JP6457272B2 - Method for reducing uneven charging of secondary battery and method for manufacturing secondary battery - Google Patents

Method for reducing uneven charging of secondary battery and method for manufacturing secondary battery Download PDF

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JP6457272B2
JP6457272B2 JP2015001292A JP2015001292A JP6457272B2 JP 6457272 B2 JP6457272 B2 JP 6457272B2 JP 2015001292 A JP2015001292 A JP 2015001292A JP 2015001292 A JP2015001292 A JP 2015001292A JP 6457272 B2 JP6457272 B2 JP 6457272B2
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JP2016126953A (en
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智輝 國川
智輝 國川
野上 光秀
光秀 野上
克 瓶子
克 瓶子
小川 浩
浩 小川
正史 加納
正史 加納
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Sekisui Chemical Co Ltd
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    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10Energy storage using batteries
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02PCLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50Manufacturing or production processes characterised by the final manufactured product

Description

本発明は、二次電池の充電ムラ低減方法及び二次電池の製造方法に関する。   The present invention relates to a method for reducing charging unevenness of a secondary battery and a method for manufacturing a secondary battery.

二次電池は、携帯機器、電気自動車、住宅若しくは事業施設用の蓄電池等の幅広い用途に展開されている。リチウムイオン二次電池はこれらの用途に適した高い放電電圧を有するため、現在の二次電池の主流になっている。   Secondary batteries are deployed in a wide range of applications such as portable devices, electric vehicles, storage batteries for homes or business facilities. Lithium ion secondary batteries have a high discharge voltage suitable for these applications, and have become the mainstream of current secondary batteries.

リチウムイオン二次電池の製造過程においては、初期充電の際に電解質を構成する有機溶媒の一部が分解することによって電池内にガスが発生する問題がある。発生したガスは電極表面を安定化するSEI(Solid Electrolyte Interface)が形成される際の副生成物であり、発生したガスが電池内に滞留したまま充放電を繰り返すと電池性能が低下する問題がある。   In the manufacturing process of the lithium ion secondary battery, there is a problem that gas is generated in the battery due to decomposition of a part of the organic solvent constituting the electrolyte during the initial charge. The generated gas is a by-product when the SEI (Solid Electrolyte Interface) that stabilizes the electrode surface is formed. If the generated gas stays in the battery and is repeatedly charged and discharged, the battery performance deteriorates. is there.

上記問題に対して、特許文献1には、有機溶媒の吸湿を防ぐために電池の外装体を一旦封止して初期充電を行い、その後、外装体の一部を開孔して減圧することによってガスを排出させること、及び、ガスの排出を促進させる目的で親水基溶媒を添加した電解液の使用が提案されている。
また、特許文献2には、ガス排出時に電極体の積層方向に圧力を加えて、所定の電池電圧に達するまで充分に放電することにより、充電ムラを低減する方法が提案されている。
In order to prevent the above-mentioned problem, Patent Document 1 discloses a method in which the battery outer body is temporarily sealed and subjected to initial charging in order to prevent moisture absorption of the organic solvent, and then a part of the outer body is opened to reduce the pressure. The use of an electrolytic solution to which a hydrophilic solvent has been added has been proposed for the purpose of discharging gas and promoting gas discharge.
Patent Document 2 proposes a method of reducing charging unevenness by applying pressure in the stacking direction of the electrode body during gas discharge and sufficiently discharging until reaching a predetermined battery voltage.

特開2003−331916号公報JP 2003-331916 A 特開2010−9983号公報JP 2010-9983 A

しかしながら、ユーザー側の電池性能に対する要求は年々高まっており、従来提案されている方法によっても依然として残る充電ムラの解消が求められている。   However, the user's demand for battery performance is increasing year by year, and there is a need to eliminate the remaining charging unevenness even by the conventionally proposed methods.

本発明は、上記事情を鑑みてなされたものであり、二次電池の充電ムラ低減方法及びこの方法を利用した二次電池の製造方法の提供を課題とする。   This invention is made | formed in view of the said situation, and makes it a subject to provide the manufacturing method of a secondary battery using the charging nonuniformity reduction method of a secondary battery, and this method.

(1)正極及び負極と、有機溶媒を含有する電解質と、を備えた二次電池の充電ムラを低減する方法であって、前記二次電池の組み立て後に行う初回の充電開始後、満充電に至る前に電池内に発生したガスを排出する排気工程を有する、二次電池の充電ムラ低減方法。
(2)前記二次電池を封止した状態で前記初回の充電を開始して、所定容量まで充電することにより発生したガスを前記二次電池内に溜めた後、前記排気工程において前記封止を一時的に解除して前記ガスを排気する、前記(1)に記載の二次電池の充電ムラ低減方法。
(3)定格容量の50〜90%まで充電した後に電池内に発生したガスを排気する、前記(1)又は(2)に記載の二次電池の充電ムラ低減方法。
(4)前記初回の充電開始後の充電曲線(横軸:電池電圧V、縦軸:蓄電量変化量/電池電圧変化量dQ/dV)において、dQ/dVが1000以上になった後も充電を継続し、dQ/dVが最大値を示した後でdQ/dVが2000以下になる前又は2000になった直後に、電池内に発生したガスを排気する、前記(1)〜(3)の何れか一項に記載の二次電池の充電ムラ低減方法。
(5)前記初回の充電開始後に、電池電圧が3.5V以上になった後も充電を継続し、その後電池電圧が4.0Vに達する前又は4.0Vに達した直後に、電池内に発生したガスを排気する、前記(1)〜(4)の何れか一項に記載の二次電池の充電ムラ低減方法。
(6)前記排気工程の後に充電を再開し、満充電に至った後で放電する放電工程を有する、前記(1)〜(5)の何れか一項に記載の二次電池の充電ムラ低減方法。
(7)前記(1)〜(6)の何れか一項に記載の充電ムラ低減方法を行う工程を有する、二次電池の製造方法。
(1) A method for reducing charging unevenness of a secondary battery comprising a positive electrode and a negative electrode, and an electrolyte containing an organic solvent, wherein the battery is fully charged after the start of the first charge performed after the secondary battery is assembled. A method for reducing charging unevenness of a secondary battery, which has an exhaust process of discharging gas generated in the battery before reaching the battery.
(2) The first charging is started in a state where the secondary battery is sealed, and after the gas generated by charging to a predetermined capacity is accumulated in the secondary battery, the sealing is performed in the exhaust process. The method for reducing uneven charging of the secondary battery according to (1), wherein the gas is exhausted by temporarily releasing the gas.
(3) The method for reducing uneven charging of the secondary battery according to (1) or (2), wherein the gas generated in the battery is exhausted after being charged to 50 to 90% of the rated capacity.
(4) Charging even after dQ / dV becomes 1000 or more in the charge curve after the first charge start (horizontal axis: battery voltage V, vertical axis: amount of change in charge / battery voltage change dQ / dV) And after the dQ / dV reaches the maximum value, before the dQ / dV becomes 2000 or less or immediately after 2000, the gas generated in the battery is exhausted (1) to (3) The method for reducing uneven charging of the secondary battery according to any one of the above.
(5) After the start of the initial charging, the charging is continued even after the battery voltage becomes 3.5V or higher, and then before the battery voltage reaches 4.0V or immediately after reaching 4.0V, The method for reducing uneven charging of the secondary battery according to any one of (1) to (4), wherein the generated gas is exhausted.
(6) Reducing charging unevenness of the secondary battery according to any one of (1) to (5), including a discharging step of restarting charging after the exhausting step and discharging after reaching full charge. Method.
(7) A method for manufacturing a secondary battery, including a step of performing the method for reducing charging unevenness according to any one of (1) to (6).

本発明の二次電池の充電ムラ低減方法によれば、初回充電時に発生したガスに起因する充電ムラを充分に低減することができる。また、従来の充電ムラ低減方法を併用することも可能であるため、従来の製造プラットフォームを大幅に変更することなく容易に本発明を適用することができる。
本発明の二次電池の製造方法によれば、二次電池が本来的に有する性能を充分に発揮させることができる。
According to the secondary battery charging unevenness reducing method of the present invention, it is possible to sufficiently reduce the charging unevenness caused by the gas generated during the initial charging. In addition, since the conventional method for reducing charging unevenness can be used in combination, the present invention can be easily applied without significantly changing the conventional manufacturing platform.
According to the method for producing a secondary battery of the present invention, the performance inherent in the secondary battery can be sufficiently exhibited.

予備試験で使用した二次電池の初回充電におけるdQ/dVカーブである。It is a dQ / dV curve in the first charge of the secondary battery used in the preliminary test. 予備試験で使用した二次電池の初回充電におけるOCVカーブである。It is an OCV curve in the first charge of the secondary battery used in the preliminary test.

本発明者らが上記課題の解決を検討したところ、従来方法においては何れも初回の充電時に満充電していることに気付いた。そこで、初回充電の開始から満充電に至るまでの「蓄電量変化量/電池電圧変化量(dQ/dV)」と電池電圧(V)の関係を示す充電曲線を描いて解析した(図1参照)。その結果、満充電状態を表す4.2Vに至る前の3.6〜3.8Vの充電期間でガスが発生していると考えられるピークが観測された。このことから、3.8〜4.2Vの充電期間においては、大量に発生したガスが滞留した状態で充電を行っていることが分かった。ガスが電極周辺に滞留した状態で満充電になるまで充電を継続することにより、電極表面において充電反応が進む箇所とガスによって充電反応が妨げられる箇所とが生じ、充電ムラが生じる。さらに、この充電ムラの影響を受けてセパレータにリチウム金属が析出する問題も生じることが分かった。   As a result of studying the solution of the above problems, the present inventors have found that all the conventional methods are fully charged at the first charge. Therefore, a charge curve indicating the relationship between “charge amount change / battery voltage change (dQ / dV)” and battery voltage (V) from the start of the initial charge to full charge was analyzed (see FIG. 1). ). As a result, a peak was considered that gas was generated during the charging period of 3.6 to 3.8 V before reaching 4.2 V representing the fully charged state. From this, it was found that during the charging period of 3.8 to 4.2 V, charging was performed in a state where a large amount of generated gas stayed. By continuing the charging until the gas is fully charged in the state where the gas stays around the electrode, a portion where the charging reaction proceeds on the surface of the electrode and a portion where the charging reaction is hindered by the gas occur, resulting in charging unevenness. Furthermore, it has been found that there is a problem that lithium metal is deposited on the separator under the influence of the charging unevenness.

以上の検討から、従来開示されている方法によっても依然として残る充電ムラは、初回充電工程において満充電することに起因することを突き止めた。さらに、本発明者らは、初回充電においてガスが発生した後で、満充電に至る前にガスを排出することにより、初回充電の終盤における充電ムラの発生を防止できることを明らかにした。   From the above examination, it has been found that the charging unevenness that remains even by the conventionally disclosed method is caused by full charge in the initial charging process. Furthermore, the present inventors have clarified that the occurrence of uneven charging at the end of the first charge can be prevented by discharging the gas after the gas is generated in the first charge and before reaching the full charge.

本発明は上記知見に基づいてなされたものであり、以下に好適な実施形態に基づいて本発明を説明するが、本発明はかかる実施形態に限定されない。
本発明は、リチウムイオン二次電池に限らず公知の種々の二次電池において実施可能である。以下では本発明の実施形態の一例として、リチウムイオン二次電池について説明する。
The present invention has been made based on the above findings, and the present invention will be described below based on preferred embodiments. However, the present invention is not limited to such embodiments.
The present invention is not limited to lithium ion secondary batteries and can be implemented in various known secondary batteries. Hereinafter, a lithium ion secondary battery will be described as an example of an embodiment of the present invention.

《充電ムラの低減方法》
本発明の第一実施形態は、正極及び負極と、リチウムイオン及び有機溶媒を含有する電解質と、を備えた二次電池の充電ムラを低減する方法である。
<Method for reducing uneven charging>
1st embodiment of this invention is a method of reducing the charge nonuniformity of the secondary battery provided with the positive electrode and the negative electrode, and the electrolyte containing a lithium ion and an organic solvent.

<二次電池の構成>
前記正極、負極及び電解質の種類は特に限定されず、公知のリチウムイオン二次電池に使用される部材が使用される。すなわち、公知のリチウムイオン二次電池の製造時に本実施形態の充電ムラ低減方法を適用することができる。
前記正極の構成としては、例えば、正極活物質、バインダー及び導電助剤を含む公知の正極材組成物を任意形状のアルミ製集電体上に塗布してなる構成が挙げられる。
前記負極の構成としては、例えば、負極活物質、バインダー及び導電助剤を含む公知の負極材組成物を任意形状の銅製集電体上に塗布してなる構成が挙げられる。
<Configuration of secondary battery>
The kind of said positive electrode, negative electrode, and electrolyte is not specifically limited, The member used for a well-known lithium ion secondary battery is used. That is, the method for reducing charging unevenness according to the present embodiment can be applied when manufacturing a known lithium ion secondary battery.
Examples of the configuration of the positive electrode include a configuration in which a known positive electrode material composition containing a positive electrode active material, a binder, and a conductive additive is applied onto an aluminum current collector having an arbitrary shape.
As a structure of the said negative electrode, the structure formed by apply | coating the well-known negative electrode material composition containing a negative electrode active material, a binder, and a conductive support agent on copper collectors of arbitrary shapes is mentioned, for example.

電極活物質としては、リチウムイオンが可逆的にインターカレートする公知の炭素材料、ケイ素化合物等が好適である。負極活物質の一つとして炭素材料が使用されている場合、初回充電時に負極活物質層の表面にSEIが生成して電極性能が高まるが、SEI生成に伴って有機溶媒の一部が分解することによりガスが発生し易い。本実施形態においては、当該ガスによる充電ムラの発生を充分に低減することができるため、電極活物質として炭素材料を使用することに支障はない。   As the electrode active material, a known carbon material, silicon compound or the like in which lithium ions are reversibly intercalated is suitable. When a carbon material is used as one of the negative electrode active materials, SEI is generated on the surface of the negative electrode active material layer during the initial charge and the electrode performance is improved, but part of the organic solvent is decomposed as the SEI is generated. Therefore, gas is easily generated. In this embodiment, since the occurrence of charging unevenness due to the gas can be sufficiently reduced, there is no problem in using a carbon material as the electrode active material.

電極の作製方法は特に限定されず、公知方法が適用される。例えば、電極活物質、導電助剤、バインダー及び希釈溶媒をヘンシェルミキサー等で混合し、得られた組成物をブレードコート法によって集電体上に塗布した後、希釈溶媒を蒸発させることにより所望の電極が得られる。形成された電極活物質層の厚みは特に限定されず、例えば5μm〜500μmの厚みに設定することができる。この厚みを調整する際にプレスや圧延処理を施しても構わない。   The method for manufacturing the electrode is not particularly limited, and a known method is applied. For example, an electrode active material, a conductive additive, a binder and a dilution solvent are mixed with a Henschel mixer or the like, and the resulting composition is applied onto a current collector by a blade coating method, and then the dilution solvent is evaporated to obtain a desired An electrode is obtained. The thickness of the formed electrode active material layer is not particularly limited, and can be set to a thickness of 5 μm to 500 μm, for example. You may perform a press and a rolling process when adjusting this thickness.

正極と負極を電池セル内に収納する際には、短絡を防ぐために両電極の間に絶縁性のセパレータを設置することが好ましい。セパレータの種類は特に限定されず、両極間に挿入可能な多孔性樹脂フィルムや、絶縁性粒子及びバインダーが電極表面に結着してなる絶縁層等が挙げられる。   When the positive electrode and the negative electrode are housed in the battery cell, it is preferable to install an insulating separator between the two electrodes in order to prevent a short circuit. The type of the separator is not particularly limited, and examples thereof include a porous resin film that can be inserted between both electrodes, and an insulating layer in which insulating particles and a binder are bound to the electrode surface.

正極、セパレータ及び負極を有する電極積層体(電極体)を外装体に収納する方法は特に限定されず、例えば、平板状の電極を積層してなる電極積層体をアルミラミネート袋内に封入するラミパック方式や、フィルム状の電極積層体を同心円のロール状に巻いて円筒形の電池ケース内に封入する巻回し方式等が挙げられる。   The method for housing the electrode laminate (electrode body) having the positive electrode, the separator and the negative electrode in the outer package is not particularly limited. For example, a rampack in which an electrode laminate formed by laminating flat electrodes is enclosed in an aluminum laminate bag. Examples thereof include a winding method in which a film-shaped electrode laminate is wound into a concentric roll and enclosed in a cylindrical battery case.

電極積層体を外装体に収納した後、リチウムイオン及び有機溶媒(非水系溶媒)を含有する電解質が電極積層体若しくはセパレータを浸漬するように、外装体内に電解質を注入する。電解質は液状の電解液であってもよいし、ゲル状のゲル電解質であってもよい。   After housing the electrode stack in the outer package, the electrolyte is injected into the outer package so that the electrolyte containing lithium ions and an organic solvent (non-aqueous solvent) immerses the electrode stack or the separator. The electrolyte may be a liquid electrolyte or a gel-like gel electrolyte.

電解質はリチウムイオンを含む電解質塩であることが好ましい。電解質塩の種類は特に限定されず、公知のリチウム塩が適用可能であり、例えば、LiBF、LiPF、LiAsF、LiCFCFO、LiSOCF、LiCFCFSO、LiClO、LiN(COCFCF、LiN(SOCF等のリチウム塩が挙げられる。これらリチウム塩の1種が単独で使用されてもよいし、2種以上が併用されてもよい。電解質塩の濃度は特に限定されず、例えば、0.3モル/L〜3.0モル/L程度が挙げられる。 The electrolyte is preferably an electrolyte salt containing lithium ions. The type of the electrolyte salt is not particularly limited, and a known lithium salt can be applied. For example, LiBF 4 , LiPF 6 , LiAsF 6 , LiCF 3 CFO, LiSO 3 CF 3 , LiCF 2 CF 2 SO 3 , LiClO 4 , Examples include lithium salts such as LiN (COCF 2 CF 3 ) 2 and LiN (SO 2 CF 3 ) 2 . One of these lithium salts may be used alone, or two or more thereof may be used in combination. The density | concentration of electrolyte salt is not specifically limited, For example, about 0.3 mol / L-3.0 mol / L is mentioned.

電解質を構成する有機溶媒の種類は特に限定されず、正極−負極間におけるリチウムイオンの伝導を可能にする有機溶媒であれば公知の有機溶媒(非水系溶媒)が適用可能である。   The kind of the organic solvent constituting the electrolyte is not particularly limited, and a known organic solvent (non-aqueous solvent) can be used as long as it is an organic solvent that enables conduction of lithium ions between the positive electrode and the negative electrode.

<ガスの排出>
本実施形態の充電ムラ低減方法においては、まず、上記のように電極積層体を外装体に収納し、更に電解質を注入した後、各電極に接続された端子用タブを外部に出した状態で外装体を封止してリチウムイオン二次電池の組み立てを行う。次に、初回の充電を開始した後、満充電状態に至る前に電池内に発生したガスを排気する。
<Gas emission>
In the charging unevenness reducing method of the present embodiment, first, the electrode laminate is housed in the exterior body as described above, and after injecting the electrolyte, the terminal tab connected to each electrode is exposed to the outside. The exterior body is sealed and a lithium ion secondary battery is assembled. Next, after starting the first charge, the gas generated in the battery is exhausted before reaching the fully charged state.

ここで「満充電」とは、当該二次電池の定格容量に相当する電気量(単位:Ah)が充電された充電率(SOC:State Of Charge)100%である状態をいう。定格容量は公知方法により決定される。初回充電においては、充電率が約0%の状態から約100%へ向けて充電が開始される。なお、負極活物質に予めリチウムプレドープ処理が施されている場合は、初回充電の開始以前に充電率が0%を超えている場合もある。充電開始から満充電に至るまでの電気量(充電量)と電池電圧の関係は、電池の開回路電圧を縦軸にとり、充電量を横軸にとったOCVカーブで表される(図2参照)。   Here, “full charge” refers to a state where the amount of electricity (unit: Ah) corresponding to the rated capacity of the secondary battery is 100% charged (SOC: State Of Charge). The rated capacity is determined by a known method. In the initial charging, charging is started from a state where the charging rate is about 0% to about 100%. In addition, when the lithium pre-doping process is performed to the negative electrode active material in advance, the charge rate may exceed 0% before the start of the first charge. The relationship between the amount of electricity (charge amount) from the start of charging to full charge and the battery voltage is represented by an OCV curve with the open circuit voltage of the battery on the vertical axis and the charge amount on the horizontal axis (see Fig. 2). ).

本実施形態においては、組み立てた二次電池を封止した状態で初回の充電を開始して、所定容量まで充電することにより発生したガスを二次電池内に溜めた後、前記封止を一時的に解除して電池内に溜めたガスを排気することが好ましい。   In this embodiment, the initial charging is started in a state where the assembled secondary battery is sealed, and after the gas generated by charging to a predetermined capacity is accumulated in the secondary battery, the sealing is temporarily performed. It is preferable that the gas accumulated in the battery is exhausted.

組み立てた電池を封止せずに初回充電を行うと、充電期間中に電解質が外気から湿気(水分)を吸収する問題が発生する。電解質の吸湿を防ぐためには乾燥雰囲気下で充電する必要があるが、充電工程は短くても数時間を要するため、充電工程を乾燥雰囲気下で行うことは二次電池の製造効率を著しく低下させる場合がある。したがって、二次電池を一旦封止して、外気からの吸湿を防いだ状態で充電工程を行うことが好ましい。   When the assembled battery is charged for the first time without sealing, there is a problem that the electrolyte absorbs moisture (moisture) from the outside air during the charging period. In order to prevent moisture absorption of the electrolyte, it is necessary to charge in a dry atmosphere. However, since the charging process takes several hours even if it is short, performing the charging process in a dry atmosphere significantly reduces the manufacturing efficiency of the secondary battery. There is a case. Therefore, it is preferable to perform the charging step in a state where the secondary battery is once sealed and moisture absorption from the outside air is prevented.

組み立てた二次電池を封止した状態で初回充電を行うと、主に充電期間の後期に電池内にガスが発生する。本実施形態においては、ガスの発生を許容し、所定容量まで充電することにより二次電池内にガスが溜まることを容認する。ガスの発生初期においては、ガスは電極およびセパレータに付着した微細な多数の気泡として存在し易い。このような微細なガスを効率的に排出することは難しい場合がある。しかし、本実施形態においては、ガスを充分に発生させて、気泡同士が結合してなる比較的大きなガス溜まりを電池内に形成させるため、後で行うガス排出工程の効率を高めることができる。   When initial charging is performed in a state where the assembled secondary battery is sealed, gas is generated in the battery mainly in the later stage of the charging period. In the present embodiment, the generation of gas is allowed, and it is allowed that gas is accumulated in the secondary battery by charging to a predetermined capacity. In the early stage of gas generation, the gas tends to exist as many fine bubbles adhering to the electrode and the separator. It may be difficult to efficiently discharge such a fine gas. However, in the present embodiment, the gas is sufficiently generated and a relatively large gas reservoir formed by combining the bubbles is formed in the battery, so that the efficiency of the gas discharge process performed later can be improved.

所定容量まで充電した電池内にガスが溜まった後、適切な時期に充電を停止して排気工程に移る。排気工程においては、公知方法によって二次電池の封止を一時的に解除して、電池内のガスを排出する。電池内に発生したガスによって内圧が高まっているため、封止を解除しても外気の湿気が電池内に侵入する恐れは少ないが、乾燥雰囲気下で排気工程を行うことが好ましい。例えば外装体を外部から加圧したり、減圧雰囲気下に置いたりする等のガス排出を促進する公知方法を併用することによって、数分〜数十分で排気を完了することができる。   After gas accumulates in the battery charged to a predetermined capacity, the charging is stopped at an appropriate time and the process proceeds to the exhaust process. In the exhaust process, the sealing of the secondary battery is temporarily released by a known method, and the gas in the battery is discharged. Since the internal pressure is increased by the gas generated in the battery, there is little risk of moisture from the outside air entering the battery even when the sealing is released, but it is preferable to perform the exhaust process in a dry atmosphere. For example, exhaustion can be completed in several minutes to several tens of minutes by using a known method for promoting gas discharge such as pressurizing the exterior body from the outside or placing it in a reduced-pressure atmosphere.

初回充電を停止して排気工程に移る好適な時期としては、初回充電の開始後、当該二次電池の定格容量の所定の充電率まで充電した時点で排気工程に移ることが好ましい。ここで所定の充電率は、ガスの発生程度にもよるが、例えば、定格容量の50〜90%が好ましく、60〜85%がより好ましく、70〜80%がさらに好ましい。   As a suitable time for stopping the first charge and moving to the exhaust process, it is preferable to move to the exhaust process after the start of the first charge and charging to a predetermined charging rate of the rated capacity of the secondary battery. Here, although the predetermined charging rate depends on the degree of gas generation, for example, 50 to 90% of the rated capacity is preferable, 60 to 85% is more preferable, and 70 to 80% is more preferable.

初回充電において充電率50%以上に充電した後で排気工程に移ることにより、電池内には充分なガスが発生しているため、効率的に排気することができる。一方、充電率が50%未満の状態で排気工程に移ると、再封止後の充電期間において新たなガスが大量に発生して充電ムラを引き起こす恐れがある。
初回充電において充電率90%以下に充電した後で排気工程に移ることにより、電池内におけるガスの発生は概ね終息しており、充電ムラを充分に低減することができる。一方、充電率が90%超の状態においても初回充電を継続すると、充電ムラを引き起こす場合がある。
By charging to a charge rate of 50% or more in the initial charge and then moving to the exhaust process, sufficient gas is generated in the battery, so that the exhaust can be efficiently performed. On the other hand, if the charge rate is less than 50% and the process proceeds to the exhaust process, a large amount of new gas may be generated in the charging period after resealing, which may cause uneven charging.
By charging to a discharge rate of 90% or less in the initial charge and then proceeding to the exhaust process, the generation of gas in the battery has almost ended, and charging unevenness can be sufficiently reduced. On the other hand, if the initial charging is continued even in a state where the charging rate exceeds 90%, charging unevenness may be caused.

初回充電を停止して排気工程に移る好適な時期としては、予め調べた充電曲線を参照して決定することもできる。例えば、横軸に開回路の電池電圧(V)をとり、縦軸に蓄電量変化量/電池電圧変化量(dQ/dV)をとったdQ/dVカーブを参照して、dQ/dV値が1000以上になった後も充電を継続して電池内に充分なガスを発生させて、dQ/dV値が最大値を示した後で下降したdQ/dV値が2000以下若しくは1500以下になる前又はなった直後に、充電を停止して排気工程に移る方法が挙げられる。   A suitable time for stopping the initial charge and moving to the exhaust process can be determined with reference to a charge curve examined in advance. For example, refer to the dQ / dV curve where the horizontal axis is the open circuit battery voltage (V) and the vertical axis is the amount of change in battery charge / battery voltage (dQ / dV). After charging reaches 1000 or more, charging continues and sufficient gas is generated in the battery, and after the dQ / dV value reaches the maximum value, the dQ / dV value that has fallen below 2000 or 1500 or less Alternatively, immediately after becoming, there is a method of stopping charging and moving to an exhaust process.

初回充電においてdQ/dV値が1000以上になった後でガスの発生が盛んになり、その後、dQ/dV値が最大値を示した後で、ガスの発生が終息に向かい、dQ/dV値が2000以下又は1500以下になる頃までにガスの発生が概ね終息していると考えられる。ガスの発生が終息した直後に排気工程に移ることにより、充電ムラを充分に低減して、二次電池が本来的に有する電池性能を最大限に発揮させることができる。   After the dQ / dV value becomes 1000 or more in the first charge, the gas generation becomes active, and after the dQ / dV value shows the maximum value, the gas generation ends, and the dQ / dV value It is considered that the generation of gas has almost ended by the time when the gas reaches 2000 or less or 1500 or less. By moving to the exhaust process immediately after the generation of gas ends, charging unevenness can be sufficiently reduced and the battery performance inherently possessed by the secondary battery can be maximized.

初回充電を停止して排気工程に移る好適な時期は、充電時の電池電圧をモニターしながら決定することもできる。例えば、開回路の電池電圧(V)を計測しながら初回充電を開始して、電池電圧が3.5V以上になった後も充電を継続し、その後電池電圧が4.0Vに達する前又は達した直後に、充電を停止して排気工程に移る方法が挙げられる。   A suitable time for stopping the initial charging and moving to the exhaust process can be determined while monitoring the battery voltage during charging. For example, the first charge is started while measuring the battery voltage (V) of the open circuit, the charge is continued even after the battery voltage becomes 3.5 V or higher, and then the battery voltage reaches or reaches 4.0 V. Immediately after this, there is a method of stopping charging and moving to an exhaust process.

初回充電において電池電圧が3.5V以上になった後でガスの発生が盛んになり、その後、電池電圧が4.0Vに達する頃までにガスの発生が概ね終息していると考えられる。ガスの発生が終息した直後に排気工程に移ることにより、充電ムラを充分に低減して、二次電池が本来的に有する電池性能を最大限に発揮させることができる。   After the battery voltage becomes 3.5 V or more in the first charge, gas generation becomes active, and then it is considered that the gas generation has almost ended by the time the battery voltage reaches 4.0 V. By moving to the exhaust process immediately after the generation of gas ends, charging unevenness can be sufficiently reduced and the battery performance inherently possessed by the secondary battery can be maximized.

本実施形態においては、排気工程において二次電池を再封止した後に充電を再開し、満充電に至った後で放電する放電工程を有することが好ましい。
初回充電後に放電して充放電サイクルを完了することにより、二次電池のサイクル特性を向上させることができる。放電後、更に数回の充放電サイクルを繰り返してもよい。この繰り返しにより電極表面が安定化して、電池のサイクル特性が更に向上する場合がある。2回目以降の充放電サイクルにおいて、もしもガスが発生する場合には、本実施形態の充電ムラ低減方法を再び行うことができる。
In the present embodiment, it is preferable to have a discharging step in which charging is resumed after the secondary battery is resealed in the exhausting step and discharged after reaching full charging.
By completing the charge / discharge cycle by discharging after the initial charge, the cycle characteristics of the secondary battery can be improved. After the discharge, several charge / discharge cycles may be repeated. By repeating this, the electrode surface may be stabilized, and the cycle characteristics of the battery may be further improved. In the second and subsequent charging / discharging cycles, if gas is generated, the charging unevenness reducing method of this embodiment can be performed again.

《二次電池の製造方法》
本発明の第二実施形態は、前述した第一実施形態の充電ムラ低減方法を行う工程を有する二次電池の製造方法である。第二実施形態は、その他の工程、例えば、正極及び負極の作製工程、電解質の調製工程、二次電池の組み立て工程等を有していてもよい。その他の工程における具体的な作製方法等は公知方法が適用可能である。
<Method for manufacturing secondary battery>
The second embodiment of the present invention is a method for manufacturing a secondary battery including the step of performing the method for reducing charging unevenness of the first embodiment described above. The second embodiment may include other steps, for example, a positive electrode and negative electrode preparation step, an electrolyte preparation step, a secondary battery assembly step, and the like. Known methods can be applied as specific manufacturing methods in other steps.

次に、実施例により本発明をさらに詳細に説明するが、本発明はこれらの例によって限定されるものではない。   EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited by these examples.

《二次電池の材料の準備》
<電解液>
シュウ酸リチウム−三フッ化ホウ素錯体(LOX−BF)溶液 (リチウム塩濃度1mol/kg、ジメチルカーボネート:エチレンカーボネート(2:1、体積比)混合溶媒)を混合及び攪拌することにより電解液を得た。
<セパレータ>
不織布(PP製、空孔率76%、厚み30μm 廣瀬製紙(株)製HOP6) を225×285mmにカットして用いた。
<正極>
LiCoO(コバルト酸リチウム)93質量部と、PVDF(ポリフッ化ビニリデン)3質量部と、導電助剤であるカーボンブラック4質量部とを混合して正極合剤を調製したのち、溶剤であるN−メチルピロリドン(NMP)に分散させて正極合剤スラリーを作製した。この正極合剤スラリーを15μmのアルミニウム箔の両面に、活物質層のない部分を15mm幅残して塗工し、更に減圧乾燥(100℃、−0.1MPa、10時間)してロールプレスすることによって、正極を得た。
<負極>
グラファイト95質量部と、PVDF(ポリフッ化ビニリデン)5質量部とを混合し負極合剤を調製したのち、溶剤であるN−メチルピロリドン(NMP)に分散させて負極合剤スラリーを作製した。15μmの銅箔の両面に、活物質層のない部分を15mm幅残して塗工し、減圧乾燥(100℃、−0.1MPa、10時間)してロールプレスすることによって、負極を得た。
上記の正極及び負極を次のようにカットした。活物質層のない部分(15mm幅)を含んで、負極は235×280mm(活物質層のある部分は220×280mm)、正極は235×280mm(活物質層のある部分は220×280mm)の大きさに成形した。
<Preparation of secondary battery materials>
<Electrolyte>
Lithium oxalate-boron trifluoride complex (LOX-BF 3 ) solution (lithium salt concentration 1 mol / kg, dimethyl carbonate: ethylene carbonate (2: 1, volume ratio) mixed solvent) was mixed and stirred to prepare an electrolyte solution. Obtained.
<Separator>
A non-woven fabric (PP, porosity: 76%, thickness: 30 μm, HOP6 manufactured by Hirose Paper Co., Ltd.) was cut into 225 × 285 mm and used.
<Positive electrode>
After preparing a positive electrode mixture by mixing 93 parts by mass of LiCoO 2 (lithium cobaltate), 3 parts by mass of PVDF (polyvinylidene fluoride) and 4 parts by mass of carbon black as a conductive additive, N is a solvent. A positive electrode mixture slurry was prepared by dispersing in -methylpyrrolidone (NMP). The positive electrode mixture slurry is coated on both sides of a 15 μm aluminum foil, leaving a portion with no active material layer 15 mm wide, and further dried under reduced pressure (100 ° C., −0.1 MPa, 10 hours) and roll-pressed. Thus, a positive electrode was obtained.
<Negative electrode>
A negative electrode mixture slurry was prepared by mixing 95 parts by mass of graphite and 5 parts by mass of PVDF (polyvinylidene fluoride) to prepare a negative electrode mixture and then dispersing it in N-methylpyrrolidone (NMP) as a solvent. The negative electrode was obtained by coating the both sides of 15-micrometer copper foil, leaving the part which does not have an active material layer 15 mm width, drying under reduced pressure (100 degreeC, -0.1 MPa, 10 hours), and roll-pressing.
The above positive electrode and negative electrode were cut as follows. Including the portion without active material layer (15 mm width), the negative electrode is 235 × 280 mm (the portion with the active material layer is 220 × 280 mm), the positive electrode is 235 × 280 mm (the portion with the active material layer is 220 × 280 mm) Molded to size.

《二次電池の組み立て》
負極2枚と正極1枚、セパレータ2枚を交互に積層した。具体的には、負極の上に負極活物質層を覆うようにセパレータを被せた。セパレータを間に挟んで、負極の活物質層のない部分と反対側に正極の活物質層のない部分とが対向するようにして、正極と負極が直接触れないように、正極を被せた。さらに、正極の上に正極活物質層を覆うようにセパレータを被せた。さらに、セパレータを間に挟んで、正極の活物質層のない部分と反対側に負極の活物質層のない部分とが対向するようにして、正極と負極が直接触れないように、負極を被せた。
上記積層体の正極、負極それぞれの活物質層のない部分に端子用タブを超音波溶接などによって電気的に接続した。
端子用タブが外部に突出するように、アルミラミネートフィルム(300×350mm)で上記積層体を挟み、三辺をラミネート加工によって封止した。電極端から2mm程度の部分で封止した。
封止せずに残した一辺から電解液を注入し、真空封止することによって、初期充電を行う前のリチウムイオン二次電池を得た。この際、電極端から2cmの余白を残して封止した。
<Assembly of secondary battery>
Two negative electrodes, one positive electrode, and two separators were alternately laminated. Specifically, a separator was placed on the negative electrode so as to cover the negative electrode active material layer. The positive electrode was covered so that the positive electrode and the negative electrode were not in direct contact with each other with the separator in between so that the portion of the negative electrode without the active material layer was opposed to the portion of the negative electrode without the active material layer. Further, a separator was placed on the positive electrode so as to cover the positive electrode active material layer. In addition, with the separator in between, place the positive electrode without the active material layer on the opposite side of the negative electrode without the active material layer so that the negative electrode is not in direct contact with the negative electrode. It was.
Terminal tabs were electrically connected by ultrasonic welding or the like to the positive electrode and negative electrode portions of the laminate without the active material layer.
The laminate was sandwiched between aluminum laminate films (300 × 350 mm) so that the terminal tabs protruded to the outside, and the three sides were sealed by lamination. Sealing was performed at a portion of about 2 mm from the electrode end.
A lithium ion secondary battery before initial charge was obtained by injecting an electrolyte solution from one side left without sealing and vacuum-sealing. At this time, sealing was performed leaving a 2 cm blank from the electrode end.

<予備試験(比較例)>
上記のように組み立てたリチウムイオン二次電池について、従来方法の通り、満充電に至るまで一定電流(200mA)で初回充電を行った。この際のOCVカーブを図2に示す。図2のOCVカーブにおいては、充電開始直後の電池電圧は約2.5Vであり、充電初期(〜180mAh、SOC約14%)において約3.6Vまで電池電圧が急速に上昇し、その後、満充電状態(約1300mAh、充電率約100%)の約4.2Vまで電池電圧が緩やかに上昇した。
<Preliminary test (comparative example)>
The lithium ion secondary battery assembled as described above was initially charged at a constant current (200 mA) until full charge as in the conventional method. The OCV curve at this time is shown in FIG. In the OCV curve of FIG. 2, the battery voltage immediately after the start of charging is about 2.5 V, and the battery voltage rapidly rises to about 3.6 V in the initial stage of charging (˜180 mAh, SOC about 14%), and then reaches the full level. The battery voltage gradually increased to about 4.2 V in the charged state (about 1300 mAh, charging rate about 100%).

上記予備試験の初回充電について、図1に示すように、電池電圧Vを横軸にとり、蓄電量変化量/電池電圧変化量を縦軸にとった充電曲線(dQ/dVカーブ)を描いて、その充電特性を解析した。その結果、前述したように、満充電状態を表す4.2Vに至る前の3.6〜3.8Vの充電期間でガスが発生し、その後の3.8〜4.2Vの充電期間においてはガスの発生が殆ど終息していると考えられた。   For the initial charge of the preliminary test, as shown in FIG. 1, draw a charge curve (dQ / dV curve) with the battery voltage V on the horizontal axis and the amount of change in battery charge / battery voltage on the vertical axis. The charging characteristics were analyzed. As a result, as described above, gas is generated in the charging period of 3.6 to 3.8 V before reaching 4.2 V representing the fully charged state, and in the charging period of 3.8 to 4.2 V thereafter. It was thought that gas generation had almost ended.

上記予備試験によって満充電に至った二次電池を分解して各部材の状態を確認した。セパレータの表面には、リチウム金属の析出が観察された。このような析出はリチウムデンドライドの発生を促す恐れがあるため好ましくない。次に負極の表面を観察したところ、充電反応によりリチウムイオンが吸蔵された箇所と充電反応が滞った箇所との色の違いがあることから、充電ムラが発生したことが確認された。この充電ムラは、その後の放電工程によっても解消されない場合があり、電池性能を低下させる原因になる。この充電ムラが発生した理由として、ガスの発生が終息した3.8〜4.2Vの充電期間においては、大量に発生したガスが電池内に滞留した状態で充電を行っていることが要因であると考えられた。   The secondary battery that was fully charged in the preliminary test was disassembled and the state of each member was confirmed. Lithium metal deposition was observed on the surface of the separator. Such precipitation is not preferable because it may promote the generation of lithium dendride. Next, when the surface of the negative electrode was observed, it was confirmed that uneven charging occurred because there was a difference in color between the location where lithium ions were occluded by the charging reaction and the location where the charging reaction was delayed. This uneven charging may not be resolved even in the subsequent discharging process, which causes a decrease in battery performance. The reason for the occurrence of this charging unevenness is that during the charging period of 3.8 to 4.2 V when the generation of gas has ended, charging is performed in a state where a large amount of generated gas stays in the battery. It was thought that there was.

<実施例1>
前述した方法で新たなリチウムイオン二次電池を組み立て、同様に初回充電を開始し、予備試験で得られた図1に示すdQ/dVカーブの最大ピークが観測された電池電圧約3.8V、充電率約54%に達した直後に充電を停止し、次のガス排出工程に移った。
具体的には、組み立て時に封止したラミネートフィルムからなる外装体の余白部分に針を刺して開孔を形成し、減圧雰囲気下において外装体を加圧して、電池内に発生したガスを排出した。その後、開口部を熱融着することにより再封止して、電池電圧が4.2Vになる満充電に至るまで充電した。再封止した後に行った充電期間における新たなガスの発生量は少なかった。
<Example 1>
A new lithium ion secondary battery was assembled by the above-described method, and the initial charge was similarly started. The battery voltage of about 3.8 V in which the maximum peak of the dQ / dV curve shown in FIG. Immediately after the charging rate reached about 54%, the charging was stopped, and the next gas discharging step was started.
Specifically, a needle is inserted into the blank portion of the outer package made of a laminate film sealed at the time of assembly to form a hole, the outer package is pressurized under a reduced pressure atmosphere, and the gas generated in the battery is discharged. . Thereafter, the opening was resealed by heat sealing, and the battery was charged until the battery voltage reached 4.2V. The amount of new gas generated during the charging period after resealing was small.

実施例1で満充電に至った二次電池を分解して各部材の状態を確認した。セパレータの表面には、リチウム金属は析出していなかった。負極の表面の色合いを観察したところ、充電反応によりリチウムイオンが吸蔵された箇所が電極表面全体に亘って均一に拡がっていることが確認された。すなわち、充電ムラは発生せず、二次電池が本来的に有する電池性能を最大限に発揮できる状態にあることが分かった。このような好結果が得られた理由としては、初回充電によって電池内に発生したガス抜きのタイミングが最適であったことが考えられる。また、ガスを排出して再封止した後に行った充電期間における新たなガスの発生は少なかったので、電池性能に与える影響は小さいといえる。   The secondary battery that was fully charged in Example 1 was disassembled and the state of each member was confirmed. Lithium metal was not deposited on the surface of the separator. When the color of the surface of the negative electrode was observed, it was confirmed that the locations where lithium ions were occluded by the charging reaction were spread uniformly over the entire electrode surface. That is, it has been found that charging unevenness does not occur and the battery performance inherent in the secondary battery can be maximized. The reason why such a good result was obtained may be that the timing of degassing generated in the battery by the initial charge was optimal. Moreover, since there was little generation | occurrence | production of the new gas in the charge period performed after discharging | emitting gas and resealing, it can be said that the influence which it has on battery performance is small.

<参考例>
前述した方法で新たなリチウムイオン二次電池を組み立て、同様に初回充電を開始し、予備試験で得られた図1に示すdQ/dVカーブの大きなピークが観測される前の電池電圧約3.5V、充電率約15%に達したときに充電を停止し、次のガス排出工程に移った。ガス排出の方法は実施例1と同様に行った。その後、開口部を熱融着することにより再封止して、電池電圧が4.2Vになる満充電に至るまで充電した。再封止した後に行った充電期間における新たなガスの発生量は多かった。
<Reference example>
A new lithium ion secondary battery is assembled by the above-described method, the initial charge is similarly started, and the battery voltage before the large peak of the dQ / dV curve shown in FIG. When 5V and the charging rate reached about 15%, charging was stopped and the next gas discharging step was started. The gas discharging method was performed in the same manner as in Example 1. Thereafter, the opening was resealed by heat sealing, and the battery was charged until the battery voltage reached 4.2V. The amount of new gas generated during the charging period after resealing was large.

参考例で満充電に至った二次電池を分解して各部材の状態を確認したところ、予備試験と同様の結果であった。すなわち、セパレータの表面には、リチウム金属の析出が観察された。また、負極の表面には充電ムラが発生したことを示す色の違いがあった。この充電ムラが発生した理由として、ガスの発生が活発になる前にガス排出工程を行ったため、再封止後の充電期間において、大量に発生したガスが滞留した状態で満充電に至るまで充電を行ったことが要因であると考えられた。   When the secondary battery that was fully charged in the reference example was disassembled and the state of each member was confirmed, the result was the same as the preliminary test. That is, lithium metal deposition was observed on the surface of the separator. Moreover, there was a color difference indicating that charging unevenness occurred on the surface of the negative electrode. The reason for this uneven charging is that the gas discharge process was performed before the generation of gas became active, so in the charging period after resealing, a large amount of generated gas was retained until full charge was reached. It was thought that this was a factor.

以上で説明した各実施形態における各構成及びそれらの組み合わせ等は一例であり、本発明の趣旨を逸脱しない範囲で、構成の付加、省略、置換、およびその他の変更が可能である。また、本発明は各実施形態によって限定されることはなく、請求項(クレーム)の範囲によってのみ限定される。   The configurations and combinations thereof in the embodiments described above are examples, and the addition, omission, replacement, and other modifications of the configurations can be made without departing from the spirit of the present invention. Further, the present invention is not limited by each embodiment, and is limited only by the scope of the claims.

本発明は、リチウムイオン二次電池等の電気化学分野で広く利用可能である。   The present invention can be widely used in the electrochemical field such as lithium ion secondary batteries.

Claims (8)

正極及び負極と、有機溶媒を含有する電解質と、を備えた二次電池の充電ムラを低減する方法であって、
前記二次電池の組み立て後に行う初回の充電開始後、満充電に至る前に電池内に発生したガスを排出する排気工程を有し、
前記排気工程は、前記初回の充電開始後の充電曲線(横軸:電池電圧V、縦軸:蓄電量変化量/電池電圧変化量dQ/dV)において、dQ/dVが1000以上になった後も充電を継続し、dQ/dVが最大値を示した後でdQ/dVが2000以下になる前又は2000になった直後に、電池内に発生したガスを排気する、二次電池の充電ムラ低減方法。
A method for reducing uneven charging of a secondary battery comprising a positive electrode and a negative electrode, and an electrolyte containing an organic solvent,
After the start of charging first it performed after assembly of the secondary battery, and have a discharge step of discharging the gas generated in the battery before reaching full charge,
The exhaust process is performed after dQ / dV becomes 1000 or more in the charge curve after the start of the first charge (horizontal axis: battery voltage V, vertical axis: amount of change in storage amount / battery voltage change amount dQ / dV). Charging is continued, and after dQ / dV shows the maximum value, before dQ / dV becomes 2000 or less or immediately after 2000, the gas generated in the battery is exhausted. Reduction method.
前記二次電池を封止した状態で前記初回の充電を開始して、所定容量まで充電することにより発生したガスを前記二次電池内に溜めた後、前記排気工程において前記封止を一時的に解除して前記ガスを排気する、請求項1に記載の二次電池の充電ムラ低減方法。   The initial charging is started in a state where the secondary battery is sealed, and after the gas generated by charging up to a predetermined capacity is accumulated in the secondary battery, the sealing is temporarily performed in the exhaust process. 2. The method for reducing uneven charging of the secondary battery according to claim 1, wherein the gas is exhausted after being released. 定格容量の50〜90%まで充電した後に電池内に発生したガスを排気する、請求項1又は2に記載の二次電池の充電ムラ低減方法。   The method for reducing charging unevenness of a secondary battery according to claim 1 or 2, wherein the gas generated in the battery is exhausted after being charged to 50 to 90% of the rated capacity. 前記初回の充電開始後に、電池電圧が3.5V以上になった後も充電を継続し、その後電池電圧が4.0Vに達する前又は4.0Vに達した直後に、電池内に発生したガスを排気する、請求項1〜の何れか一項に記載の二次電池の充電ムラ低減方法。 After the start of the initial charging, the charging is continued even after the battery voltage becomes 3.5V or higher, and then the gas generated in the battery before the battery voltage reaches 4.0V or immediately after reaching 4.0V. The method of reducing charging unevenness of the secondary battery according to any one of claims 1 to 3 . 前記排気工程の後に充電を再開し、満充電に至った後で放電する放電工程を有する、請求項1〜の何れか一項に記載の二次電池の充電ムラ低減方法。 The method for reducing uneven charging of the secondary battery according to any one of claims 1 to 4 , further comprising a discharging step of restarting charging after the exhausting step and discharging after reaching full charging. 前記正極にコバルト酸リチウムが含まれる、請求項1〜5の何れか一項に記載の二次電池の充電ムラ低減方法。The method for reducing uneven charging of the secondary battery according to claim 1, wherein the positive electrode contains lithium cobalt oxide. 前記正極の活物質がコバルト酸リチウムのみからなる、請求項1〜6の何れか一項に記載の二次電池の充電ムラ低減方法。The method for reducing uneven charging of the secondary battery according to any one of claims 1 to 6, wherein the active material of the positive electrode is composed only of lithium cobalt oxide. 請求項1〜の何れか一項に記載の充電ムラ低減方法を行う工程を有する、二次電池の製造方法。 Having Claim 1-7 or step of charging unevenness reduction method according to one of method of manufacturing a secondary battery.
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