first temperature and the second temperature, the ratio of the high temperature phase LCO to the positive electrode layer is made larger than the low temperature phase LCO. Therefore, by forming the low-temperature phase LCO, it is possible to suppress a decrease in the capacity of the thin-film lithium secondary battery by the high-temperature phase LCO while reducing the film stress generated in the LCO layer.

  (3) Since the first temperature is set to 400 ° C. or more and 500 ° C. or less, in the first heating step, crystallization of the high-temperature phase LCO is difficult to proceed, while a part of the LCO layer is crystallized as the lower-temperature phase LCO. It becomes easy to become. Therefore, the LCO layer can be further prevented from being peeled off from the substrate.

  (4) When the substrate of the thin film lithium secondary battery is a glass substrate, the second temperature is set to 660 ° C. or less, which is a temperature lower than the strain point of the glass substrate, so that the deformation of the glass substrate is suppressed. Can do. In addition, since the first heating process is performed at a temperature of 400 ° C. or more and 500 ° C. or less in a shorter time than the second heating process, the low temperature phase LCO is formed while forming the low temperature phase LCO in the LCO layer. Can be prevented from becoming dominant in the crystals forming the LCO layer. Therefore, it can be suppressed that the LCO layer is peeled off from the substrate and the capacity of the thin film lithium secondary battery is reduced.

  (5) By maintaining the LCO layer at the first temperature, crystallization of the low-temperature phase LCO proceeds throughout the LCO layer. Also, by maintaining the LCO layer at the second temperature, this also advances the crystallization of the high temperature phase LCO throughout the LCO layer. As a result, in the LCO layer after the crystallization process, the low temperature phase LCO and the high temperature phase LCO are uniformly distributed over the entire surface of the substrate. Therefore, it is possible to suppress the positive electrode layer from being peeled from the substrate over the entire surface of the substrate. Further, the capacity of the thin film lithium secondary battery can be increased over the entire surface of the substrate.

In addition, the said embodiment can be changed and implemented suitably as follows.
Although the LCO layer was formed by the sputtering apparatus 10, as long as an amorphous LCO layer can be formed, other known film forming apparatuses may be used instead of the sputtering apparatus. .

Although the size of the target 14 is set to 300 mm, it can be appropriately changed within a range in which the LCO layer can be formed on the substrate S.
The TS distance, which is the distance between the target 14 and the substrate S, is set to 60 mm, but can be appropriately changed as long as the LCO layer can be formed on the substrate S.

  A high frequency power source RF and a direct current power source DC are connected to the target 14 and power is simultaneously supplied from these power sources to the target 14. Not only this but if the target 14 can be sputtered, either high-frequency power or DC power is supplied continuously, while the other is supplied intermittently, or these powers are supplied alternately. You may do it.

The target 14 may be connected to either the high frequency power source RF or the direct current power source DC.
The sputter apparatus 10 has the magnet 15 that forms a vertical magnetic field on the inner surface of the target 14, but the magnet 15 may be omitted.

  The sputtering gas supply unit 17 supplies argon gas as the sputtering gas. However, the sputtering gas supply unit 17 may supply a rare gas other than an argon gas such as helium gas, neon gas, krypton gas, or xenon gas as a sputtering gas. An inert gas that does not react may be supplied as a sputtering gas.

  The substrate stage 12 may be a water cooling stage by providing a passage for the cooling water in the substrate stage 12 and providing a temperature control unit for adjusting the temperature of the cooling water flowing through the passage. Thereby, since the substrate S can be cooled during the formation of the LCO layer, the temperature of the LCO layer during the film formation process can be adjusted. Therefore, the LCO layer is easily formed in an amorphous state.

The heating gas supply unit 28 supplies nitrogen gas, but oxygen gas may be supplied in addition to nitrogen gas .

-The period of a 2nd heating process may be longer than the above-mentioned preferable period.
The LCO layer crystallized by the first heating step and the second heating step has a discharge capacity of a thin film lithium secondary battery having the LCO layer that is less than 70% of the theoretical capacity, and is formed by the sputtering apparatus 10. It is sufficient if the discharge capacity is larger than that of the LCO layer that is only formed, that is, the LCO layer in which the amorphous LCO is dominant. For example, the discharge capacity of a thin film lithium secondary battery having an amorphous LCO layer formed by the sputtering apparatus 10 is 0.004 mAh under the same conditions as in the above embodiment, and is 0.53% of the theoretical capacity. For this reason, by heating the LCO layer, a discharge capacity larger than that of the amorphous LCO layer can be obtained. In the present embodiment, since the high-temperature phase LCO having a relatively large discharge capacity is included in the LCO layer, the discharge capacity is higher than that of the LCO layer consisting only of the low-temperature phase LCO.

  The sputter apparatus 10 and the RTA apparatus 20 are cluster apparatuses connected via the same transfer chamber, but the sputter apparatus 10 and the RTA apparatus are not part of the cluster apparatus as described above, and are independent. It may be embodied as a device.

  The heating apparatus is the RTA apparatus 20 that heats the substrate S by the lamp heater 26. For example, a heater may be provided in the substrate stage 12 and the substrate S may be heated using a heater in an inert gas atmosphere such as nitrogen gas. An apparatus for heating the substrate S by induction heating using electromagnetic waves, an apparatus for heating the substrate S by an electric furnace, an apparatus for heating the substrate S by laser irradiation, or an apparatus for heating the substrate S by energizing the substrate S itself It is good.

· Substrate formed of LCO layer and the collector layer but it may also be rather than a glass substrate.

In the LCO layer after heating, as long as a desired capacity can be obtained in a thin film lithium secondary battery having the LCO layer, it may be configured to include a high temperature phase LCO and a low temperature phase LCO. The proportion of LCO need not be greater than the proportion of low-temperature phase LCO.

  DESCRIPTION OF SYMBOLS 10 ... Sputtering device, 11 ... Vacuum chamber, 11a, 21a ... Exhaust port, 11b, 21b ... Gas supply port, 12 ... Substrate stage, 13 ... Backing plate, 14 ... Target, 15 ... Magnet, 16 ... Exhaust part, 17 ... Sputtering gas supply unit, 20 ... heating device, 21 ... vacuum chamber, 22 ... reflector, 23 ... mounting unit, 24 ... heater vessel, 25 ... glass window, 26 ... lamp heater, 26a ... reflective cover, 26b ... infrared lamp , 27 ... exhaust part, 28 ... heated gas supply part, 31 ... glass substrate, 32 ... current collector layer, 33A, 33B, 33C ... LCO layer, 40 ... thin-film lithium secondary battery, 41 ... substrate, 42 ... positive electrode collection Electric current layer, 43 ... negative electrode current collector layer, 44 ... positive electrode layer, 45 ... solid electrolyte layer, 46 ... negative electrode layer, 47 ... protective layer, DC ... DC power supply, F ... LC filter, M ... matching box, F ... high-frequency power supply, S ... substrate.

Claims (3)

A film forming step of forming a positive electrode layer made of lithium cobalt oxide on a substrate;
A method of manufacturing a thin film lithium secondary battery comprising a crystallization step of heating the positive electrode layer to promote crystallization of lithium cobalt oxide,
The crystallization step includes
Maintaining a temperature of the positive electrode layer at a first temperature, a first heating step of promoting crystallization of low-temperature phase lithium cobalt oxide in a part of the positive electrode layer;
And a second heating step in which crystallization of the high-temperature phase lithium cobalt oxide is advanced in the positive electrode layer by maintaining the temperature of the positive electrode layer at a second temperature higher than the first temperature after the first heating step. ,
The first temperature is 400 ° C. or more and 500 ° C. or less,
The second temperature is 660 ° C. or lower,
The method of manufacturing a thin film lithium secondary battery , wherein the period of the second heating step is longer than the period of the first heating step . The crystallization step includes
The method for producing a thin film lithium secondary battery according to claim 1, wherein a ratio of the high temperature phase lithium cobaltate in the positive electrode layer is made larger than a ratio of the low temperature phase lithium cobaltate in the positive electrode layer. A film forming step of forming a positive electrode layer made of lithium cobalt oxide on a substrate;
A thin film lithium secondary battery having a positive electrode layer formed by a crystallization step of heating the positive electrode layer to promote crystallization of lithium cobalt oxide,
In the crystallization step,
Maintaining a temperature of the positive electrode layer at a first temperature, a first heating step of promoting crystallization of low-temperature phase lithium cobalt oxide in a part of the positive electrode layer;
A second heating step is performed in which after the first heating step, the temperature of the positive electrode layer is maintained at a second temperature higher than the first temperature, whereby crystallization of the high-temperature phase lithium cobalt oxide is advanced in the positive electrode layer. We,
The first temperature is 400 ° C. or more and 500 ° C. or less,
The second temperature is 660 ° C. or lower,
The thin film lithium secondary battery , wherein the period of the second heating step is longer than the period of the first heating step .