JP2008004466A - Manufacturing method for lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a lithium ion secondary battery of supplying a lithium equivalent in amount to an irreversible amount of a negative electrode active material containing at least one substance selected out of a group of substances consisting of a silicon, a silicon oxide, a tin, and a tin oxide; and carrying out stable film formation. <P>SOLUTION: The manufacturing method is for the lithium ion secondary battery including a negative electrode containing a negative active material layer formed on a negative electrode current collector, a positive electrode containing a positive active material layer formed on a positive electrode current collector, and a nonaqueous electrolyte. The manufacturing method includes a step of setting the negative electrode opposite to a lithium supply source, inserting the lithium equivalent in amount to the irreversible amount into the negative electrode active material layer by carrying out at least one cycle of charge/discharge using a first nonaqueous electrolyte in which a film forming agent and a carbon dioxide are dissolved, and then separating the negative electrode from the lithium supply source; a step of inserting a battery group consisting of the negative electrode and the positive electrode opposite to and separated from each other via the separator into a battery case; and a step of injecting a second nonaqueous electrolyte made by dissolving a lithium salt in a nonaqueous solvent into the battery case, and then sealing the battery case. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a lithium ion secondary battery, and in particular, a negative electrode active material layer containing at least one selected from the group consisting of silicon, silicon oxide, tin, and tin oxide. The present invention relates to a method for producing a lithium ion secondary battery using a negative electrode formed on a body.

  In recent years, lithium-ion secondary batteries, which are secondary batteries with high energy density and high output, are frequently used as power sources for driving multifunctional and high-performance portable devices. In order to realize a higher capacity for such a lithium ion secondary battery, a lithium ion secondary battery using silicon or its oxide, or tin or its oxide, which is a group 14 element, as a negative electrode active material. Secondary batteries are being considered.

  However, the volume of the negative electrode material expands and contracts when lithium is occluded / released during charge / discharge, and the negative electrode active material falls off from the negative electrode current collector or is pulverized. As a result, the current collecting property inside the electrode is lowered, and the repeated charge / discharge characteristics (cycle characteristics) are deteriorated.

  In order to improve cycle characteristics, it is known that it is effective to form a film on the surface of the negative electrode with carbon dioxide. However, carbon dioxide can cause gas generation because its solubility in the electrolyte decreases at high temperatures.

  In Patent Document 1, a negative electrode and a positive electrode are brought into contact with a first nonaqueous electrolyte in which carbon dioxide is dissolved, and at least one cycle of charge / discharge is performed. Cycle characteristics are improved by a manufacturing method including a step of assembling a battery using a second nonaqueous electrolyte with a small amount of dissolution.

  On the other hand, it is also known that cycle characteristics can be improved by adding a film-forming agent such as vinylene carbonate (VC) to the electrolyte (see, for example, Patent Document 2).

  Further, even when lithium is occluded by charging, the above-mentioned negative electrode material does not release all the lithium during discharging, and remains in the negative electrode as a so-called “irreversible capacity”. If such an irreversible capacity is present in the negative electrode, it is not possible to efficiently use the lithium initially possessed by the positive electrode. Therefore, the positive electrode is excessively contained in the battery, and the positive electrode and the negative electrode are well balanced in the battery case. It is necessary to contain. However, since the volume of the battery case is limited, the total battery capacity cannot be increased.

In Patent Document 3, when a carbon material is used as the negative electrode active material, in order to compensate for the irreversible capacity of the carbon material, a manufacturing method in which lithium corresponding to the irreversible capacity is doped into the negative electrode in advance before assembling the battery. Has been proposed.
JP 2005-268016 A Japanese Patent Laid-Open No. 10-106624 JP 7-235330 A

  However, since the manufacturing method described in Patent Document 1 is a method in which only an electrolyte containing a large amount of carbon dioxide is replaced with an electrolyte containing a small amount of carbon dioxide, a film is generated on the surface of the negative electrode and cycle characteristics are improved. There is no disclosure regarding capacity. In this method, the irreversible capacity is not compensated.

  Further, in the method of adding vinylene carbonate in the electrolyte as described in Patent Document 2, when the vinylene carbonate remains excessively in the electrolyte, the film forming agent is oxidatively decomposed at a high temperature or during charging, There is a risk of generating gas.

  In the manufacturing method described in Patent Document 3, the irreversible capacity of the negative electrode is obtained in advance by configuring another battery, and preliminary charging is performed for the irreversible capacity. In this case, when at least one selected from the group consisting of silicon, silicon oxide, tin, and tin oxide having a large volume variation is used as the negative electrode active material, only the volume change corresponding to the irreversible capacity is obtained. When it occurs and operates as an actual battery, the film formed on the negative electrode active material is destroyed by further volume change (expansion), and a fresh surface is exposed. As a result, an extra amount of electricity is consumed to form a new film, and gas generation due to decomposition of the electrolyte can occur.

  Thus, the negative electrode active material using at least one selected from the group consisting of silicon, silicon oxide, tin, and tin oxide has a large charge / discharge capacity, but also has a large irreversible capacity, and therefore corresponds to an irreversible capacity. It is desirable to compensate for the lithium content. Moreover, since the negative electrode active material is accompanied by a large volume change during charge and discharge, the surface film of the negative electrode is destroyed and a fresh surface is exposed. As a result, undesirable side reactions such as gas generation due to decomposition of the electrolyte are likely to occur.

  The present invention supplements lithium corresponding to the irreversible capacity of the negative electrode active material using at least one selected from the group consisting of silicon, silicon oxide, tin, and tin oxide, and performs stable film formation. Provides a method for producing a lithium ion secondary battery that does not cause problems such as gas generation during repeated charge / discharge and high temperature storage.

In order to solve the above-described conventional problems, a method for producing a lithium ion secondary battery of the present invention includes:
A negative electrode comprising: a negative electrode current collector; and a negative electrode active material layer comprising at least one selected from the group consisting of silicon, silicon oxide, tin, and tin oxide formed on the negative electrode current collector;
A positive electrode comprising a positive electrode current collector and a positive electrode active material layer comprising a lithium-containing transition metal oxide or a lithium-containing transition metal sulfide formed on the positive electrode current collector;
A method for producing a lithium ion secondary battery comprising a non-aqueous electrolyte in which a lithium salt is dissolved in an organic solvent,
Lithium corresponding to an irreversible capacity is formed in the negative electrode active material layer by charging and discharging at least one cycle using a first non-aqueous electrolyte in which a negative electrode and a lithium supply source are opposed to each other and a film forming agent and carbon dioxide are dissolved. After inserting the negative electrode and the lithium source,
After inserting the electrode group in which the separated negative electrode and the positive electrode are opposed to each other through the separator into the battery case, and after pouring the second nonaqueous electrolyte in which the lithium salt is dissolved in the nonaqueous solvent into the battery case And a step of sealing the battery case.

  By this manufacturing method, a negative electrode active material containing at least one selected from the group consisting of silicon, silicon oxide, tin, and tin oxide is doped with lithium corresponding to irreversible capacity, and at the same time, a stable film is formed. can do.

  According to the method for producing a lithium ion secondary battery of the present invention, in the negative electrode active material containing at least one selected from the group consisting of silicon, silicon oxide, tin, and tin oxide, lithium corresponding to irreversible capacity At the same time as doping, a stable film can be formed, and a lithium ion secondary battery having high capacity and excellent cycle characteristics can be provided.

  Hereinafter, embodiments of the present invention will be described in detail.

(Embodiment 1)
In Embodiment 1 of the present invention, a case where a lithium-containing transition metal oxide or a lithium-containing transition metal sulfide is included as a lithium source will be described.

  In Embodiment 1 of the present invention, the negative electrode is at least selected from the group consisting of a metal foil as a negative electrode current collector and silicon, an oxide of silicon, tin, and an oxide of tin formed on the metal foil. A negative electrode active material layer including one kind. As a method for producing the negative electrode active material layer on the metal foil, a thin film forming method such as a vapor deposition method, a sputtering method, or a CVD method is applied. The negative electrode active material layer obtained by the thin film formation method is preferably low crystalline or amorphous.

  The term “low crystallinity” as used herein refers to a region where the crystal grain size is 50 nm or less. The crystal grain size is calculated by the Scherrer equation from the half-value width of the peak with the highest intensity in the diffraction image obtained by X-ray diffraction analysis. The term “amorphous” means that the diffraction image obtained by X-ray diffraction analysis has a broad peak in the range of 2θ = 15 to 40 °.

  As the metal foil used for the negative electrode current collector, a metal that is not alloyed with lithium, such as copper, nickel, stainless steel, platinum, or an alloy mainly composed of these, can be used.

  The positive electrode includes a metal foil as a positive electrode current collector and a positive electrode active material layer including a lithium-containing transition metal oxide or a lithium-containing transition metal sulfide formed on the metal foil. As a method for producing the positive electrode active material layer on the metal foil, a thin film forming method such as a vapor deposition method, a sputtering method, a CVD method, a lithium-containing transition metal oxide or a lithium-containing transition metal sulfide powder, a conductive agent, and a binder Can be dispersed in a solvent and kneaded to form a paste, and the paste can be prepared on a metal foil through steps of coating, drying, and rolling.

  As the lithium-containing transition metal oxide, lithium cobaltate, lithium nickelate, lithium manganate, or those obtained by partially replacing the transition metal of these compounds with another metal can be used. As for the lithium-containing transition metal sulfide, lithium disulfide titanate can be used in addition to the lithium-containing transition metal oxide in which oxygen is substituted with sulfur. In order to increase the energy density, the lithium-containing transition metal oxide is preferably used because the working potential region is higher. As the metal foil used for the positive electrode current collector, aluminum, nickel, platinum, or the like can be used.

  The positive electrode produced as described above is used as a positive electrode in battery construction, but the same positive electrode is also used as a lithium source.

  Hereinafter, the manufacturing method of the lithium ion secondary battery in Embodiment 1 of this invention is described.

  First, the negative electrode produced as described above is opposed to the positive electrode as the lithium application source. As a method of making it oppose, the method of making it face through the same porous film used for a separator and producing an electrode group can be illustrated.

  Next, the obtained electrode group is immersed in a first non-aqueous electrolyte in which a lithium salt (supporting salt), a film forming agent, and carbon dioxide are dissolved in an organic solvent.

  The organic solvent used here comprises at least one selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and γ-butyrolactone.

  Examples of supporting salts include inorganic acid anion lithium salts typified by lithium perchlorate, lithium tetrafluoroborate and lithium hexafluorophosphate, and organic acid anion lithiums such as lithium trifluoromethanesulfonate and lithium bistrifluoromethanesulfonate imide. Salt can be applied.

  As the film forming agent, at least one selected from vinylene carbonate (VC), ethylene sulfite (ES), propane sultone (PS), vinyl ethylene carbonate (VEC), and fluorinated ethylene carbonate (FEC) can be applied.

  As a method for dissolving carbon dioxide in the organic solvent, a method in which carbon dioxide is aerated in the organic solvent and the concentration of carbon dioxide in the organic solvent is intentionally increased can be applied. When a large amount of carbon dioxide is present in the first nonaqueous electrolyte, a strong and stable film can be formed by interaction with the film forming agent.

  In order to cancel the irreversible capacity, the following three methods can be cited as a method of doping lithium into the negative electrode active material.

(1) A method of forming a local cell by attaching metallic lithium to a portion of the negative electrode current collector where no negative electrode active material is present and injecting it, and then doping lithium into the negative electrode active material. (2) On the negative electrode active material (3) Method of electrochemically doping lithium in the electrolyte in the negative electrode before battery construction, in which metal lithium is formed into a film by vapor deposition or sputtering and solid-phase reaction is performed to dope lithium into the negative electrode active material. When lithium is electrochemically doped as in (3) above,
(A) Method of charging the amount of electricity corresponding to the irreversible capacity (B) After charging, the discharge may also be performed to leave lithium corresponding to the irreversible capacity in the negative electrode.

In the above (1), since lithium metal is locally present, it is difficult for lithium ions to diffuse “uniformly” throughout the negative electrode. In (2) above, it is necessary to obtain the irreversible capacity in advance. In (A) of (3) above, it is necessary to separately determine the irreversible capacity of the negative electrode active material in advance, and an active material with a significant volume expansion such as silicon (Si) or silicon oxide (SiO _x ) is used. When it is used, the film formation tends to be insufficient because it does not reach a sufficient expansion region.

  However, in (B) of (3) above, there is no need to obtain the irreversible capacity of the negative electrode active material in advance, and an active material with a significant volume expansion such as silicon (Si) or silicon oxide (SiOx) is used. The film can be formed to every corner.

  From this point of view, in Embodiment 1, after charging the electrode group in the first non-aqueous electrolyte until the potential of the negative electrode becomes 0 V (vs. Li), 1.0 V (vs. Discharge until Li) is exceeded. Note that in this specification, a reaction in which lithium is inserted (occluded) into the negative electrode active material is referred to as charge, and a reaction in which lithium is desorbed from the negative electrode active material is referred to as discharge.

  In other words, in the charging process, the volume of the negative electrode active material expands as the negative electrode active material occludes lithium from the active material application source. This volume expansion gradually increases the contact area between the negative electrode active material and the electrolyte, but by charging to 0 V, film formation proceeds until the increase, and at the entire interface of the negative electrode active material and the non-aqueous electrolyte. A film can be formed. Further, in the discharge process, lithium corresponding to the irreversible capacity can be left in the negative electrode active material.

  Note that the amount of lithium contained in the lithium-containing transition metal oxide or lithium-containing transition metal sulfide used as the active material application source needs to include an amount that can be charged until the potential of the negative electrode becomes 0V.

  The charging / discharging requires at least one cycle. In order to cause self-healing when the active material surface film is damaged due to volume fluctuations, or to further strengthen the film, the charging / discharging of one cycle or more is required. Although discharge may be carried out, it is preferable that the discharge state be set at the end.

  The “discharge state at the end” is preferably a state in which only lithium corresponding to the irreversible capacity remains, but is not limited thereto. When charging is performed until the potential of the negative electrode reaches 0 V (vs. Li), the charging rate is 100%, and the state in which only lithium corresponding to the irreversible capacity remains is 0%. The lower the charging rate in the “discharged state”, the more effectively lithium in the positive electrode active material can be used in the subsequent battery fabrication. From the viewpoint of effectively utilizing lithium in the positive electrode active material, the charging rate in the “discharged state at the end” is preferably 10% or less, and most preferably 0%.

  Then, an electrode group is isolate | separated into a negative electrode and an active material provision source. The separated negative electrode and a new positive electrode that has not been charged / discharged are opposed to each other through a separator made of a porous film or the like, and an electrode group is formed again and inserted into the battery case.

  Next, the second non-aqueous electrolyte is injected into the battery case and sealed to produce the battery of the first embodiment. As the second nonaqueous electrolyte, a lithium salt dissolved in a nonaqueous solvent is used.

  The second non-aqueous electrolyte used here is at least one selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and γ-butyrolactone as the organic solvent, and perchloric acid as the supporting salt. Inorganic acid anion lithium salts such as lithium acid, lithium tetrafluoroborate and lithium hexafluorophosphate, and organic acid anion lithium salts such as lithium trifluoromethanesulfonate and lithium bistrifluoromethanesulfonate imide are used as the organic solvent. Use the dissolved one.

  Since the film-forming agent has a lower oxidative decomposition potential than the charge / discharge reaction potential of the positive electrode, if it remains in the battery, it causes gas generation due to oxidative decomposition and deteriorates battery characteristics such as cycle characteristics. End up. Moreover, the additive used for film formation tends to cause deterioration of characteristics by generating gas during high temperature storage or charge / discharge cycles. Therefore, in the conventional battery configuration, the addition of the film forming agent is minimized, but it is necessary to strictly control so that an excessive additive does not remain in the electrolyte.

  However, according to the method of manufacturing a lithium ion secondary battery in the first embodiment, a stable film is sufficiently formed by recombining the electrolyte, and the electrolyte (second non-ionic) in the lithium ion secondary battery is further formed. The water electrolyte) can contain a small amount of film-forming agent necessary for restoration when the film is damaged, but it is not added as much as necessary for film formation from the beginning. It has a favorable effect that no excess additive is present. The second non-aqueous electrolyte does not contain any film-forming agent, and since the film-forming agent does not undergo oxidative decomposition during charging at a temperature higher than room temperature, from the viewpoint of suppressing characteristic deterioration. preferable.

  In addition, it is known that the presence of carbon dioxide in the electrolyte leads to stable film formation. It is released as gas from the battery, which causes the battery to swell.

Therefore, when there is a possibility that the lithium ion secondary battery manufactured in this embodiment is exposed to an atmosphere at room temperature or higher, it is preferable that the amount of carbon dioxide dissolved in the second nonaqueous electrolyte is small.

  Therefore, it is more preferable to use a second electrolyte that is sufficiently degassed by aeration of argon gas as the second electrolyte used in configuring the lithium ion secondary battery in the first embodiment. When the argon gas is vented, it is preferably performed at 25 ° C. or more and 60 ° C. or less in consideration of the solubility of carbon dioxide in the electrolyte and the guaranteed temperature of the battery. 60 ° C. is recommended as the upper limit temperature of the guaranteed battery temperature. When argon gas is passed under a condition where the temperature is higher than 60 ° C., the solvent volatilizes before the second nonaqueous electrolyte is injected, and the composition change may become remarkable.

(Embodiment 2)
In Embodiment 2 of the present invention, metallic lithium is used as the lithium application source. Other conditions are the same as those in the first embodiment. In the second embodiment as well, a negative electrode and metallic lithium constitute an electrode group, and charging is performed until the potential of the negative electrode becomes 0 V (vs. Li), and then discharging is performed until it exceeds 1.0 V (vs. Li). You can do it. Further, the amount of metallic lithium needs to include an amount that can be charged until the potential of the negative electrode becomes 0V.

  Also in the second embodiment, the same actions and effects as those of the first embodiment can be obtained.

(Embodiment 3)
In Embodiment 3 of the present invention, instead of the method of depositing the negative electrode active material layer on the metal foil by the thin film formation method in Embodiment 1 to produce a negative electrode, silicon, silicon oxide, tin, And a negative electrode active material powder containing at least one selected from the group consisting of tin oxides, a conductive agent, and a binder are dispersed in a solvent, kneaded to form a paste, and the paste is applied onto a metal foil, dried, and rolled. Thus, a negative electrode is produced. Other conditions are the same as those in the first embodiment.

  Also in the third embodiment, the same actions and effects as those of the first embodiment are obtained.

  The method of manufacturing a lithium ion secondary battery according to the present invention compensates for lithium corresponding to the irreversible capacity of a negative electrode active material containing at least one selected from the group consisting of silicon, silicon oxide, tin, and tin oxide. At the same time, stable film formation can be performed. Thereby, problems such as gas generation in the lithium ion secondary battery after manufacture are reduced, which is useful in that the reliability can be improved. Moreover, the manufacturing method of the lithium ion secondary battery concerning this invention is applicable also to the manufacturing method of the lithium ion secondary battery using the conventional carbon-type negative electrode material and other negative electrode materials.

Claims (7)

A negative electrode comprising: a negative electrode current collector; and a negative electrode active material layer comprising at least one selected from the group consisting of silicon, silicon oxide, tin, and tin oxide formed on the negative electrode current collector;
A positive electrode comprising a positive electrode current collector and a positive electrode active material layer comprising a lithium-containing transition metal oxide or a lithium-containing transition metal sulfide formed on the positive electrode current collector;
A method for producing a lithium ion secondary battery comprising a non-aqueous electrolyte in which a lithium salt is dissolved in an organic solvent,
The negative electrode active material layer is equivalent to an irreversible capacity by charging and discharging at least one cycle using the first nonaqueous electrolyte in which the negative electrode and the lithium supply source are opposed to each other and the film forming agent and carbon dioxide are dissolved. Separating the negative electrode and the lithium source after inserting the lithium,
Inserting an electrode group in which the separated negative electrode and the positive electrode are opposed to each other through a separator, into a battery case;
A method of manufacturing a lithium ion secondary battery, comprising: injecting a second nonaqueous electrolyte in which a lithium salt is dissolved in a nonaqueous solvent into the battery case, and then sealing the battery case. The lithium application source includes a lithium-containing transition metal oxide or a lithium-containing transition metal sulfide,
The manufacturing method of the lithium ion secondary battery of Claim 1. The lithium application source includes a metal lithium foil,
The manufacturing method of the lithium ion secondary battery of Claim 1. The film forming agent is at least one selected from the group consisting of vinylene carbonate (VC), ethylene sulfite (ES), propane sultone (PS), vinyl ethylene carbonate (VEC), and fluorinated ethylene carbonate (FEC). It is characterized by
The manufacturing method of the lithium ion secondary battery in any one of Claims 1-3. In the second non-aqueous electrolyte, the film-forming agent contains a smaller amount than the first non-aqueous electrolyte, or does not contain the film-forming agent.
The manufacturing method of the lithium ion secondary battery in any one of Claims 1-4. Including degassing carbon dioxide from the second non-aqueous electrolyte,
The manufacturing method of the lithium ion secondary battery in any one of Claims 1-5. The carbon dioxide degassing of the second non-aqueous electrolyte is performed by venting an inert gas at 25 ° C. or more and 60 ° C. or less,
The manufacturing method of the lithium ion secondary battery of Claim 6.