JP4833594B2 - Lithium secondary battery and manufacturing method thereof - Google Patents

Description

  The present invention relates to a lithium secondary battery using a solid electrolyte and a method for manufacturing the same.

  In recent years, social demands for downsizing and thinning of electronic devices have increased remarkably in various fields, and as a result, the size of electronic components mounted on the devices has been reduced. Miniaturization and weight reduction are also essential. Further, considering the characteristics required for batteries, further increase in energy density is a very important issue.

  At present, chargeable / dischargeable lithium ion batteries are widely used for such applications. However, paper displays and ultra-small active ID tags, which are expected to become popular in the future, are difficult to deal with in the current lithium-ion battery because there are restrictions on the housing and the like to prevent liquid leakage. From such a situation, a solid positive electrode, a solid electrolyte, and a solid negative electrode are laminated using a thin film production technique such as RF sputtering method and spin coating method such as high frequency sputtering method, magnetron sputtering method, and high frequency magnetron sputtering method, Attempts have been made to make all-solid batteries in which no liquid is used.

For example, J. et al. B. Bate et al. Formed a film of LiCoO ₂ (positive electrode) using an RF sputtering apparatus, crystallized by further heat treatment at 700 ° C., and then laminated a LiPON (solid electrolyte) and Li (negative electrode) thin film. A solid battery was manufactured and an energy density of about 800 μWh / cm ² was achieved (see Non-Patent Document 1). As for oxide thin film production, not only a dry process such as sputtering but also a wet process such as a sol-gel method has been studied. Y. H. Rho et al. Produced a LiCoO ₂ thin film by spin-coating a Li—Co—O sol solution to which polyvinylpyrrolidone was added as a stabilizer on a substrate and further performing a heat treatment at 800 ° C. (Non-patent Document 2). reference). However, with this technique, only a film thickness of 0.1 μm can be obtained by one spin coating, and in order to produce a thicker film, the spin coating and heat treatment processes must be repeated a plurality of times. For this reason, in the technique of Non-Patent Document 2, it takes a lot of time to produce a practical film thickness on the order of several μm, which is a very complicated process.

  By the way, as described above, further increase in energy density is a very important issue, but RF sputtering using a mixed gas of argon and oxygen, which is widely used as an oxide film forming method. In this case, the film formation rate is about several nm / min, and even if the gas pressure and the target voltage are maximized, the film formation rate can only be increased to about 10 nm / min. In addition, an oxide film formed by an RF sputtering method is close to an amorphous state, and heat treatment is required to promote crystallization of the oxide after the film is deposited. As described above, there is a problem in terms of cost with respect to the process of long-time sputtering for thickening and heat treatment for crystallization. This problem is also the same in the sol-gel method, and many repetitions of spin coating and heat treatment cause a significant increase in cost.

J.B.Bete, et al., "Preferred Orientatin of Polycrystalline LiCoO2 Films", Journal of the ElectroChemical Society, Vol.147, No.1, pp59-70, 2000. Y.H.Rho, et al., "LiCoO2 and LiMn2O4 Thin-Film electrodes for Rechargeable Lithium Batteries", Journal of the ElectroChemical Society, Vol.150, No.1, ppA107-A111, 2003.

  As described above, the current problems of the method for producing an oxide electrode for an all-solid-state battery are that the film formation rate is slow, the cost is high, and it is difficult to increase the energy density, and the heat treatment is necessary and the process becomes complicated. Can be mentioned. Under these circumstances, in order to realize an all-solid-state battery, a low-priced and simple technique is required in place of conventional oxide thin film manufacturing methods such as RF sputtering and spin coating.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to make it possible to more easily manufacture an all-solid lithium secondary battery.

  The method of manufacturing a lithium secondary battery according to the present invention includes a step of forming a solid electrolyte layer through which lithium ions are conducted, and a solid negative electrode in which at least one insertion and extraction of metallic lithium and lithium ions is performed. A target formed of an oxide containing at least lithium, generating a plasma composed of an inert gas and an oxygen gas supplied at a predetermined composition ratio. A solid positive electrode composed of an oxide containing at least lithium is deposited on the electrolyte layer by causing a sputtering phenomenon by causing particles generated from plasma to collide with the target by applying a high frequency to the target and depositing a material constituting the target. The plasma is generated by electron cyclotron resonance. The divergent magnetic field is obtained as is an electron cyclotron resonance plasma kinetic energy given.

In the method for manufacturing the lithium secondary battery, the positive electrode, M a Co, Ni, Fe, Ru der those composed of Li _1-x MO ₂ where at least one of Mn (0 ≦ x <1) . Note that the high-frequency power and the microwave power applied to generate plasma may be in a range in which all types of atoms constituting the target are sputtered. The composition ratio of the oxygen gas was such that unnecessary side reactions with oxygen were suppressed before the metal particles constituting the target sputtered from the target reached the surface to be deposited. Any range is acceptable.

  The lithium secondary battery according to the present invention is manufactured by the above-described method for manufacturing a lithium secondary battery.

  As described above, according to the present invention, the solid positive electrode composed of an oxide containing at least lithium is formed by the sputtering method using electron cyclotron resonance plasma. An excellent effect that the battery can be manufactured more easily is obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a process diagram showing an example of a method for manufacturing a lithium secondary battery according to an embodiment of the present invention. First, as shown in FIG. 1A, a metal plate 101 made of stainless steel such as SUS304 is prepared. The substrate 101 is preferably one that can be easily provided with electric wiring in consideration of an electrode film for use in a battery. Specifically, the substrate itself may be made of a metal such as stainless steel, titanium, or nickel. Alternatively, one or a plurality of metals selected from gold, platinum, titanium, and the like may be formed on a quartz glass substrate. Moreover, you may make it use what forms the metal layer which consists of one type or several materials from gold | metal | money, platinum, titanium, copper etc. on the bendable polymer film.

Next, as shown in FIG. 1B, LiCoO ₂ is selectively deposited on the prepared substrate 101 by an ECR (Electron Cyclotron Resonance) sputtering method, and the positive electrode 102 is formed. And For example, the positive electrode 102 can be formed on the substrate 101 by performing sputter deposition using a mask plate having an opening in a desired region. The positive electrode 102 may be made of LiCoO ₂ having a stoichiometric composition.

To describe more detailed sputtering conditions in forming the positive electrode 102, first, LiCoO ₂ is used as a target. A mixed gas of argon and oxygen is used. The power of microwave (2.45 GHz) is 800 W, the power of RF (13.5 MHz) applied to the target is 500 W, the gas pressure during sputtering is 0.13 Pa, and the flow rate of argon is 20 sccm (97.6 vol%). The oxygen flow rate was 0.5 sccm (2.4 vol%), and the film formation time (sputtering time) was 6 hours. Under this condition, the positive electrode 102 made of a LiCoO ₂ layer having a thickness of 6 μm is formed. Sccm is a unit of flow rate, and indicates that a fluid at 0 ° C. and 1 atm flows 1 cm ³ per minute.

Next, as shown in FIG. 1C, a state in which the solid electrolyte layer 103 made of LiPON [chemical formula: Li ₃ P (O, N) ₄ ] is formed so as to cover all of the side surface and the upper surface of the positive electrode 102. And For example, the solid electrolyte layer 103 can be formed by RF sputtering using Li ₃ PO ₄ as a target and generating plasma of a mixed gas of argon and nitrogen gas by RF. In this sputtering method, as described above, the solid electrolyte layer 103 can be formed by depositing LiPON only in a desired region using a mask plate. Next, as shown in FIG. 1 (d), the anode 104 made of lithium (metallic lithium) is formed on the solid electrolyte layer 103. For example, the negative electrode 104 can be formed by selectively depositing metallic lithium by a vacuum evaporation method using a mask plate. Thereafter, the all-solid lithium secondary battery is formed, for example, by making the negative electrode 104 sealed and protected with an insulating resin having heat resistance.

  Here, an ECR sputtering apparatus used for forming the positive electrode 102 will be described. FIG. 2 is a cross-sectional view showing a configuration example of the ECR sputtering apparatus. First, a processing chamber 201 and a plasma generation chamber 202 communicating with the processing chamber 201 are provided. The processing chamber 201 communicates with an evacuation device (not shown) through an exhaust pipe 203, and the inside of the processing chamber 201 is evacuated together with the plasma generation chamber 202 by this vacuum evacuation device. A substrate holder 204 on which a substrate to be processed is placed (fixed) is provided inside the processing chamber 201.

An opening region into which plasma from the plasma generation chamber 202 inside the processing chamber 201 is introduced is provided with a target 205 made of LiCoO ₂ formed in a ring shape so as to surround the opening region. A high frequency power supply 212 is connected to the target 205 via a matching unit 211 so that, for example, a high frequency of 13.5 MHz can be applied. In addition, a reactive gas introduction unit 208 is connected to the processing chamber 201 so that, for example, oxygen gas can be supplied. The target 205 is not limited to a circular shape as viewed from above, and may be a polygonal shape.

  On the other hand, microwaves can be introduced into the plasma generation chamber 202 via the microwave introduction tube 206, and in addition, a magnetic field is generated by a magnetic coil (magnetic field forming means) 207 disposed around the plasma generation chamber 202. It is possible. In addition, an inert gas introduction unit 209 is connected to the plasma generation chamber 202 so that, for example, an inert gas such as argon can be supplied. In FIG. 2, a reactive gas such as oxygen and an inert gas such as argon are supplied from different locations, but the present invention is not limited to this, and both are supplied from the same introduction section. It may be. For example, oxygen gas and argon gas may be supplied from a supply unit communicating with the processing chamber 201.

  Hereinafter, an operation example of the ECR sputtering apparatus shown in FIG. 2 will be described. First, an inert gas such as argon gas is introduced into the plasma generation chamber 202 from the inert gas introduction unit 209, and the plasma generation chamber 202 The inside is set to a predetermined pressure. At this time, oxygen gas may be introduced from the reactive gas introduction unit 208. Further, oxygen gas may be supplied after ECR plasma described below is generated.

  Next, a microwave is introduced into the plasma generation chamber 202 through a microwave introduction tube 206 from a microwave generator (not shown). The power of the introduced microwave can be arbitrarily adjusted. Further, by passing a current through the magnetic coil 207, a magnetic field is generated inside the plasma generation chamber 202, and by satisfying the electron cyclotron resonance (ECR) condition in the state where the above-described microwave is introduced, An ECR plasma containing an inert gas and oxygen ion particles may be generated in the plasma generation chamber 202. As the inert gas introduced here, it is desirable to use argon from the viewpoint of cost and versatility. The oxygen gas is used as a reactive gas when forming an oxide film. When an oxide film is formed, oxygen is used. For example, nitrogen is introduced when forming a nitride film, and hydrogen is introduced when forming a hydride film.

As described above, the ECR plasma generated in the plasma generation chamber 202 is given kinetic energy by the divergent magnetic field (magnetic field) formed by the magnetic coil 207 and is guided to the processing chamber 201. At this time, if radio frequency (RF) power is applied to the target 205, the extracted plasma is attracted to the target 205, and ions (particles) in the attracted plasma collide with the surface of the target 205. . As a result, a sputtering phenomenon occurs on the surface of the target 205, and particles constituting the target 205 are ejected from the surface of the target 205. The target 205 is made of LiCoO ₂ , and metal ion particles and oxygen ion particles of lithium and cobalt are ejected from the surface of the target 205 by the sputtering phenomenon.

  Here, as the target 205, the same composition as the target film composition is used, or in consideration of the difference in sputtering efficiency between lithium (Li) and transition metal (Co), the target is excessive in lithium or in excess of transition metal. These targets can also be used. The ejected ion particles are struck against the substrate on the substrate holder 204 together with the plasma flow, and the metal ion particles are oxidized by the oxygen ion particles originally contained in the plasma flow or the oxygen ion particles from the target 205, and the metal oxide A layer is formed on the substrate (surface to be deposited).

According to the above-mentioned ECR sputtering method, compared with the RF sputtering method, the plasma density is generally large, the damage to the substrate is small, and the resulting film has excellent flatness and high uniformity. Further, in the ECR sputtering method, the sputtering energy is large, and when an oxide is deposited, crystallization at a low temperature is expected. As described with reference to FIG. 1, the microwave power described above is 800 W or more, the RF power is 500 W or more, and the oxygen concentration y in the mixed gas of argon and oxygen is 0 <y <4.5 (capacity). %)), It is possible to form a LiCoO ₂ film which is excellent in crystallinity and orientation and has few impurity phases. By setting the oxygen concentration within the above range, as shown below, the peak of the crystal plane (003) is shown in the X-ray diffraction pattern, and the crystal is formed in a state having remarkable crystal orientation. Become.

Next, FIG. 3 shows an X-ray diffraction (XRD) pattern of the positive electrode 102 made of LiCoO ₂ formed by the manufacturing method shown in FIG. In FIG. 3, the Miller index of the crystal plane indicated by each peak is also shown. As shown in FIG. 3, the crystal structure of the positive electrode 102 is attributed to ICDD number: 50-0653, and although it has a similar structure, the electrode material is not a low-temperature phase that is considered to have low performance, but has better electrode characteristics. It was confirmed that a high-temperature phase LiCoO ₂ having an α-NaFeO ₂ type structure was generated. Further, from the sharpness of the peak, the crystallinity is good, and the peak of the crystal plane (003) selectively shows a large intensity, so that it can be seen that it has a remarkable crystal orientation. Also, no peaks due to impurities are confirmed. The * mark in FIG. 3 is a substrate fixing compound for XRD measurement, and the downward black triangle mark is a peak due to a stainless steel substrate, and is not obtained from LiCoO ₂ .

Thus, according to the manufacturing method shown in FIG. 1, a positive electrode made of LiCoO ₂ having a single phase, high crystallinity and high orientation at a film formation rate of 1 μm per hour (16.6 nm / min). It can be easily formed. Further, no heat treatment after film formation is necessary. Moreover, according to the all-solid-state battery shown in FIG. 1D using the positive electrode 102 formed in this way, a high energy density state can be obtained. According to this all solid state battery, charge / discharge characteristics as shown in FIG. 4 are obtained. The charge / discharge characteristics of this all-solid battery are the results of measurement in the range of 4.3-3.0 V with a charge / discharge current of 20 μA, and are the 20th charge / discharge curve. The average discharge voltage is a sufficiently high voltage of about 3.8 V, the discharge capacity is as large as 240 μAh / cm ² , shows a reversible charge / discharge profile with no difference from the charge capacity, and has high performance. It is shown.

  Next, the charge / discharge cycle dependency of the discharge capacity of the all solid state battery shown in FIG. 1 (d) will be described with reference to FIG. FIG. 5 is a characteristic diagram showing the charge / discharge cycle dependency of the discharge capacity of the all-solid-state battery. Although the capacity is initially reduced, a stable discharge capacity is shown thereafter. 5A shows the charge / discharge cycle dependency of the discharge capacity of the all-solid-state battery shown in FIG. 1D, and FIG. 5B shows a comparative example created by the prior art described below. The characteristics of the all-solid-state battery are shown.

  In the example of the manufacturing method illustrated in FIG. 1, after the positive electrode 102 is formed on the substrate 101, the solid electrolyte layer 103 and the negative electrode 104 are formed to be stacked in this order, but the present invention is not limited to this. For example, the negative electrode, the solid electrolyte layer, and the positive electrode may be formed in this order on the substrate. It has been confirmed that the battery characteristics similar to those described above can be obtained even with the all-solid battery formed in this way.

  Here, the conditions required for the positive electrode used in the solid state battery will be considered. This condition includes a single phase containing no impurities, high crystallinity, high orientation, and good adhesion to the substrate. These various conditions are desirably achieved without heat treatment in order to simplify the manufacturing process, and can be realized by optimizing various film formation parameters of the ECR sputtering apparatus. The main parameters are as follows.

  The first is the strength of the ECR plasma, which can be controlled by the microwave power introduced from the microwave introduction tube into the plasma generation chamber. The second parameter is the RF power applied to the target. By increasing this RF power, the plasma generated in the plasma generation chamber is strongly struck and sputtered onto the target surface, and the concentration of lithium ions and cobalt ions that jump out of the target surface, and the substrate (film formation target surface, The impact speed (energy) on the surface changes. These two parameters are important when using a target including a plurality of metals having different sputtering efficiencies. In order for all types of atoms (elements) constituting a target including metal ions (atoms) to be sputtered and jump out of the target, the plasma strength above a certain threshold value must be applied to each element constituting the target. Power to attract plasma to the target is required. These two are determined by microwave power and RF power.

  For example, if both of these values are less than or equal to the threshold value, lithium jumps out of the target due to the sputtering phenomenon, but the transition metal (Co) remains in the target without change, resulting in an unbalanced state. The composition of the resulting film deviates from the target value and becomes a mixed phase with impurities. Therefore, when the transition metal oxide is sputtered, all the metal ions constituting the target are sputtered evenly, so that microwave power and RF power of a certain value or more are necessary.

  Further, the gas atmosphere at the time of sputtering is very important for obtaining a target oxide film. The metal ion particles jumped out by sputtering collide with oxygen ion particles in the ECR plasma or oxygen ion particles sputtered out from the oxide target. Due to this collision, the sputtered metal ion particles do not reach the deposition surface (the surface to be deposited), and non-uniform distribution occurs as lithium oxide or transition metal (cobalt) oxide. In some cases, the film reaches the deposition surface in a state where either of the transition metal and the transition metal is insufficient, and is formed as a film, deviating from the composition desired as the electrode material, and may affect the crystallinity of the film. As the oxygen concentration increases, the probability of these collisions increases, and an oxygen concentration above a certain value causes a reduction in the quality of the formed film.

  Therefore, the unnecessary collision described above is suppressed, and before the metal ions sputtered from the target (metal particles constituting the target) reach the substrate (the surface to be deposited), unnecessary side collision with oxygen is performed. In order to reach the deposition surface with the reaction suppressed and to form a higher quality film, the oxygen concentration is desirably below a certain value. A film having a composition suitable as an electrode material can be formed within an appropriate oxygen concentration ratio range. However, if the oxygen concentration is set to an extremely small value, the oxygen ion particles in the ECR plasma are reduced, the oxygen ions reaching the deposition surface are also deficient, the oxygen content in the film is insufficient, and the composition is not intended. , Impurities are mixed to form a metal ion excess film, which is not preferable.

  Therefore, it is desirable that oxygen be circulated in a certain concentration range as a parameter for obtaining a lithium transition metal oxide film having good electrode characteristics. Each parameter described above varies depending on the type and size of the device used, the structure of the vacuum chamber constituting the film formation chamber and the plasma generation chamber, the distance between the target and the substrate (deposition surface), etc. A value is set for each device.

In addition, as described above, according to the ECR sputtering method in which each condition (parameter) is appropriately set, all solids composed of a lithium-containing transition metal oxide film as a positive electrode, a lithium ion conductive solid electrolyte, and a negative electrode material. A battery, in particular, an all solid-state lithium secondary battery can be easily produced. As the solid electrolyte, any substance having lithium ion conductivity can be used, and LiPON in which some of the oxygen ions of Li ₃ PO ₄ are replaced with nitrogen ions, solid polymer electrolyte, etc. can be used. It is.

  The negative electrode material may be any material that can store (occlude) and release lithium ions at a base potential in addition to lithium metal, and silicon, tin, or an alloy containing these materials can be used. Even when the negative electrode is made of lithium metal, lithium ions are released from the negative electrode, and lithium ions are accumulated in the negative electrode. The solid electrolyte and the negative electrode may be formed by a known method such as a sputtering method, a vacuum evaporation method, or a sol-gel method. As a laminated structure of these films, the substrate, the positive electrode, the solid electrolyte, and the negative electrode may be laminated in this order, or the substrate, the negative electrode, the solid electrolyte, and the positive electrode may be laminated in this order. In any case, any solid electrolyte can function as a battery as long as it has a structure in which a film is formed between both electrodes so as to prevent a short circuit due to contact between the positive electrode and the negative electrode. The all solid state battery thus produced is preferably protected by a moisture-proof film such as a polymer film covering the battery or a non-conductive nitride film in order to prevent deterioration due to moisture.

The all-solid-state battery using the lithium-containing transition metal oxide positive electrode according to the present invention manufactured as described above has characteristics of high crystallinity, high orientation, and high adhesion suitable for the electrode material. . For this reason, it has excellent characteristics as a battery such that the discharge voltage is increased by reducing the overvoltage, and the decrease in the discharge capacity is remarkably suppressed even if the charge / discharge cycle is repeated. In addition, film formation (formation) of lithium-containing transition metal oxides by ECR sputtering can be performed in a short time without the need for heat treatment by optimizing the film formation parameters described above, thus reducing manufacturing costs. There is an advantage that an all-solid-state battery having excellent energy efficiency and a large energy density can be produced. In the above description, lithium cobalt oxide (LiCoO ₂ ), which has been clearly shown to have excellent cycle stability and thermal stability, has been described as an example from previous reports. However, the present invention is not limited to this. Instead, according to the manufacturing method of the present invention described above, by determining each of the above-described parameters, any lithium-containing transition metal oxide Li _1-x MO ₂ (0 ≦ x <1, M is Co, Ni, It is also applicable to a transition metal composed of at least one or more of Fe and Mn), and it has been confirmed that the produced all-solid battery has excellent battery performance.

Next, the results of investigation on the above-described film formation parameters will be described. First, a LiCoO ₂ film based on the film formation parameters in the manufacturing method example described with reference to FIGS.

Further, a LiCoO ₂ film formed with “microwave power: 800 W, RF power: 500 W, oxygen concentration: 4.8%, sputtering time: 6 h” is referred to as Production Method Example 2. A LiCoO ₂ film formed with “microwave power: 800 W, RF power: 500 W, oxygen concentration: 50%, sputtering time: 6 h” is referred to as Production Method Example 3. Further, a LiCoO ₂ film formed with “microwave power: 500 W, RF power: 500 W, oxygen concentration: 20% sputtering time: 6 h” is referred to as Production Method Example 4.

In any one of Production Method Examples 2 to 4, LiCoO ₂ having an α-NaFeO ₂ type structure is formed in a single phase. Further, it was confirmed that charging and discharging are possible in the all solid state battery having these films as the positive electrode and configured in the same manner as in FIG. From these, it can be seen that the film formation by the ECR sputtering method is effective for the formation of the LiCoO ₂ film.

However, compared to the LiCoO ₂ film by the manufacturing method Example 1, LiCoO ₂ film by the manufacturing method Example 2-4, the difference in crystallinity and orientation, as shown in FIG. 6 is observed. FIG. 6 is a characteristic diagram showing the XRD pattern of the LiCoO ₂ film produced under the conditions of Production Method Example 1 and Production Method Example 2 to Production Method Example 4, particularly focusing on the peak of the crystal plane (003). Incidentally, In FIG. 6, (a) is shows the XRD pattern of the LiCoO ₂ film manufacturing method Example 1, (b) is shows the XRD pattern of the LiCoO ₂ film manufacturing method Example 2, the (c), producing It shows the XRD pattern of the LiCoO ₂ film method example 3, (d) is shows the XRD pattern of the LiCoO ₂ film manufacturing method example 4. In addition, the * mark in the figure is a peak due to the compound for fixing the substrate for XRD measurement, and is not obtained from LiCoO ₂ .

As apparent from FIG. 6, only the production method example 1 has a sharp peak intensity indicating the (003) orientation of LiCoO ₂ and has good orientation and crystallinity. In the films of the other production method examples 2 to 4, although there is no impurity phase, such a sharp peak is not observed at all, and the characteristics as a solid battery are described with reference to FIG. Lower than for all solid state batteries. As can be seen from these, as exemplified in the parameters of the manufacturing method described with reference to FIG. 1, the microwave power is set to 800 W or more, the RF power is set to 500 W or more, and oxygen is mixed in the mixed gas of argon and oxygen. It can be seen that an oxide film with higher crystallinity and orientation can be obtained by using optimized film formation conditions such that the concentration y is in the range of 0 <y <4.5 (Vol%). In addition, it can be seen that according to the all-solid battery using the positive electrode manufactured in this way, the battery characteristics are further improved.

Next, a comparison result between the case of forming by the ECR sputtering method and the case of forming by the RF sputtering method is shown. First, a LiCoO ₂ film based on the film formation parameters in the manufacturing method example described with reference to FIGS. This is the same as described above.

Also, a LiCoO ₂ film formed with “microwave power: 500 W, RF power: 500 W, argon flow rate 20 sccm, oxygen flow rate 5 sccm (concentration conversion: 25%), sputtering time: 6 h” is referred to as Production Method Example 5.

In addition, the gas pressure during sputtering is 3.7 Pa, RF power: 300 W, argon flow rate 48 sccm, oxygen flow rate 16 sccm (concentration conversion: 25%), sputtering time: 18 h, and a LiCoO ₂ film formed by an RF sputtering apparatus is compared. LiCoO ₂ film formed by an RF sputtering apparatus in Example 1 with “gas pressure during sputtering: 3.7 Pa, RF power: 600 W, argon flow rate 48 sccm, oxygen flow rate 16 sccm (concentration conversion: 25%), sputtering time: 13 h” Is referred to as Comparative Example 2.

  As described above, the film formation speed is 16.6 nm / min under the conditions of the manufacturing method example 1, and the film formation speed is 7.7 nm / min (total thickness is 2.7 μm) under the conditions of the manufacturing method example 5. is there. On the other hand, under the conditions of Comparative Example 1, the deposition rate is 2.4 nm / min (total thickness 2.6 μm), and under the conditions of Comparative Example 2, the deposition rate is 4.4 nm / min (total thickness 4.4 μm). ) As described above, it can be seen that the film formation by the manufacturing method examples 1 and 5 using the ECR sputtering method has a clearly higher film forming speed than the comparative examples 1 and 2 by the RF sputtering method.

  Generally, in the RF sputtering method, in order to improve the deposition rate (film formation rate) of the film, a method of increasing the power applied to the target and increasing the gas pressure to about several Pa is used. Yes. In general, when the oxygen concentration is high, the film formation rate is decreased, and thus sputtering is sometimes performed in a state where oxygen is diluted. However, these methods are not preferable because there is a high possibility that only oxygen-deficient oxides deviating from the target composition can be obtained.

In contrast to these RF sputtering methods, in the ECR sputtering method of the present invention, the applied microwave power and RF power can be set to be very large compared to the RF sputtering apparatus of the same scale, and the high speed It is advantageous for film formation. Further, ECR sputtering in a low concentration region such as an oxygen concentration of 2.4%, which is the condition of Production Method Example 1, is suitable for high-speed film formation, and the composition of the obtained film is almost stoichiometric composition. There is no event that LiCoO ₂ is formed and an oxygen-deficient oxide is formed.

In ECR sputtering, since the plasma density is very high, the film can be formed at a sufficiently high speed with a gas pressure of about 0.1-0.2 Pa. Further, even in the film formation by the same ECR sputtering method, the production method example 1 shows a larger film formation speed than the production method example 5, and this is because the production method example 1 has a larger set power and a lower oxygen content. This is because the film is formed under a concentration. Under the conditions of the present invention, as described above, high-speed film formation is possible. By optimizing the conditions, specifically, LiCoO ₂ having a film thickness of about 1 μm can be formed by sputtering film formation for 1 hour. In addition, the film according to the present invention is excellent in crystallinity and orientation even without heat treatment, and as described above, exhibits sufficient electrode activity and is considered to contribute greatly to simplification of the manufacturing process. As described above, according to the manufacturing method described with reference to FIGS. 1A to 1D, the positive electrode made of LiCoO ₂ can be formed at a high speed without the need for heat treatment. This is a very advantageous production method.

Here, using the LiCoO ₂ film formed in Comparative Example 2 described above as a positive electrode, an all-solid battery was prepared in the same manner as the manufacturing method described with reference to FIGS. 1C and 1D, and this was compared. Let us take a battery example. FIG. 5B shows the result of measuring the battery characteristics of the all-solid-state battery of this comparative battery example in the voltage range of 4.3 to 3.0 V with a charge / discharge current of 20 μA. Although the battery of the comparative battery example shows a relatively large value of the initial discharge capacity of 200 μAh / cm 2, the capacity decreases linearly when charging and discharging are repeated, and in the 15th cycle, it is only about 25% of the first time. .

This tendency is markedly different from the characteristics of the all-solid-state battery shown in FIG. 5 (d) showing a stable cycle. This tendency is considered because the crystallinity and orientation of the LiCoO ₂ film constituting the positive electrode of the comparative battery example are inferior to those of the film formed by the ECR sputtering method.

  As shown in the above specific examples, the film formation of the lithium-containing transition metal oxide in the manufacturing method of the present invention has a higher crystallinity and higher orientation than the conventionally widely used RF sputtering method. It is very advantageous in that the oxide film can be obtained, high-speed film formation is possible in terms of process, and heat treatment is unnecessary, and a solid in which the oxide electrode obtained in the present invention is incorporated as a positive electrode. It was confirmed that the battery also showed better characteristics. For example, by using the positive electrode, an all solid state secondary battery having stable cycle characteristics at a high energy density can be produced. In addition, the all-solid-state battery manufactured as shown in FIG. 1 has a feature of a thin film shape, and compared with a conventional coin battery, etc. in consideration of mounting on a small and thin electronic device. However, it is very advantageous from the viewpoint of shape.

It is process drawing which shows the example of a manufacturing method of the lithium secondary battery in embodiment of this invention. It is sectional drawing which shows the structural example of an ECR sputtering apparatus. It is a characteristic diagram showing the X-ray diffraction (XRD) patterns of the positive electrode 102 that is composed of LiCoO ₂ formed by the manufacturing method shown in FIG. It is a characteristic view which shows the charging / discharging characteristic of the all-solid-state battery which shows a part in FIG.1 (d). It is a characteristic view which shows the charging / discharging cycle dependence of the discharge capacity of the all-solid-state battery shown in FIG.1 (d). It is a characteristic diagram showing the XRD pattern of the LiCoO ₂ film by the manufacturing method Examples 1-4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Metal plate, 102 ... Positive electrode, 103 ... Solid electrolyte layer, 104 ... Negative electrode.

Claims (4)

A step of forming a solid electrolyte layer through which lithium ions are conducted; and
A step of forming a solid negative electrode on which accumulation and release of lithium ions are formed on one surface of the electrolyte layer;
A plasma composed of an inert gas and an oxygen gas supplied at a predetermined composition ratio is generated, and a high frequency is applied to a target composed of an oxide containing at least lithium, and particles generated from the plasma collide with the target. Causing a sputtering phenomenon, and depositing a material constituting the target, whereby a solid positive electrode composed of an oxide containing at least lithium is formed on one surface of the electrolyte layer; and Comprising at least
The plasma, Ri Oh an electron cyclotron resonance plasma kinetic energy provided by the divergent magnetic field is generated by electron cyclotron resonance,
The method of manufacturing a lithium secondary battery, wherein the positive electrode is made of Li _1-x MO ₂ (0 ≦ x <1) in which M is at least one of Co, Ni, Fe, and Mn. . Oite the manufacture how the lithium secondary battery of claim 1 Symbol placement,
The method for producing a lithium secondary battery, wherein the high-frequency power and the microwave power applied to generate the plasma are within a range in which all atoms constituting the target are sputtered. . In the manufacturing method of the lithium secondary battery of Claim 1 or 2 ,
The composition ratio of the oxygen gas is
The lithium particles sputtered from the target are in a range in which unnecessary side reactions with oxygen are suppressed before reaching the surface to be deposited. A method for manufacturing a secondary battery. Lithium secondary batteries, characterized by being manufactured by the manufacturing method of a lithium secondary battery according to any one of claims 1-3.

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