Manufacturing method of lithium ion storage element

Abstract

To provide a method for efficiently producing a lithium ion storage element in which the deposition of metallic lithium on a surface of a negative electrode is suppressed, even when an electrode body is large.SOLUTION: The method for producing the lithium ion storage element includes: deaerating the inside of an element container in which the electrode body having a positive electrode and the negative electrode is housed and a liquid injection port is provided; and injecting a nonaqueous electrolytic solution and carbon dioxide from a container for liquid injection, which is filled with the nonaqueous electrolytic solution and the carbon dioxide, into the deaerated element container through the liquid injection port.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a lithium ion storage element. [Background technology]

[0002] Due to their high energy density, lithium ion storage elements such as lithium ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. In addition to lithium ion secondary batteries, lithium ion storage elements such as lithium ion capacitors are also widely used.

[0003] Generally, a lithium ion storage element is manufactured by placing an electrode assembly, in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween, in a container, and then injecting a non-aqueous electrolyte into the container (see Patent Document 1). This results in a lithium ion storage element in which the electrode assembly is impregnated with the non-aqueous electrolyte. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-110399 Summary of the Invention [Problem to be solved by the invention]

[0005] In the manufacture of lithium-ion storage devices, the nonaqueous electrolyte may be efficiently injected into the device container and impregnated into the electrode body by reducing the pressure inside the device container before the injection. However, particularly when the electrode body is large, the nonaqueous electrolyte may not fully penetrate the center of the electrode body even after the pressure inside the device container is reduced, leaving air or other substances inside the electrode body as bubbles (gas pockets). When a lithium-ion storage device is used with bubbles remaining inside the electrode body, charge / discharge reactions do not occur in the positive and negative electrodes facing the bubbles, and current concentrates around the bubbles, leading to the deposition of metallic lithium on the negative electrode surface in this peripheral area. The deposition of metallic lithium is undesirable because it can cause a decrease in charge / discharge performance. Therefore, for example, after the injection of the nonaqueous electrolyte, it may be considered to leave the device for a sufficient period of time so that the nonaqueous electrolyte penetrates into the center of the electrode body, but this is inefficient and reduces productivity.

[0006] The present invention has been made based on the above circumstances, and its object is to provide a method for efficiently manufacturing a lithium ion storage element in which deposition of metallic lithium is suppressed on the negative electrode surface even when the electrode body is large. [Means for solving the problem]

[0007] A method for manufacturing a lithium ion storage element according to one aspect of the present invention includes degassing the inside of an element container that houses an electrode body having a positive electrode and a negative electrode and that is provided with a liquid filling port, and injecting the nonaqueous electrolyte solution and carbon dioxide from a liquid filling container filled with the nonaqueous electrolyte solution and carbon dioxide into the degassed inside of the element container through the liquid filling port. [Effects of the Invention]

[0008] According to one aspect of the present invention, it is possible to provide a method for efficiently manufacturing a lithium ion storage element in which deposition of metallic lithium on the negative electrode surface is suppressed even when the electrode body is large. [Brief explanation of the drawings]

[0009] [Figure 1]FIG. 1 is a flow chart showing one embodiment of a method for manufacturing a lithium ion storage element. [Figure 2] FIG. 2 is an explanatory diagram of one embodiment of a method for manufacturing a lithium ion storage element. [Figure 3] FIG. 3 is an explanatory diagram of another embodiment of the method for manufacturing a lithium ion storage element. DETAILED DESCRIPTION OF THE INVENTION

[0010] First, an outline of the method for manufacturing the lithium ion storage element disclosed in this specification will be described.

[0011] A method for manufacturing a lithium ion storage element according to one aspect of the present invention includes degassing the inside of an element container that houses an electrode body having a positive electrode and a negative electrode and that is provided with a liquid filling port, and injecting the nonaqueous electrolyte solution and carbon dioxide from a liquid filling container filled with the nonaqueous electrolyte solution and carbon dioxide into the degassed inside of the element container through the liquid filling port.

[0012] According to this manufacturing method for a lithium-ion storage element, it is possible to efficiently manufacture a lithium-ion storage element in which deposition of metallic lithium on the negative electrode surface is suppressed, even when the electrode body is large. In other words, according to this manufacturing method for a lithium-ion storage element, it is possible to efficiently manufacture a lithium-ion storage element in which deposition of metallic lithium on the negative electrode surface is suppressed, regardless of whether the electrode body is small or large. The reason why this manufacturing method for a lithium-ion storage element has such an effect is unclear, but the following reason is presumed. In this manufacturing method for a lithium-ion storage element, the nonaqueous electrolyte and carbon dioxide are injected from an injection container filled with the nonaqueous electrolyte and carbon dioxide into a degassed element container containing the electrode body. By doing so, even if carbon dioxide is injected into the element container together with the nonaqueous electrolyte, and air bubbles remain inside the electrode body after injection, most of the air bubbles remain as carbon dioxide bubbles. These carbon dioxide bubbles shrink, decrease, or disappear when the carbon dioxide reacts with lithium ions in the nonaqueous electrolyte during pre-charging, etc., as described below, to form lithium carbonate, which is then fixed to the negative electrode surface. This reaction is thought to proceed according to the following scheme in the presence of a small amount of water in the non-aqueous electrolyte: Although this reaction occurs in a non-aqueous electrolyte, carbon dioxide has high solubility in general non-aqueous electrolytes, and it is thought that the consumption of carbon dioxide in the non-aqueous electrolyte by this reaction promotes the dissolution of carbon dioxide present as bubbles into the non-aqueous electrolyte, causing the carbon dioxide bubbles to shrink, decrease, or disappear. Li + +2H2O → LiOH·H2O+H + LiOH+H2O+CO2→LiHCO3+H2O 2LiHCO3 → Li2CO3 + H2O + CO2 Therefore, in the lithium-ion storage element obtained by this manufacturing method for a lithium-ion storage element, it is presumed that bubbles are less likely to remain inside the electrode body, and charge / discharge reactions occur highly uniformly inside the electrode body, thereby suppressing the deposition of metallic lithium on the negative electrode surface. Furthermore, in this manufacturing method for a lithium-ion storage element, a nonaqueous electrolyte solution and carbon dioxide are injected into the element container using a liquid injection container filled with these, so that the nonaqueous electrolyte solution and carbon dioxide flow into the element container substantially simultaneously, and it is presumed that the carbon dioxide efficiently penetrates into the electrode body together with the nonaqueous electrolyte solution. Thus, according to this manufacturing method for a lithium-ion storage element, a lithium-ion storage element in which the deposition of metallic lithium on the negative electrode surface is suppressed can be efficiently manufactured, even when the electrode body is large, by using a relatively simple method of injecting the nonaqueous electrolyte solution and carbon dioxide into the element container using a liquid injection container filled with these.

[0013] In the "filling container filled with a non-aqueous electrolyte and carbon dioxide," the carbon dioxide is filled in the filling container as a gas, and part of the carbon dioxide may be dissolved in the non-aqueous electrolyte.

[0014] During the injection, it is preferable that the injection container is filled with the nonaqueous electrolyte and the carbon dioxide in amounts to be injected in a single operation. In this case, the injection amount of the nonaqueous electrolyte can be easily controlled, and particularly when injection is performed in multiple operations, each injection operation can be performed efficiently with an accurate amount.

[0015] Preferably, the method for manufacturing the lithium ion storage element further comprises replacing the gas inside the element container with carbon dioxide before the degassing. By previously replacing the gas inside the element container with carbon dioxide in this manner, it is possible to prevent bubbles other than carbon dioxide from remaining inside the electrode body when the nonaqueous electrolyte solution and carbon dioxide are injected.

[0016] Preferably, the method for producing a lithium ion storage element further comprises pre-charging after the above-mentioned injection. Pre-charging causes the carbon dioxide to react with the lithium ions in the non-aqueous electrolyte solution or the like to form lithium carbonate, as described above, and effectively reduces, decreases, or eliminates carbon dioxide bubbles, thereby more reliably producing a lithium ion storage element in which deposition of metallic lithium on the negative electrode surface is suppressed.

[0017] For example, even if pre-charging and leaving at a high temperature described below are not performed, carbon dioxide reacts with lithium ions in the non-aqueous electrolyte solution, etc., to form lithium carbonate during initial normal charge and discharge. Therefore, the effects of the present invention can be achieved even without pre-charging and leaving at a high temperature. However, pre-charging generates gas all at once, making it easier to discharge the gas, and leaving at a high temperature described below allows the generated gas to be completely absorbed by the negative electrode. Therefore, performing these steps is more preferable because it further suppresses the deposition of metallic lithium. Furthermore, "pre-charging" refers to preliminary charging performed after injection. Pre-charging does not have to be charging to a 100% charge rate, but may be partial charging below a 100% charge rate. The charge rate refers to the percentage of the amount of electricity to be charged relative to the charge capacity when the lithium-ion storage element is brought from a fully discharged state to a fully charged state.

[0018] In the manufacturing method of the lithium ion storage element, after the injection, it is preferable to store the element for a predetermined time in a low dew point environment and then perform the pre-charging. In this way, by storing the non-aqueous electrolyte and carbon dioxide for a predetermined time in a low dew point environment, the non-aqueous electrolyte is sufficiently impregnated into the electrode assembly. Therefore, by performing pre-charging after storing for a predetermined time, it is possible to reliably shrink, reduce, or eliminate air bubbles. Storage in an environment other than a low dew point environment may cause the non-aqueous electrolyte to absorb moisture, which may generate gas due to electrolysis of water during pre-charging, resulting in the non-aqueous electrolyte being ejected outside the element container. Such ejection of non-aqueous electrolyte outside the element container is undesirable because it may contaminate the manufacturing equipment, the lithium ion storage element, etc.

[0019] Note that a "low dew point environment" refers to an environment where the dew point is -30°C or lower.

[0020] In the method for manufacturing the lithium ion storage element, it is preferable to perform the combination of the degassing and the injection one or more times after the pre-charging. If the pre-charging is performed after the entire amount of nonaqueous electrolyte to be sealed in the element container is injected, the nonaqueous electrolyte is likely to spray out of the element container due to gas generation during the pre-charging. Therefore, by not injecting the entire amount of nonaqueous electrolyte to be sealed in the element container before the pre-charging and injecting the remaining nonaqueous electrolyte after the pre-charging, it is possible to prevent the nonaqueous electrolyte from spraying out of the element container during the pre-charging.

[0021] Preferably, the method for manufacturing the lithium ion storage element further comprises pressurizing the inside of the element container by further injecting carbon dioxide through the injection port between the above-mentioned injection and the above-mentioned pre-charging. By pressurizing the inside of the element container by further injecting carbon dioxide before the pre-charging in this way, the nonaqueous electrolyte is more thoroughly impregnated into the electrode body. Therefore, by performing this operation, not only are the bubbles present before the pre-charging reduced, but the pre-charging also promotes the production of lithium carbonate by the reaction of carbon dioxide with lithium ions in the nonaqueous electrolyte, etc., so that fewer bubbles remain inside the electrode body and a lithium ion storage element can be obtained in which the deposition of metallic lithium on the negative electrode surface is further suppressed.

[0022] Preferably, the method for manufacturing the lithium ion storage element further comprises, after the pre-charging, compressing the element container to a predetermined size, sealing the inlet with a plug in the compressed state of the element container, and welding the plug to the element container. By sealing the inlet in the compressed state of the element container in this way, a lithium ion storage element in which swelling is suppressed can be obtained.

[0023] The method for manufacturing the lithium ion storage element is to set the negative electrode potential to 100 mV vs. Li / Li by the pre-charging. + It is preferable to further include leaving the element container at a temperature of 35° C. or higher after the above-mentioned treatment. By carrying out such treatment, the production of lithium carbonate due to the reaction between carbon dioxide and lithium ions in the non-aqueous electrolyte solution or the like progresses, and the air bubbles remaining inside the electrode body are further reduced in size, decreased, or eliminated, so that the resulting lithium ion storage element has more suppressed deposition of metallic lithium on the negative electrode surface.

[0024] The electrode body is preferably a wound-type electrode body in which the positive electrode and the negative electrode are wound in a stacked state, and the length of the electrode body in the direction of the winding axis is 300 mm or more. In the case of such a wound-type electrode body that is long in the direction of the winding axis, it is generally difficult for the nonaqueous electrolyte to penetrate particularly to the center of the electrode body, and air bubbles tend to remain inside the electrode body. Therefore, when one embodiment of the present invention is applied to the production of a lithium ion storage device including such an electrode body, the effect of reducing the air bubbles remaining inside the electrode body and obtaining a lithium ion storage device in which precipitation of metallic lithium is suppressed is significantly achieved.

[0025] In the method for manufacturing a lithium ion storage element, the electrode body is preferably contained in the element container so that the surface of the element container provided with the inlet and the winding axis of the electrode body are parallel. When a wound electrode body is contained in the element container so that the surface of the element container provided with the inlet and the winding axis of the electrode body are parallel, air bubbles are usually particularly likely to remain inside the electrode body. Therefore, when one embodiment of the present invention is applied to manufacturing a lithium ion storage element having such a structure, the advantage of being able to reduce the amount of air bubbles remaining inside the electrode body and to obtain a lithium ion storage element in which precipitation of metallic lithium is suppressed is particularly pronounced.

[0026] Hereinafter, a method for manufacturing a lithium ion storage element according to one embodiment of the present invention and other embodiments will be described in detail. Note that the names of the components (elements) used in each embodiment may differ from the names of the components (elements) used in the background art.

[0027] <Method of manufacturing lithium-ion storage element> A method for manufacturing a lithium ion storage element according to one embodiment of the present invention includes the steps of: Replacing the gas inside the element container containing the electrode body with carbon dioxide (CO2) (CO2 replacement step S1); Degassing the inside of the element container (degassing step S2); Injecting a non-aqueous electrolyte solution and carbon dioxide into the degassed element container (injection step S3); Pressurizing the inside of the element container by further injecting carbon dioxide (pressurizing step S4); Pre-charging (pre-charging step S5), The inside of the element container is degassed again (degassing step S2'). Injecting the non-aqueous electrolyte and carbon dioxide into the degassed element container again (injection step S3'); Compressing the element container (compression step S6); The liquid inlet of the element container is sealed with a plug and the plug is welded (sealing step S7); The element container is left at a temperature of 35°C or higher (high temperature leaving step S8). (See Figure 1.) Note that any steps other than the degassing step S2 and the injection step S3 are optional. The order of the steps is preferably the above-mentioned order, but is not limited to the above order as long as the same effect is achieved. Furthermore, multiple steps may be performed simultaneously, or the same step may be performed multiple times. For example, the degassing step S2' and the injection step S3' may be performed two or more times. The method for manufacturing an energy storage device may further include steps other than the above-mentioned steps (such as a storage step and a cleaning step).

[0028] (Structure of electrode body and element container) First, the structures of the electrode assembly 1 and element container 2 used in this embodiment will be described with reference to Fig. 2. The electrode assembly 1 is a wound-type electrode assembly in which a strip-shaped positive electrode and a strip-shaped negative electrode are stacked together with a strip-shaped separator interposed therebetween and wound around a winding axis 5. The electrode assembly 1 has a flat shape with its thickness direction being perpendicular to the winding axis 5 (the Y direction in Fig. 2). In other words, the electrode assembly 1 is a flat wound-type electrode assembly.

[0029] The lower limit of the length of the electrode body 1 in the direction of the winding axis (X direction in FIG. 2 ) may be, for example, 100 mm or 200 mm, but may be preferably 300 mm, and more preferably 400 mm. By making the electrode body 1 long in the direction of the winding axis in this way, the energy density of the lithium ion storage element can be increased. On the other hand, if the electrode body 1 is long in the direction of the winding axis, it becomes difficult for the nonaqueous electrolyte to penetrate all the way to the center of the electrode body 1, and therefore, there is a great advantage to applying one embodiment of the present invention. The upper limit of the length of the electrode body 1 in the direction of the winding axis may be, for example, 4,000 mm, 2,000 mm, 1,500 mm, or 1,000 mm.

[0030] The thickness of the electrode body 1 (length in the Y direction in FIG. 2) is preferably 5 mm to 50 mm, and more preferably 10 mm to 30 mm. The height of the electrode body 1 (length in the Z direction in FIG. 2) is preferably 40 mm to 300 mm, and more preferably 80 mm to 200 mm.

[0031] The element container 2 has a square (rectangular) shape, and is provided with a liquid pouring port 3 on its top surface 4. There is no particular limitation on the number of liquid pouring ports 3, but in this embodiment, one liquid pouring port 3 is provided.

[0032] The size of the element container 2 is set appropriately in accordance with the size of the electrode assembly 1. For example, the length of the element container 2 (length in the X direction in FIG. 2) is preferably 100 mm or more and 3,000 mm or less, more preferably 200 mm or more and 2,000 mm or less, even more preferably 300 mm or more and 1,500 mm or less, and in some cases even more preferably 400 mm or more and 1,000 mm or less. The thickness of the element container 2 (length in the Y direction in FIG. 2) is preferably 5 mm or more and 50 mm or less, more preferably 10 mm or more and 30 mm or less. The height of the element container 2 (length in the Z direction in FIG. 2) is preferably 40 mm or more and 300 mm or less, more preferably 80 mm or more and 200 mm or less.

[0033] The material of the element container 2 is not particularly limited, and a resin container, a metal container, or the like can be used, but a metal container is preferable when sealing the liquid inlet 3 by welding, for example.

[0034] The electrode assembly 1 is housed in the element container 2 so that the surface of the element container 2 on which the liquid inlet 3 is provided (top surface 4 in FIG. 2) is parallel to the winding axis 5 of the electrode assembly 1. Although the external terminals for the positive and negative electrodes are not shown in FIG. 2, these terminals may be located at any position. For example, it is preferable that the positive and negative electrode terminals are provided on the side surfaces of the element container 2 (left and right surfaces in FIG. 2). The positive and negative electrode terminals may also be provided on the surface on which the liquid inlet 3 is provided (top surface 4 in FIG. 2).

[0035] The method for accommodating the electrode body 1 in the element container 2 is not particularly limited, and can be performed by a known method. For example, the electrode body 1 can be accommodated in an open-shaped element container 2 (element container body) that does not have a lid portion corresponding to the top surface 4, and then the opening is covered with a lid provided with a liquid inlet 3 corresponding to the top surface 4, and the lid and the element container body are welded together, for example. Furthermore, each step described below is usually performed in a state where the element container 2 is placed so that the top surface 4 provided with the liquid inlet 3 is located on the upper side.

[0036] The specific configurations of the positive electrode, negative electrode, and separator that constitute the electrode assembly 1, as well as the non-aqueous electrolyte solution, will be described in detail later.

[0037] (Injection device) Next, a liquid injection device 11 used in the manufacturing method of the lithium ion storage element of this embodiment will be described. The liquid injection device 11 mainly includes a liquid injection nozzle 12, an exhaust means 13, a liquid injection container 14, a non-aqueous electrolyte supply means 15, and a carbon dioxide supply means 16. The liquid injection nozzle 12 has a structure that allows it to be airtightly attached to the liquid injection port 3 of the element container 2. The exhaust means 13 evacuates the inside of the element container 2 while the liquid injection nozzle 12 is attached to the liquid injection port 3, and an exhaust valve 17 is provided between the exhaust means 13 and the liquid injection nozzle 12. The exhaust means 13 can be, for example, a pressure reduction pump. The liquid injection container 14 stores the non-aqueous electrolyte and carbon dioxide to be injected into the element container 2 through the liquid injection nozzle 12, and an injection valve 18 is provided between the liquid injection container 14 and the liquid injection nozzle 12. The nonaqueous electrolyte supply means 15 supplies the nonaqueous electrolyte to the injection container 14, and a nonaqueous electrolyte supply valve 19 is provided between the nonaqueous electrolyte supply means 15 and the injection container 14. The nonaqueous electrolyte supply means 15 can be, for example, a combination of a tank for storing the nonaqueous electrolyte and a pump connected to the tank. The carbon dioxide supply means 16 supplies carbon dioxide to the injection container 14, and a carbon dioxide supply valve 20 is provided between the carbon dioxide supply means 16 and the injection container 14. The carbon dioxide supply means 16 can be, for example, a cylinder for storing carbon dioxide.

[0038] 2 schematically shows a state in which the injection container 14 is filled with the non-aqueous electrolyte solution 21 and carbon dioxide 22 before the injection in the injection step S3. Each step will be described below in the order of one form in which the steps are basically carried out.

[0039] (CO2 replacement step S1) In the CO2 substitution step S1, the gas inside the element container 2, which houses the electrode assembly 1 and has the inlet 3, is replaced with carbon dioxide (CO2). From the CO2 substitution step S1 to the pressurization step S4, the injection nozzle 12 is airtightly attached to the inlet 3 of the element container 2. Then, with at least the injection valve 18 closed and the exhaust valve 17 open, the inside of the element container 2 is degassed by operating the exhaust means 13. At this time, it is preferable to degas the inside of the element container 2 until the pressure inside the element container 2 becomes 0.1 MPa or less, or even 0.05 MPa or less. Thereafter, the exhaust valve 17 is closed, and with the nonaqueous electrolyte supply valve 19 closed, the injection valve 18 and the carbon dioxide supply valve 20 are opened, thereby filling the inside of the element container 2 with carbon dioxide. By this operation, the gas inside the element container 2 can be replaced with carbon dioxide.

[0040] (Degassing process S2) In the degassing step S2, the injection valve 18 is closed, the exhaust valve 17 is opened, and the exhaust means 13 is operated to degas the inside of the element container 2 accommodating the electrode body 1. At this time, it is preferable to degas the inside of the element container 2 until the pressure therein becomes 0.1 MPa or less, and further 0.05 MPa or less.

[0041] (Injection process S3) In the injection step S3, first, the injection valve 18 is closed, the nonaqueous electrolyte supply valve 19 and the carbon dioxide supply valve 20 are opened, and the nonaqueous electrolyte 21 and the carbon dioxide 22 are filled into the injection container 14 by the nonaqueous electrolyte supply means 15 and the carbon dioxide supply means 16. At this time, it is preferable to adjust the amount of nonaqueous electrolyte 21 so that the injection container 14 is filled with the amounts of nonaqueous electrolyte 21 and carbon dioxide 22 to be injected in a single operation. For example, the carbon dioxide supply valve 20 is first opened to fill the injection container 14 with carbon dioxide 22, and then the nonaqueous electrolyte supply valve 19 is opened and a predetermined amount of nonaqueous electrolyte 21 is filled into the injection container 14 by the nonaqueous electrolyte supply means 15. Note that, because injection can be performed in multiple batches, the entire amount of nonaqueous electrolyte 21 to be ultimately injected into the element container 2 does not need to be filled into the injection container 14 at one time.

[0042] Next, by opening injection valve 18 while the valves other than injection valve 18 (exhaust valve 17, nonaqueous electrolyte supply valve 19, and carbon dioxide supply valve 20) are closed, nonaqueous electrolyte 21 and carbon dioxide 22 are injected from injection container 14, which is filled with nonaqueous electrolyte 21 and carbon dioxide 22, into the evacuated element container 2 through injection port 3. At this time, carbon dioxide supply valve 20 may be in an open state.

[0043] The amount of nonaqueous electrolyte injected into the element container 2 in this injection step S3 may be 100% by mass of the total amount of nonaqueous electrolyte finally injected into the element container 2, but is preferably 95% by mass or less, and more preferably 90% by mass or less. By not injecting the entire amount of nonaqueous electrolyte before pre-charging in this way, it is possible to prevent the nonaqueous electrolyte from spraying out of the element container during pre-charging. Meanwhile, the amount of nonaqueous electrolyte injected into the element container 2 in the injection step S3 is preferably 50% by mass or more, and more preferably 60% by mass or more, 70% by mass or more, or 80% by mass or more, of the total amount of nonaqueous electrolyte finally injected into the element container 2. Injecting a sufficient amount of nonaqueous electrolyte before pre-charging allows the nonaqueous electrolyte to thoroughly permeate the electrode assembly 1, enhancing the effect of pre-charging.

[0044] In the pouring step S3, it is preferable that the element container 2 and the electrode assembly 1 contained in the element container 2 are preheated. Also, in the pouring step S3, it is preferable that the nonaqueous electrolyte solution 21 to be poured into the element container 2 is preheated. In such a case, the viscosity of the nonaqueous electrolyte solution 21 is reduced, facilitating impregnation into the electrode assembly 1. The temperatures of the electrode assembly 1, element container 2, and nonaqueous electrolyte are preferably, for example, 35°C or higher, and more preferably 40°C or higher. The upper limit of these temperatures can be, for example, 70°C, 60°C, or 50°C.

[0045] (Pressure step S4) As the pressurizing step S4, it is preferable to further inject carbon dioxide following the injection step S3, thereby pressurizing the inside of the element container 2. Specifically, by opening the carbon dioxide supply valve 20 from a state in which the valves other than the injection valve 18 (the exhaust valve 17, the nonaqueous electrolyte supply valve 19, and the carbon dioxide supply valve 20) are closed, carbon dioxide is further supplied into the inside of the element container 2, thereby pressurizing the inside of the element container 2. Note that the injection step S3 and the pressurizing step S4 may be performed integrally or consecutively by performing the injection step S3 with the carbon dioxide supply valve 20 open.

[0046] In the pressurizing step S4, the pressure when pressurizing the inside of the element container 2 with carbon dioxide is preferably 10 kPa or more, more preferably 20 kPa or more, and even more preferably 50 kPa or more or 100 kPa or more. Pressurizing at such a pressure allows the nonaqueous electrolyte to be sufficiently impregnated into the inside of the electrode body 1, and effectively reduces, reduces, or eliminates remaining carbon dioxide bubbles in the pre-charging step S5, etc. The upper limit of this pressure may be, for example, 10 MPa or 1 MPa.

[0047] After the injection step S3, or after the pressurizing step S4 if it is performed, centrifugal force may be applied to the element container 2 containing the electrode assembly 1 and the nonaqueous electrolyte in order to promote impregnation of the nonaqueous electrolyte into the electrode assembly 1. In this case, it is preferable to rotate the element container 2 containing the electrode assembly 1 and the nonaqueous electrolyte so that the centrifugal force is applied in the direction of the winding axis 5 of the electrode assembly 1.

[0048] (Storage process) After the filling step S3, or after the pressurizing step S4 if performed, it is preferable to store the element container 2 containing the electrode assembly 1 and the nonaqueous electrolyte in a low dew-point environment for a predetermined time. That is, the manufacturing method of the lithium ion storage element may further include a storage step. This allows the nonaqueous electrolyte to be sufficiently impregnated inside the electrode assembly 1. Furthermore, by storing in a low dew-point environment, it is possible to prevent the nonaqueous electrolyte from absorbing moisture and spraying out of the element container during pre-charging, as well as to prevent variations in the open-circuit voltage of the resulting lithium ion storage element. When storing in a low dew-point environment, the element container 2 may be stored with the inlet 3 of the element container 2 open (i.e., the interior of the element container 2 is not sealed), or the element container 2 may be stored with the inlet 3 temporarily sealed. Note that, from the viewpoint of preventing moisture absorption into the nonaqueous electrolyte, each step in which the element container 2 is not sealed is preferably performed in a low dew-point environment.

[0049] The storage time is preferably 30 minutes to 4 hours, more preferably 1 hour to 2 hours. By setting the storage time to the above lower limit or more, the nonaqueous electrolyte can be more thoroughly impregnated into the electrode body 1. Furthermore, by setting the storage time to the above upper limit or less, productivity can be increased.

[0050] (Pre-charging step S5) In the preliminary charging step S5, preliminary charging is performed on an incomplete lithium ion storage element (an unsealed storage element in which the electrode body 1 and non-aqueous electrolyte are housed in the element container 2). This preliminary charging is preferably performed to a charge rate of 5% or more and 50% or less, more preferably 10% or more and 30% or less. In addition, the preliminary charging is performed when the negative electrode potential is 100 mV vs. Li / Li + By carrying out such preliminary charging, lithium carbonate is sufficiently produced by the reaction between the carbon dioxide dissolved in the non-aqueous electrolyte in the element container 2 and the lithium ions in the non-aqueous electrolyte, etc., and the air bubbles remaining in the electrode body 1 are effectively reduced in size, decreased, or eliminated.

[0051] Preliminary charging may be performed with the liquid inlet 3 of the element container 2 open (with the inside of the element container 2 not sealed), and in this case, preliminary charging is preferably performed in a low dew point environment.

[0052] In the pre-charging step S5, the temperatures of the electrode assembly 1 and the element container 2 are preferably higher than room temperature. In this case, the production of lithium carbonate due to the reaction between carbon dioxide and lithium ions in the non-aqueous electrolyte is promoted, and air bubbles remaining in the electrode assembly 1 can be more effectively shrunk, reduced, or eliminated. The temperature of the electrode assembly 1 and the element container 2 in the pre-charging step S5 is preferably, for example, 35°C or higher, and more preferably 40°C or higher. The upper limit of this temperature can be, for example, 70°C, 60°C, or 50°C.

[0053] (Degassing step S2' and injection step S3') As described above, after the preliminary charging step S5, the combination of the degassing step S2' and the injection step S3' can be performed again one or more times using the injection device 11. The specific methods of the degassing step S2' and the injection step S3' performed after the preliminary charging step S5 are the same as the degassing step S2 and the injection step S3 performed before the preliminary charging step S5. However, the injection amount in each injection step S3, S3' is adjusted so that the total injection amount of the nonaqueous electrolyte in the multiple injection steps S3, S3' equals the set total amount of nonaqueous electrolyte injected into the element container 2. The combination of the degassing step S2' and the injection step S3' performed after the preliminary charging step S5 may be performed only once, or may be performed two or more times. Furthermore, the composition of the nonaqueous electrolyte injected in the multiple injection steps S3, S3' may be the same or different. Furthermore, by injecting carbon dioxide together with the non-aqueous electrolyte in the injection step S3' after the preliminary charging step S5, the generation of air bubbles and the like within the electrode body 1 can be suppressed, and the resulting lithium ion storage element can exhibit good charge / discharge performance.

[0054] (Compression process S6) In the compression step S6, the element container 2 that has expanded due to pre-charging or the like is compressed. The element container 2 is preferably compressed to a fixed dimension that is at least equal to or less than the dimension of the element container 2 (for example, the thickness of the original rectangular parallelepiped shape). Alternatively, for example, the element container 2 may be compressed so that the side surfaces are recessed. By compressing the element container 2, the resulting lithium ion energy storage element can be given a good shape and can be put into a state in which it can exhibit good charge / discharge performance.

[0055] (Cleaning process) In the manufacturing method of the lithium ion storage element, it is preferable to clean the periphery of the liquid filling port 3 between the compressing step S6 and the sealing step S7. That is, the manufacturing method of the lithium ion storage element may further include a cleaning step. If the liquid filling port 3 is sealed by welding or the like without cleaning the periphery of the liquid filling port 3, welding defects may occur. Therefore, cleaning the periphery of the liquid filling port 3 before sealing can prevent welding defects. This cleaning is preferably performed by wiping off dirt (such as sprayed nonaqueous electrolyte) around the liquid filling port 3 with paper, nonwoven fabric, or the like impregnated with an organic solvent. For example, if dry paper, nonwoven fabric, or the like is used, electrolyte salt in the nonaqueous electrolyte is likely to remain around the liquid filling port 3. Therefore, by using paper, nonwoven fabric, or the like impregnated with an organic solvent, even this electrolyte salt can be sufficiently wiped away. As the organic solvent, alcohol, a nonaqueous solvent used for nonaqueous electrolytes, or the like is preferably used. Among these, non-aqueous solvents used in non-aqueous electrolytes are preferred, and chain carbonates such as diethyl carbonate and dimethyl carbonate are more preferred. By using such organic solvents, if these organic solvents are mixed into the element container 2, it is possible to prevent the organic solvents from decomposing at the positive and negative electrodes of the lithium ion storage element during charging and discharging, thereby preventing gas generation and other problems.

[0056] It is preferable to clean the periphery of the liquid injection port 3 in a low dew point environment. By cleaning in a low dew point environment, swelling of the element container 2 due to moisture entering the element container 2 can be suppressed.

[0057] (Sealing process S7) In the sealing step S7, the liquid inlet 3 is sealed with a plug while the element container 2 is compressed, and the plug is welded to the element container 2. By sealing the element container 2 while it is compressed, swelling is suppressed, and a lithium ion energy storage element with a highly uniform thickness can be obtained.

[0058] The plug used for sealing is preferably made of metal. The plug is also preferably made of the same material as the element container 2. For example, if the element container 2 is made of aluminum, it is preferable to use an aluminum plug. Sealing with the plug can be preferably performed by welding such as laser welding or resistance welding.

[0059] (High temperature leaving step S8) In the high-temperature storage step S8, the negative electrode potential is set to 100 mV vs. Li / Li by pre-charging. + After the temperature is increased to 100 mV vs. Li / Li, the element container 2 is left at a temperature of 35° C. or higher. + The element container 2 may be left at a temperature of 35° C. or higher under the following conditions: Apart from the pre-charging step S5 performed before sealing, pre-charging may be performed again to set the negative electrode potential at 100 mV vs. Li / Li + or less, and then may be subjected to high-temperature leaving step S8. Such high-temperature leaving step S8 promotes the production of lithium carbonate through the reaction between carbon dioxide and lithium ions in the electrolyte, and further reduces the number of bubbles remaining in the electrode body 1, thereby resulting in a lithium ion storage element in which deposition of metallic lithium is further suppressed. The upper limit of the temperature of the leaving environment can be, for example, 80°C, 60°C, or 50°C.

[0060] Furthermore, in the method for manufacturing the lithium ion storage element, the lithium ion storage element after sealing the injection port may be subjected to charging and discharging for activation treatment (chemical conversion treatment), capacity confirmation, etc. This charging and discharging may involve charging up to a charge rate of 100% or may involve charging at a charge rate of less than 100%.

[0061] The positive electrode, negative electrode, separator, and non-aqueous electrolyte used in the method for producing a lithium ion storage element according to one embodiment of the present invention will be described in detail below.

[0062] (positive electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or via an intermediate layer.

[0063] The positive electrode substrate is electrically conductive. Whether or not it has "electrical conductivity" is determined by whether the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 7 The threshold value is Ω·cm. The material of the positive electrode substrate is a metal such as aluminum, titanium, tantalum, or stainless steel, or an alloy of these. Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high conductivity, and cost. Positive electrode substrates include foils, vapor-deposited films, meshes, and porous materials, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30, as specified in JIS-H-4000 (2014) or JIS-H4160 (2006).

[0064] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, the strength of the positive electrode substrate can be increased while increasing the energy density per volume of the lithium ion storage element.

[0065] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The configuration of the intermediate layer is not particularly limited, and may contain, for example, a binder and a conductive agent.

[0066] The positive electrode active material layer contains a positive electrode active material and, if necessary, optional components such as a conductive agent, a binder, a thickener, and a filler.

[0067] The positive electrode active material can be appropriately selected from known positive electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the positive electrode active material for a lithium ion secondary battery. Examples of the positive electrode active material include lithium transition metal composite oxides having an α-NaFeO2 crystal structure, lithium transition metal composite oxides having a spinel crystal structure, polyanion compounds, chalcogen compounds, and sulfur. Examples of lithium transition metal composite oxides having an α-NaFeO2 crystal structure include Li[Li x Ni (1-x) ]O2(0≦x<0.5), Li[Li x Ni γ Co (1-x-γ) ]O2(0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li x Co (1-x) ]O2(0≦x<0.5), Li[Li x Ni γ Mn (1-x-γ) ]O2(0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li x Ni γ Mn β Co (1-x-γ-β) ]O2(0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1-x-γ-β), Li[Li x Ni γ Co β Al (1-x-γ-β) ]O2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1-x-γ-β). Lithium transition metal composite oxides with spinel-type crystal structures include Li x Mn2O4, Li x Ni γ Mn (2-γ)Examples of polyanion compounds include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, and Li2CoPO4F. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. Atoms or polyanions in these materials may be partially substituted with atoms or anion species of other elements. The surfaces of these materials may be coated with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more may be used in combination.

[0068] The positive electrode active material is usually in the form of particles (powder). The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. By setting the average particle size of the positive electrode active material to the above lower limit or more, the positive electrode active material becomes easier to manufacture and handle. By setting the average particle size of the positive electrode active material to the above upper limit or less, the electronic conductivity of the positive electrode active material layer is improved. Note that when a composite of the positive electrode active material and another material is used, the average particle size of the composite is taken as the average particle size of the positive electrode active material. The "average particle size" refers to the value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50% based on the particle size distribution measured by laser diffraction / scattering in a diluted solution obtained by diluting particles with a solvent in accordance with JIS-Z-8825 (2013).

[0069] To obtain powders with a predetermined particle size, grinders, classifiers, etc. are used. Grinding methods include, for example, methods using a mortar, ball mill, sand mill, vibration ball mill, planetary ball mill, jet mill, counter jet mill, swirling airflow jet mill, or sieves. Wet grinding in the presence of water or an organic solvent such as hexane can also be used during grinding. As classification methods, sieves, air classifiers, etc. are used as needed for both dry and wet methods.

[0070] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% by mass to 99% by mass, more preferably 70% by mass to 98% by mass, and even more preferably 80% by mass to 95% by mass. By setting the content of the positive electrode active material within this range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

[0071] The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Examples of carbonaceous materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. The conductive agent may be in the form of powder or fiber. As the conductive agent, one of these materials may be used alone, or two or more may be mixed. These materials may also be used in combination. For example, a composite of carbon black and CNTs may be used. Among these, carbon black is preferred from the viewpoints of electronic conductivity and coatability, and acetylene black is particularly preferred.

[0072] The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass to 10% by mass, more preferably 3% by mass to 9% by mass. By setting the content of the conductive agent within this range, the energy density of the lithium ion storage element can be increased.

[0073] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0074] The content of the binder in the positive electrode active material layer is preferably 1% by mass to 10% by mass, more preferably 3% by mass to 9% by mass. By setting the binder content within this range, the positive electrode active material can be stably maintained.

[0075] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC), methyl cellulose, etc. When the thickener has a functional group that reacts with lithium or the like, this functional group may be deactivated in advance by methylation or the like.

[0076] The filler is not particularly limited, and examples of the filler include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, substances derived from mineral resources such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, and artificial products thereof.

[0077] The positive electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0078] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed on the negative electrode substrate directly or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from the configurations exemplified for the positive electrode above, for example.

[0079] The negative electrode substrate is conductive. Metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, alloys thereof, and carbonaceous materials are used as the material for the negative electrode substrate. Among these, copper or copper alloys are preferred. Examples of the negative electrode substrate include foils, vapor-deposited films, meshes, and porous materials, with foils being preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0080] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, the strength of the negative electrode substrate can be increased while increasing the energy density per volume of the lithium ion storage element.

[0081] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler, as needed. The optional components such as the conductive agent, the binder, the thickener, and the filler can be selected from the materials exemplified for the positive electrode above.

[0082] The negative electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.

[0083] The negative electrode active material can be appropriately selected from known negative electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the negative electrode active material for lithium ion secondary batteries. Examples of the negative electrode active material include metallic Li; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; and Li4Ti5O 12 , LiTiO 2、Examples include titanium-containing oxides such as TiNb2O7; polyphosphate compounds; silicon carbide; and carbon materials such as graphite and non-graphitic carbon (easily graphitized carbon or non-graphitized carbon). Among these materials, lithium carbonate is easily fixed to the negative electrode surface by reacting with carbon dioxide and lithium ions in the non-aqueous electrolyte, so that the negative electrode potential when absorbing lithium ions is 1 V vs. Li / Li. + The following materials are preferred, with Si, Si oxides, and carbon materials being more preferred, carbon materials being even more preferred, and graphite and non-graphitic carbon being even more preferred. In the negative electrode active material layer, these materials may be used alone or in combination of two or more.

[0084] "Graphite" refers to graphite that has an average lattice spacing (d 002 ) is 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the viewpoint of being able to obtain a material with stable physical properties.

[0085] "Non-graphitic carbon" refers to the carbon that has an average lattice spacing (d 002 ) is 0.34 nm or more and 0.42 nm or less. Non-graphitic carbon includes non-graphitizable carbon and graphitizable carbon. Examples of non-graphitic carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, and alcohol-derived materials.

[0086] Here, the "discharged state" refers to a state in which the negative electrode active material, a carbonaceous material, is discharged so that lithium ions capable of being absorbed and desorbed during charging and discharging are sufficiently released. For example, this refers to a state in which the open circuit voltage of a half cell using a negative electrode containing a carbonaceous material as a negative electrode active material as a working electrode and metallic Li as a counter electrode is 0.7 V or higher.

[0087] "Non-graphitizable carbon" means the above d 002This refers to carbon materials with a particle size of 0.36 nm or more and 0.42 nm or less.

[0088] "Graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.34 nm or more and less than 0.36 nm.

[0089] The negative electrode active material is usually in the form of particles (powder). The average particle size of the negative electrode active material can be, for example, 1 nm or more and 100 μm or less. When the negative electrode active material is a carbon material, a titanium-containing oxide, or a polyphosphate compound, the average particle size may be 1 μm or more and 100 μm or less. When the negative electrode active material is Si, Sn, Si oxide, Sn oxide, or the like, the average particle size may be 1 nm or more and 1 μm or less. By setting the average particle size of the negative electrode active material to be equal to or greater than the above-mentioned lower limit, the negative electrode active material can be easily produced or handled. By setting the average particle size of the negative electrode active material to be equal to or less than the above-mentioned upper limit, the electronic conductivity of the negative electrode active material layer is improved. To obtain powder with a predetermined particle size, a pulverizer, a classifier, or the like is used. The pulverization method and the powder classification method can be selected from, for example, the methods exemplified for the positive electrode. When the negative electrode active material is a metal such as metallic Li, the negative electrode active material layer may be in the form of a foil.

[0090] The content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass to 99% by mass, more preferably 90% by mass to 98% by mass. By setting the content of the negative electrode active material within this range, both high energy density and manufacturability of the negative electrode active material layer can be achieved.

[0091] (separator) The separator can be appropriately selected from known separators. Examples of separators that can be used include separators consisting of only a substrate layer and separators in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both surfaces of the substrate layer. Examples of the shape of the substrate layer of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin films are preferred from the viewpoint of strength, and nonwoven fabrics are preferred from the viewpoint of non-aqueous electrolyte retention. Materials for the substrate layer of the separator are preferably polyolefins such as polyethylene and polypropylene from the viewpoint of shutdown function, and polyimide and aramid from the viewpoint of oxidative decomposition resistance. A composite material of these resins may also be used for the substrate layer of the separator.

[0092] The heat-resistant particles contained in the heat-resistant layer preferably exhibit a mass loss of 5% or less when heated from room temperature to 500°C in an air atmosphere at 1 atmosphere pressure, and more preferably exhibit a mass loss of 5% or less when heated from room temperature to 800°C. Examples of materials exhibiting a mass loss of a predetermined value or less include inorganic compounds. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalently bonded crystals such as silicon and diamond; mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, as well as artificial products thereof. As the inorganic compound, these substances may be used alone or in the form of a complex, or two or more of them may be used in combination. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferred from the viewpoint of the safety of the energy storage device.

[0093] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and is preferably 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0094] The separator may be a polymer gel composed of a polymer and a non-aqueous electrolyte. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, and polyvinylidene fluoride. The use of a polymer gel has the effect of suppressing leakage. The separator may be a combination of the porous resin film or nonwoven fabric described above and a polymer gel.

[0095] (Non-aqueous electrolyte) The non-aqueous electrolyte can be appropriately selected from known non-aqueous electrolytes, and includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

[0096] The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, carboxylic acid esters, phosphate esters, sulfonic acid esters, ethers, amides, and nitriles. Non-aqueous solvents in which some of the hydrogen atoms contained in these compounds have been substituted with halogens may also be used.

[0097] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, etc. Among these, EC is preferred.

[0098] Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, bis(trifluoroethyl) carbonate, etc. Among these, EMC is preferred.

[0099] It is preferable to use a cyclic carbonate or a chain carbonate as the non-aqueous solvent, and it is more preferable to use a combination of a cyclic carbonate and a chain carbonate. The use of a cyclic carbonate can promote dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. The use of a chain carbonate can reduce the viscosity of the non-aqueous electrolyte. When a cyclic carbonate and a chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate:chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

[0100] The electrolyte salt can be appropriately selected from known electrolyte salts, such as lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Of these, lithium salts are preferred.

[0101] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, and LiN(SO2F)2, lithium oxalates such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP), and lithium salts having a halogenated hydrocarbon group such as LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, and LiC(SO2C2F5)3. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred.

[0102] The content of electrolyte salt in the non-aqueous electrolyte is 0.1 mol / dm at 20°C and 1 atmosphere. 3More than 2.5mol / dm 3 It is preferable that the value is 0.3 mol / dm or less. 3 More than 2.0mol / dm 3 It is more preferable that it is 0.5 mol / dm or less. 3 More than 1.7mol / dm 3 It is more preferable that it is 0.7 mol / dm or less. 3 More than 1.5mol / dm 3 By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0103] The non-aqueous electrolyte may contain additives in addition to the non-aqueous solvent and the electrolyte salt. Examples of additives include halogenated carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); oxalates such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI); aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, and the like. Carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1 ,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1,3-propene sultone, 1,3-propane sultone, 1,4-butane sultone, 1,4-butene sultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, lithium monofluorophosphate, lithium difluorophosphate, etc. These additives may be used alone or in combination of two or more.

[0104] The content of the additive contained in the non-aqueous electrolyte is preferably 0.01% by mass to 10% by mass, more preferably 0.1% by mass to 7% by mass, even more preferably 0.2% by mass to 5% by mass, and particularly preferably 0.3% by mass to 3% by mass. By setting the content of the additive within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, and further improve safety.

[0105] The lithium ion storage element manufactured by the manufacturing method of the lithium ion storage element of this embodiment can be mounted as a storage unit (battery module) consisting of a plurality of lithium ion storage elements in automotive power sources such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), power sources for electronic devices such as personal computers and communication terminals, or power sources for power storage.

[0106] <Other embodiments> The method for manufacturing a lithium ion storage element of the present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, or part of the configuration of one embodiment can be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment can be deleted. Also, well-known technology can be added to the configuration of one embodiment.

[0107] For example, the element container may be provided with multiple liquid injection ports. The element container 102 in FIG. 3 has three liquid injection ports 103 provided on the top surface 4, and the liquid injection device 111 in FIG. 3 has three injection nozzles 112 corresponding to the three liquid injection ports 103. The element container 102 and liquid injection device 111 in FIG. 3 are substantially the same as the element container 2 and liquid injection device 11 in FIG. 2 except for the points described above. When multiple liquid injection ports 103 are provided in this way, efficient liquid injection and the like are possible. When multiple liquid injection ports are provided, the number of liquid injection ports is preferably 2 to 5, and more preferably 3 to 4.

[0108] In the above embodiment, the lithium ion storage element is described as being used as a lithium ion secondary battery, but the type, shape, size, capacity, etc. of the lithium ion storage element are arbitrary. The present invention can also be applied to capacitors such as lithium ion capacitors. Furthermore, the manufacturing method for a lithium ion storage element of the present invention can also be applied to manufacturing lithium ion storage elements having a stacked electrode body, lithium ion storage elements having an element container other than a prismatic container, etc. [Example]

[0109] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0110] [Example 1] (Preparation of positive electrode) A positive electrode mixture paste was prepared using LiFePO4 as a positive electrode active material, acetylene black (AB) as a conductive agent, polyvinylidene fluoride (PVDF) as a binder, and N-methylpyrrolidone (NMP) as a dispersion medium. The mass ratio of the positive electrode active material, AB, and PVDF was 90:5:5 (solid content equivalent). The positive electrode mixture paste was applied to both sides of a strip-shaped aluminum foil as a positive electrode substrate, so that a positive electrode substrate exposed portion was provided at one end in the width direction of the aluminum foil, and then dried. Thereafter, roll pressing was performed to obtain a strip-shaped positive electrode having a positive electrode active material layer width of 66 mm, a positive electrode substrate exposed portion width of 14 mm, and a length of 1009 mm.

[0111] (Preparation of negative electrode) A negative electrode mixture paste was prepared by mixing graphite (negative electrode active material), styrene-butadiene rubber (SBR) (binder), carboxymethyl cellulose (CMC) (thickener), and water (dispersion medium). The mass ratio of the negative electrode active material, SBR, and CMC was 96.7:0.3:3 (solid content equivalent). The negative electrode mixture paste was applied to both sides of copper foil as a negative electrode substrate, so that a negative electrode substrate exposed portion was provided at one end in the width direction of the copper foil, and then dried. Subsequently, roll pressing was performed to obtain a strip-shaped negative electrode having a negative electrode active material layer width of 70 mm, a negative electrode substrate exposed portion width of 14 mm, and a length of 1040 mm.

[0112] (Non-aqueous electrolyte) A 1.2 mol / dm 3 A non-aqueous electrolyte solution was obtained by dissolving LiPF6 in the solution.

[0113] (separator) A 75 mm wide strip of polyolefin microporous membrane was used as the separator.

[0114] (Assembling lithium-ion storage elements) The positive electrode, negative electrode, and separator were wound with the positive electrode and negative electrode offset from each other along the winding axis to obtain a flat, wound electrode assembly with only the exposed positive electrode substrate portion laminated at one end of the winding axis and only the exposed negative electrode substrate portion laminated at the other end. The electrode assembly had a length along the winding axis (the length in the X direction in electrode assembly 1 of FIG. 2) of 97 mm. This electrode assembly was placed in a rectangular element container with an open top and a length (the length in the X direction in element container 2 of FIG. 2) of 100 mm, with the winding axis aligned horizontally. A lid with a liquid inlet was attached to the top of the rectangular element container. Subsequently, the CO2 substitution step S1, degassing step S2, injection step S3, pressurization step S4, pre-charging step S5, degassing step S2', injection step S3', compression step S6, sealing step S7, and high-temperature storage step S8 were performed according to the flow diagram of FIG. 1. Storage for one hour was performed between the pressurization step S4 and pre-charging step S5. The storage, pre-charging step S5, compression step S6, and sealing step S7 were carried out in a low dew point environment with a dew point of -30°C or less. The other steps, CO2 substitution step S1, degassing step S2, injection step S3, pressurization step S4, degassing step S2', injection step S3', and high-temperature leaving step S8, were carried out with the element container sealed. In the injection step S3, 80 mass% of the non-aqueous electrolyte to be finally injected was injected, and the remaining 20 mass% of the non-aqueous electrolyte was injected in the injection step S3. In the pre-charging step S5, charging was carried out up to a state of 20% charge rate. In the high-temperature leaving step S8, the negative electrode potential was 100mV vs. Li / Li + The following conditions were maintained and the sample was left in a 40°C environment for 8 hours. Under the above conditions, the lithium ion storage element of Example 1 was obtained.

[0115] [Examples 2 to 5, Reference Examples 1 and 2, Comparative Examples 1 to 4] The lithium ion storage elements of Examples 2 to 5, Reference Examples 1 and 2, and Comparative Examples 1 to 4 were obtained in the same manner as in Example 1, except that the length of the element container and the length of the electrode assembly were as shown in Table 1; that in the injection steps S3 and S3′, the injection container was filled with the gas shown in Table 1 together with the nonaqueous electrolyte, and the gas shown in Table 1 was injected into the element container together with the nonaqueous electrolyte; and that the storage time between the pressurization step S4 and the pre-charging step S5 was as shown in Table 1. The lengths of the element container and the electrode assembly are the lengths in the direction of the winding axis of the electrode assembly (the X direction in FIG. 2 ). The length of the electrode assembly was adjusted by changing the widths of the strip-shaped positive electrode, strip-shaped negative electrode, and strip-shaped separator. Specifically, in the preparation of the positive and negative electrodes, the widths of the exposed positive electrode substrate portion and exposed negative electrode substrate portion were the same as in Example 1, and the widths of the positive electrode active material layer and negative electrode active material layer were changed as appropriate. Furthermore, "dry air" refers to air with a dew point of -30°C or lower.

[0116] [evaluation] Each lithium-ion storage element obtained was initially charged and discharged at 25°C as follows: Constant current charging was performed at a charging current of 0.1C up to 3.5V, followed by constant voltage charging at 3.5V. The charge termination condition was the time when the current decayed to 0.02C. After a 10-minute rest period, constant current discharging was performed at a discharging current of 0.1C down to 2.5V, followed by another 10-minute rest period. Subsequently, constant current charging was performed at a charging current of 1.0C up to 3.5V, followed by constant voltage charging at 3.5V. The charge termination condition was the time when the current decayed to 0.05C. After a 10-minute rest period, constant current discharging was performed at a discharging current of 1.0C down to 2.5V. After the initial charge and discharge, the lithium ion storage element was disassembled and the presence or absence of deposition of metallic lithium on the surface of the negative electrode was visually confirmed. The results are shown in Table 1.

[0117] [Table 1]

[0118] As shown in Table 1, when dry air was injected into the element container together with the nonaqueous electrolyte, no deposition of metallic lithium was observed on the negative electrode surface of the resulting lithium-ion storage element when the electrode body was small (Reference Example 1), but when the length of the electrode body was over 100 mm (Comparative Examples 1 to 4), deposition of metallic lithium occurred on the negative electrode surface of the resulting lithium-ion storage element. Furthermore, when dry air was injected into the element container together with the nonaqueous electrolyte, as in Reference Example 2, the deposition of metallic lithium on the negative electrode surface decreased as the storage time was extended, but the extended storage time resulted in poor productivity. Thus, the method of injecting the nonaqueous electrolyte and dry air into the element container using a liquid injection container filled with the nonaqueous electrolyte and dry air was unable to efficiently produce a lithium-ion storage element in which deposition of metallic lithium on the negative electrode surface was suppressed when the electrode body was large. In contrast, the methods of Examples 1 to 5, in which a liquid injection container filled with a nonaqueous electrolyte and carbon dioxide is used to inject the nonaqueous electrolyte and carbon dioxide into the element container, made it possible to efficiently produce lithium ion storage elements in which deposition of metallic lithium on the negative electrode surface was suppressed regardless of whether the electrode body was large or small. [Industrial Applicability]

[0119] The present invention can be applied to a method for manufacturing a lithium ion storage element used as a power source for electronic devices such as personal computers and communication terminals, automobiles, etc. [Explanation of symbols]

[0120] 1 Electrode body 2, 102 Element container 3, 103 Filling port 4 Top side 5 Winding shaft 11, 111 Injection device 12, 112 Injection nozzle 13 Exhaust means 14 Injection container 15 Nonaqueous electrolyte supply means 16 Carbon dioxide supply means 17 Exhaust valve 18 Injection valve 19 Non-aqueous electrolyte supply valve 20 Carbon dioxide supply valve 21 Nonaqueous electrolyte 22 Carbon dioxide

Claims

1. Degassing the inside of an element container in which an electrode assembly having a positive electrode and a negative electrode is housed and which is provided with a liquid injection port; and Injecting the nonaqueous electrolyte and the carbon dioxide from a liquid injection container filled with the nonaqueous electrolyte and the carbon dioxide through the liquid injection port into the degassed interior of the element container. Equipped with After the above injection, Pre-charging Further equipped After the injection, the lithium ion storage element is stored for a predetermined time in a low dew point environment, and then the preliminary charging is performed.

2. 2. The method for manufacturing a lithium ion storage element according to claim 1, wherein, during the injection, the injection container is filled with the nonaqueous electrolyte and the carbon dioxide in amounts to be injected in a single operation.

3. Before the degassing, the gas inside the element container is replaced with carbon dioxide. The method for manufacturing a lithium ion storage element according to claim 1 or 2, further comprising:

4. 4. The method for producing a lithium ion storage element according to claim 1, wherein the combination of the degassing and the injection is carried out one or more times after the preliminary charging.

5. Between the injecting and the precharging, Pressurizing the inside of the element container by further injecting carbon dioxide through the injection port. The method for manufacturing a lithium ion storage element according to claim 1 , further comprising:

6. After the above preliminary charging, compressing the element container to a predetermined size; and sealing the liquid inlet with a plug while the element container is compressed, and welding the plug to the element container; The method for manufacturing a lithium ion storage element according to claim 1 , further comprising:

7. The negative electrode potential was set to 100 mV vs. Li / Li by the above preliminary charging. ＋ After the above, leave the element container at a temperature of 35°C or higher. The method for manufacturing a lithium ion storage element according to claim 1 , further comprising:

8. the electrode body is a wound electrode body in which the positive electrode and the negative electrode are wound in a stacked state, The method for manufacturing a lithium ion storage element according to any one of claims 1 to 7, wherein the length of the electrode body in the direction of the winding axis is 300 mm or more.

9. 9. The method for manufacturing a lithium ion storage element according to claim 8, wherein the electrode body is housed in the element container so that a surface of the element container provided with the liquid inlet and a winding axis of the electrode body are parallel to each other.

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