JP2014164861A - Lithium battery manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium battery manufacturing method capable of improving safety and productivity while achieving good long-term storage performance.SOLUTION: The method includes: a step of housing a negative electrode material 4 made of lithium and a lithium alloy, a positive electrode material 3, and an organic electrolyte in a battery can 2 on which one of positive and negative electrode terminal parts 11 is formed, and assembling a lithium battery 1 by sealing an opening 13 of the battery can by a sealing body 9 also serving as the other electrode terminal part 7; and a preliminary discharging step s12 of discharging a predetermined ratio of electric capacitance relative to a theoretical capacity to the assembled lithium battery. In the preliminary discharging step, a load of 20 Ω or more and 50 Ω or less is connected and discharged between one electrode terminal part and the other electrode terminal part.

Description

  The present invention relates to a method for manufacturing a lithium battery, and more particularly to a preliminary discharge process for a lithium battery after assembly.

  A lithium battery using a positive electrode material containing manganese dioxide, graphite fluoride, copper oxide or the like as a positive electrode active material, a negative electrode material made of lithium metal or a lithium alloy, and an organic electrolyte has high energy density and is excellent In addition, it is widely used as a power source and backup for various small portable devices.

  By the way, the outstanding preservation | save performance in a lithium battery is acquired by performing the process called preliminary discharge in the manufacturing process of a battery. The preliminary discharge is performed by discharging several percent (for example, 2%) of the theoretical capacity in advance immediately after battery assembly. Accordingly, in the lithium battery, lithium ions are electrochemically inserted into the positive electrode active material, the activity of the positive electrode active material is lowered, and characteristic deterioration due to decomposition of the electrolyte during storage is prevented.

  Specifically, an organic electrolyte mainly composed of propylene carbonate (PC) is used as an electrolyte in a lithium battery. However, when the positive electrode contains a carbon material as a conductive material, the decomposition potential of PC is 0. When the potential on the positive electrode side is less than 0.8 V with respect to metallic lithium, PC decomposes and a resistor is generated on the surface of the carbon material, and gas is generated accordingly. If the preliminary discharge is performed by a method in which a large current is passed in a short time, for example, by short-circuiting between the positive and negative terminals, the positive electrode potential falls below the PC decomposition voltage. For this reason, conventionally, a predetermined capacity is preliminarily discharged by flowing a small current over a long period of time while monitoring so as not to be lower than the decomposition potential of the PC. Patent Document 1 below discloses a technique for improving the storage performance of a lithium battery by defining predischarge conditions and the like. The structure of various lithium batteries is described in Non-Patent Document 1 below.

JP 2009-152030 A

Ina Denki Co., Ltd., “Manufacturer List”, [online], [Search February 14, 2013], Internet <URL: http://www.inedenki.co.jp/pdf/sanyo_lit.pdf>

  As described above, in a lithium battery, preliminary discharge is an essential process in the manufacturing process, and the preliminary discharge is small, including the technique described in Patent Document 1, in order to suppress decomposition of the electrolytic solution. This was performed by a so-called “constant current method” in which a current is applied for a long time. For this reason, it has been difficult to dramatically improve the productivity of lithium batteries. Further, in the preliminary discharge by the constant current method, the discharge is performed while monitoring the current for each of the batteries, so that the equipment used for the preliminary discharge becomes complicated and the initial cost in the manufacturing equipment is increased. Furthermore, since the discharge is performed while monitoring the current, if any trouble occurs in the current monitoring system of the facility related to the preliminary discharge, the current may continue to flow and the battery may even ignite.

  Of course, by connecting a resistance element having a small resistance value between the positive and negative electrodes of the battery, and pre-discharging in the “short circuit method” in which a current flows in a substantially short-circuited state, as described above, a large current flows in a short time, The decomposition of the electrolytic solution and various problems associated therewith occur. Further, in the preliminary discharge by the short-circuit method, the temperature rise generated due to Joule heat becomes non-uniform in the battery, and a temperature difference is generated in the battery. Due to the Seebeck effect associated with the temperature difference, metal lithium or lithium alloy fine powder constituting the negative electrode material is deposited in the battery. If this fine powder enters the porous structure of the separator, an extremely fine short circuit (fine short circuit) occurs. The short-circuit caused by the fine powder of the negative electrode material causes a loss of a small amount of capacity equivalent to several percent below the decimal point when stored for a long period of time.

  Accordingly, an object of the present invention is to provide a method for producing a lithium battery that can improve safety and productivity while achieving good long-term storage performance.

  In order to achieve the above object, the present invention accommodates a negative electrode material made of lithium and a lithium alloy, a positive electrode material, and an organic electrolyte in a battery can in which one of positive and negative electrode terminal portions is formed. The process of assembling a lithium battery by sealing the opening of the battery can with a sealing body that also serves as the other electrode terminal part, and preliminary discharge for discharging a predetermined ratio of electric capacity to the theoretical capacity of the assembled lithium battery In the preliminary discharge process, a load of 20Ω or more and 50Ω or less is connected between the one electrode terminal portion and the other electrode terminal portion to discharge the lithium battery. Yes.

  In the preliminary discharge step, it is more preferable to discharge with a constant load of 35Ω to 50Ω over the period of the step. Alternatively, in the preliminary discharge step, the load of 20Ω or more and 50Ω or less may be discharged while being switched stepwise during the period of the step.

  According to the method for manufacturing a lithium battery according to the present invention, productivity can be improved and safety during manufacturing can be ensured. In addition, a lithium battery having good long-term storage performance can be provided. Other effects will be clarified in the following description.

It is a structural diagram of a bobbin type lithium battery. It is a figure which shows an example of the manufacturing method of a bobbin type lithium battery. It is a figure which shows the discharge characteristic at the time of carrying out preliminary discharge of the bobbin type lithium battery based on the manufacturing method which concerns on the Example of this invention.

=== Structure of lithium battery ===
FIG. 1 shows a cylindrical lithium battery 1 called a bobbin type (or inside-out type) as an example of a lithium battery that is an object of the present invention. In addition, in this figure, the longitudinal cross-sectional view when the extending direction of the cylindrical axis | shaft 100 is made into the up-down (vertical) direction is shown. The lithium battery 1 includes a bottomed cylindrical battery can 2 that also serves as a positive electrode terminal, a positive electrode material (hereinafter, positive electrode mixture) 3 formed into a hollow cylindrical shape, a negative electrode material 4, a cylindrical cup-shaped separator 5, and a negative electrode terminal. It is comprised by the board 7 grade | etc.,.

  The battery can 2 is made of metal, and a convex positive terminal portion 11 is formed on the outer bottom surface thereof by pressing. The positive electrode mixture 3 is obtained by molding and solidifying a mixture of manganese dioxide (EMD) as a positive electrode active material, a carbon material as a conductive material, and a fluorine-based binder (PTFE) into a hollow cylindrical core. Has been. The separator 5 has a cylindrical bag shape and is made of a composite material made of polypropylene, polyethylene, and glass fiber.

  The negative electrode material 4 is obtained by rolling a metallic lithium plate as a negative electrode active material into a hollow cylindrical shape, and one end portion 6a of the negative electrode lead 6 is attached in advance to a part thereof. The negative electrode lead 6 is a strip-shaped metal thin plate, and its one end 6a is connected to the negative electrode material 4 in a planar state to form a negative electrode current collector. There is also a lithium battery that uses a lithium alloy (for example, lithium / aluminum alloy) as the negative electrode material 4.

  In addition, the upper opening of the battery can 2 is sealed by the sealing body 9 with the opening end 13 side of the battery can 2 facing upward. The sealing body 9 is formed by laminating a disc-shaped sealing plate 8 below the flat plate-shaped metallic negative electrode terminal plate 7, and the other end 6 b of the negative electrode lead 6 is connected to the lower surface of the sealing plate 8 (inside the battery). Spot welded to the side). Thereby, the negative electrode terminal plate 7 which is the negative electrode terminal portion and the negative electrode material 4 are electrically connected.

=== Production Method of Lithium Battery ===
FIG. 2 shows an example of a manufacturing procedure of the lithium battery 1 having the above structure. The positive electrode mixture 3 is inserted into the battery can 2 (s1). After performing a predetermined drying process, the separator 5 is disposed inside the positive electrode mixture 3 (s2), and the negative electrode material 4 in a state where the one end portion 6a of the negative electrode lead 6 is fixed is inserted into the separator 5 ( s3).

  Next, the beading portion 12 is formed around the upper end side of the battery can 2, and the other end portion 6b of the negative electrode lead 6 is welded to the sealing plate 8 through the central hole of the gasket 10 (s4, s5). Further, a cylindrical insulator (insulating cylinder) is detachably attached to the battery can 2, and an organic electrolyte containing PC as a solvent is injected into the battery can 2 (s6). The can 2 is placed while inserting the sealing plate 8 with the previous beading portion 12 as a seat through the gasket 10 (s7). Further, the negative electrode terminal plate 7 is inserted into the battery can 2 while being laminated above the sealing plate 8 (s8). After the insulating cylinder attached to the battery can 2 is removed, the opening end 13 of the battery can 2 is subjected to curling (bending) processing (s9, s10), and the region from the beading 12 to the opening end 13 of the battery can 2 The battery can 2 is hermetically sealed by caulking inward (s11). The assembly of the lithium battery 1 is completed through the above steps. Then, preliminary discharge (s12) is performed on the assembled lithium battery 1 to complete the lithium battery 1. Each member has been previously dried, and the above-described battery assembly is performed in a dry atmosphere.

=== Embodiment of the Invention ===
As a lithium battery manufactured by the manufacturing method according to the embodiment of the present invention, the bobbin type lithium battery 1 shown in FIG. 1 is given. That is, the manufacturing method according to the embodiment of the present invention follows the procedure shown in FIG. However, the method for manufacturing a lithium battery according to the present embodiment is characterized by the contents of the preliminary discharge step (s12), thereby improving the productivity of the lithium battery and the long-term storage characteristics of the lithium battery after manufacture. Has been successful. In general, during the preliminary discharge step (s12), the discharge is performed under a constant load, not a constant current. Hereinafter, the method of performing preliminary discharge in a state where a certain load is applied will be referred to as a “constant resistance method”. The preliminary discharge by the constant resistance method, which is a feature of the method for manufacturing a lithium battery according to the embodiment of the present invention, will be described below.

  First, in order to confirm the effectiveness of the manufacturing method of the lithium battery according to the example of the present invention, a CR2 / 38L type lithium battery was prepared as a sample. There were 6 types of samples with different predischarge conditions, and 1000 specimens were prepared for each type. Then, an initial characteristic test for measuring the open circuit voltage (OV) after aging was performed on all the individuals, and the appearance rate (%) of individuals that became defective below the specified value was obtained. Also, this initial characteristic test Then, a long-term storage characteristic test was performed on individuals whose OV was equal to or higher than the standard value. The long-term storage characteristic test was performed by obtaining the defective individual appearance rate (%) at which the OV was below the standard value after storage at 70 ° C. for 114 days (corresponding to about 10 years).

  Table 1 below shows the preliminary discharge conditions and test results of each sample.

  In Table 1, Sample 1 was subjected to preliminary discharge by the short circuit method. Samples 2 to 6 were pre-discharged by a constant resistance method after the samples were assembled by the manufacturing method shown in FIG. In Samples 2 to 5, a constant load was continuously connected between the positive and negative electrode terminals (11, 7) until a predetermined ratio (about 2.0%) of the theoretical capacity was discharged. It was discharged in a state. The loads in samples 2 to 5 are 40Ω, 35Ω, 30Ω, and 20Ω, respectively.

  Sample 6 is not subjected to preliminary discharge by continuously applying a constant load for a certain period of time as in samples 2 to 5, but each load of 20Ω, 30Ω, and 40Ω is shown in (a) to ( The preliminary discharge was performed by the constant resistance method while switching in the order of e). Sample 6 was also discharged so that the discharge capacity was about 2% in the preliminary discharge step (s12). Table 1 also shows the discharge capacity (%) in each sample.

  As shown in Table 1, Sample 1 subjected to preliminary discharge by the short circuit method could not satisfy the initial characteristics required by 0.2% of the individuals. In the long-term storage characteristic test, 2.8% of defective individuals were generated. In the preliminary discharge in the short-circuit method, since the battery immediately after assembly is discharged at the maximum current that can be output, a temperature difference occurs in the battery until 2% of the capacity is discharged (about 10 minutes). This temperature difference causes the above-described fine short circuit, which seems to have deteriorated initial characteristics and long-term storage characteristics. In addition, in the short-circuit type preliminary discharge, the closed-circuit voltage during discharge continues to be almost 0 (V), so that a small amount of PC in the electrolyte may be decomposed or manganese in the positive electrode mixture may be reduced. Sex is also considered. In any case, in the preliminary discharge in the short circuit method, productivity was lowered due to a decrease in yield, and reliability was lowered due to characteristic deterioration.

  On the other hand, in samples 2 to 6 where preliminary discharge was performed by the constant resistance method, the initial characteristics could be satisfied with all solids. In Samples 2 to 5 in which the preliminary discharge was performed while continuously applying a certain load, the time until the predetermined capacity was preliminarily discharged was shorter as the load was smaller. Among samples 2 to 5, in sample 4 in which preliminary discharge was performed with a load of 30Ω, a defect occurred in 0.2% of the solid in the long-term storage test, and in sample 5 in which preliminary discharge was performed with a load of 20Ω, all Although the initial characteristics could be secured with the solid, 2.0% of the solids were defective in the long-term storage test. However, it was confirmed that the defect occurrence rate was reduced as compared with the sample 1 in which the preliminary discharge was performed by the short circuit method. Further, in sample 6 in which preliminary discharge was performed by changing the load value stepwise, no failure occurred in the initial characteristic test and the long-term storage characteristic test in all the individuals.

  From the above results, by performing preliminary discharge with a low resistance method with a load of 20Ω or more, it is possible to reliably reduce the time required for preliminary discharge while ensuring initial characteristics, and to improve productivity. . From the test results of Samples 2 to 5, if the load is made larger than 50Ω, the preliminary discharge time is expected to exceed 50 minutes, so a large time reduction effect cannot be obtained.

  FIG. 3 is a graph 200 showing the relationship between the load and discharge time in Samples 2 to 6 in Table 1. In the graph 200, a white circle “◯” and a linear approximate straight line 201 indicated by a solid line indicate the load and discharge time for the samples 2 to 5 shown in Table 1. A black line “●” and a linear approximate straight line 202 indicated by a dotted line indicate the relationship between the load and the discharge time when the discharge capacities of the samples 2 to 5 are normalized to 2.0% uniformly. The points indicated by triangles “Δ” indicate the average load value (≈33Ω) and the discharge time (35 minutes) in sample 6. As is apparent from this graph 200, the time required for the preliminary discharge and the load to be connected are substantially proportional to each other, and the time required for the preliminary discharge can be shortened as the load is reduced. As for the load suitable for the preliminary discharge by the constant resistance method, when the load is too small, it becomes a state close to a short circuit, and with a load of 20Ω, a solid that has become defective in the initial characteristic test does not occur. Since the defect occurrence rate in the test was about 70% of the sample 1 subjected to the preliminary discharge by the short circuit method, the lower limit was defined as 20Ω or more.

  The upper limit was defined as 50Ω. As expected from the approximate straight lines (201, 202) shown in the graph 200 shown in FIG. 3, the discharge time is about 50 to 55 minutes with a load of 50Ω, and about 1 hour with a load larger than 50Ω. This is because, since the discharge time becomes necessary, it is determined that a large time reduction effect cannot be obtained with a load larger than 50Ω. In Samples 2 to 5 in which a predetermined capacity is continuously discharged with a constant load with respect to the theoretical capacity, the preliminary discharge with the load of 20Ω of Sample 5 and the load of 30Ω of Sample 4 is defective in the long-term storage test. In the case where a predetermined capacity is continuously discharged with a constant load with respect to the theoretical capacity, it is more preferable to perform preliminary discharge with a load of 35Ω to 50Ω.

  On the other hand, sample 6 was pre-discharged with a low load of 20Ω or 30Ω, but the defect occurrence rate in the long-term storage test could be 0%. That is, if preliminary discharge at a low load is not continued for the entire period of the discharge, extremely excellent initial characteristics and long-term storage characteristics can be ensured even if the above conditions of 35Ω to 50Ω are not satisfied. I understood. In addition, the discharge time in this case was 35 minutes, and the average load over the entire discharge time was about 33Ω. This means that a predetermined capacity can be predischarged in a time equivalent to the 30 Ω load of sample 4 lower than 33 Ω. In addition, like Samples 2 and 3, it means that it has extremely long-term storage test characteristics. Therefore, it is more preferable to perform the discharge stepwise with a plurality of different loads of 20Ω to 50Ω in the preliminary discharge.

  As described above, according to the manufacturing method of the present embodiment, the time required for the preliminary discharge can be shortened, and the complicated equipment that has been a problem in the preliminary discharge by the constant current method becomes unnecessary, thereby reducing the initial cost in the manufacturing equipment. Can be made. Furthermore, since there is no need to monitor the current, it is not necessary to consider troubles in the facility itself related to preliminary discharge (ignition due to overdischarge, etc.), and safety is high. In the above embodiment, the method for manufacturing the bobbin-type lithium battery has been described. However, the present invention may be any lithium battery that requires preliminary discharge in the manufacturing process, such as a coin-type lithium battery or a cylindrical spiral lithium battery. It can also be applied to a manufacturing method. Of course, the present invention can also be applied to a lithium battery having a structure in which a battery can that also serves as a negative electrode terminal is sealed with a sealing body that also serves as a positive electrode terminal.

1 Bobbin-type lithium battery, 2 battery can, 3 cathode mix, 4 anode material,
5 Separator, 6 negative electrode lead, 7 negative electrode terminal plate, 8 sealing plate, 9 sealing body,
10 Gasket, 11 Positive terminal, 200 Predischarge characteristic graph

Claims (3)

  In a battery can in which one of the positive and negative electrode terminal portions is formed, a negative electrode material made of lithium or a lithium alloy, a positive electrode material, and an organic electrolyte are housed, and the opening of the battery can is connected to the other electrode terminal portion. Including a step of assembling a lithium battery by sealing with a sealing body that also serves as an assembly, and a preliminary discharge step of discharging a predetermined ratio of electric capacity to the theoretical capacity with respect to the assembled lithium battery, A method for producing a lithium battery, comprising discharging a load of 20Ω to 50Ω between the one electrode terminal portion and the other electrode terminal portion.   2. The method of manufacturing a lithium battery according to claim 1, wherein in the preliminary discharging step, discharging is performed with a constant load of 35Ω to 50Ω over a period of the step.   2. The method of manufacturing a lithium battery according to claim 1, wherein in the preliminary discharging step, discharging is performed while the load of 20Ω or more and 50Ω or less is switched stepwise during the period of the step.

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