JP2011216408A - Lithium secondary battery, and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery with less generation of a gap between electrodes and capable of easily being manufactured, in a laminate type battery.SOLUTION: The lithium secondary battery is provided with: power generation elements (11, 12, 13) each equipped with a sheet-like separator 13, and a plurality of positive electrode and negative electrode plates 11, 12 alternately laminated through the separator 13; and a covering material 14 with communication holes for communicating between front and back surfaces thereof formed, running around a circumference of the power generation elements (11, 12, 13) by one round or more to cover it, and having a hydrophilic surface. By using a material having a hydrophilic surface as the covering material for covering the power generation elements, permeability of electrolyte solution is improved.

Description

  The present invention relates to a lithium secondary battery having high output and high energy density and excellent durability, and a method for manufacturing the same.

  With the rapid market expansion of portable electronic devices such as notebook PCs and mobile phones, there is an increasing demand for small, large-capacity secondary batteries with high energy density and excellent charge / discharge cycle characteristics. Yes. In order to meet this demand, a secondary battery using lithium ions as a charge carrier and utilizing an electrochemical reaction accompanying charge transfer by the charged particles has been developed.

  By the way, as a structure of the power generation element of the lithium secondary battery, a jelly roll structure in which a strip-like positive and negative electrodes are wound via a separator, a laminated structure in which a plurality of sets of positive and negative electrodes are stacked, and the like are known. In the jelly roll structure, excessive stress is easily generated in the inner periphery of the winding, and it is difficult to exhibit sufficient cycle characteristics. Although a battery having a laminated structure is unlikely to cause problems such as stress, it is difficult to fix the electrodes and it is difficult to maintain the shape of the power generation element over a long period of time.

  In order to solve the problems in the laminated lithium secondary battery, a method of fixing with three adhesives or the like at the three end surface portions where the electrode terminals are not formed among the end surface portions of the electrode is disclosed (patent) Reference 1).

  Then, a plurality of electrochemical cells whose basic unit is a full cell in which a positive electrode, a separation membrane, and a negative electrode are sequentially stacked, and each overlapping portion is an electrochemical element in which a separation film is interposed, and the separation film is an electrochemical cell. Each electrochemical cell has a unit length that can be wrapped, and is folded outward for each unit length, starting from the electrochemical cell at the first end to the electrochemical cell at the final end in a continuous Z-shape. It has been disclosed to provide an electrochemical element in which an extra separation film wraps around the outer periphery of the overlapping cell and is interposed in the overlapping portion of the electrochemical cell (Patent Document 2).

  Moreover, the lithium secondary battery is provided with an electrode group, and a positive electrode plate and a negative electrode plate are laminated on the electrode group via a separator made of porous polyethylene resin. Negative electrode plates are arranged at both ends of the electrode group in the stacking direction. A porous film made of polyethylene resin is wound at least once around both end faces of the electrode group in the stacking direction and two side faces perpendicular to both end faces and facing each other. In the porous film, a large number of holes having a diameter larger than that of the separator are formed. The laminated structure of the electrode group is maintained by the tight force of the porous film. A lithium secondary battery having such a configuration is disclosed (Patent Document 3).

JP 2008-204706 A (summary etc.) Special table 2003-523061 gazette (summary etc.) JP 2005-294150 A (summary etc.)

  However, in the lithium secondary battery disclosed in Patent Document 1, it is cumbersome to fix with the tape, and the tape directly fixes the electrode, so the part fixed with the tape and the other part There is a problem that the stress becomes unbalanced between the two. And in the lithium secondary battery disclosed in Patent Document 2, since the periphery of the power generation element is covered with a thin film of the same material as the separator, the penetration of the electrolyte into the interior may not be sufficient during battery production. There is a problem. Moreover, it was difficult to say that the lithium secondary battery disclosed in Patent Document 3 has sufficient penetration of the electrolyte.

  In view of the above circumstances, the present invention should solve the problem of providing a lithium secondary battery and a method for manufacturing the same that can be easily manufactured in a stacked battery in which positive and negative electrodes are stacked with little occurrence of displacement between electrodes. Let it be an issue.

The lithium secondary battery according to claim 1 that solves the above problem is characterized in that a power generation element including a sheet-like separator and a plurality of positive and negative electrode plates alternately stacked via the separator,
A communication hole communicating between the front and back surfaces is formed, covering the power generation element around one or more turns, covering the surface with a hydrophilic surface,
It is in having. The present invention has been completed on the basis of the knowledge that the permeability of the electrolytic solution is improved by adopting a coating material covering the power generation element that has a hydrophilic surface.

A feature of the lithium secondary battery according to claim 2 that solves the above problem is that the separator is a band-shaped member, and is sequentially from the end in the stacking direction of the positive and negative electrodes stacked from one end of the separator toward the other end. In between, it is inserted while folding back in the longitudinal direction,
The other end is integrated with the covering material. By adopting a material that is integrated with the separator as the covering material, it is possible to wind and cover the power generation element after the separator is interposed, thereby facilitating the manufacture of the battery.

  The feature of the lithium secondary battery according to claim 3 for solving the above-mentioned problem is that the covering material is formed by hydrophilizing the vicinity of the other end of the separator. By using a separator subjected to a hydrophilization treatment as a covering material, the separator is interposed, and then it can be easily manufactured by winding and fixing as it is around the power generation element. Here, it is desirable that the hydrophilic treatment is not performed on the portion interposed between the positive and negative electrodes, but only on the portion corresponding to the covering material.

  The feature of the lithium secondary battery according to claim 4 that solves the above problem is that the hydrophilization treatment is a treatment in which one or more of corona discharge, plasma irradiation, and ultraviolet irradiation is combined. is there. In these treatments, the separator can be hydrophilized under relatively mild conditions, and even when wound around the power generation element, the hydrophilic treatment can be performed without significantly affecting the power generation element. In addition, since these treatments can be performed only on the portion to be treated, even when the hydrophilic treatment is performed before winding around the power generation element, only the portion corresponding to the covering material is performed. Processing is also easy.

  A feature of the lithium secondary battery according to claim 5 that solves the above problem is that the covering material has a communication hole having a larger hole diameter than a hole of the separator. The covering material can be provided with a communication hole having a larger hole diameter than the separator. If there is a communication hole having a large hole diameter, the electrolyte solution permeates through the communication hole. Here, since it is not necessary for the covering material to prevent a short circuit between the positive and negative electrodes like a separator, a communication hole having a large hole diameter can be provided.

  A feature of the lithium secondary battery according to claim 6 for solving the above-described problem is that the covering material is wound around the power generation element once and then fused or adhered to itself at an end portion to attach the power generation element. It is to restrain. The power generating element can be firmly fixed without affecting the power generating element by fixing the covering material by fusing or adhering at the portion of the covering material.

A feature of the method of manufacturing a lithium secondary battery according to claim 7 for solving the above-described problem is that the lithium secondary battery having a power generation element including a strip-shaped separator and a plurality of positive and negative electrode plates alternately stacked via the separator. A method for manufacturing a secondary battery, comprising:
A power generation element forming step of forming the power generation element by sequentially interposing between the positive and negative electrodes while folding back from one end of the separator toward the other end;
Winding around the power generation element one or more times in the separator extending from the power generation element, and fixing the other end of the wound separator,
There is a hydrophilization treatment step of hydrophilizing the portion of the separator that winds around the power generation element before the electrolyte is injected. By adopting a separator whose surface is hydrophilized as a covering material for covering the power generation element, the permeability of the electrolytic solution can be improved.

  The feature of the method of manufacturing a lithium secondary battery according to claim 8 that solves the above-described problem is that the hydrophilization treatment step includes corona discharge, plasma irradiation, and ultraviolet irradiation of the separator before the winding step. It is a process for performing a process combining one or two or more. In particular, by performing the hydrophilic treatment before the winding step, the hydrophilic treatment can be performed without affecting the power generation element.

  The feature of the method of manufacturing a lithium secondary battery according to claim 9 for solving the above-described problem is that the hydrophilic treatment step includes corona discharge with respect to the separator wound around the power generation element after the winding step. It is a process of performing a process combining one or more of plasma irradiation and ultraviolet irradiation. By performing the hydrophilic treatment after winding around the power generating element, the hydrophilic treatment can be sufficiently performed without considering the force applied to the coating material during the winding process.

It is a schematic sectional drawing of the lithium secondary battery of embodiment. It is one schematic of the method (electric power generation element formation process, hydrophilic treatment process) of manufacturing the lithium secondary battery of embodiment. It is one schematic of the method (power generation element formation process) which manufactures the lithium secondary battery of embodiment. It is one schematic of the method (hydrophilic treatment process) of manufacturing the lithium secondary battery of embodiment.

  The lithium secondary battery and the manufacturing method thereof according to the present invention will be described below in detail based on the embodiments. In addition, the figure used for description includes a portion in which the scale, the number of members, and the like are not accurately written for ease of description.

(Lithium secondary battery)
The lithium secondary battery of this embodiment includes a power generation element having a positive and negative electrode and a separator, a covering material, and other necessary members. Other necessary members include an electrolytic solution and a case.

  As illustrated in FIG. 1, the lithium secondary battery of this embodiment includes a power generation element (11, 12, 13) and a covering material 14 that is wound around the power generation element (11, 12, 13). The power generation elements (11, 12, 13) covered with the covering material 14 are inserted into the case (not shown) or the like together with the electrolyte in that state.

  The positive and negative electrodes 11 and 12 in the power generation elements (11, 12, and 13) are plate-like bodies, each having a plurality thereof, and are alternately stacked via the separators 13.

The positive and negative electrodes include an active material capable of occluding and releasing lithium ions. Examples of the positive electrode active material include lithium-containing transition metal oxides. The lithium-containing transition metal oxide is a material capable of removing and inserting Li ⁺ , and can be exemplified by a lithium-metal composite oxide having a layered structure or a spinel structure. Specifically, Li ₁ -Z NiO ₂ , Li ₁ -Z MnO ₂ , Li ₁ -Z Mn ₂ O ₄ , Li ₁ -Z CoO ₂ and other metal oxide materials, Li ₁ -Z βPO ₄ (β is And LiFePO ₄ which is Fe), and one or more of them can be included. Z in this illustration shows the number of 0-1. A material obtained by adding or substituting a transition metal such as Li, Mg, Al, or Co, Ti, Nb, or Cr may be used. Moreover, not only these lithium-metal composite oxides are used alone, but also a plurality of them can be mixed and used. Moreover, a conductive polymer material, a material having a radical, or the like can be employed alone or mixed.

  As the negative electrode active material, one or more compounds selected from the group consisting of carbon materials such as graphite and amorphous carbon, metal materials capable of forming an alloy with lithium, titanium oxide, and vanadium oxide can be employed. In these active materials, insertion / extraction of lithium (ion) proceeds as the battery reaction proceeds.

  When these positive electrode active materials and negative electrode active materials are used to form an electrode, it can be used in a state in which a composite material layer is formed on a current collector after forming a composite material together with other necessary members. Other necessary members include a conductive material and a binder.

  Examples of the conductive material include ketjen black, acetylene black, carbon black, graphite, carbon nanotube, and amorphous carbon. Moreover, conductive polymers (polyaniline, polypyrrole, polythiophene, polyacetylene, polyacene, etc.) whose aspect ratio is not limited can be exemplified.

  The binder is preferably formed of a polymer material, and is desirably a material that is chemically and physically stable in the atmosphere in the secondary battery. For example, a fluorine-based polymer material (polyvinylidene fluoride and the like) can be given. In addition, a conductive polymer can be used as the binder.

  Such a composite material layer is formed on the surface of an appropriate current collector. An example of the current collector is a foil formed of an electrochemically stable metal. Examples of the method of forming the electrode mixture layer on the surface of the current collector include a method in which the material constituting the mixture layer is dispersed or dissolved in an appropriate dispersion medium and then applied to the surface of the current collector and dried. it can.

  The separator is a sheet-like member interposed between the laminated positive and negative electrodes, and is a member that achieves both electrical insulation and ion conduction. When the electrolytic solution is liquid, the separator also plays a role of holding the liquid supporting electrolyte. For the purpose of ensuring the insulation between the positive electrode and the negative electrode, the separator preferably adopts a form that is larger than the area of the positive electrode and the negative electrode. The separator may adopt a form in which the gap between the positive and negative electrodes is one by one, or as shown in FIG. 1, a strip-shaped separator is adopted as shown in FIG. You may interpose while turning back. The separator can be formed of a porous film having communication holes communicating with the front and back surfaces, or an ion conductive material such as a solid electrolyte. Examples of the porous film include polyolefin films such as polypropylene and polyethylene, and porous films made of polyester, polyamide, and fluororesin.

  The covering material is a member that covers the power generation element by winding it one or more times. If there is no need (strength, other needs), it is desirable to make the winding once. This winding is preferably performed with one direction as the winding axis. Therefore, it is desirable that the wound power generation element is opened in the winding axis direction of the wound covering material. It is desirable to send and receive electric power to the outside by forming a terminal in this open part.

  The covering material is a member having a communicating hole that communicates the front and back surfaces and having a hydrophilic surface. By making the surface hydrophilic, the electrolyte easily penetrates into the power generation element. In this specification, “the surface is hydrophilic” means that the surface of the material constituting the coating material is made more hydrophilic by some surface treatment or is more hydrophilic than the separator. It is either formed using a material. The degree of hydrophilicity is determined by the affinity with water or the electrolyte used. Affinity can be determined by contact angle. The thickness of the covering material is not particularly limited. For example, a thickness of about 5 μm to 50 μm can be employed. The size of the communication hole is not particularly limited. For example, a hole diameter larger than that of the separator can be adopted. Unlike the separator, the coating material does not need to insulate between the positive and negative electrodes. Therefore, by adopting a communication hole larger than the communication hole of the separator, penetration of the electrolyte can be promoted. Specifically, a pore diameter of about 0.1 μm to 100 μm can be employed.

  As the covering material, a material integrated with the separator can be employed. There are a coating material formed from a member different from the separator and connected to the end of the separator, and a coating material obtained by processing a part of the separator. Among them, as a method of processing a part of the separator, a method of combining one or more of corona discharge, plasma irradiation, and ultraviolet irradiation, a method of modifying the surface with an oxidizing agent, and the like can be given. A method of combining one or more of corona discharge, plasma irradiation, and ultraviolet irradiation is desirable.

  The covering material covers the power generation element by winding it from the surroundings, thereby preventing a deviation between the positive and negative electrode plates stacked in the power generation element. In order to prevent displacement in the power generation element, the covering material is fixed after being wound around the power generation element. The covering material can be fixed securely by winding or adhering the end of the covering material to the covering material one round before the winding element is wound around the power generation element. Here, the fusion is performed by melting the end portion of the coating material by heating or the like and then pressing it against the coating material of the fusion partner. Adhesion is performed by attaching an adhesive between the end of the covering material and the covering material of the bonding partner. It can also be adhered with tape or the like. Since it is after winding around the electric power generation element more than once, even if it fixes using a tape, the influence which the nonuniformity of the stress derived from the bias | inclination of the position fixed with a tape has on an electric power generation element can be decreased.

  Although it does not specifically limit as electrolyte solution, What melt | dissolved electrolyte in solvents, such as an organic solvent, the ionic liquid which is liquid itself, and what melt | dissolved electrolyte further with respect to the ionic liquid can be illustrated.

  As an organic solvent, the organic solvent normally used for the electrolyte solution of a lithium secondary battery can be illustrated. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, oxolane compounds and the like can be used. In particular, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and the like, and mixed solvents thereof are suitable. Among these organic solvents mentioned in the examples, in particular, by using one or more non-aqueous solvents selected from the group consisting of carbonates and ethers, the solubility, dielectric constant and viscosity of the electrolyte are excellent, and the battery Charge / discharge efficiency is also high, which is preferable.

An ionic liquid will not be specifically limited if it is an ionic liquid normally used for the electrolyte solution of a lithium secondary battery. For example, examples of the cation component of the ionic liquid include N-methyl-N-propylpiperidinium and dimethylethylmethoxyammonium cation, and examples of the anion component include BF ⁴⁻ , N (SO ₂ CF ₃ ) ^2−. Etc.

The electrolyte is not particularly limited. For example, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiSbF ₆ , LiSCN, LiClO ₄ , LiAlCl ₄ , NaClO ₄ , BClO ₄ , NaI, and salt compounds such as derivatives thereof. Among these, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiN (FSO ₂ ) ₂ , LiN (CF ₃ One or more selected from the group consisting of a derivative of SO ₂ ) (C ₄ F ₉ SO ₂ ), a derivative of LiCF ₃ SO _3, a derivative of LiN (CF ₃ SO ₂ ) _{2 and} a derivative of LiC (CF ₃ SO ₂ ) ₃ It is preferable to use a salt from the viewpoint of electrical characteristics.

  The case is a member that houses a power generation element, an electrolytic solution, and the like. Since the electrolytic solution deteriorates due to the presence of moisture, it is desirable to form it from a structure / material that can prevent moisture from entering from the outside. The case may exhibit an effect as an electrode terminal for exchanging electric power with the outside.

(Method for producing lithium secondary battery)
The method for manufacturing a lithium secondary battery according to the present embodiment includes a lithium secondary battery as shown in FIG. 1 having a power generation element including a strip-shaped separator and a plurality of positive and negative electrode plates alternately stacked via the separator. It is a manufacturing method.

  The method for manufacturing a lithium secondary battery according to this embodiment includes a power generation element forming step, a winding step, a hydrophilization treatment step, and other necessary steps. The power generation element forming step is a step of forming a power generation element, the winding step is a step of winding a coating material around the power generation element, and the hydrophilization treatment step is a step of hydrophilizing the coating material. In addition, since the member demonstrated in the column of the lithium secondary battery of this embodiment can be employ | adopted as it is for the positive / negative electrode, separator, coating | covering material, and other necessary members which are employ | adopted in this embodiment, the description Is omitted.

(Power generation element formation process)
This step is a step of forming the power generation elements (11, 12, 13) by sequentially interposing between the positive and negative electrodes 11, 12 while being folded back from the one end 131 to the other end 132 of the separator 13.

  The method for interposing the separator between the positive and negative electrodes is not particularly limited. For example, as shown in FIG. 2, a power generation element having a necessary number of positive and negative electrodes is obtained by repeating Step A in which the positive and negative electrodes 11 and 12 are overlapped on the front and back surfaces of the separator 13 and then the separator 12 is folded back. be able to. Further, as shown in FIG. 3, the power generating element can be formed by repeating the process B in which the positive and negative electrodes 11 and 12 are alternately overlapped on the front and back surfaces of the separator 13 and the separator 13 is folded back in this state.

(Winding process)
In this step, the separator 13 extending from the power generation element is wound around the power generation element (11, 12, 13) one or more times, and the other end 142 of the wound separator 13 (which eventually becomes the covering material 14) is attached. It is the process of fixing. That is, the covering material 14 is formed from the separator 13 and is integrated with the separator 13. Examples of fixing the other end of the separator include welding by heat, adhesion by an adhesive, and adhesion by a connecting member such as a tape. The other end 142 corresponding to the separator 13 (covering material 14) is preferably fixed in the vicinity of the one end 141 of the covering material 14.

(Hydrophilic treatment process)
This step is a step of making the coating material 14 by hydrophilizing the part of the separator 13 (corresponding to the coating material 14) around the power generation element (11, 12, 13). Examples of the hydrophilization treatment include a method of combining one or more of corona discharge, plasma irradiation, and ultraviolet irradiation, and a method of modifying the surface with an oxidizing agent or the like. In particular, a method of combining one or more of corona discharge, plasma irradiation, and ultraviolet irradiation is a preferable treatment.

  By performing the hydrophilic treatment, the electrolyte easily penetrates into the power generation element. Therefore, it is sufficient that the hydrophilization treatment step is performed before the electrolytic solution is injected. For example, the hydrophilization treatment can be performed together with the power generation element in a state where the periphery of the power generation element is covered with a separator (which becomes a coating material by the hydrophilization treatment) (FIG. 1). Corona discharge, plasma irradiation, and ultraviolet irradiation are preferable hydrophilic treatment because conditions can be set so that only the outermost surface of the material is hydrophilic. Further, as shown in FIG. 4, the separator 13 is processed by the hydrophilic treatment apparatus 5 that performs the hydrophilic treatment before winding the separator 13 around the power generation element (11, 12, 13) to form the covering material 14. be able to. In this case, since only the separator 13 is subjected to hydrophilic treatment, even if the treatment conditions for the hydrophilic treatment that affect the power generation elements (11, 12, 13) are selected, the power generation elements (11, 12, 13) are selected. There is no influence.

(Other necessary processes)
Other necessary steps include a step of inserting the power generation elements (11, 12, 13) covered with the covering material 14 into a case (not shown), a step of injecting an electrolytic solution, a step of sealing the case, and an initial stage. Examples include charging and conditioning. A general thing can be employ | adopted for these processes. Here, the step of injecting the electrolytic solution can be performed smoothly by the hydrophilic treatment of the coating material and is firmly fixed, so that the manufactured lithium secondary battery has high durability.

  Hereinafter, the lithium secondary battery of the present invention will be described in detail based on examples.

(Create test battery)
Test batteries of Example 1 and Comparative Examples 1 to 3 were prepared. Each test battery is a lithium secondary battery using a lithium nickel composite oxide represented by the composition formula LiNiO ₂ as a positive electrode active material and graphite as a negative electrode active material.

The positive electrode of each test battery was manufactured as follows. First, 87 parts by mass of the above LiNiO ₂ , 10 parts by mass of carbon black as a conductive material, and 3 parts by mass of polyvinylidene fluoride (PVdF) as a binder are mixed, and an appropriate amount of N-methyl-2 is mixed. -A paste-like positive electrode mixture was obtained by adding pyrrolidone and kneading. This positive electrode mixture was applied to both surfaces of a positive electrode current collector made of aluminum foil having a thickness of 15 μm, dried, and a sheet-like positive electrode was produced through a pressing process. This positive electrode was cut into a width of 100 mm and a length of 100 mm to obtain a positive electrode plate.

  The negative electrode is obtained by mixing 95 parts by mass of graphite and 5 parts by mass of PVdF as a binder, adding an appropriate amount of N-methyl-2-pyrrolidone and kneading to obtain a paste-like negative electrode mixture. It was. This negative electrode mixture was applied to both sides of a copper foil negative electrode current collector having a thickness of 10 μm, dried, and subjected to a pressing step to produce a sheet-like negative electrode. The negative electrode was cut into a width of 105 mm and a length of 105 mm to obtain a negative electrode plate.

  A separator having a strip shape was adopted, and a power generation element was formed by repeating the process of folding the separator after the positive and negative plates were superimposed on the front and back surfaces of the separator as shown in FIG. The number of positive and negative electrode plates was the same for all test batteries.

  A covering material was wound around the generated power generation element (Example 1, Comparative Examples 1 and 2). The winding was performed once, and the ends of the covering material were fused by heat. The covering material was interposed between the positive and negative electrodes, and the remaining separator was wound around the power generation element as it was. After winding around the power generation element, the end of the separator was heat-sealed. In the test battery of Comparative Example 3, the power generation element was not wound with the covering material.

  A test battery of Comparative Example 1 was prepared with the separator wound around the power generation element. In the test battery of Example 1, corona discharge was performed in a state where the separator was wound around the power generation element, and the separator (corresponding to the coating material) wound around the power generation element was subjected to a hydrophilic treatment, and the coating material and did. In the test battery of Comparative Example 2, in addition to the covering material portion, the portion interposed between the positive and negative electrode plates (the portion corresponding to a conventional separator) was corona discharged before being interposed between the positive and negative electrode plates. To make it hydrophilic.

  Then, this power generation element was inserted into the case, and after injecting an electrolytic solution, it was sealed to obtain a test battery.

(Injection test)
Regarding the test batteries of Example 1 and Comparative Example 1, the state of the electrolyte injection was examined. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7 was used. The state of the injection was evaluated by inserting the power generation element into the case and then injecting the electrolyte. After injecting a predetermined amount of the electrolytic solution, the time required until the liquid level of the electrolytic solution was not observed was measured.

  As a result, the test battery of Example 1 is 300 seconds, and the test battery of Comparative Example 1 is 500 seconds. By adopting a porous membrane that has been subjected to a hydrophilic treatment as a coating material, a significant (40% reduction) is achieved. The permeability of the electrolytic solution could be improved. This is presumably because the electrolyte became easy to permeate into the power generation element because the electrolyte became easy to permeate through the cover because the coating was made hydrophilic.

(Cycle test)
The test batteries of Example 1 and Comparative Example 2 after injecting the electrolytic solution were subjected to initial charge and discharge and conditioned, and then charged and discharged at 60 ° C. for 500 cycles. Charging / discharging in the cycle test was performed between 3.0 V and 4.2 V, charging was CC-CV charging at 1/3 C, and discharging was CC discharging at 1 C. The ratio between the discharge capacity at the first cycle and the discharge capacity at the 500th cycle was compared.

  As a result, the test battery of Example 1 had a discharge capacity at the 500th cycle of 85%, whereas the test battery of Comparative Example 2 had a discharge capacity at the 500th cycle of 75%. In the test battery of Comparative Example 2, since the hydrophilic treatment was performed on the separator in addition to the coating material, it is considered that the separator was damaged by the hydrophilic treatment. In other words, it has been found that a decrease in the cycle characteristics of the battery can be suppressed by performing the hydrophilic treatment only on the coating material without performing the hydrophilic treatment on the separator.

(Drop test)
The test battery of Example 1 and the test battery of Comparative Example 3 were conditioned by injecting an electrolytic solution and then performing initial charge / discharge. In a state where charging was completed, dropping from a height of 1 m was repeated 10 times as a drop test. The terminal voltage before and after the drop test and the discharge capacity during charge and discharge performed before and after the drop test were measured.

  As a result, no change in terminal voltage was observed in both the test batteries of Example 1 and Comparative Example 3 before and after the drop test. The discharge capacity was not changed in the test battery of Example 1, but was 99% in the test battery of Comparative Example 3, and a 1% capacity reduction was observed. This is considered to be because the deviation between the positive and negative electrode plates could be effectively suppressed by winding the power generation element with the covering material.

  From the above tests, in lithium secondary batteries that employ a power generation element formed by laminating positive and negative electrode plates, it is desirable to wind around the power generation element with a coating material, and the coating material is made hydrophilic. It has become clear that it is desirable to perform the treatment, and it is desirable not to perform the hydrophilic treatment on the separator (portion interposed between the positive and negative electrodes).

DESCRIPTION OF SYMBOLS 11 ... Positive electrode plate 12 ... Negative electrode plate 13 ... Separator 14 ... Coating material 5 ... Hydrophilization processing apparatus

Claims (9)

A power generation element comprising a sheet-like separator and a plurality of positive and negative electrode plates alternately stacked via the separator;
A communication hole communicating between the front and back surfaces is formed, covering the power generation element around one or more turns, covering the surface with a hydrophilic surface,
A lithium secondary battery comprising: The separator is a band-shaped member, and is interposed while being folded back in the longitudinal direction in order from the end in the stacking direction of the stacked positive and negative electrodes toward the other end from one end of itself.
The other end is integrated with the covering material,
The lithium secondary battery according to claim 1.   The lithium secondary battery according to claim 2, wherein the covering material is formed by hydrophilizing the vicinity of the other end of the separator.   The lithium secondary battery according to claim 3, wherein the hydrophilic treatment is a treatment in which one or more of corona discharge, plasma irradiation, and ultraviolet irradiation is combined.   The lithium secondary battery according to claim 1, wherein the covering material has a communication hole having a larger hole diameter than a hole of the separator.   6. The lithium secondary according to claim 1, wherein the covering material winds around the power generation element once and then is fused or bonded to itself at an end portion to restrain the power generation element. battery. A method for producing a lithium secondary battery having a power generation element comprising a strip-shaped separator and a plurality of positive and negative electrode plates alternately stacked via the separator,
A power generation element forming step of forming the power generation element by sequentially interposing between the positive and negative electrodes while folding back from one end of the separator toward the other end;
Winding around the power generation element one or more times in the separator extending from the power generation element, and fixing the other end of the wound separator,
A method for producing a lithium secondary battery, comprising a hydrophilization treatment step of hydrophilizing a portion of the separator that winds around the power generation element before the electrolyte is injected.   The said hydrophilization treatment process is a process of performing the process which combined the 1 or 2 or more of corona discharge, plasma irradiation, and ultraviolet irradiation with respect to the said separator before the said winding process. A method for producing a lithium secondary battery.   In the hydrophilization treatment step, after the winding step, the separator wound around the power generation element is subjected to a treatment combining one or more of corona discharge, plasma irradiation, and ultraviolet irradiation. The method for producing a lithium secondary battery according to claim 7, which is a process.

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