JP6728724B2 - First charge method of lithium secondary battery - Google Patents

Description

The present invention relates to a method for initially charging a lithium secondary battery, and more particularly to a method for improving productivity and quality of a large lithium secondary battery of 5 Ah or more.

BACKGROUND ART Lithium secondary batteries have recently been used as a power source for portable devices such as digital cameras, laptop computers and mobile phones, taking advantage of their high energy density. Further, in recent years, in order to deal with environmental problems, research and development of large-sized lithium secondary batteries for use in electric vehicles and for power storage have been actively conducted.

Generally, a lithium secondary battery includes a positive electrode plate in which a positive electrode active material containing a lithium transition metal composite oxide is applied to a positive electrode current collector such as an aluminum foil, and a negative electrode active material containing a carbon material is a negative electrode current collector such as a copper foil. The negative electrode plate applied to, the electrode plate group laminated or wound via a porous separator made of an insulating material is housed in a battery container and is prepared by injecting a non-aqueous electrolyte solution. It The wound type has the advantages that the production process is easier and the productivity is higher than the laminated type.

The dimensions of a typical wound-type lithium secondary battery used in portable equipment and the like are 18 mm in diameter and 65 mm in height, and are called 18650 type batteries. The battery capacity of the 18650 type battery is about 1.0 to 3.5 Ah. On the other hand, lithium secondary batteries used in electric vehicles and power storage applications are required to have not only high capacity but also high output, long life, and cost reduction. In order to achieve high capacity and high output, it is general to increase the size of the wound electrode group or increase the number of turns of the wound electrode group.

However, when the wound electrode group becomes large, it takes time for the electrolytic solution to penetrate into the wound electrode group. If charging/discharging is performed with insufficient penetration of the electrolytic solution, not only the rated battery capacity will not develop, but the charging/discharging reaction inside the wound electrode group will be non-uniform, so the actual charging current density will be local. In some cases, metallic lithium may be deposited on the negative electrode and penetrate the separator to cause an internal short circuit.

Therefore, in Patent Document 1, in a large-sized wound-type lithium secondary battery in which a positive electrode plate and a negative electrode plate are wound 40 times or more, 24 hours or more after injection of the non-aqueous electrolyte solution, the first time It proposes to charge.

JP, 2003-308878, A

However, when the negative electrode active material contains a carbon material and the current collector is copper, the dissolution of copper starts at the time when the electrolytic solution is poured. This is because the potential of the negative electrode at the stage of not charging is about 3.4 V, which is higher than the potential (about 3 V) at which copper is dissolved in the electrolytic solution. When copper is dissolved in the electrolytic solution, it causes clogging of the separator and reduces the current collecting performance of the negative electrode current collector, which not only causes an increase in battery resistance, but also the copper dissolved in the electrolytic solution on the negative electrode. There is a concern that it may be deposited on the inner surface and may lead to an internal short circuit. Although the battery container is generally made of a metal material, if the battery container is electrically neutral and does not serve as a positive electrode or a negative electrode, the only element that may be dissolved in the electrolytic solution after injection is copper. is there.

An object of the present invention is to suppress the dissolution of copper, which is a negative electrode current collector, in an electrolytic solution, and to allow the electrolytic solution to sufficiently penetrate into a wound-type electrode group, and to provide a first charging method for a lithium secondary battery. It is to propose.

The present invention provides a wound electrode group in which a negative electrode containing copper in a negative electrode current collector holding a negative electrode active material and a positive electrode having a positive electrode active material held in a positive electrode current collector are wound with a separator interposed therebetween. The first charging method is a first charging method for a lithium secondary battery having a design capacity of 5 Ah or more, which is housed in an electrically neutral battery container, and an electrolytic solution is injected into the battery container. It is realized by the leaving step and the second charging step. In the first charging step, the surfaces of the negative electrode active material of the negative electrode and the positive electrode active material of the positive electrode are completely covered with the electrolytic solution within the first period starting from the time of injecting the electrolytic solution into the battery container. In the state of being touched, the first charge is performed so that the potential of the negative electrode decreases until it falls below the potential at which copper dissolves in the electrolytic solution. It is to be noted that the first round of the start of charging may be carried out in the liquid injection simultaneously with the start of the electrolyte solution, it may start charging after a lapse of some time to start pouring. In the standing step, after the first charging step, the charging is stopped and left standing until a second period in which the electrolytic solution penetrates into the negative electrode active material and the positive electrode active material elapses. Then, in the second charging step, the second charging is performed until the battery is fully charged after the second period has elapsed.

The basic idea of the present invention is that the first charging step (temporary charging) is performed as soon as possible, a small amount of electricity is applied to prevent copper elution, and a normal initial charging is performed after a sufficient impregnation period. Is to improve quality. Therefore, in the present invention, in the first charging step, the first charging is performed so that the potential of the negative electrode decreases until the potential falls below the potential at which copper dissolves in the electrolytic solution within the first period, thereby making the electrode group It is possible to promote the permeation of the electrolytic solution into the wound-type electrode group and to sufficiently secure the permeation time while suppressing the charge-discharge non-uniform reaction inside. As a result, it is possible to manufacture a high-quality non-aqueous lithium secondary battery with almost no dissolution of copper contained in the negative electrode current collector, and it is possible to shorten the electrolyte penetration period and improve productivity. ..

In the present invention, the design capacity of the lithium secondary battery is limited to 5 Ah or more because the small lithium secondary battery such as the 18650 type battery has a permeation rate of the electrolytic solution relative to the size of the wound electrode group. This is because, because of the high speed, even if the first charge is performed immediately after the injection of the electrolytic solution, the non-uniform charge/discharge reaction does not occur inside the electrode group, and the above problems do not occur.

The minimum electrolyte permeation time required for permeation of the electrolyte into the positive electrode active material and the negative electrode active material of a lithium secondary battery having a design capacity of 5 Ah or more is proportional to the size of the lithium secondary battery, that is, the design capacity. However, the necessary electrolyte permeation time (hours)∝0.5×X(Ah) is satisfied. Therefore, by charging 0.5% or more of the design capacity of the lithium secondary battery after injecting the electrolytic solution, the potential of the negative electrode is below the potential at which copper dissolves in the electrolytic solution, and considering self-discharge of the battery, It is possible to prevent the potential of the negative electrode from returning to the potential at which copper is dissolved again. Furthermore, by performing the above-mentioned charging, the active material forming the electrodes performs a contracting movement, which has the effect of accelerating the permeation of the electrolytic solution. Specifically, the first period is set within 10 hours after the electrolytic solution is injected, and the charge capacity in the first charging step is 0.5% or more of the designed capacity. Then, in the leaving step, when the design capacity of the lithium secondary battery is expressed as XAh, the second period is set so that the lithium secondary battery is left in a leaving state for 0.5 X hours or more after the electrolyte is injected.

The charge capacity of the first charging step is preferably 0.5 to 40% of the designed capacity. The upper limit of the first period is 10 hours regardless of the battery capacity. After the injection of the electrolytic solution, it is preferable to carry out the above-mentioned charging in a time as short as possible in order to prevent the dissolution of copper, but if it is within about 10 hours, the dissolution reaction of copper hardly progresses, so there is no problem. According to the research conducted by the inventor, it is known that when the first period exceeds 10 hours, the elution of copper used for the negative electrode progresses, which is a problem. There is no lower limit to the first period, and the shorter the shorter the better.

The charging current in the first charging step is preferably in the range of 0.02 to 1.20 ItA. When the charging current in the first charging step becomes smaller than 0.02, the first period becomes too long. Further, when the charging current is larger than 1.20 ItA, the charge/discharge non-uniform reaction inside the electrode group is promoted. Therefore, it is preferably 1.20 ItA or less.

Here, assuming that the charge capacity of the first charge is 0.5% of the designed capacity, the upper limit of the electrolyte solution permeation time in consideration of self-discharge is 240 hours. From a different point of view, the period from the injection of the electrolytic solution to the start of the second charging, including the second period, is within 250 hours. If the lithium secondary battery is left without being charged for the second time more than this, there is a concern that the potential of the negative electrode may return to the potential that dissolves copper due to self-discharge.

According to the present invention, by performing the first charge (specifically, charging a small capacity of 0.5% or more of the designed capacity of the lithium secondary battery after injecting the electrolyte solution), the electrode group While minimizing the charge/discharge heterogeneous reaction inside, it is possible to promote the permeation of the electrolytic solution into the wound electrode group and to secure a sufficient permeation time. It is possible to manufacture a high-quality non-aqueous lithium secondary battery with almost no problem and to shorten the period of permeation of the electrolytic solution, which leads to an improvement in productivity.

After the injection of the electrolytic solution, it is preferable to carry out the above-mentioned charging in a time as short as possible in order to prevent the dissolution of copper, but if it is within about 10 hours, the dissolution reaction of copper hardly progresses, so there is no problem.

In the present invention, the charge capacity of the first charge is preferably less than 30% of the designed capacity of the lithium secondary battery, and more preferably for the purpose of minimizing the charge/discharge nonuniform reaction inside the electrode group. Is within 25%, and most preferably within 20%. Further, when the charging current value of the first charging is high, the charge/discharge non-uniform reaction inside the electrode group is promoted. Therefore, it is preferably 1.0 ItA or less. On the other hand, if the current value of the first charging is too low, the time until the completion of charging is long and the productivity is impaired. Therefore, the preferable range of the current value of the first charging is 0.01 to 1.0 ItA. Is more preferable, 0.03 to 0.75 ItA is more preferable, and 0.05 to 0.5 ItA is still more preferable. The charging method of the first charging in the present invention is not particularly limited as long as it is within the technical idea of the present specification, and any charging method can be implemented. For example, constant current charging, constant voltage charging, constant power charging, pulse charging method and the like can be mentioned.

1 is a sectional view of a lithium secondary battery according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings and the like. The following description shows specific examples of the content of the present invention, the present invention is not limited to these descriptions, and various modifications by those skilled in the art within the scope of the technical idea disclosed in the present specification. Changes and modifications are possible.

In the lithium secondary battery 20, a positive electrode plate in which a positive electrode active material is applied to a belt-shaped positive electrode collector and a negative electrode in which a negative electrode active material is applied to a belt-shaped negative electrode current collector are laminated via a belt-shaped separator W5. The electrode group 6 configured by winding the strip-shaped laminated body configured as described above in the longitudinal direction is used. The electrode group 6 is housed in the battery container 5, and the electrolytic solution is also housed in the battery container 5. A positive electrode current collecting tab is connected to the positive electrode terminal, a negative electrode current collecting tab is provided to the negative electrode terminal, and a safety valve 10 is attached to the battery lid 4 that seals the battery container 5.

The material of the battery container 5 is selected so as not to be corroded by the electrolytic solution or deteriorated by alloying with lithium ions. It is selected from materials such as aluminum, stainless steel, and nickel-plated steel . The battery container 5 is placed in an electrically neutral state.

As the shaft core 11, any known one can be used as long as it can support the electrode group 6. If the shape of the electrode group can be maintained without the shaft core 11, the shaft core 11 may not be used.

The electrode group 6 can be applied as long as it has a rolled shape such as a flat shape other than the cylindrical shape shown in FIG. The shape of the battery container 5 may be selected in accordance with the shape of the electrode group 6 such as a cylindrical shape, a flat oval shape, or a flat elliptical shape.

<Positive electrode>
The positive electrode is composed of a positive electrode active material, a conductive agent, a binder and a current collector foil. Examples of the positive electrode active material include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , Fe(MoO ₄ ) ₃ , FeF ₃ , LiFePO ₄ , and LiMnPO ₄ . However, the present invention is not limited to these active materials, and other positive electrode active materials can be used.

The particle size of the positive electrode active material is usually defined so as to be not more than the thickness of the mixture layer formed on the positive electrode current collector foil by the positive electrode active material, the conductive agent and the binder. If there are coarse particles having a size equal to or larger than the mixture layer thickness in the powder of the positive electrode active material, remove the coarse particles in advance by sieving or air flow classification, and select particles having a mixture layer thickness or less. Is preferred.

In addition, since the positive electrode active material is generally an oxide type, it has a high electric resistance. Therefore, in order to supplement the electrical conductivity, a conductive agent made of carbon powder is added to the positive electrode active material. Since both the positive electrode active material and the conductive agent are usually powders, it is possible to mix the powders with a binder to bond the powders to each other and at the same time to bond them to the coated positive electrode current collector.

For the positive electrode current collector, an aluminum foil having a thickness of 10 to 100 μm, an aluminum perforated foil having a thickness of 10 to 100 μm and a pore diameter of 0.1 to 10 mm, an expanded metal, a foam metal plate, or the like is used. In addition to aluminum, materials such as stainless steel and titanium are also applicable. In the present invention, any current collector foil can be used without being limited by the material, shape, manufacturing method, and the like.

<Negative electrode>
The negative electrode is composed of a negative electrode active material, a binder and a collector foil. A conductive auxiliary material is used as necessary. A carbon-based material is generally used as the negative electrode active material, but an oxide-based material such as lithium titanate or a material containing Si or Ge can also be used.

The binder is not particularly limited, but for example, polyvinylidene fluoride or a binder whose main skeleton is polyacrylonitrile may be used. This is a preferable selection because the heat treatment temperature in the heat treatment described later can be lowered and the flexibility of the obtained electrode is excellent.

The negative electrode current collector contains copper, and the other materials are not particularly limited in terms of material and shape, and may be used in the form of foil, perforated foil, band-shaped mesh or the like. Further, a porous material such as porous metal (foamed metal) or carbon paper can also be used.

<Electrolyte>
The electrolytic solution is composed of an electrolyte, a non-aqueous solvent and an additive. Representative examples of the electrolyte include LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiN(SO ₂ F) ₂ , and LiN(C ₂ F ₅ SO ₂ ) ₂ , and in particular, LiPF ₆ , LiBF ₄ or LiN(CF ₃ SO ₂ ) ₂ , LiN(SO ₂ F) ₂ are preferred. These electrolytes may be used alone or in any combination of two or more in any ratio.

Examples of the non-aqueous solvent include chain and cyclic carbonates, chain and cyclic carboxylic acid esters, chain and cyclic ethers, phosphorus-containing organic solvents, sulfur-containing organic solvents and boron-containing organic solvents. The non-aqueous electrolyte solution used in the lithium ion battery of the present invention may contain various additives as long as the effects of the present invention are not significantly impaired.

Any conventionally known additives can be used as the above-mentioned additive. As the additive, one kind may be used alone, and two kinds or more may be used in optional combination and ratio. Examples of the additive include an overcharge inhibitor, an auxiliary agent for improving capacity retention characteristics and cycle characteristics after high temperature storage, and a flame retardant agent for imparting flame retardancy to an electrolytic solution.

Among these, it is preferable to add a carbonate having at least one of an unsaturated bond and a halogen atom as an auxiliary agent for improving the capacity retention characteristics after high temperature storage and the cycle characteristics.

<Separator>
The separator has a film thickness of 1 to 300 μm, a porosity of 20 to 90%, and a heat shrinkage rate of 20% or less when exposed to an environment of 100° C. for 1 hour. For example, an olefin made of polypropylene or polyethylene. A porous film made of a series resin, a porous film made of a fluororesin such as polytetrafluoroethylene, a porous film made of cellulose, and a porous film made of aramid. As a structure in which two or more kinds of these porous films are laminated. Alternatively, the surface of these porous membranes may be coated with a mixture of ceramics and binders, an acrylic adhesive, or the like.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

The lithium-ion battery of Example 1 used in the test was manufactured as follows.

As the negative electrode active material, graphitizable carbon having an average particle diameter of 10 μm and polyvinylidene fluoride binder were mixed in a solid mass ratio of 93:7, mixed in a 70 L kneader, and NMP was appropriately added for viscosity adjustment. Then, a slurry was prepared. The average particle diameter can be measured, for example, by dispersing the sample in purified water containing a surfactant and measuring with a laser diffraction particle size distribution analyzer (for example, SALD-3000J manufactured by Shimadzu Corporation). The diameter is calculated as the median diameter (d50). This slurry was applied by a coating machine to both sides of a rolled copper foil (lithium battery grade) having a thickness of 10 μm so as to be substantially even and homogeneous. The coating amount was 80 g/m ² . At this time, 50 mm of the active material uncoated portion was left on the rolled copper foil, and the uncoated portion was cut into a width of 10 mm at intervals of 20 mm to obtain a lead piece of the negative electrode plate. After that, a drying process was performed, and a negative electrode plate was produced by pressing so that the electrode density was 1.0 g/cm ³ , and the wound negative electrode plate had a width of 195 mm and a length of 8450 mm.

LiMn ₂ O ₄ having an average particle diameter of 25 μm as a positive electrode active material, LiNi _1/3 Co _1/3 Mn _1/3 having an average particle diameter of 7 μm, Denka Black (HS-100 manufactured by Denki Kagaku Kogyo), graphite powder (Nippon Graphite) J-SP-H), polyvinylidene fluoride binder are mixed in a solid mass ratio of 65:25:4:1:5, mixed in a 70 L kneader, and NMP is appropriately added for viscosity adjustment. To prepare a slurry. This slurry was applied by a coating machine to both sides of an aluminum foil (lithium battery grade) having a thickness of 20 μm so as to be substantially even and homogeneous. At this time, a 50 mm active material uncoated portion was left on the aluminum foil, and the uncoated portion was cut into a width of 10 mm at intervals of 20 mm to obtain a positive electrode lead piece. After that, a drying treatment was performed, and a positive electrode was manufactured by pressing so that the electrode density was 2.5 g/cm ³ , and the wound positive electrode had a width of 190 mm and a length of 9570 mm.

FIG. 1 shows a cross-sectional view of the lithium secondary battery. The positive electrode and the negative electrode were wound with a polyethylene separator W5 having a thickness of 30 μm interposed therebetween so that they would not come into direct contact with each other. At this time, the lead piece of the positive electrode and the lead piece of the negative electrode were respectively positioned at opposite ends of the winding group. The length of the positive electrode, the negative electrode, and the separator was adjusted so that the winding group diameter was 65±0.1 mm.

Next, as shown in FIG. 1, the lead pieces led out from the positive electrode were deformed, and all of them were collected and brought into contact with the vicinity of the bottom of the flange portion 7 on the positive electrode side. The positive electrode-side collar portion 7 is integrally formed so as to project from the periphery of the pole (the positive electrode external terminal 1) that is substantially on the extension line of the axis of the winding group 6, and has a bottom portion and side portions. After that, the lead piece was connected and fixed to the bottom portion of the collar portion 7 by ultrasonic welding. The lead piece led out from the negative electrode and the bottom of the negative electrode-side collar portion 7 were similarly connected and fixed. The collar portion 7 on the negative electrode side is integrally molded so as to project from the periphery of the pole (negative electrode external terminal 1′) which is substantially on the extension line of the axis of the winding group 6, and has a bottom portion and side portions. .. The thickness of the insulating coating (the number of windings of the adhesive tape) is adjusted so that the maximum diameter part of the winding group 6 is slightly smaller than the inner diameter of the battery container 5 made of stainless steel, and the winding group 6 is placed in the battery container 5. Inserted. The battery container 5 had an outer diameter of 67 mm and an inner diameter of 66 mm.

Next, as shown in FIG. 1, the ceramic washer 3'is fitted into the pole column whose tip constitutes the positive electrode external terminal 1 and the pole column whose tip constitutes the negative electrode external terminal 1', respectively. The ceramic washer 3'is made of alumina, and has a thickness of 2 mm, an inner diameter of 16 mm, and an outer diameter of 25 mm, which is in contact with the back surface of the battery lid 4. Next, with the ceramic washer 3 placed on the battery lid 4, the positive electrode external terminal 1 is passed through the ceramic washer 3, and the other ceramic washer 3 is placed on the other battery lid 4, with the negative electrode external terminal Thread 1'through another ceramic washer 3. The ceramic washer 3 is made of alumina and has a flat plate shape with a thickness of 2 mm, an inner diameter of 16 mm and an outer diameter of 28 mm.

After that, the end face around the battery lid 4 is fitted into the opening of the battery container 5, and the entire area of both contact portions is laser-welded. At this time, the positive electrode external terminal 1 and the negative electrode external terminal 1 ′ respectively penetrate the hole (hole) in the center of the battery lid 4 and project to the outside of the battery lid 4. The battery lid 4 is provided with a cleaving valve 10 that cleaves in response to an increase in internal pressure of the battery. The cleavage pressure of the cleavage valve 10 was 1.3 to 1.8 MPa.

Then, the metal nut 2 is screwed to the positive electrode external terminal 1 and the negative electrode external terminal 1', respectively, and the battery cover 4 is tightened between the collar portion 7 and the nut 2 through the ceramic washer 3 and the ceramic washer 3'. Fix it. The tightening torque value at this time was 7 N·m. In this state, the power generation element inside the battery container 5 is shielded from the outside air by the compression of the rubber (EPDM) O-ring interposed between the back surface of the battery lid 4 and the collar portion 7.

After that, the inside of the battery container 5 is decompressed through the liquid injection port 15 provided in the battery lid 4, 350 g of the electrolytic solution is injected into the battery container 5, and then the liquid injection port 15 is sealed to form a cylindrical lithium The ion battery 20 was completed.

As an electrolytic solution, 1.2 mol/L of lithium hexafluorophosphate (LiPF ₆ ) was dissolved in a mixed solution in which ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate were mixed at a volume ratio of 2:3:2. What was done was used. It should be noted that the cylindrical lithium secondary battery 20 manufactured in this example is not provided with a current interruption mechanism that operates so as to interrupt the current in response to an increase in the internal pressure of the battery container 5.

All the steps were performed in a dry room (dew point temperature: -60°C or lower), and the charge capacity ratio of the positive electrode and the negative electrode was designed to be negative electrode/positive electrode = 1.1 and the discharge capacity of the battery was 40 Ah.

(Example 1)
The cylindrical lithium secondary battery 20 into which the electrolytic solution was injected was charged to a capacity of 0.5% with respect to the designed capacity of the lithium secondary battery with a charging current of 0.1 ItA 10 hours after the injection (first (1st charge), 20 hours after the liquid injection (a period including the second period in the standing step), a constant current constant voltage charge of 4.2 hours was performed at a charge current of 1.0 ItA for 3 hours to charge a lithium secondary battery. Fully charged (second charge). The lithium secondary battery, which has been charged for the second time, is discharged with a constant current at a discharge current of 1.0 ItA until the voltage of the lithium secondary battery reaches 2.7 V, and the discharge capacity is measured by integrating the current value. did. For example, in the case of constant current discharge, the discharge capacity (Ah) is obtained by the following formula.

Discharge capacity (Ah) = discharge current (A) x discharge time (hours)
(Example 2)
Example 1 was the same as Example 1 except that the time from the liquid injection to the second charging (the period including the second period in the standing step) was 250 hours.

(Examples 3 to 4)
The same procedure was performed as in Example 1 except that the charging current for the first charging was changed. In Example 3, it was 0.02 ItA, and in Example 4, it was 1.2 ItA.

(Example 5)
Example 1 except that the charge capacity of the first charge was 40% of the design capacity, and the time from liquid injection to the second charge (the period including the second period in the standing step) was 160 hours. Same as.

(Example 6)
Example 1 was the same as Example 1 except that the time from the liquid injection to the second charge (the period including the second period in the standing step) was 250 hours, and the charge current for the first charge was 1.2 ItA.

(Example 7)
The time from the injection to the second charge (the period including the second period in the leaving step) is 250 hours, the charge current for the first charge is 1.2 ItA, and the charge capacity for the first charge is the design capacity. The same procedure as in Example 1 was carried out except that 40% was used.

(Example 8)
Example 1 is the same as Example 1 except that the designed capacity was 80 Ah and the time from the liquid injection to the second charge (the period including the second period in the standing step) was 40 hours.

(Comparative Example 1)
The same procedure as in Example 1 was performed except that the first charging was not performed.

(Comparative example 2)
Example 1 was the same as Example 1 except that the charge capacity of the first charge was 0.4% of the design capacity.

(Comparative example 3)
Example 1 was the same as Example 1 except that the time from the injection of liquid to the second charging (the period including the second period in the leaving step) was 15 hours.

(Comparative Example 4)
The same procedure as in Example 1 was performed except that the time from the liquid injection to the first charging (first period) was 15 hours.

(Comparative example 5)
The same procedure was performed as in Example 1 except that the charging current for the first charging was 1.5 ItA.

(Comparative example 6)
Example 1 was the same as Example 1 except that the time from the injection of liquid to the second charge (the period including the second period in the standing step) was 300 hours.

(Copper dissolution amount determination)
The batteries of Examples 1 to 8 and Comparative Examples 1 to 6 were measured by an inductively coupled plasma emission spectroscopic analyzer (for example, iCAP6300 manufactured by Thermo Fisher Scientific) immediately before the first charging and immediately before the second charging. The electrolytic solution was sampled, and the concentration of copper contained in the electrolytic solution was measured. When the electrolytic solution immediately before the first charging and the electrolytic solution immediately before the second charging both had a copper concentration of less than 0.5 ppm, the result was “◯”, and one of the electrolytic solutions had a copper concentration of 0.5 ppm or more and less than 1.0 ppm. It was judged to be “Δ” when it was, and it was judged to be “x” when either of the electrolytic solutions had a copper concentration of 1.0 ppm or more.

(Judgment of discharge capacity)
Regarding the discharge capacities of the batteries of Examples 1 to 8 and Comparative Examples 1 to 6, when the capacity of 100% or more of the designed capacity was obtained, “◯” was given, and when the capacity of 95% or more and less than 100% was obtained. The case where “Δ” and a capacity of less than 95% were obtained was judged as “x”.

As shown in Table 1, in each of the examples, there was no "x" in the determination of the amount of copper dissolved and the determination of the discharge capacity. In Comparative Example 1, since the first charging was not performed, the dissolution of copper could not be prevented. In Comparative Example 2, the charge amount of the first charge was insufficient, and the potential of the negative electrode returned to the potential before the first charge due to self-discharge of the lithium secondary battery, resulting in the copper It does not prevent dissolution. In Comparative Example 3, since the time from the liquid injection to the second charge was too short, the time for the electrolyte solution to infiltrate the lithium secondary battery was insufficient, and the discharge capacity was insufficient. In Comparative Example 4, the time from injection to the first charging is too long to prevent copper dissolution.

In each of the examples, there is an example in which the determination of the amount of copper dissolved or the determination of the discharge capacity is “Δ”, but there is no problem in practical use of the lithium secondary battery. In addition, in Examples 2, 6, and 7, since the time from the liquid injection to the second charging was relatively long, the negative electrode potential returned to near the original potential by self-discharging, and the copper was dissolved before the second charging. Was beginning to be seen. In Examples 4, 6 and 7, the charging current of the first charging was relatively large, and in Examples 5 and 7, the charging capacity of the first charging was relatively large, so the charge and discharge were non-uniform within the electrode group. The reaction occurred, and the lithium ion originally used for charging and discharging was insufficient due to the precipitation reaction of metallic lithium and the like, so that the discharge capacity was slightly insufficient.

According to the present invention, it is possible to manufacture a high-quality lithium secondary battery with almost no dissolution of copper contained in the negative electrode current collector, and it is possible to shorten the electrolyte permeation period and improve productivity. Connect

1 Positive External Terminal 1'Negative External Terminal 2 Metal Nut 3 Ceramic Washer 3'Ceramic Washer 4 Battery Lid (Part of Battery Container)
5 Battery Container 6 Winding Group 7 External Terminal Collar 10 Cleavage Valve 11 Shaft Core 15 Injection Port 20 Cylindrical Lithium Secondary Battery W1 Positive Electrode Current Collector (Part of Positive Electrode)
W2 Positive electrode active material layer (part of positive electrode)
W3 Negative electrode current collector (part of negative electrode)
W4 Negative electrode active material layer (a part of negative electrode)
W5 separator

Claims (4)

A wound electrode group in which a negative electrode containing copper in a negative electrode current collector that holds a negative electrode active material and a positive electrode in which a positive electrode active material is held on a positive electrode current collector are wound via a separator is electrically A method of initially charging a lithium secondary battery having a design capacity of 5 Ah or more, which is housed in a neutral battery container and in which an electrolytic solution is injected into the battery container,
During the first period starting after injecting the electrolytic solution into the battery container, the surfaces of the negative electrode active material of the negative electrode and the positive electrode active material of the positive electrode are entirely in contact with the electrolytic solution. A first charging step in which the first charging is performed so that the potential of the negative electrode decreases until the potential of the negative electrode decreases below the potential at which the copper dissolves in the electrolytic solution,
And a step of leaving charging and stopping the charging until a second period in which the electrolytic solution permeates into the negative electrode active material and the positive electrode active material elapses.
A second charging step of performing a second charging until the battery is fully charged after the second period has passed ,
The first period is within 10 hours after injecting the electrolytic solution,
The charge capacity in the first charging step is 0.5% or more of the design capacity,
In the leaving step, when the design capacity of the lithium secondary battery is expressed as XAh, the second period is determined such that the lithium secondary battery is left for 0.5X hours or more after the electrolyte solution is injected. The first charging method for a lithium secondary battery. The initial charging method for a lithium secondary battery according to claim 1 , wherein the charging capacity in the first charging step is 0.5 to 40% of the designed capacity. The method for initially charging a lithium secondary battery according to claim 1 or 2 , wherein the charging current in the first charging step is within a range of 0.02 to 1.20 ItA. The lithium secondary according to any one of claims 1 to 3 , wherein a period from the injection of the electrolytic solution to the start of the second charging is within 250 hours including the second period. How to charge the battery for the first time.