JP7025163B2 - Manufacturing method of non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a method for manufacturing a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery.

Since the lithium ion secondary battery has a high energy density and a high capacity, it is used as a driving power source for an electric vehicle (EV), a hybrid vehicle (HV), or the like. If the lithium ion secondary battery is an electrode body in which positive electrode plates and negative electrode plates having active material layers provided on both sides of the electrode core are wound or laminated via a separator, the facing area between the positive electrode plate and the negative electrode plate is large. It becomes easy to take out a large current.

On the other hand, lithium-ion secondary batteries may have problems such as self-discharge and deterioration of battery performance that occur when stored for a long period of time. Therefore, for example, Patent Document 1 describes an example of a technique for suppressing deterioration of battery performance by suppressing the production of hydrofluoric acid (HF) that promotes metal outflow from the positive electrode.

The lithium ion secondary battery described in Patent Document 1 has a non-aqueous electrolyte containing lithium hexafluorophosphate (LiPF ₆ ), and the non-aqueous electrolyte contains lithium phosphate (Li ₃ PO ₄ ).

Japanese Unexamined Patent Publication No. 2005-71641

According to the technique described in Patent Document 1, even if lithium hexafluorophosphate (LiPF ₆ ) in a non-aqueous electrolyte contains lithium phosphate (Li ₃ PO ₄ ) and comes into contact with water, hydrofluoric acid is used. The production of (HF) is suppressed.

By the way, it is also known that in a lithium ion secondary battery, self-discharge and deterioration of battery performance that occur when stored for a long period of time are caused by the reaction between the electrode body and the gas in the battery case. In this respect, the technique described in Patent Document 1 can suppress the reaction between the electrode body and the non-aqueous electrolyte, but does not suppress the reaction between the electrode body and the gas in the electric tank. Further, although it is a reaction between the electrode body and the gas in the battery case, when it is a reaction in long-term storage, deterioration of battery performance due to this reaction cannot be ignored.

The present invention has been made in view of such circumstances, and an object thereof is a non-aqueous electrolyte that can suppress deterioration of battery performance caused by a reaction between an electrode body and a gas in a battery case. The purpose is to provide a method for manufacturing a next battery.

The method for manufacturing a non-aqueous electrolyte secondary battery that solves the above problems is a method for manufacturing a non-aqueous electrolyte secondary battery in which an electrode body is housed in an electric tank, and both sides of a positive electrode plate and a metal collector foil are used. A winding step of manufacturing the electrode body by winding a negative electrode plate having an active material with a separator sandwiched between them, a housing step of accommodating the electrode body and a non-aqueous electrolyte in the electric tank, and the electrode. An inert gas filling step of substituting a part of the gas in the electric tank containing the body and the non-aqueous electrolyte with an inert gas and sealing the electric tank in this replaced state, and the electric power. It is provided with a discharge step of discharging the sealed secondary battery of the tank after charging, and in the winding step, the negative electrode plate is wound so as to have a portion arranged on the outer periphery of the positive electrode plate, and the inactivity. In the gas filling step, the discharging step when the ratio of the active gas in the electric tank after the discharging step does not replace a part of the gas in the electric tank with the inert gas in the inert gas filling step. A part of the gas in the electric tank is replaced with an inert gas so as to be a predetermined ratio or less, which is a ratio lower than the ratio of the active gas in the electric tank later.

A non-aqueous electrolyte secondary battery in a charged state is in a state where lithium ions are retained in a negative electrode plate, but if this is stored for a long period of time, self-discharge and deterioration of battery performance occur. That is, the lithium ions held in the negative electrode plate are deactivated by reacting with the active gas to become lithium carbonate (Li ₂ CO ₃ ), or the potential difference between the inner and outer circumferences of the negative electrode plate causes the negative electrode plate to be deactivated. Lithium ions move from the inner circumference to the outer circumference, reducing the amount of charge. In this regard, according to such a method, a part of the gas in the electric tank is an inert gas in the inert gas filling step so that the ratio of the active gas in the electric tank after the discharge step becomes a predetermined ratio or less. Is replaced by. As a result, the ratio of the negative electrode active material of the outermost negative electrode plate reacting with the active gas in the battery case is reduced, and the decrease of lithium ions held in the negative electrode plate in the charged state is suppressed. Therefore, it becomes possible to suppress the deterioration of the battery performance caused by the gas in the battery case.

As a preferred method, in the winding step, the electrode body is rotated so that the negative electrode plate is arranged on at least a part of the outermost periphery.

According to such a method, even if the negative electrode plate of the electrode body is arranged on the outermost circumference and is in a state where it easily reacts with the gas in the electric tank, the inert gas sealed in the electric tank reacts with the active gas. Will be suppressed.

As a preferred method, in the inert gas filling step, a part of the gas in the electric tank is replaced with the inert gas so that the predetermined ratio is 30% or less.

According to such a method, since the ratio of the active gas after the discharge step becomes 30% or less, the deactivation and self-discharge of lithium ions in the negative electrode plate in contact with the gas in the electric tank can be suppressed.

As a preferred method, in the inert gas filling step, at least one of helium gas (He) and argon gas (Ar) is used as the inert gas.

According to such a method, the deactivation of lithium ions in the negative electrode plate is suppressed by the helium gas and the argon gas.

As a preferred method, between the inert gas filling step and the end of the discharging step, a charging step of charging the secondary battery with a predetermined charging amount, and a charging step of charging in the charging step, only for a predetermined period of time. It is provided with a high temperature aging step for maintaining the secondary battery under a predetermined high temperature environment.

According to such a method, even if the ratio of the active gas increases in the charging step and the high temperature aging step after sealing, the ratio of the active gas in the battery case is kept at a predetermined ratio after the charging step and the high temperature aging step. You will be able to suppress it.

As a preferred method, in the inert gas filling step, a part of the gas in the electric tank is replaced with the inert gas by a predetermined replacement amount, and the inert gas is previously performed prior to the inert gas filling step. Based on the ratio of replacing the gas in the electric tank acquired in the gas filling step with the inert gas and the ratio of the active gas in the electric tank acquired after the discharge step also performed in advance. Further provided is a replacement amount calculation step for obtaining the replacement amount.

According to such a method, the amount of replacement with the inert gas in the inert gas filling step is the ratio of replacing the air in the electric tank with the inert gas in the inert gas filling step, and the ratio after the discharging step. It is determined in advance based on the ratio of the active gas in the battery case.

As a preferred method, a lithium ion secondary battery is manufactured as the non-aqueous electrolyte secondary battery.

According to such a method, it becomes possible to suppress self-discharge and deterioration of battery performance of a lithium ion secondary battery that has been stored for a long period of time in a charged state.

The non-aqueous electrolyte secondary battery that solves the above-mentioned problems is a non-aqueous electrolyte secondary battery in which an electrode body and a non-aqueous electrolyte are housed in an electric tank, and the electrode body has a negative electrode body rather than a positive electrode plate. The positive electrode plate and the negative electrode plate are wound around the separator so as to have a portion arranged on the outer periphery, and the negative electrode plate has negative electrode active materials arranged on both sides of a metal current collector foil. The gas in the electric tank has a larger proportion of the inert gas than the atmosphere, and the proportion of the active gas is 30% or less.

According to such a configuration, the ratio of the negative electrode active material of the negative electrode plate on the outer periphery reacting with the active gas in the battery case decreases, so that the lithium ions held in the negative electrode plate in the charged state are reduced. Is suppressed, and the deterioration of battery performance caused by the gas in the battery case can be suppressed.

According to the present invention, it is possible to suppress the deterioration of battery performance caused by the reaction between the electrode body and the gas in the battery case.

Schematic diagram of the structure of one embodiment embodying a non-aqueous electrolyte secondary battery. The schematic diagram which shows the cross-sectional structure of the electrode plate group of the same embodiment. The flowchart which shows the procedure about the method of manufacturing the non-aqueous electrolyte secondary battery of the same embodiment. It is a schematic diagram which shows the charge state of the electrode plate group of the same embodiment, (a) is a schematic diagram which shows the state after charging for the first time, (b) is the schematic which shows the state after maintaining the charge state for a predetermined period. figure. It is a schematic diagram which shows the charge state of the conventional electrode plate group, (a) is a schematic diagram which shows the state after charging for the first time, (b) is a schematic diagram which shows the state after maintaining the charge state for a predetermined period. The flowchart which shows the procedure which embodied the method of calculating the substitution ratio of the inert gas used in the inert gas filling step of the manufacturing method of the same embodiment. The graph for calculating the substitution ratio of the inert gas by the manufacturing method of the same embodiment. The graph which shows the relationship between the charge amount and the potential difference of the negative electrode plate of the same embodiment for each type of carbon constituting a negative electrode active material.

A method for manufacturing a non-aqueous electrolyte secondary battery and an embodiment embodying the non-aqueous electrolyte secondary battery will be described with reference to FIGS. 1 to 8. In the present embodiment, the secondary battery 10 as the non-aqueous electrolyte secondary battery is a lithium ion secondary battery.

A plurality of the secondary batteries 10 of the present embodiment are connected by a bus bar to form an assembled battery. The assembled battery is mounted on an electric vehicle or a hybrid vehicle to supply electric power to an electric motor or the like. The secondary battery 10 is a closed-type battery having a rectangular parallelepiped outer shape.

As shown in FIG. 1, the secondary battery 10 includes a rectangular battery case 11 having an opening on the upper side, a lid 12 for sealing the battery case 11, and an electrode body housed inside the battery case 11. 20 and the liquid non-aqueous electrolyte 27 injected into the battery case 11 are provided. The battery case 11 and the lid 12 are made of a metal such as an aluminum alloy. The secondary battery 10 is configured by attaching a lid 12 to the battery case 11 to form a sealed battery case. Further, the secondary battery 10 has a lid 12 provided with two external terminals 13 used for charging and discharging electric power.

The electrode plate group 20 is formed by flatly winding a positive electrode plate 21, a negative electrode plate 22, and a separator 23 arranged between them. The electrode plate group 20 is laminated in multiple layers by being folded back at both ends 26 in the winding direction (winding direction). The electrode plate group 20 has a positive electrode portion 21A having a positive electrode plate 21 protruding from one end side in a direction orthogonal to the winding direction (winding axis direction) and a negative electrode portion 22 protruding from the other end side in the same orthogonal direction. It has 22A. A part of the positive electrode portion 21A and the negative electrode portion 22A is compressed, and an electrode terminal 14 connected to the external terminal 13 is welded to each of the compressed portions of the positive electrode portion 21A and the negative electrode portion 22A. There is.

The separator 23 is a non-woven fabric made of polypropylene or the like for holding the non-aqueous electrolyte 27 between the positive electrode plate 21 and the negative electrode plate 22. Further, as the separator 23, a porous polymer film such as a porous polyethylene film, a porous polyolefin film, and a porous polyvinyl chloride film, or a lithium ion or ionic conductive polymer electrolyte film is used alone or in combination. You can also do it.

Therefore, the non-aqueous electrolyte 27 in the battery case 11 is absorbed and held by the separator 23, and a portion that is not absorbed by the separator 23 stays around the electrode plate group 20. That is, a part of the electrode plate group 20 is submerged in the non-aqueous electrolyte 27, and the other part is arranged in the space inside the battery case 11 and exposed to gas.

(Non-water electrolyte)
The non-aqueous electrolyte 27 is a composition in which a supporting salt is contained in a non-aqueous solvent. Here, as the non-aqueous solvent, one or two selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and the like. More than seed materials can be used. As supporting salts, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiI One or more kinds of lithium compounds (lithium salts) selected from the above can be used.

(Positive plate)
The configuration of the electrode plate group 20 will be described with reference to FIG. 2.

First, the positive electrode will be described in detail. The positive electrode plate 21 is coated with the positive electrode mixture 212 and 213, respectively, on the inner peripheral surface 211A and the outer peripheral surface 211B of the positive electrode base material 211 as the current collecting foil which is the electrode core. The inner surface when wound is the inner peripheral surface 211A, and the outer surface is the outer peripheral surface 211B. As the positive electrode base material 211 of the positive electrode plate 21, the same components as those of the conventional secondary battery can be used. For example, as the material of the base material, a conductive material made of a metal having good conductivity is preferably used. For example, as the positive electrode base material 211, a thin film made of aluminum or an alloy containing aluminum as a main component can be used.

The positive electrode mixture 212 and 213 have a positive electrode active material. The positive electrode active material may additionally contain one or more elements in addition to the transition metal element (ie, at least one of Ni, Co, and Mn). Additional elements include Group 1 (alkali metals such as sodium), Group 2 (alkaline earth metals such as magnesium and calcium), Group 4 (transition metals such as titanium and zirconium), and Group 6 (chromium) in the periodic table. , Transition metal such as tungsten), and any element belonging to Group 8 (transition metal such as iron) can be contained. In addition, the additional element may include any element belonging to Group 13 (metalloid element such as boron or aluminum) and Group 17 (halogen such as fluorine) in the periodic table. can. Preferably, the positive electrode active material is "LiNiComnO ₂ system positive electrode active material". The "LiNiCoMnO ₂ -based positive electrode active material" means a composite oxide containing Li, Ni, Co, and Mn, and may further contain a metal element different from Li, Ni, Co, and Mn.

Further, the positive electrode mixture 212 and 213 may contain a conductive material. As the conductive material, for example, carbon black such as acetylene black (AB) and Ketjen black, and graphite (graphite) can be used.

The positive electrode plate 21 is obtained by, for example, kneading a positive electrode active material, a conductive material, a solvent, and a binder, and applying the kneaded positive electrode mixture 212 to the positive electrode base material 211 and drying the positive electrode plate 21. It is made. Here, as the solvent, for example, an NMP (N-methyl-2-pyrrolidone) solution can be used. Further, as the binder, for example, polyvinylidene fluoride (PVdF), styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC) and the like can be used.

(Negative electrode plate)
Next, in the negative electrode plate 22, the negative electrode mixture 222, 223 is applied to the inner peripheral surface 221A and the outer peripheral surface 221B of the negative electrode base material 221 as the current collecting foil which is the electrode core, respectively. The inner surface when wound is the inner peripheral surface 221A, and the outer surface is the outer peripheral surface 221B. As the negative electrode base material 221 of the negative electrode plate 22, the same components as those of the conventional secondary battery can be used. For example, as the material of the base material, a conductive material made of a metal having good conductivity is preferably used. For example, as the negative electrode base material 221, a thin film made of copper, nickel, or an alloy thereof can be used.

The negative electrode mixture 222,223 has a negative electrode active material. The negative electrode active material is a material that can occlude and release lithium, and for example, a powdered carbon material made of graphite or the like can be used. The negative electrode plate 22 is manufactured by kneading the negative electrode active material, the solvent, and the binder in the same manner as in the positive electrode plate 21, applying the kneaded negative electrode mixture 222 to the negative electrode base material 221 and drying the negative electrode plate 22. .. In this embodiment, the binder comprises carboxymethyl cellulose (CMC) having sodium salts.

(Procedure for manufacturing secondary batteries)
A procedure related to the manufacturing process of the secondary battery 10 will be described with reference to FIG.

The manufacturing process of the secondary battery 10 includes a winding step (step S10) in which the electrode plate and the like are wound to manufacture the electrode plate group 20, and a terminal welding step (step S11) in which the electrode terminal 14 is welded to the electrode plate group 20. And a film inserting step (step S12) of inserting into an insulating film (not shown) in the battery case 11. Further, the manufacturing process of the secondary battery 10 includes an electrode plate group insertion step (step S13) for inserting the electrode plate group 20 into the battery case 11 and a can sealing step (step S14) for attaching the lid 12 to the battery case 11. The battery case 11 has a drying step (step S15) for drying the electrode plate group 20 in the battery case 11. Further, the manufacturing process of the secondary battery 10 includes a liquid injection step (step S16) of injecting the non-aqueous electrolyte 27 into the battery case 11 and an inert gas filling step (step S17) of enclosing the inert gas in the battery case 11. ) And a sealing step (step S18) for sealing the battery case 11. The manufacturing process of the secondary battery 10 includes an initial charging step (step S19) for charging the secondary battery 10 for the first time and a high temperature aging step (step S20) for maintaining the secondary battery 10 in a high temperature environment for a predetermined period. It has a self-discharging step (step S21) of self-discharging the secondary battery 10. The manufacturing process of the secondary battery 10 includes a shipping inspection step (step S22) for inspecting the secondary battery 10 for shipping. When these manufacturing processes are completed, the secondary battery 10 that can be distributed on the market is manufactured.

Each of the above steps will be described in detail.

In the winding step (step S10), the electrode plate group 20 is manufactured by winding the positive electrode plate 21 and the negative electrode plate 22 flatly in the winding direction so that the separator 23 is interposed between them. For example, in the laminated body before winding, the positive electrode plate 21, the separator 23, the negative electrode plate 22, and the separator 23 are laminated in this order, and the overlap between the positive electrode plate 21 and the negative electrode plate 22 is slightly shifted in the winding axis direction. There is. Therefore, from the laminated body before winding, the electrode plate group 20 in which the positive electrode portion 21A protrudes from one end in the winding axis direction and the negative electrode portion 22A protrudes from the other end is manufactured.

Further, a negative electrode plate 22 is arranged on the outermost circumference of the electrode plate group 20. For example, in the above-mentioned laminated body before winding, the negative electrode plate 22 is arranged on the outermost circumference by winding the positive electrode plate 21 so as to be inside. That is, at the outermost periphery of the electrode plate group 20, the portion of the negative electrode plate 22 exposed from the non-aqueous electrolyte 27 in the battery case 11 is exposed to the gas in the battery case 11. On the other hand, in the negative electrode plate 22, the portion immersed in the non-aqueous electrolyte 27 and the portion inside the outermost periphery to which the separator 23 containing the non-aqueous electrolyte 27 is in close contact are exposed to gas in the battery case 11. The risk is low. Although the area of the electrode plate group 20 is relatively small, the negative electrode plate 22 is also exposed to the gas in the battery case 11 at the end face in the winding axis direction of the electrode plate group 20.

In the terminal welding step (step S11), a part of each of the positive electrode portion 21A and the negative electrode portion 22A is compressed at the winding axial end portion of the electrode plate group 20, and the positive electrode portion 21A and the negative electrode portion 22A are compressed. The electrode terminals 14 connected to the external terminals 13 are welded to the respective portions.

In the film insertion step (step S12), the insulating film is inserted into the battery case 11 along the inner wall of the battery case 11.

In the electrode plate group insertion step (step S13), the electrode plate group 20 is inserted and arranged in the battery case 11 so as to be arranged inside the insulating film facing the inner wall of the battery case 11.

In the can sealing step (step S14), the lid 12 is welded to the opening of the battery case 11 with the electrode plate group 20 inserted. As a result, the battery case 11 is closed except for the liquid injection port (not shown) of the lid 12.

In the drying step (step S15), the electrode plate group 20 in the battery case 11 is dried.

In the liquid injection step (step S16), the non-aqueous electrolyte is injected into the battery case 11.

In the inert gas filling step (step S17), the inert gas is filled in the battery case 11. The space inside the battery case 11 is filled with a gas (usually air) in the atmosphere before the inert gas filling step. Therefore, for example, the inert gas is injected into the battery case 11 from the inert gas injection pipe inserted into the injection port of the lid 12, and the gas having the atmosphere of the battery case 11 is also injected from the injection port (hereinafter,). Part of the pre-replacement gas) is discharged. As a result, a part of the pre-replacement gas is replaced with the inert gas in the battery case 11, and the gas becomes the replaced gas containing the inert gas at a predetermined ratio (hereinafter referred to as the replaced gas). In the present embodiment, the inert gas is helium gas (He), which is one of the rare gases. The inert gas may be a gas that does not react with lithium ions (Li ⁺ ) or a gas that does not easily react, and is, for example, argon gas (Ar), which is Group 18 (noble gas) in the periodic table. It is preferable to have it. For example, argon gas (Ar) having a large specific gravity to the atmosphere is more difficult to escape from the battery case 11 than helium (He) having a small specific gravity to the atmosphere, so that the possibility that the ratio of the inert gas in the battery case 11 decreases is small. can do.

In the inert gas filling step, the amount of the inert gas injected into the battery case 11, that is, the amount of replacement with the gas before replacement is based on the replacement ratio predetermined as the ratio to the space in the battery case 11. It is calculated. For example, if the replacement ratio is 5%, an inert gas corresponding to 5% of the total capacity of the space in the battery case 11 is injected into the battery case 11, and if the replacement ratio is 20%. Inert gas corresponding to 20% of the total capacity of the space in the battery case 11 is injected into the battery case 11.

Here, the replacement ratio is a ratio determined so that the ratio of the "active gas" contained in the gas in the battery case 11 after the self-discharge step is a predetermined ratio, for example, 30% or less. The predetermined ratio is lower than the ratio (reference value) normally measured as the ratio of the active gas contained in the gas in the battery case 11 after the self-discharge step when the replacement ratio is set to 0% in the inert gas filling step. Is set. For example, when the replacement ratio is 0% and the normally measured ratio (reference value) is 35%, the predetermined ratio is set to 30% or less. In this embodiment, the active gas is carbon dioxide (CO ₂ ), carbon monoxide (CO), and oxygen (O ₂ ). The active gas may further contain fluoroethane (CH ₃ CH ₂ F) and hydrofluoric acid (HF), which are gas components that easily cause an oxidation reaction.

In the sealing step (step S18), the injection port of the lid 12 is sealed and the battery case 11 is sealed. By the steps up to this point, the configuration as the secondary battery 10 is assembled.

Subsequently, a step of adjusting the battery performance of the secondary battery 10 is performed.

In the initial charging step (step S19), the secondary battery 10 is charged until it is fully charged.

In the high temperature aging step (step S20), the fully charged secondary battery 10 is maintained (preserved) in an environment where the temperature reaches a predetermined temperature for a predetermined period with the two external terminals 13 open. The predetermined temperature is, for example, 50 ° C.

The self-discharge step (step S21) is a step of discharging the secondary battery 10 to a predetermined remaining battery level with the external terminal 13 open. The self-discharge step is a step that starts after the end of the initial charge step and proceeds including the period of the high temperature aging step. In FIG. 3, the high temperature aging step and the self-discharge step are described in series, but in the high temperature aging step and the self-discharge step, the end of the high temperature aging step is earlier than the end of the self-discharge step. Part of the period of the above has an overlapping relationship. For example, in the self-discharge step, the predetermined remaining battery level is set to "0". If the predetermined remaining battery level is less than the full charge amount, an appropriate value can be set.

By the way, in the initial charging step, the high temperature aging step, and the self-discharge step, a charge / discharge reaction occurs between the positive electrode plate 21, the negative electrode plate 22, and the non-aqueous electrolyte 27, and in this process, an active gas is generated, and the battery case 11 It is known that the proportion of active gas in the gas is high. Here, the generation of the active gas will be described. Since the non-aqueous electrolyte 27 existing in the charged secondary battery 10 is in a state where a potential is applied by the positive electrode plate 21 or the negative electrode plate 22, the oxidative decomposition reaction of the non-aqueous electrolyte 27 occurs on the positive electrode plate 21. It is easy to proceed, and the reduction and decomposition reaction of the non-aqueous electrolyte 27 is easy to proceed on the negative electrode plate 22. Further, in the positive electrode plate 21 and the negative electrode plate 22, an electrolyte decomposition reaction caused by a supporting salt (LiPF ₆ or the like) in the non-aqueous electrolyte 27 also occurs. Since the non-aqueous electrolyte 27 is composed of an organic solvent and an inorganic compound (LiPF ₆ , etc.), a film made of an organic substance or an inorganic substance is formed on the positive electrode plate 21 and the negative electrode plate 22 at the time of electrolyte decomposition, and an active gas is formed. (CO, CO ₂ , etc.) is generated together with inorganic gases such as hydrogen gas (H ₂ ) and low boiling hydrocarbons such as methane, ethane, and ethylene.

The inventors have determined that the degree to which the proportion of active gas is high is the nature of the battery (battery capacity, type of secondary battery, etc.), the environment of the battery (environmental temperature, etc.), and the material of the battery (positive electrode mixture or negative electrode). It has been confirmed that it differs for each secondary battery depending on the mixture, non-aqueous electrolyte components, additives, etc.). On the other hand, the inventors also confirmed that the degree of increase in the proportion of active gas has the same tendency for each secondary battery if the properties of the battery, the environment of the battery and the material of the battery are the same. ing. For example, a plurality of secondary batteries 10 industrially manufactured as the same product have the same high rate of active gas in the battery case 11 after undergoing an initial charging step, a high temperature aging step, and a self-discharge step. There is a tendency. For these reasons, the inventors inject the inert gas into the battery case 11 based on a predetermined substitution ratio in the inert gas filling step, thereby injecting the inert gas into the battery case 11 after the self-discharge step. It was found that the ratio of can be set to a predetermined ratio. In other words, the inventors have found that the replacement ratio can be predetermined so that the ratio of the active gas in the battery case 11 after the self-discharge step can be a predetermined ratio.

The shipping inspection step (step S22) is an inspection performed when the secondary battery 10 is shipped. After that, the secondary battery 10 is shipped and put into a state of being distributed in the market. In other words, the secondary battery 10 before shipment is in a manufactured state and is in an unused state.

(Action)
With reference to FIGS. 4 and 5, the secondary battery 10 manufactured as described above will be described with respect to self-discharge and deterioration of battery performance when the secondary battery 10 is stored in a charged state for a long period of time. Note that FIGS. 4 and 5 show a portion where the negative electrode plate 22 is on the outermost circumference.

As shown in FIG. 4A, for example, the secondary battery 10 manufactured by injecting an inert gas having a replacement ratio in the inert gas filling step is charged, and after charging, the negative electrode mixture 222,223 of the negative electrode plate 22 is used. Lithium ion (Li ⁺ ) and lithium (Li) are held in it. At this time, in the outermost negative electrode plate 22, the negative electrode mixture 223 on the outer peripheral surface 221B is in contact with the gas in the battery case 11, and the gas may react with the negative electrode mixture 223.

As shown in FIG. 4 (b), for example, the secondary battery 10 manufactured by injecting an inert gas having a replacement ratio in the inert gas filling step has a long-term state in which the external terminal 13 is opened after charging. Even if it is stored, lithium ions (Li ⁺ ) and lithium (Li) are retained in the negative electrode mixture 222 and 223 of the negative electrode plate 22. Normally, when the proportion of the active gas in the battery case 11 increases in the high temperature aging step or the self-discharge step, the possibility that the negative electrode mixture 223 on the outermost periphery reacts with the active gas increases, but in the inert gas filling step, the gas Since part of the gas is replaced with helium gas (He), the relative proportion of the active gas can be kept low. Therefore, the negative electrode mixture 223 on the outer peripheral surface 221B is prevented from being inactivated by oxidation of lithium ions (Li ⁺ ) and lithium (Li) in contact with the active gas. That is, self-discharge as the secondary battery 10 and deterioration of battery performance are suppressed.

5 (a) and 5 (b) show a case where the replacement ratio in the inert gas filling step is low, for example, the case where the replacement ratio is 0%.

As shown in FIG. 5A, in the secondary battery 10, lithium ions (Li ⁺ ) and lithium (Li) are held in the negative electrode mixture 222 and 223 of the negative electrode plate 22 after charging is completed. At this time, for example, in the secondary battery 10 manufactured without injecting the inert gas in the inert gas filling step, the proportion of the active gas in the battery case 11 is high in the high temperature aging step or the self-discharge step. .. That is, since part of the gas (air) is not replaced with helium gas (He) in the inert gas filling step, the negative electrode mixture 223 on the outer peripheral surface 221B immediately comes into contact with the active gas (for example, CO ₂ ). It is likely to react. For example, the negative electrode mixture 223 on the outer peripheral surface 221B is deactivated by the oxidation of lithium ions (Li ⁺ ) and lithium (Li) with an active gas to form lithium carbonate (Li ₂ CO ₃ ) and precipitates on the negative electrode mixture 223. The layer 30A will be formed. Therefore, the secondary battery 10 causes self-discharge and deterioration of battery performance.

As shown in FIG. 5B, for example, the secondary battery 10 manufactured without injecting the inert gas in the inert gas filling step is stored for a long period of time with the external terminal 13 open after charging. As a result, the outermost negative electrode mixture 223 further reacts with the active gas. That is, the outermost negative electrode mixture 223 is exposed to the gas in the battery case 11 in which the proportion of the active gas is high, and the lithium ions (Li ⁺ ) and lithium (Li) of the negative electrode mixture 223 react with the active gas. It is inevitable that lithium carbonate (Li ₂ CO ₃ ) is precipitated by being oxidized to form a wide precipitation layer 30B on the negative electrode mixture 223. That is, the secondary battery 10 causes self-discharge and deterioration of battery performance.

Further, referring to FIG. 5 (b), the negative electrode plate 22 has a negative electrode mixture 223 on the outer peripheral surface 221B and a negative electrode mixture 222 on the inner peripheral surface 221A with the negative electrode base material 221 interposed therebetween. Normally, lithium ions (Li ⁺ ) do not move between the negative electrode mixture 223 and the negative electrode mixture 222 beyond the negative electrode base material 221 which is a metal film. However, when the lithium ion (Li ⁺ ) of the negative electrode mixture 223 on the outer peripheral surface 221B is greatly reduced, it becomes large between the negative electrode mixture 223 on the outer peripheral surface 221B and the negative electrode mixture 222 on the inner peripheral surface 221A in the negative electrode plate 22. A potential difference occurs. When this happens, the large potential difference attracts the lithium ions (Li ⁺ ) of the negative electrode mixture 222 on the inner peripheral surface 221A to the negative electrode base material 221 and further bypasses the end portion of the negative electrode base material 221 which is a cut. It moves to the negative electrode mixture 223 on the outer periphery (arrows J1 and J2).

In addition, the reaction rate of lithium ions (Li ⁺ ) may decrease during discharge due to being attracted to the negative electrode base material 221.

Further, since the outer peripheral surface 221B of the outermost negative electrode plate 22 does not face the positive electrode plate 21, it is not related to the charge amount, but the negative electrode mixture 223 of the outer peripheral surface 221B has a negative electrode of the inner peripheral surface 221A that contributes to the charge amount. Lithium ions (Li ⁺ ) move from the mixture 222. As a result, the lithium ions (Li ⁺ ) on the inner peripheral surface 221A that contributes to the charge amount are reduced, and the charge amount as the secondary battery 10 is reduced. That is, self-discharge occurs and the charge amount also decreases.

Further, the lithium ion (Li ⁺ ) transferred to the negative electrode mixture 223 on the outer peripheral surface 221B further reacts with the active gas and is oxidized to form lithium carbonate (Li ₂ CO ₃ ) on the negative electrode mixture 223 to form a wide precipitation layer 30B. It will also form. Further, if the lithium ion (Li ⁺ ) that has moved to the outer peripheral surface 221B and once reduced the potential difference becomes lithium carbonate (Li ₂ CO ₃ ), the potential difference will increase again. Then, the phenomenon that lithium ions (Li ⁺ ) move from the negative electrode mixture 222 on the inner peripheral surface 221A to the negative electrode mixture 223 on the outer peripheral surface 221B and the charge amount as the secondary battery 10 decreases continuously continues. It will be like.

With respect to these points, in the present embodiment, by enclosing the inert gas in the battery case 11 in the inert gas encapsulation step, self-discharge as the secondary battery 10 and deterioration of battery performance are suppressed.

Further, as shown on the left side of FIGS. 4 (b) and 5 (b), if a portion (uncoated portion) in which the negative electrode mixture 222, 223 is not coated is provided at the end portion of the negative electrode base material 221. It is not easy for lithium ions (Li ⁺ ) to move from the negative electrode mixture 222 on the inner peripheral surface 221A to the negative electrode mixture 223 on the outer peripheral surface 221B over the negative electrode base material 221 (arrow J2). On the contrary, as shown on the right side of FIGS. 4 (b) and 5 (b), when the negative electrode mixture 222,223 is applied to the end of the negative electrode base material 221, lithium ions (Li ⁺ ) are generated. It is easy to get over the negative electrode base material 221 and move from the inner peripheral surface 221A to the outer peripheral surface 221B (arrow J1). Therefore, by providing the uncoated portion, it is possible to suppress the self-discharge of the secondary battery 10 and the deterioration of the battery performance.

(Calculation of replacement rate)
A predetermined method for calculating the substitution ratio used in the inert gas filling step will be described with reference to FIGS. 6 and 7.

A plurality of secondary batteries 10 are used for calculating the replacement ratio, but for convenience of explanation, two secondary batteries 10 will be described as an example. Further, for convenience of explanation, the flowcharts of FIGS. 3 and 6 will be described assuming that the two secondary batteries 10 are processed in each step.

First, for the secondary battery 10 for which the replacement ratio is to be obtained, a secondary battery 10 equivalent to this is created. That is, two equivalent secondary batteries 10 are prepared from the winding step (step S10 in FIG. 3) to the liquid injection step (step S16 in FIG. 3).

Then, for the equivalent secondary battery 10, the test inert gas filling step (step S170 in FIG. 6) and the self-discharge step (step S21 in FIG. 6) from the sealing step (step S18 in FIG. 6) are performed. Execute under the same conditions. Further, for the same secondary battery 10, the active gas ratio acquisition step (step S30 in FIG. 6) and the replacement ratio calculation step (step S31 in FIG. 6) as the replacement amount calculation step are the same conditions. To execute. The steps from the sealing step (step S18 in FIG. 6) to the self-discharge step (step S21 in FIG. 6) are the same as those from the sealing step (step S18) to the self-discharge step (step S21) in FIG. The detailed explanation of the process is omitted.

More specifically with reference to FIG. 6, in the test inert gas filling step (step S170 of FIG. 6), different substitution rates are applied to the two secondary batteries 10. For example, the replacement ratio of the secondary battery 10 for one test in the inert gas filling step is set to "15%", and the replacement ratio of the secondary battery 10 for the other test in the inert gas filling step is set to "15%". Is set to "0%". Then, the sealing step (step S18 in FIG. 6) to the self-discharge step (step S21 in FIG. 6) are executed for each of the two secondary batteries 10.

After that, in the active gas measuring step, the ratio of the active gas in the battery case 11 is measured. As a result, the "concentration [%]" (reference value) of the active gas in the cell after self-discharge is measured from the other test secondary battery 10 when the replacement ratio is "0%". Further, from one of the test secondary batteries 10, the "concentration [%]" (improved value) of the active gas in the cell after self-discharge is measured when the replacement ratio is "15%". Then, based on the measured "reference value" and "improvement value", the replacement ratio for setting the ratio of the active gas of the secondary battery 10 after the self-discharge step to a predetermined ratio (for example, "30%") is set. The replacement ratio calculation step to be calculated is performed (step S31 in FIG. 6). As a result, the replacement ratio for the secondary battery 10 for which the replacement ratio is to be obtained is calculated. Then, this calculated replacement ratio is also used as the replacement ratio determined in the inert gas filling step when the equivalent secondary battery 10 is manufactured.

The calculation of the replacement ratio will be described with reference to FIG. 7.

Graph C1 of FIG. 7 shows an example of the replacement ratio required to set the reference value to the target value “30%”. The target value "30%" is a predetermined ratio and is a value of the ratio of the active gas in the battery case 11 after the self-discharge step. As shown in graph C1, if a reference value and an improved value of the secondary battery 10 having the reference value are obtained, the replacement ratio required to set the secondary battery 10 as the target value is the reference value. , It can be calculated based on the improvement value, the target value, and the replacement ratio that makes the reference value the improvement value. For example, the replacement ratio can be calculated by "(reference value-target value) / (reference value-improvement value) x (replacement ratio to be an improvement value)".

The example shown in the graph C1 of FIG. 7 shows the relationship between the reference value obtained from the plurality of secondary batteries 10 and the replacement ratio to be the target value. As shown in Graph C1, the higher the reference value, the larger the replacement ratio to be the target value. According to the graph C1, when the reference value is 40%, the replacement ratio is determined to be about 15%, and when the reference value is 50%, the replacement ratio is determined to be about 35%. With the graph C1 thus obtained, the substitution ratio in the inert gas filling step with respect to the secondary battery 10 can be determined.

(Potential difference of negative electrode plate)
With reference to FIG. 8, the potential difference generated in the negative electrode plate 22 of the electrode plate group 20 will be described.

FIG. 8 shows two graphs C2 regarding the relationship between the charge amount Q of the negative electrode plate 22 and the potential difference generated between the negative electrode mixture 223 on the outer peripheral surface 221B and the negative electrode mixture 222 on the inner peripheral surface 221A in the negative electrode plate 22. C3 is shown. Of these, graph C2 shows the case where the negative electrode active material is graphite having three-dimensional crystals, and graph C3 shows the case where the negative electrode active material is soft carbon or hard carbon made of amorphous carbon.

In the present embodiment, the negative electrode active material contained in the negative electrode mixture 222,223 is graphite. When the charge amount Q of the negative electrode active material containing graphite as a main component is in the range of a certain value or more, the potential difference is small and kept low with respect to the change of the charge amount Q. On the other hand, when the charge amount Q is in the range of less than a certain value, the potential difference with respect to the change in the charge amount Q has a characteristic that the potential difference becomes very large. Generally, when the secondary battery 10 is stored for a long period of time, the charge amount is not controlled, so that the charge amount Q is likely to drop to less than a certain level. Then, once the charge amount Q drops to less than a certain level, if a difference in charge amount Q occurs between the inner peripheral surface 221A and the outer peripheral surface 221B of the negative electrode plate 22 due to the above-mentioned reason or the like, the inner peripheral surface Q The potential difference between the peripheral surface 221A and the outer peripheral surface 221B suddenly increases. Then, as described above, the movement of lithium ions (Li ⁺ ) from the negative electrode mixture 222 on the inner peripheral surface 221A to the negative electrode mixture 223 on the outer peripheral surface 221B caused by the potential difference is further promoted by the large potential difference. Become. That is, once the charge amount Q drops to a range below a certain level, self-discharge and deterioration of ionization performance may rapidly progress.

In this respect, in the secondary battery 10 of the present embodiment, the lithium ion (Li ⁺ ) of the outermost negative electrode mixture 223 is deactivated and moved from the inner peripheral surface 221A to the outer peripheral surface 221B in the inert gas filling step. Since it is suppressed, the decrease in the charge amount Q is also suppressed, and the period in which the charge amount Q is maintained above a certain level can be extended even if the charge amount Q is stored for a long period of time. Therefore, according to the present embodiment, even if the secondary battery 10 is stored for a long period of time, the deterioration of the battery performance caused by the reaction between the electrode plate group 20 and the gas in the battery case 11 can be suppressed.

As described above, according to the present embodiment, the effects described below can be obtained.

(1) The secondary battery 10 in the charged state is in a state where lithium ions (Li ⁺ ) are held in the negative electrode plate 22, but if this is stored for a long period of time, self-discharge and deterioration of battery performance occur. That is, the lithium ion (Li ⁺ ) held in the negative electrode plate 22 reacts with the active gas to be deactivated to become lithium carbonate (Li ₂ CO ₃ ), or the inner peripheral surface 221A of the negative electrode plate 22. Due to the potential difference from the outer peripheral surface 221B, lithium ions (Li ⁺ ) move from the inner peripheral surface 221A of the negative electrode plate 22 to the outer peripheral surface 221B, and the charge amount decreases.

In this respect, in the present embodiment, a part of the gas in the electric tank is replaced with the inert gas in the inert gas filling step so that the ratio of the active gas in the electric tank after the self-discharge step becomes a predetermined ratio or less. .. As a result, the ratio of the negative electrode active material of the outermost negative electrode plate 22 reacting with the active gas in the electric tank is reduced, and the decrease of lithium ions (Li ⁺ ) held in the negative electrode plate 22 in the charged state is suppressed. Will be done. Therefore, it is possible to suppress the deterioration of the battery performance caused by the gas in the battery case.

(2) Even if the negative electrode plate 22 of the electrode plate group 20 is arranged on the outermost circumference and is in a state where it easily reacts with the gas in the electric tank, the reaction with the active gas is suppressed by the inert gas sealed in the electric tank. Will be able to.

(3) Since the ratio of the active gas after the self-discharge step is 30% or less, the deactivation and self-discharge of lithium ions (Li ⁺ ) in the negative electrode plate 22 in contact with the gas in the electric tank can be suppressed.

(4) By using helium gas (He) and argon gas (Ar) as the inert gas, deactivation of lithium ions in the negative electrode plate 22 is suppressed.

(5) Even if the ratio of active gas increases in the charging step and the high temperature aging step after sealing the battery case 11, the ratio of the active gas in the battery case is suppressed to a predetermined ratio after the charging step and the high temperature aging step. You will be able to do it.

(6) The amount of substitution with the inert gas in the inert gas filling step is the ratio of replacing the air in the electric tank with the inert gas in the inert gas filling step and the amount in the electric tank after the self-discharge step. It is determined in advance based on the ratio of the active gas.

(7) It becomes possible to suppress self-discharge and deterioration of battery performance of a lithium ion secondary battery that has been stored for a long period of time in a charged state.

(Other embodiments)
The above embodiment can also be carried out in the following embodiments.

-In the above embodiment, the case where the electrode plate group 20 has a structure in which the positive electrode plate 21, the negative electrode plate 22, and the separator 23 are wound is exemplified. However, the present invention is not limited to this, and may be appropriately changed depending on the shape of the secondary battery and the purpose of use. For example, it may have a structure of a type in which the positive electrode plate, the negative electrode plate, and the separator are laminated (not wound).

-In the above embodiment, the case where a part of the atmosphere in the battery case 11 is replaced with the inert gas has been illustrated. However, the present invention is not limited to this, and the entire atmosphere inside the battery case may be replaced with an inert gas (for example, the replacement ratio is 100%).

-In the above embodiment, the case where the ratio of the inert gas is replaced with the gas in the battery case 11 in the inert gas filling step is illustrated. However, the present invention is not limited to this, and the inert gas filling step can be omitted by performing the work before the inert gas filling step in an atmosphere in which the ratio of the inert gas corresponds to the replacement ratio. Alternatively, the proportion of the inert gas injected in the inert gas filling step can be reduced.

-In the above embodiment, the case where the inert gas is helium gas or argon gas has been exemplified. However, the present invention is not limited to this, and the inert gas may be a mixture of helium gas and argon gas, or may be a mixture of helium gas and argon gas with other gases. Further, as the inert gas, a gas other than Group 18 in the periodic table, for example, nitrogen gas (N ₂ ) may be used.

-In the above embodiment, the case where the predetermined ratio is, for example, 30% or less is illustrated, but the present invention is not limited to this, and the predetermined ratio may be less than 30% or the predetermined ratio may be larger than 30%. The predetermined ratio can be set according to the battery characteristics and applications of the secondary battery.

-In the above embodiment, the case where the outermost circumference of the electrode plate group 20 is the negative electrode plate 22 is illustrated. However, the present invention is not limited to this, and a separator wound around the outer periphery of the negative electrode plate may be arranged on the outermost circumference of the electrode plate group. For example, in the laminated body before winding, the separator wound around the negative electrode plate can be arranged on the outermost periphery by winding the laminated body so that the positive electrode plate is on the inside. Further, even if the separator is arranged on the outer periphery of the negative electrode plate, the fiber density is lower than that of the separator sandwiched between the electrode plates, so that the gas in the battery case reaches the negative electrode mixture. I don't have much to do.

-In the above embodiment, the case of having the self-discharge step is illustrated, but the self-discharge step is not limited to this, and the self-discharge step may be a discharge step in which a resistor or the like is connected between the terminals.

-The secondary battery 10 does not have to be mounted on an electric vehicle or a hybrid vehicle. For example, the secondary battery 10 may be mounted on a vehicle such as a gasoline vehicle or a diesel vehicle. Further, the secondary battery 10 may be used as a power source for moving objects such as railways, ships, and aircraft, and electric products such as robots and information processing devices.

10 ... Secondary battery, 11 ... Battery case, 12 ... Lid, 13, 14 ... Electrode terminal, 20 ... Electrode plate group, 21 ... Positive electrode plate, 21A ... Positive electrode part, 22 ... Negative electrode plate, 22A ... Negative electrode part, 23 ... Separator, 26 ... Edge, 27 ... Non-aqueous electrolyte, 30A, 30B ... Precipitated layer, 211 ... Positive electrode base material, 211A ... Inner peripheral surface, 211B ... Outer peripheral surface, 212, 213 ... Positive electrode mixture, 221 ... Negative electrode base material , 221A ... Inner peripheral surface, 221B ... Outer peripheral surface, 222,223 ... Negative electrode mixture.

Claims (6)

It is a method of manufacturing a non-aqueous electrolyte secondary battery in which an electrode body is housed in an electric tank.
A winding step of manufacturing the electrode body by winding a positive electrode plate and a negative electrode plate having an active material on both sides of a metal current collector foil with a separator sandwiched between them.
The accommodating step of accommodating the electrode body and the non-aqueous electrolyte in the electric tank, and
A part of the gas in the electric tank containing the electrode body and the non-aqueous electrolyte is replaced with the inert gas by a predetermined replacement amount, and the electric tank is not sealed in this replaced state. The active gas filling process and
A discharge step of discharging the sealed secondary battery of the battery case after charging, and
It is provided with a substitution amount calculation step for obtaining the substitution amount.
In the winding step, the negative electrode plate is wound so as to have a portion to be arranged on the outer periphery of the positive electrode plate.
In the inert gas filling step, the ratio of the active gas composed of carbon dioxide, carbon monoxide, and oxygen in the electric tank after the discharge step is one of the gases in the electric tank in the inert gas filling step. A part of the gas in the electric tank is inactive so as to be a predetermined ratio or less, which is a ratio lower than the ratio of the active gas in the electric tank after the discharge step when the portion is not replaced with the inert gas. Replace with gas,
The substitution amount calculation step is the inert gas filling step separately performed for a test secondary battery equivalent to the secondary battery for which the substitution amount is to be calculated in advance prior to the inert gas filling step. The ratio of the acquired gas in the electric tank replaced with the inert gas and the active gas in the electric tank acquired after the discharge step separately performed separately for the test secondary battery in advance. A method for manufacturing a non-aqueous electrolyte secondary battery for which the substitution amount is determined based on the ratio. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1, wherein in the winding step, the electrode body is wound so that the negative electrode plate is arranged at least a part of the outermost periphery. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein in the inert gas filling step, a part of the gas in the battery case is replaced with the inert gas so that the predetermined ratio becomes 30% or less. Production method. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein at least one of helium gas (He) and argon gas (Ar) is used as the inert gas in the inert gas filling step. Manufacturing method. Further, between the end of the inert gas filling step and the end of the discharging step,
A charging process that charges the secondary battery with a predetermined amount of charge,
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, further comprising a high temperature aging step of maintaining the secondary battery in a predetermined high temperature environment for a predetermined period after being charged in the charging step. Manufacturing method. A lithium ion secondary battery is manufactured as the non-aqueous electrolyte secondary battery.
The method for manufacturing a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5 .

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