Lithium metal negative electrode, method for manufacturing same, and secondary battery

Abstract

Provided is a lithium metal negative electrode having enhanced lithium-ion conductivity and low internal resistance in a battery. The lithium metal negative electrode comprises a first solid electrolyte layer containing LLZO formed on lithium metal, and a second solid electrolyte layer containing LATP formed on the first solid electrolyte layer.

Description

Lithium metallic anode and method for manufacturing the same, and secondary battery

[0001] This invention relates to a metallic lithium anode, a method for manufacturing the same, and a secondary battery.

[0002] Secondary batteries using metallic lithium as electrodes are widely used industrially, and efforts are being made to improve their performance. Because metallic lithium is highly reactive, it is necessary to protect the lithium surface with another substance in order to use it as a stable electrode.

[0003] Generally, materials that do not increase the internal resistance of the battery are preferred as materials for forming the layer on which metallic lithium is coated. For example, Patent Document 1 discloses a lithium electrode in which an aluminum oxide layer and a carbon layer are laminated on a metallic lithium layer, and a lithium secondary battery containing the same.

[0004] However, aluminum oxide layers have low lithium-ion conductivity, which leads to a problem of increased internal resistance in the battery. Furthermore, increasing the number of layers, such as by laminating a carbon layer on top of the aluminum oxide layer, increases the number of interfaces, and impurities introduced into these interfaces may increase internal resistance. Higher internal resistance in the battery can lead to increased heat generation during fast charging. In addition, reactions with impurities during charging and discharging may progress, potentially degrading cycle performance.

[0005] Special Publication 2020-511752

[0006] This invention was made in view of solving the above-mentioned problems, and aims to provide a metallic lithium anode that enhances lithium ion conductivity and lowers the internal resistance of the battery. It also aims to provide a method for manufacturing a metallic lithium anode that prevents impurities from being mixed into the layer interface when stacked with metallic lithium.

[0007] As a result of diligent research, the inventors have confirmed that a metallic lithium anode, in which metallic lithium, a first solid electrolyte layer containing LLZO, and a second solid electrolyte layer containing LATP are stacked in this order, can stably exist in air. Using this metallic lithium anode makes it possible to manufacture batteries with low internal resistance. Furthermore, they have discovered that by using an inductively coupled plasma antenna, plasma treatment can be performed separately from the sputtering film deposition process of the first and second solid electrolyte layers, thus completing the present invention. That is, the present invention includes the following embodiments.

[0008] Item 1. A metallic lithium anode comprising: a first solid electrolyte layer containing LLZO formed on metallic lithium; and a second solid electrolyte layer containing LATP formed on the first solid electrolyte layer. Item 2. The metallic lithium anode according to Item 1, wherein the thickness of the second solid electrolyte layer is 5 nm to 80 nm. Item 3. The metallic lithium anode according to Item 1 or 2, wherein the thickness of the first solid electrolyte layer is 1 nm to 20 nm. Item 4. A method for manufacturing a metallic lithium anode according to any one of Items 1 to 3, wherein the first solid electrolyte layer and the second solid electrolyte layer are formed by a sputtering process using inductively coupled plasma. Item 5. The method for manufacturing a metallic lithium anode according to Item 4, further comprising a surface modification step using inductively coupled plasma before the sputtering step for forming the first solid electrolyte layer and / or the second solid electrolyte layer. Item 6. The method for manufacturing a metallic lithium anode according to item 5, wherein the surface modification step using inductively coupled plasma prior to the sputtering step for forming the first solid electrolyte layer is performed using a gas other than oxygen gas. Item 7. The method for manufacturing a metallic lithium anode according to item 6, wherein the gas other than oxygen is the same gas used in the sputtering step for forming the first solid electrolyte layer. Item 8. A secondary battery comprising a metallic lithium anode, the anode comprising: a first solid electrolyte layer containing LLZO formed on metallic lithium; and a second solid electrolyte layer containing LATP formed on the first solid electrolyte layer.

[0009] The lithium metallic anode of the present invention has a layer containing LLZO with a wide potential window that suppresses reaction with highly reducible lithium metallic, thereby suppressing the formation of a high-resistance interfacial reaction layer. Furthermore, since the layer containing LLZO and LATP is a solid electrolyte that conducts lithium ions, its internal resistance can be reduced. In addition, by protecting LLZO with LATP, a highly stable anode in air can be obtained, making it suitable for mass production of anodes. According to the manufacturing method of the lithium metallic anode of the present invention, by using an inductively coupled plasma antenna, bias application to the target can be started while the inductively coupled plasma is lit when depositing a film on the lithium metallic surface with a different material. Therefore, continuous processing becomes possible, and a cleaner and higher-quality layer interface can be formed. As a result, the internal resistance of the lithium metallic anode can be reduced.

[0010] (A) A diagram showing the metallic lithium anode 100 of the present invention. (B) A diagram showing the metallic lithium anode 110 of the present invention. A diagram showing the schematic configuration of the sputtering apparatus 1 used when manufacturing the metallic lithium anode 100 or 110 of the present invention. A diagram showing an example of the process in the manufacturing method of the metallic lithium anode 110 of the present invention. A diagram showing the surface state when LLZO and LATP deposited on a Si substrate are stored in the atmosphere.

[0011] The present invention will be described in detail below.

[0012] In this specification, "contains" and "include" are concepts that encompass all of the following: "comprise," "consist essentially of," and "consist of."

[0013] In this specification, when a numerical range is indicated as "A to B", the numerical range means "greater than or equal to A and less than or equal to B".

[0014] 1. Metallic Lithium Anode The metallic lithium anode of the present invention comprises a first solid electrolyte layer containing LLZO formed on metallic lithium, and a second solid electrolyte layer containing LATP formed on the first solid electrolyte layer.

[0015] The metallic lithium anode of the present invention will be described with reference to the figures. Figure 1(A) is a diagram showing the metallic lithium anode 100 (structural example 1) of the present invention. Figure 1(B) is a diagram showing the metallic lithium anode 110 (structural example 2) of the present invention. In Figure 1(A), the metallic lithium anode 100 of the present invention comprises metallic lithium 101, a first solid electrolyte layer 102, and a second solid electrolyte layer 103 in that order. In Figure 1(B), the metallic lithium anode 110 of the present invention comprises a substrate 104, metallic lithium 101, a first solid electrolyte layer 102, and a second solid electrolyte layer 103 in that order.

[0016] This invention uses metallic lithium 101 as the negative electrode. By using metallic lithium, which has the lowest potential among all elements, as the negative electrode, the energy density can be improved. However, metallic lithium is highly reducing and reacts immediately with many compounds such as nitrogen, oxygen, water, or carbon dioxide in the electrolyte and atmosphere, producing impurities and forming a high-resistance interfacial reaction layer (SEI) on the metallic lithium surface. Therefore, metallic lithium alone cannot be used as an electrode. Thus, it is necessary to coat metallic lithium 101 with some kind of coating layer. In the metallic lithium negative electrode of this invention, the first solid electrolyte layer 102 containing LLZO, which has a wide potential window, suppresses the reaction with the highly reducing metallic lithium 101, thereby suppressing the formation of a high-resistance interfacial reaction layer. Furthermore, since the first solid electrolyte layer 102 containing LLZO and the second solid electrolyte layer 103 containing LATP are solid electrolytes that conduct lithium ions, the internal resistance can be reduced. Moreover, since the metallic lithium negative electrode of this invention protects LLZO with LATP, it is possible to obtain a negative electrode with high stability in the atmosphere and suppressed changes over time, making it suitable for mass production of negative electrodes.

[0017] In the lithium metallic anode 100 (Structural Example 1) and lithium metallic anode 110 (Structural Example 2) of the present invention, the lithium metallic 101 may be in the form of a foil (Figure 1(A)), or it may be in the form of a film deposited on a substrate 104 (Figure 1(B)). Methods for depositing the lithium metallic film on the substrate include, for example, vapor deposition, but are not limited to this and any other film deposition method can be used. The substrate can be an organic film or a metal for bipolar electrodes that has low reactivity with lithium. Examples of such substrates include copper and stainless steel.

[0018] In this invention, a solid electrolyte is used as the electrolyte for the negative electrode. A solid electrolyte is an ionic conductor, not an electron conductor. By using a solid electrolyte, the growth of lithium dendrites, which cause short circuits, is suppressed, allowing metallic lithium to be used as the negative electrode material. Furthermore, when a solid electrolyte is used, leakage and ignition are suppressed compared to conventional lithium-ion batteries that use flammable solvents as electrolytes, resulting in higher safety. In this specification, a layer on which a solid electrolyte film has been deposited is referred to as a solid electrolyte layer (or "solid electrolyte film"). Generally, solid electrolytes are known to have lower ionic conductivity compared to conventional liquid electrolytes. However, LLZO and LATP used in the metallic lithium negative electrodes 100 and 110 of this invention have relatively high lithium ion conductivity among solid electrolytes, and by coating metallic lithium 101 with these, the interfacial resistance between metallic lithium and the electrolyte can be lowered. Thus, because the metallic lithium negative electrodes 100 and 110 according to the present invention have low interfacial resistance, using the metallic lithium negative electrodes according to this invention improves the battery's cycle performance, which is advantageous. In other words, the metallic lithium anode of the present invention can be suitably used as the anode of a lithium-ion secondary battery.

[0019] LATP (lithium aluminum titanium phosphate) has the chemical formula Li 1+x Al x Ti 2-x An oxide represented by (PO4)3, preferably Li 1.3 Al 0.3 Ti 1.7 The composition ratio is represented by (PO4)3.

[0020] LLZO (lithium lanthanum zirconate) has the chemical formula Li7La3Zr2O 12 It is an oxide represented by [formula]. When an LLZO layer is fabricated by film deposition, amorphous regions are also formed, so a compositional deviation of about 20% from the stoichiometric ratio is acceptable for each element.

[0021] Because LLZO has a wide potential window (low reactivity with metallic lithium), coating metallic lithium 101 with a first solid electrolyte layer 102 containing LLZO suppresses the reaction between the electrolyte and metallic lithium, thereby suppressing the formation of an interfacial reaction layer. Therefore, LLZO is suitable as the first layer for coating metallic lithium. Using LLZO as the metallic lithium anode is advantageous because it suppresses the formation of an interfacial reaction layer, thereby reducing the internal resistance of the battery and further improving the battery's cycle performance.

[0022] LLZO readily reacts with moisture and carbon dioxide. Therefore, when stored in the atmosphere, it forms lithium carbonate near the surface of the LLZO, causing deterioration and a change in surface condition over time. A negative electrode with a deteriorated surface condition increases internal resistance and is therefore unsuitable for use as an electrode. On the other hand, LATP has higher stability in the atmosphere than LLZO, and its surface condition does not change easily over time. If the first solid electrolyte layer 102 containing LLZO is coated with a second solid electrolyte layer 103 containing LATP, the surface condition of the negative electrode does not change over time, and the negative electrode can be stored stably. Therefore, the metallic lithium negative electrodes 100 and 110 of the present invention are advantageous because they can be stored while maintaining their surface condition, for example, during mass production of electrodes where the time until the next cycle is not constant for each negative electrode. In other words, using a negative electrode with LLZO coated with LATP can improve the yield of battery manufacturing.

[0023] In the present invention, the first solid electrolyte layer 102 preferably has a thickness of 1 nm to 20 nm. Furthermore, the second solid electrolyte layer 103 preferably has a thickness of 5 nm to 80 nm. By setting the lower limit of the solid electrolyte layer thickness within the above range, dendrite growth of the metallic lithium anode is suppressed, making short circuits between the positive and negative electrodes less likely and improving cycle characteristics. On the other hand, by setting the upper limit of the solid electrolyte layer thickness within the above range, the internal resistance of the battery becomes lower. Therefore, it is preferable that the thickness of the solid electrolyte layer be within an appropriate range.

[0024] 2. Method for Manufacturing a Metallic Lithium Anode The method for manufacturing a metallic lithium anode of the present invention includes a step in which a first solid electrolyte layer and a second solid electrolyte layer are formed by a sputtering process using inductively coupled plasma. Normally, a certain thickness is required for the anode of a battery, but the sputtering process, which is characterized by thin-film molding, is not used in the manufacture of the anode. According to the method for manufacturing anode of the present invention, a high-density plasma can be generated. As a result, the deposition rate of the dielectric (an ion conductor but not an electron conductor) can be increased, making it possible to manufacture anodes using sputtering.

[0025] 2.1 Configuration of the Sputtering Apparatus The method for manufacturing the metallic lithium anode of the present invention will be explained with reference to the figures. Figure 2 is a diagram showing the schematic configuration of a sputtering apparatus 1 used when manufacturing the metallic lithium anode 100 or 110 of the present invention. In Figure 2, the sputtering apparatus 1 includes a plasma chamber 20. Inside the plasma chamber 20, the sputtering apparatus 1 includes a sputtering target 10, a backing plate 31, a stage 41, and a holder 42 for holding the workpiece W on which film formation is to be performed. Furthermore, the sputtering apparatus 1 includes a plasma generation mechanism 30 including the backing plate 31 and a gas line 61.

[0026] The gas line 61 introduces the required gas into the plasma chamber 20. In the present invention, the gas line 61 supplies plasma raw material gas (e.g., argon gas and / or oxygen gas) when sputtering film deposition is performed.

[0027] The plasma chamber 20, which also serves as a vacuum vessel, has its internal space evacuated by an exhaust device (not shown) and controlled to the required vacuum level. The vacuum level used for sputtering film deposition is selected from a range that facilitates the generation of inductively coupled plasma (ICP), and is typically around 0.1 Pa to 10 Pa. A window section 21 is provided in a part of the wall surface of the plasma chamber 20.

[0028] A holder 42 for holding the workpiece W is mounted on or held on the stage 41. The stage 41 may be grounded, or it may be configured to have a bias voltage applied to it.

[0029] Typically, the sputtering apparatus 1 is configured such that the sputtering target 10, held on the backing plate 31, is positioned above the workpiece W on the stage 41, and the main surfaces of the backing plate 31 and the stage 41 facing inward into the plasma chamber 20 are horizontal.

[0030] However, in the manufacturing method of the present invention, the arrangement of each part of the sputtering apparatus 1 is not necessarily limited to such cases. The distance between the workpiece W and the sputtering target 10 is preferably about 50 to 300 mm.

[0031] The plasma generation mechanism 30 is a mechanism that generates magnetron sputtering on the sputtering target 10. The plasma generation mechanism 30 includes a backing plate 31, a housing 32, a refrigerant path 33, a magnet 34, an insulating flange 35, an anode 36, and a power supply 39 for the target.

[0032] A high-frequency voltage is applied to the sputtering target 10 from the target power supply 39 via the housing 32 and backing plate 31, causing the plasma source gas supplied from the gas line 61 to become plasma inside the plasma chamber 20. The sputtering target 10 is then sputtered by the generated plasma, resulting in film formation on the surface of the workpiece W. The frequency of the high-frequency power supplied by the target power supply 39 is generally 13.56 MHz, but is not limited to this.

[0033] The antenna 51 is arranged in parallel along a window portion 21 which is airtightly provided on the side wall of the plasma chamber 20 outside the plasma chamber 20. The window portion 21 is composed of a plate-shaped member made of an electromagnetic wave transmitting material that transmits the electromagnetic wave generated by the antenna 51.

[0034] When a high-frequency current is introduced from the antenna power supply 59 into the antenna 51, an electromagnetic wave is generated from the antenna 51. Then, an induced electric field is generated in the plasma chamber 20, and an inductively coupled plasma (ICP) is generated. That is, the antenna 51 is an ICP assist antenna that assists in the generation of plasma in the plasma chamber 20. The frequency of the high-frequency power supplied from the antenna power supply 59 is generally 13.56 MHz, but it is not limited to this.

[0035] 2.2 Sputtering method Hereinafter, a method of forming a film of LLZO or LATP on the surface of the workpiece W by the sputtering apparatus 1 to which the sputtering target 10 is applied will be described.

[0036] A holder 42 on which a substrate as the workpiece W is mounted is placed on the stage 41, and the plasma chamber 20 is evacuated. Next, argon gas and oxygen gas as plasma source gases are supplied from the gas line 61. Next, the exhaust device is controlled to maintain the inside of the plasma chamber 20 at a required degree of vacuum. Next, the plasma generation mechanism 30 and the ICP assist mechanism (antenna 51 and antenna power supply 59) are operated to generate plasma in the plasma chamber 20.

[0037] The generated plasma is plasma using an inert gas, such as argon plasma or a mixed plasma of oxygen and argon. Mainly argon ions and the like in the plasma collide with the surface of the sputtering target 10, and LATP or LLZO is sputtered from the sputtering target 10 and adheres to the surface of the opposing workpiece W, forming a film of LATP or LLZO.

[0038] In the sputtering apparatus 1 used to manufacture the metallic lithium anode 100 or 110 of the present invention, plasma is generated by an antenna 51 separately from the plasma generation mechanism 30 used when sputtering the sputtering target 10. By introducing a high-frequency current from the antenna power supply 59 to the antenna 51, plasma generation and plasma processing by the antenna 51 are possible without applying a high-frequency voltage to the sputtering target 10. By switching the bias application to the sputtering target 10, it is possible to light only the inductively coupled plasma or sputter the sputtering target 10, thus enabling the application of a high-frequency voltage to the sputtering target 10 and the surface modification process to be performed continuously. According to the manufacturing method of the metallic lithium anode of the present invention, it is possible to perform inductively coupled plasma processing immediately before target application, which enables the formation of a higher quality interface. As a result, the internal resistance of the battery can be reduced. In addition, since the target application and the surface modification process can be processed continuously, the cycle time can be shortened, which is advantageous when mass-producing electrodes.

[0039] Figure 3 shows an example of the manufacturing process for the metallic lithium anode 110 of the present invention. In Figure 3, the metallic lithium anode 110 of the present invention is manufactured by (A) an inductively coupled plasma surface modification process before the sputtering process for depositing the first solid electrolyte layer 102 and / or the second solid electrolyte layer 103, (B) a sputtering film deposition process for the first solid electrolyte layer 102, and (C) a sputtering film deposition process for the second solid electrolyte layer 103. The above processes (A) to (C) will be described in order below.

[0040] The manufacturing method of the metallic lithium negative electrode of the present invention preferably includes a surface modification step using inductively coupled plasma before the sputtering step of forming the first solid electrolyte layer 102 and / or the second solid electrolyte layer 103 (FIG. 3(A)). FIG. 3(A) is a diagram showing metallic lithium 101 deposited on a substrate 104 and its surface 101a. In the surface modification step, the surface 101a of the metallic lithium 101 is irradiated with plasma. By performing a surface modification treatment using inductively coupled plasma before the sputtering step of forming the solid electrolyte layer, a better-quality interface can be formed. As a result, an increase in the internal resistance of the battery and a deterioration in the cycle characteristics of the battery can be further suppressed.

[0041] The surface modification step in the present invention is a step of removing impurities such as organic substances and moisture on the surface of the metallic lithium 101 and the surface of the first solid electrolyte layer 102 by inductively coupled plasma. By removing the surface impurities immediately before applying a high-frequency voltage to the sputtering target 10, a clean and high-quality interface can be formed, and an increase in the internal resistance can be suppressed. As a result, during charge and discharge, the reaction between the electrode and the solid electrolyte and the impurities is suppressed, and a deterioration in the cycle characteristics of the battery can be suppressed. In particular, when a plurality of coating layers are laminated on metallic lithium, gas replacement, plasma extinguishing, etc. may occur, and when changing the layer structure, impurities may adhere to the surface of the negative electrode. Adhesion of impurities is a factor that increases the internal resistance of the negative electrode, and generally, the internal resistance increases as the number of layers (interfaces) increases. By using the manufacturing method of the metallic lithium negative electrode of the present invention including a surface modification step using inductively coupled plasma before the sputtering step of forming the first solid electrolyte layer 102 and / or the second solid electrolyte layer 103, even when manufacturing a negative electrode having a plurality of layers (having a plurality of interfaces), the impurities on the surface of the negative electrode can be removed before forming the sputtering target, so that an increase in the internal resistance accompanying an increase in the interface can be suppressed, which is advantageous.

[0042] In the present invention, the inductively coupled plasma surface modification step prior to the sputtering step for depositing the first solid electrolyte layer 102 is preferably performed using a gas other than oxygen gas. The gas other than oxygen gas is not particularly limited as long as it is an inert gas, but argon gas is an example. Metallic lithium is highly reactive with oxygen, and when the surface of metallic lithium is exposed to oxygen plasma, an interfacial reaction layer of oxygen and lithium is formed on the surface of the metallic lithium. This interfacial reaction layer increases the internal resistance of the battery. By using a gas other than oxygen gas in the inductively coupled plasma surface modification step prior to the sputtering step for depositing the first solid electrolyte layer 102, the formation of the above-mentioned oxygen-lithium interfacial reaction layer can be further suppressed, and the internal resistance of the battery can be further suppressed.

[0043] Figure 3(B) shows the state in which the first solid electrolyte layer 102 is sputtered onto the metallic lithium 101. The gas used in the sputtering process for forming the first solid electrolyte layer 102 of the present invention is not particularly limited as long as it is a gas containing an inert gas that can efficiently sputter the target. It is preferable to use a gas other than oxygen gas. For example, argon gas can be used as such a gas.

[0044] In the present invention, it is preferable that the gas used in the inductively coupled plasma surface modification step prior to the sputtering step for depositing the first solid electrolyte layer 102 is the same gas used in the sputtering step for depositing the first solid electrolyte layer 102. Using the same gas as the sputtering step for depositing the first solid electrolyte layer 102 as the gas used in the surface modification step eliminates the need to replace the gas in the deposition apparatus after the surface modification step. This is advantageous because it allows deposition to begin simply by applying a bias to the target while maintaining a clean surface. The elimination of the need for gas replacement contributes to the efficient mass production of the negative electrode according to the present invention.

[0045] FIG. 3(C) is a diagram showing a state where the second solid electrolyte layer 103 is sputtered on the first solid electrolyte layer 102. In the present invention, as the gas used in the sputtering process for forming the second solid electrolyte layer 103, any type of gas can be used as long as it is an inert gas, but a gas containing a certain amount of oxygen gas is preferable. The content of oxygen gas in the entire gas used in the sputtering process is preferably 5% or more. Also, the upper limit of the content of oxygen gas in the entire gas used in the sputtering process is not particularly limited, but is preferably 50% or less from the viewpoint of further improving the plasma density and film formation rate. LATP contained in the second solid electrolyte layer 103 according to the present invention is an oxide. Oxygen, which is a light element, is easily ejected from the target surface, and there is a risk of film quality deterioration due to oxygen depletion of the target. Therefore, it is preferable to supplement oxygen to stabilize the composition of the target surface. In the present invention, by using a gas containing oxygen gas for film formation, oxygen depletion of the target can be prevented. By preventing oxygen depletion of the target, an aluminum oxide layer (layer containing LATP) having sufficient electron insulation can be formed. Therefore, by using the method for manufacturing a negative electrode of the present invention, the oxygen gas used in the sputtering process for forming the second solid electrolyte layer 103 can promote the oxidation of the second solid electrolyte membrane, and thus the film quality is also improved.

[0046] In the present invention, the sputtering target 10 when forming LLZO has the chemical formula Li 1+x Al x Ti 2-x (PO4)3, preferably Li 1.3 Al 0.3 Ti 1.7 (PO4)3 is preferably an oxide having a composition ratio represented by. Also, the target when forming LATP is an oxide represented by the chemical formula Li7La3Zr2O 12 and in each element, a composition deviation of about 20% from the stoichiometric ratio may be present.

[0047] 3. Secondary Battery The secondary battery of the present invention is equipped with a metallic lithium anode according to the present invention. A lithium-ion secondary battery is preferred as the secondary battery used. The metallic lithium anode according to the present invention includes, for example, a first solid electrolyte layer 102 containing LLZO formed on metallic lithium 101, and a second solid electrolyte layer 103 containing LATP formed on the first solid electrolyte layer 102, as shown in Figure 3(C). As described above, the secondary battery of the present invention has a first solid electrolyte layer 102 containing LLZO with a wide potential window, so the formation of an interfacial reaction layer with high resistance can be suppressed. Furthermore, since the first solid electrolyte layer 102 is covered with a second solid electrolyte layer 103 containing LATP which is stable in air, a anode with a stable surface state can be provided. Moreover, since these layers are formed by a sputtering process using inductively coupled plasma, a clean interface is maintained even if the number of layers increases. Therefore, the secondary battery equipped with the metallic lithium anode according to the present invention has low internal resistance. Because the internal resistance is low, it is less likely to generate heat during fast charging. Furthermore, by using metallic lithium for the negative electrode of the battery, the energy density of the negative electrode is improved, making it possible to provide a secondary battery with good cycle characteristics and high energy density.

[0048] The positive electrode material of the secondary battery of the present invention is not particularly limited, and any material can be used. High-potential metal oxides are preferably used as the positive electrode material, and examples include lithium cobalt oxide (LiCoO2) and ternary materials (NCM). By using a high-potential metal oxide as the positive electrode, the energy density can be further improved.

[0049] The present invention is further illustrated by the following embodiments, which should not be construed as further limitations.

[0050] Using the sputtering apparatus shown in Figure 2, a voltage was applied to the antenna power supply 59 to generate argon gas plasma from the antenna 51. Using the argon gas plasma, organic matter and moisture were removed from the surface 101a of the metallic lithium 101 deposited on the substrate 104 (surface modification process using plasma). With the argon gas plasma still running, a negative voltage was applied to the oxide target through the target power supply 39 to deposit a first solid electrolyte layer 102 containing LLZO (Comparative Example 1). Furthermore, a mixed gas containing 95% argon gas and 5% oxygen gas was supplied, and a negative voltage was applied to the oxide target to deposit a second solid electrolyte layer 103 containing LATP (Example 1). Example 1 and Comparative Example 1 were left to stand for about 3 days in an atmosphere of about 25°C with a dew point of about -80°C, and the composition of the sample surface was analyzed by XPS. The results are shown in Figure 4.

[0051] Comparing Comparative Example 1 (only the layer containing LLZO) with Example 1 (LLZO coated with LATP), it was found that the surface of Example 1 had less carbon, presumably due to lithium carbonate (Li2CO3), and was chemically stable. On the other hand, the surface of Comparative Example 1 formed lithium carbonate, suggesting that the surface state had been altered. Thus, it is clear that a negative electrode with an altered surface state is unsuitable as an electrode. As described above, the negative electrode of the present invention has high stability in the atmosphere, and it is considered that, according to the present invention, a negative electrode that does not change easily over time even when exposed to the atmosphere for a long period of time can be obtained.

[0052] 1 Sputtering apparatus 10 Sputtering target 20 Plasma chamber 30 Plasma generation mechanism 31 Backing plate 32 Housing 33 Coolant path 34 Magnet 35 Insulating flange 36 Anode 39 Power supply for target 41 Stage 42 Holder 51 Antenna 59 Power supply for antenna 61 Gas line W Workpiece (substrate) 100 Metallic lithium anode (Structural example 1) 101 Metallic lithium 101a Surface of metallic lithium 102 First solid electrolyte layer (LLZO) 103 Second solid electrolyte layer (LATP) 104 Substrate 110 Metallic lithium anode (Structural example 2)

Claims

1. A metallic lithium anode comprising: a first solid electrolyte layer containing LLZO formed on metallic lithium; and a second solid electrolyte layer containing LATP formed on the first solid electrolyte layer.

2. The metallic lithium anode according to claim 1, wherein the thickness of the second solid electrolyte layer is 5 nm to 80 nm.

3. The metallic lithium anode according to claim 1, wherein the thickness of the first solid electrolyte layer is 1 nm to 20 nm.

4. A method for manufacturing a metallic lithium anode according to claim 1, wherein the first solid electrolyte layer and the second solid electrolyte layer are formed by a sputtering process using inductively coupled plasma.

5. A method for producing a metallic lithium anode according to claim 4, comprising a surface modification step using inductively coupled plasma prior to a sputtering step for forming the first solid electrolyte layer and / or the second solid electrolyte layer.

6. The method for manufacturing a metallic lithium anode according to claim 5, wherein the inductively coupled plasma surface modification step prior to the sputtering step for forming the first solid electrolyte layer is performed using a gas other than oxygen gas.

7. The method for manufacturing a metallic lithium anode according to claim 6, wherein the gas other than the oxygen gas is the same gas used in the sputtering step for forming the first solid electrolyte layer.

8. A secondary battery comprising a metallic lithium anode, the first solid electrolyte layer containing LLZO formed on metallic lithium, and a second solid electrolyte layer containing LATP formed on the first solid electrolyte layer.

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