JP2017139107A - Method for initially charging lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for initially charging a lithium secondary battery, which enables the adequate permeation of an electrolyte into an electrode group while suppressing copper dissolution from a negative electrode current collector.SOLUTION: A method for initially charging a lithium secondary battery, of which the design capacity is 5 Ah or higher, comprises the steps of: charging the lithium secondary battery to 0.5% or more of the design capacity within 10 hours after injecting an electrolyte; and leaving the lithium secondary battery as it is for 0.5X hour or longer time after injecting the electrolyte, provided that the design capacity of the lithium secondary battery is represented by X Ah.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an initial charging method of a lithium secondary battery, and more particularly, to an improvement in productivity and quality of a large lithium secondary battery of 5 Ah or more.

  Lithium secondary batteries have been used as a power source for portable devices such as digital cameras, notebook computers and mobile phones, taking advantage of the high energy density. In recent years, research and development of large lithium secondary batteries for the purpose of electric vehicle use and power storage have been actively conducted in order to cope with environmental problems.

  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 current collector such as a copper foil in which a negative electrode active material containing a carbon material is applied. The negative electrode plate applied to the electrode plate is prepared by storing the electrode plate group laminated or wound through a porous separator made of an insulating material in a battery container and injecting a non-aqueous electrolyte. The Compared to the stacked type, the wound type has the advantage that the production process is easier and the productivity is higher.

  The dimensions of a general wound lithium secondary battery used in portable devices 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 approximately 1.0 to 3.5 Ah. On the other hand, lithium secondary batteries used for 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 common to enlarge the wound electrode group or increase the number of turns of the wound electrode group.

  However, when the wound electrode group is enlarged, it takes time for the electrolyte to penetrate into the wound electrode group. If charging / discharging is performed with insufficient electrolyte penetration, not only the rated battery capacity will be developed, but also the charging / discharging reaction inside the wound electrode group will be non-uniform, so the actual charging current density will be locally In some cases, metallic lithium is deposited on the negative electrode, and in some cases, it penetrates the separator and leads to an internal short circuit.

  Therefore, in Patent Document 1, in a large wound lithium secondary battery in which the positive electrode plate and the negative electrode plate are wound 40 times or more, the first time is passed after 24 hours or more after pouring the non-aqueous electrolyte. Propose to charge.

JP 2003-308878 A

  However, when the negative electrode active material includes a carbon material and the current collector is copper, dissolution of copper starts from the time when the electrolytic solution is injected. This is because the potential of the negative electrode at the stage where charging is not performed is about 3.4 V and is equal to or higher than the potential (about 3 V) at which copper dissolves in the electrolytic solution. When copper dissolves in the electrolyte, it causes clogging of the separator and the current collection performance of the negative electrode current collector decreases, causing not only an increase in battery resistance, but also the copper dissolved in the electrolyte on the negative electrode. In some cases, it may cause an internal short circuit. The battery container is generally made of a metal material. However, if the battery container is electrically neutral, which serves as both a positive electrode and a negative electrode, copper is the only element that may be dissolved in the electrolyte after injection. is there.

  An object of the present invention is to provide an initial charging method for a lithium secondary battery in which the electrolytic solution is sufficiently infiltrated into a wound electrode group while suppressing dissolution of copper, which is a negative electrode current collector, into the electrolytic solution. 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 in which the positive electrode current collector is held in a positive electrode current collector are wound through a separator. However, an initial charging method of a lithium secondary battery having a design capacity of 5 Ah or more, which is housed in an electrically neutral battery container and an electrolyte is injected into the battery container, the first charging step, This is realized by the leaving step and the second charging step. In the first charging step, the negative electrode active material of the negative electrode and the surface of the positive electrode active material of the positive electrode are entirely in contact with the electrolyte within a first period that starts after the injection of the electrolyte into the battery container is started. In the touched state, the first charge is performed such that the potential of the negative electrode is lowered until the potential of copper is lower than the potential at which the copper dissolves in the electrolytic solution. Note that the first charging start may be performed simultaneously with the start of the electrolyte injection, or the charging may be started after a while from the start of the injection. In the leaving step, after the first charging step, the charging is stopped and left until a second period in which the electrolytic solution penetrates into the negative electrode active material and the positive electrode active material has elapsed. Then, in the second charging step, the second charging is performed until the full charge is reached after the second period has elapsed.

  The basic idea of the present invention is that the first charging step (preliminary charging) is performed as soon as possible, a small amount of electricity is added to prevent elution of copper, and a normal initial charging is performed after a sufficient impregnation period. The aim is to improve quality. Therefore, in the present invention, in the first charging step, the first charging is performed such that the potential of the negative electrode is lowered until the potential of the copper dissolves in the electrolytic solution within the first period, whereby the electrode group is obtained. While minimizing the internal charge / discharge heterogeneous reaction, the penetration of the electrolyte into the wound electrode group can be promoted, and a sufficient penetration time can be secured. As a result, it is possible to manufacture a high-quality non-aqueous lithium secondary battery that hardly dissolves copper contained in the negative electrode current collector, and it is possible to shorten the period of infiltration of the electrolytic solution, thereby improving productivity. .

  In the present invention, the design capacity of the lithium secondary battery is limited to 5 Ah or more. The small lithium secondary battery such as a 18650 type battery has an electrolyte penetration rate relative to the size of the wound electrode group. Because it is fast, even if the first charge is performed immediately after injecting the electrolytic solution, the charge / discharge heterogeneous reaction does not occur inside the electrode group, and the above-described problems do not occur.

  The penetration time of the electrolyte required for the penetration of the electrolyte into the positive electrode active material and the negative electrode active material of a lithium secondary battery with a design capacity of 5 Ah or more is proportional to the size of the lithium secondary battery, that is, the design capacity. The required electrolyte penetration time (time) ∝ 0.5 × X (Ah). Therefore, by charging 0.5% or more of the design capacity of the lithium secondary battery after injecting the electrolyte, the potential of the negative electrode is lower than the potential at which copper dissolves in the electrolyte, and the self-discharge of the battery is considered. It is possible to prevent the negative electrode potential from returning to the potential at which copper dissolves again. Furthermore, since the active material which comprises an electrode carries out contraction movement by performing said charging, there exists an effect which accelerates | stimulates the penetration | invasion of electrolyte solution. Specifically, the first period is within 10 hours after the electrolyte injection, and 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, a second period is determined so that the battery is left in a standing state for 0.5 X hours or longer after the electrolyte solution injection.

  The charge capacity of the first charging step is preferably 0.5 to 40% of the design capacity. In the first period, the upper limit is 10 hours regardless of the size of the battery capacity. After injecting the electrolytic solution, it is preferable to perform the above charging in a time as short as possible in order to prevent the dissolution of copper. However, if it is within about 10 hours, the dissolution reaction of copper hardly progresses, so that there is no problem. According to the inventor's research, it has been found that when the first period exceeds 10 hours, the elution of copper used in the negative electrode proceeds, which causes a problem. There is no lower limit in the first period, and it is better if it is shorter.

  The charging current of the first charging step is preferably in the range of 0.02 to 1.20 ItA. If the charging current of the first charging step becomes smaller than 0.02, the first period becomes too long. Moreover, when this charging current becomes larger than 1.20 ItA, the charge / discharge heterogeneous reaction inside the electrode group is promoted, so that it is preferably 1.20 ItA or less.

  Here, assuming that the charge capacity of the first charge is 0.5% of the design capacity, the upper limit of the electrolyte penetration time considering self-discharge is 240 hours. In other words, the period from the injection of the electrolyte solution to the start of the second charge, including the second period, is within 250 hours. Further, if the lithium secondary battery is left without performing the second charge, there is a concern that the potential of the negative electrode returns to the potential at which copper is dissolved by self-discharge.

  According to the present invention, the first charge is performed (specifically, a small capacity charge of 0.5% or more of the design capacity of the lithium secondary battery is performed after electrolyte injection) While minimizing the internal charge / discharge heterogeneous reaction, it promotes the penetration of the electrolyte solution into the wound electrode group and ensures sufficient penetration time. A high-quality non-aqueous lithium secondary battery with almost no battery can be manufactured and the infiltration period of the electrolyte can be shortened, leading to an improvement in productivity.

  After injecting the electrolytic solution, it is preferable to perform the above charging in a time as short as possible in order to prevent the dissolution of copper. However, if it is within about 10 hours, the dissolution reaction of copper hardly progresses, so that there is no problem.

  In the present invention, the charge capacity of the first charge is preferably less than 30% of the design capacity of the lithium secondary battery for the purpose of minimizing the charge / discharge heterogeneous reaction inside the electrode group, and more preferably. Is within 25%, most preferably within 20%. Moreover, since the charge / discharge heterogeneous reaction inside an electrode group will be accelerated | stimulated when the charging current value of the said 1st charge is high, it is preferable that it is 1.0 ItA or less. On the other hand, if the current value of the first charge is too low, the time until the charge is completed becomes longer and the productivity is impaired. Therefore, the preferred range of the current value of the first charge is 0.01 to 1.0 ItA. More preferably, it is 0.03-0.75 ItA, More preferably, it is 0.05-0.5 ItA. The charging method of the first charge in the present invention is not particularly limited as long as it is within the scope of the technical idea of the present specification, and any charging method can be implemented. For example, a constant current charge, a constant voltage charge, a constant power charge, a pulse charge method, etc. are mentioned.

It is sectional drawing of the lithium secondary battery which concerns on one Embodiment of this invention.

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

  The lithium secondary battery 20 is formed by laminating a positive electrode plate coated with a positive electrode active material on a strip-shaped positive electrode current collector and a negative electrode coated with a negative electrode active material on a strip-shaped negative electrode current collector via a strip-shaped separator W5. An electrode group 6 is used, which is formed by winding a belt-like laminate formed in the longitudinal direction. The electrode group 6 is accommodated in the battery container 5, and the electrolytic solution is also accommodated 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 connected 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 that the material does not deteriorate due to corrosion by the electrolytic solution or alloying with lithium ions. It is selected from materials such as aluminum, stainless steel, and nickel-plated steel. The battery case 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. Even if the shaft core 11 is not provided, the shaft core 11 may not be used as long as the shape of the electrode group can be maintained.

  The electrode group 6 can be applied as long as it is a wound shape such as a flat shape in addition to the cylindrical shape shown in FIG. The shape of the battery case 5 may be selected from shapes such as a cylindrical shape, a flat oval shape, and a flat oval shape according to the shape of the electrode group 6.

<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 LiCoO2, LiNiO2, LiMn2O4, Fe (MoO4) 3, FeF3, LiFePO4, and LiMnPO4. However, the present invention is not limited to these active materials, and other positive electrode active materials can also be used.

  The particle size of the positive electrode active material is usually defined so as to be equal to or less 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. When the positive electrode active material powder has coarse particles having a size larger than the thickness of the mixture layer, the coarse particles are removed in advance by sieving classification or wind classification, and sorted into particles having a thickness of the mixture layer thickness or less. Is preferred.

  Moreover, since a positive electrode active material is generally an oxide type, its electrical resistance is high. Therefore, in order to supplement 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, a binder can be mixed with the powders to bond the powders to each other and to adhere to the coated positive electrode current collector.

  As 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 current collector foil. A conductive auxiliary material is used as necessary. A carbon-based material is generally used for the negative electrode active material, but materials including lithium titanate, Si and Ge, which are oxidation-based materials, can also be used.

  The binder is not particularly limited. For example, it is preferable to use polyvinylidene fluoride and a binder whose main skeleton is polyacrylonitrile. This is a preferred choice because the heat treatment temperature in the heat treatment described below can be lowered and the flexibility of the resulting electrode is excellent.

  The negative electrode current collector contains copper, and other than that, the material and shape are not particularly limited, and the negative electrode current collector may be used in the form of foil, perforated foil, strip-shaped mesh, or the like. 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. Typical 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 . LiPF ₆ , LiBF _4, LiN (CF ₃ SO ₂ ) ₂ , LiN (SO ₂ F) ₂ are preferable. These electrolytes may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios.

  Examples of the non-aqueous solvent include linear and cyclic carbonates, linear and cyclic carboxylic acid esters, linear and cyclic ethers, phosphorus-containing organic solvents, sulfur-containing organic solvents, and boron-containing organic solvents. The non-aqueous electrolyte 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.

  A conventionally well-known thing can be arbitrarily used for the said additive. An additive may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and a ratio. Examples of the additive include an overcharge inhibitor, an auxiliary agent for improving capacity maintenance characteristics and cycle characteristics after high-temperature storage, and a flame retardant that imparts flame retardancy to the electrolyte.

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

<Separator>
The separator has a film thickness of 1 to 300 μm, a porosity of 20 to 90%, and a thermal 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 of a fluororesin, a porous film of a fluororesin made of polytetrafluoroethylene, a porous film made of cellulose, a porous film made of aramid, and a structure in which these two or more porous films are laminated Alternatively, a ceramic or binder mixture or an acrylic adhesive may be applied to the surface of the porous film.

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

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

For the negative electrode active material, graphitizable carbon having an average particle size of 10 μm and polyvinylidene fluoride binder are blended so that the solid mass ratio is 93: 7, mixed in a 70 L kneader, and NMP is appropriately added for viscosity adjustment. A slurry was prepared. The average particle size can be measured with a laser diffraction particle size distribution analyzer (for example, SALD-3000J, manufactured by Shimadzu Corporation) by dispersing a sample in purified water containing a surfactant, for example. The diameter is calculated as the median diameter (d50). This slurry was coated on a both sides of a rolled copper foil (lithium battery grade) having a thickness of 10 μm by a coating machine so as to be substantially uniform 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. Then, the drying process was implemented, it pressed so that an electrode density might be set to 1.0 g / cm < ³ >, the negative electrode plate was produced, and the dimension of the negative electrode plate wound was made into width 195mm and length 8450mm.

LiMn ₂ O ₄ having an average particle size of 25 μm, LiNi _1/3 Co _1/3 Mn _1/3 having an average particle size of 7 μm, Denka Black (HS-100 manufactured by Denki Kagaku Kogyo), graphite powder (Nippon Graphite) J-SP-H) and polyvinylidene fluoride binder are mixed at a solid mass ratio of 65: 25: 4: 1: 5, mixed in a 70 L kneader, and NMP is added as appropriate for viscosity adjustment. A slurry was prepared. This slurry was applied to both sides of a 20 μm thick aluminum foil (lithium battery grade) with a coating machine so as to be substantially uniform and homogeneous. At this time, an active material uncoated portion of 50 mm was left on the aluminum foil, and the uncoated portion was cut into a width of 10 mm at intervals of 20 mm to form a positive electrode lead piece. Thereafter, a drying process was performed, the electrode density was pressed to 2.5 g / cm ³ to produce a positive electrode, and the dimensions of the wound positive electrode were 190 mm wide and 9570 mm long.

  FIG. 1 shows a cross-sectional view of a lithium secondary battery. The positive electrode and the negative electrode were wound with a separator W5 made of polyethylene having a thickness of 30 μm interposed therebetween so that they were not in 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 lengths of the positive electrode, negative electrode, and separator were adjusted, and the wound 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 near the bottom of the flange 7 on the positive electrode side and brought into contact with each other. The positive electrode side flange portion 7 is integrally formed so as to protrude from the periphery of the pole column (positive electrode external terminal 1) substantially on the extension line of the axis of the wound group 6, and has a bottom portion and a side portion. Thereafter, the lead piece was connected and fixed to the bottom of the flange 7 by ultrasonic welding. Similarly, the lead piece led out from the negative electrode and the bottom of the flange 7 on the negative electrode side were connected and fixed. The negative electrode side flange portion 7 is integrally formed so as to protrude from the periphery of the pole column (negative electrode external terminal 1 ′) substantially on the extension line of the axis of the wound group 6, and has a bottom portion and a side portion. . The thickness of the insulating coating (the number of windings of the adhesive tape) is adjusted so that the maximum diameter portion of the wound group 6 is slightly smaller than the inner diameter of the stainless steel battery container 5, and the wound 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 a pole column whose tip constitutes the positive electrode external terminal 1 and a pole column whose tip constitutes the negative electrode external terminal 1 ′. The ceramic washer 3 ′ is made of alumina, and the thickness of the portion in contact with the back surface of the battery lid 4 is 2 mm, the inner diameter is 16 mm, and the outer diameter is 25 mm. Next, with the ceramic washer 3 placed on the battery lid 4, the positive external terminal 1 is passed through the ceramic washer 3, and with the other ceramic washer 3 placed on the other battery lid 4, the negative external terminal Pass 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.

  Then, the end surface 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 ′ protrude through the hole (hole) in the center of the battery cover 4 and protrude outside the battery cover 4. The battery lid 4 is provided with a cleavage valve 10 that cleaves in response to an increase in the internal pressure of the battery. The cleavage pressure of the cleavage valve 10 was 1.3 to 1.8 MPa.

  Next, the metal nut 2 is screwed to the positive external terminal 1 and the negative external terminal 1 ′, and the battery cover 4 is tightened between the flange 7 and the nut 2 via 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 compression of a rubber (EPDM) O-ring interposed between the back surface of the battery lid 4 and the flange 7.

  Thereafter, the inside of the battery container 5 is depressurized from the liquid injection port 15 provided in the battery lid 4, the electrolytic solution is injected into the 350 g battery container 5, and then the liquid injection port 15 is sealed to thereby form 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. Note that the cylindrical lithium secondary battery 20 manufactured in this example is not provided with a current interrupting mechanism that operates so as to interrupt the current in accordance with the increase in the internal pressure of the battery container 5.

  All 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 has been injected is charged to a capacity of 0.5% with respect to the design capacity of the lithium secondary battery at a charging current of 0.1 ItA 10 hours after the injection (No. 1). 1st charge), 20 hours after injection (period including the second period in the neglecting step), charge with constant current and constant voltage for 3 hours up to 4.2V with a charge current of 1.0 ItA, and recharge the lithium secondary battery. Fully charged (second charge). Discharge the lithium secondary battery after the second charge at a constant current of 1.0 ItA until the voltage of the lithium secondary battery reaches 2.7 V, and measure the discharge capacity by integrating the current value. did. For example, in the case of constant current discharge, the discharge capacity (Ah) is obtained by the following equation.

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

(Examples 3 to 4)
Example 1 was performed except that the charging current of the first charge 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 is 40% of the design capacity and the time from the injection to the second charge (the period including the second period in the leaving step) is 160 hours. And the same.

(Example 6)
The time from the injection to the second charge (the period including the second period in the leaving step) was 250 hours, and the charge current for the first charge was set to 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 of the first charge is 1.2 ItA, and the charge capacity of the first charge is the design capacity. Except for 40%, it was the same as Example 1.

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

(Comparative Example 1)
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 to the second charge (the period including the second period in the leaving step) was 15 hours.

(Comparative Example 4)
Example 1 was repeated except that the time from the injection to the first charge (first period) was 15 hours.

(Comparative Example 5)
The same operation as in Example 1 was performed except that the charging current of the first charge was 1.5 ItA.

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

(Copper dissolution amount determination)
For the batteries of Examples 1 to 8 and Comparative Examples 1 to 6, the inductively coupled plasma emission spectroscopic analyzer (for example, iCAP6300 manufactured by Thermo Fisher Scientific) was used immediately before the first charge and immediately before the second charge. The electrolytic solution was collected and the copper concentration contained in the electrolytic solution was measured. When both the electrolyte immediately before the first charge and the electrolyte immediately before the second charge had a copper concentration of less than 0.5 ppm, “◯” indicates that any one of the electrolytes has a copper concentration of 0.5 ppm or more and less than 1.0 ppm. And the case where any electrolyte solution had a copper concentration of 1.0 ppm or more was judged as “x”.

(Determination of discharge capacity)
In the discharge capacities of the batteries of Examples 1 to 8 and Comparative Examples 1 to 6, “◯” represents a case where a capacity of 100% or more of the designed capacity was obtained, and represents a case where a capacity of 95% or more and less than 100% was obtained. When “Δ”, a capacity of less than 95% was obtained, it was determined as “x”.

As shown in Table 1, in each Example, there was no “x” in both the determination of the amount of dissolved copper and the determination of the discharge capacity. Since the comparative example 1 is not performing the 1st charge, it cannot prevent dissolution of copper. In Comparative Example 2, the charge amount of the first charge is insufficient, and the potential of the negative electrode returns to the potential before the first charge due to the 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 injection to the second charge was too short, the time for the electrolyte to infiltrate the lithium secondary battery was insufficient, and the discharge capacity was insufficient. In Comparative Example 4, the time from the injection to the first charge is too long, and the dissolution of copper cannot be prevented.

  In each example, there is an example in which the determination of the amount of dissolved copper or the determination of the discharge capacity is “Δ”, but there is no problem in practical use of the lithium secondary battery. In Examples 2, 6, and 7, since the time from the injection to the second charge was relatively long, the negative electrode potential returned to the vicinity of the original potential by self-discharge, and the copper dissolved before the second charge. Some have begun to be seen. In Examples 4, 6, and 7, the charge current of the first charge was relatively large, and in Examples 5 and 7, the charge capacity of the first charge was relatively large. Since the reaction occurred and the lithium ions originally used for charging and discharging were insufficient due to the deposition reaction of metallic lithium, the discharge capacity was slightly insufficient.

  According to the present invention, it is possible to manufacture a high-quality lithium secondary battery that hardly dissolves copper contained in the negative electrode current collector, and it is possible to shorten the infiltration period of the electrolytic solution, thereby improving productivity. Connected.

1 Positive External Terminal 1 ′ Negative External Terminal 2 Metal Nut 3 Ceramic Washer 3 ′ Ceramic Washer 4 Battery Cover (Part of Battery Container)
5 Battery container 6 Winding group 7 External terminal flange 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 (part of negative electrode)
W5 separator

Claims (6)

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 in which a positive electrode active material is held in a positive electrode current collector is wound through a separator is electrically The battery is stored in a neutral battery container, and an electrolytic solution is injected into the battery container, and the initial charging method of the lithium secondary battery having a design capacity of 5 Ah or more,
In the first period that starts after the injection of 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 in full contact with the electrolytic solution. A first charging step in which the first charging is performed so that the potential of the negative electrode is lowered until the copper is lower than the potential at which the copper dissolves in the electrolytic solution;
And then leaving the charging to stop until a second period in which the electrolytic solution penetrates into the negative electrode active material and the positive electrode active material has passed,
An initial charging method for a lithium secondary battery, wherein a second charging step is performed in which a second charging is performed until the second charging period is fully charged after the second period has elapsed. The first period is within 10 hours after the electrolyte injection,
The charging 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 set so as to be left in a standing state for 0.5 X hours or more after the electrolyte injection. The initial charging method of the lithium secondary battery according to claim 1.   3. The method for initially charging a lithium secondary battery according to claim 2, wherein the charging capacity of the first charging step is 0.5 to 40% of the designed capacity. 4.   4. The method for initially charging a lithium secondary battery according to claim 2, wherein a charging current of the first charging step is in a range of 0.02 to 1.20 ItA. 5.   5. The lithium secondary according to claim 1, 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. First battery charging method.   The method for initially charging a lithium secondary battery according to claim 1, wherein the first period is within 10 hours.