WO2013088622A1 - Lithium-ion secondary battery - Google Patents

Lithium-ion secondary battery Download PDF

Info

Publication number
WO2013088622A1
WO2013088622A1 PCT/JP2012/006716 JP2012006716W WO2013088622A1 WO 2013088622 A1 WO2013088622 A1 WO 2013088622A1 JP 2012006716 W JP2012006716 W JP 2012006716W WO 2013088622 A1 WO2013088622 A1 WO 2013088622A1
Authority
WO
WIPO (PCT)
Prior art keywords
secondary battery
ion secondary
lithium
lithium ion
active material
Prior art date
Application number
PCT/JP2012/006716
Other languages
French (fr)
Japanese (ja)
Inventor
昌洋 木下
名倉　健祐
Original Assignee
パナソニック株式会社
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by パナソニック株式会社 filed Critical パナソニック株式会社
Publication of WO2013088622A1 publication Critical patent/WO2013088622A1/en

Links

Images

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0569—Liquid materials characterised by the solvents
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H01M2300/0028—Organic electrolyte characterised by the solvent
    • H01M2300/0037—Mixture of solvents
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • Y—GENERAL 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a lithium ion secondary battery having a high set voltage for the end-of-charge voltage.
  • Lithium ion secondary batteries are widely used as drive power sources for portable electronic devices and communication devices.
  • a carbon material capable of inserting and extracting lithium is used for a negative electrode, and a composite oxide of a transition metal such as LiMnO 2 and lithium is used as an active material for a positive electrode.
  • High power and high capacity secondary batteries have been realized.
  • a typical lithium ion secondary battery has a configuration in which an electrode group in which a positive electrode and a negative electrode are wound through a separator is housed in a battery case together with a nonaqueous electrolyte.
  • the nonaqueous electrolyte dissolves a solute composed of a lithium salt such as LiPF 6 or LiBF 4 in a nonaqueous solvent composed of a carbonate such as ethylene carbonate (EC), dimethyl carbonate (DMC), or diethyl carbonate (DEC). Is used.
  • a lithium salt such as LiPF 6 or LiBF 4
  • a nonaqueous solvent composed of a carbonate such as ethylene carbonate (EC), dimethyl carbonate (DMC), or diethyl carbonate (DEC).
  • the conventional non-aqueous solvent comprising a carbonate ester has low oxidation resistance, the non-aqueous solvent is decomposed and a film is formed on the positive electrode, thereby increasing internal resistance and reducing cycle characteristics. There is a problem.
  • Patent Document 1 describes that a nonaqueous solvent containing a fluorinated carboxylic acid ester is used as the nonaqueous solvent.
  • the non-aqueous solvent containing the fluorinated carboxylic acid ester is highly resistant to oxidation and thus is not easily decomposed. For this reason, it is possible to suppress a decrease in cycle characteristics due to film formation on the positive electrode.
  • the end-of-charge voltage of a lithium ion secondary battery is set to 4.1 to 4.2V. If the end-of-charge voltage can be increased to 4.2V or more, the capacity of the lithium ion secondary battery is increased. Can be made.
  • the inventors of the present application have evaluated the characteristics of a lithium ion secondary battery produced using a nonaqueous solvent containing a fluorinated carboxylic acid ester by increasing the end-of-charge voltage to 4.2 V or higher. It was found that the cycle characteristics deteriorated.
  • the present invention has been made in view of such a problem, and a main object thereof is to provide a lithium ion secondary battery with little deterioration in cycle characteristics even when the end-of-charge voltage is increased to 4.2 V or higher.
  • a lithium ion secondary battery according to the present invention is a lithium ion secondary battery including a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte
  • the negative electrode is a negative electrode active material made of a carbon material formed on a current collector.
  • the nonaqueous electrolyte includes a solute composed of a lithium salt and fluorine represented by the following formula: And a non-aqueous solvent comprising a carboxylic acid ester.
  • the metal oxide is preferably made of lithium titanate.
  • the present invention it is possible to provide a lithium ion secondary battery with little deterioration in cycle characteristics even when the end-of-charge voltage is increased to 4.2 V or higher.
  • (A), (b) is sectional drawing explaining the state when the metal eluted from the positive electrode active material deposited on the negative electrode surface. It is sectional drawing which showed the structure of the lithium ion secondary battery in one Embodiment of this invention. It is sectional drawing which showed the structure of the negative electrode in one Embodiment of this invention. (A), (b) is sectional drawing explaining the state when the metal eluted from the positive electrode active material deposited on the negative electrode surface in this invention.
  • Table 1 shows a mixed solvent (mass ratio 1: 1) of ethylene carbonate (EC) and dimethyl carbonate (DMC) and a mixed solvent of ethylene carbonate (EC) and a fluorinated carboxylic acid ester (non-aqueous solvent).
  • Cycle characteristics (capacity retention rate) when lithium ion secondary batteries (battery 1 to battery 6) were prepared using mass ratios 1: 1) and the end-of-charge voltage was changed to 4.1 to 4.4V. ) Shows the measurement results.
  • fluoromethyl propionate methyl 3,3,3-trifluoropropionate CAS: 18830-44-9; FMP
  • FMP fluorinated carboxylic acid ester.
  • LiNi 0.5 Mn 0.5 O 2 was used as the positive electrode active material
  • artificial graphite as the carbon material was used as the negative electrode active material
  • LiPF 6 was used as the nonaqueous electrolyte.
  • the cycle characteristics were evaluated as follows. First, in an environment of 25 ° C., after constant current charging at 0.2 C to the end-of-charge voltage (4.1 to 4.4 V), constant-voltage charging to the end current of 0.05 C, and then at 2 C at 2 C . Constant current discharge to 5V. This charging / discharging was performed 100 cycles, and the ratio of the discharge capacity after 100 cycles to the discharge capacity at the first cycle (capacity maintenance ratio) was determined to evaluate the cycle characteristics.
  • the capacity retention ratio is about 3 even when the end-of-charge voltage is increased from 4.1 V to 4.4 V.
  • the end-of-charge voltage is increased from 4.1 V to 4.4 V. It can be seen that the capacity retention rate has decreased by about 24%.
  • the fluorinated carboxylic acid ester used in the batteries 4 to 6 has a structure represented by the following formula (1).
  • H 2 (proton) bonded to C ( ⁇ O) is adjacent to C having an F group with high electronegativity, and the charge is attracted, while the opposite carbonyl group is conjugated. Since it becomes a structure and electrons are delocalized, it is stabilized in a state where protons are desorbed. Therefore, when the end-of-charge voltage is set to 4.1 V or more, protons are easily released from the nonaqueous solvent.
  • Protons released from the nonaqueous solvent react with the positive electrode active material (LiNi 0.5 Mn 0.5 O 2 ), and the elution of metal (for example, Mn 2+ ) from the positive electrode active material is accelerated.
  • the metal (Mn 2+ ) eluted from the positive electrode active material is deposited on the surface of the active material layer 11 formed on the current collector 10 of the negative electrode, and FIG. As shown in FIG. 2, a film 20 is formed on the surface of the active material layer 11.
  • the metal in the coating 20 (Mn 2+) by binding with lithium occluded in the active material layer 11 (Li +), lithium in the active material layer 11 (Li +) is decreased.
  • the battery whose cycle characteristics were evaluated was disassembled, and the amount of Li present in the coating 20 on the negative electrode surface was measured.
  • the amount of Li was measured by the following method. First, the battery was disassembled in a state where the battery was discharged to 2.5 V, and a cell in which the extracted negative electrode and Li metal were combined was produced. After this cell was charged to 1.5 V at 0.01 C, the cell was again disassembled and the negative electrode was taken out. An acid was added to the extracted negative electrode to dissolve it, and the amount of remaining Li was measured using an ICP-MS (inductively coupled plasma mass spectrometry) method. The results are shown in Table 2.
  • ICP-MS inductively coupled plasma mass spectrometry
  • the present inventors have been able to suppress the reaction between the metal (Mn 2+ ) eluted from the positive electrode active material and the lithium (Li + ) occluded in the negative electrode active material. Even if the voltage is increased to 4.2 V or higher, it is considered that the decrease in cycle characteristics (capacity maintenance ratio) can be suppressed, and the present invention has been conceived.
  • FIG. 2 is a cross-sectional view showing the configuration of the lithium ion secondary battery 100 in one embodiment of the present invention.
  • an electrode group 4 in which a positive electrode 1 and a negative electrode 2 are wound through a separator 3 is accommodated in a cylindrical battery case 7 together with a nonaqueous electrolyte (not shown).
  • the positive electrode 1 is joined to a sealing body 8 that also serves as a positive electrode terminal via a positive electrode lead 5
  • the negative electrode 2 is joined to the bottom of a battery case 7 that also serves as a negative electrode terminal via a negative electrode lead 6.
  • the opening of the battery case 7 is sealed with a sealing body 8 via a gasket 9.
  • the lithium ion secondary battery 100 according to the present invention is not particularly limited with respect to the other components constituting the lithium ion secondary battery, except for the non-aqueous electrolyte material described later and the configuration of the negative electrode 2.
  • the member used etc. can be used.
  • the lithium ion secondary battery 100 in the present invention is not limited to a cylindrical secondary battery, and may be, for example, a square secondary battery.
  • the electrode group 4 may be one in which the positive electrode 1 and the negative electrode 2 are laminated via the separator 3.
  • the non-aqueous electrolyte in the present invention is formed by dissolving a solute composed of a lithium salt such as LiPF 6 or LiBF 4 in a non-aqueous solvent containing a fluorinated carboxylic acid ester.
  • the fluorinated carboxylic acid ester has a structure represented by the above formula (1).
  • the non-aqueous solvent may be a mixed solvent containing other solvents such as ethylene carbonate (EC). In that case, the mixing ratio of the fluorinated carboxylic acid ester and the other solvent in the mixed solvent can be appropriately determined within the range where the effects of the present invention are exhibited.
  • FIG. 3 is a cross-sectional view showing the configuration of the negative electrode 2 in the present embodiment.
  • the negative electrode 2 includes a current collector 10, an active material layer 11 containing an active material formed on the current collector 10, and lithium ions formed on the active material layer 11. And a protective layer 12 containing a metal oxide capable of occluding and releasing.
  • the active material contained in the active material layer 11 is made of a carbon material, and examples thereof include graphite, carbon black, acetylene black, and carbon fiber.
  • the metal oxide contained in the protective layer 12 include molybdenum oxide in addition to lithium titanate (LixTiyOz: LTO).
  • the active material layer 11 may contain a predetermined amount of a binder.
  • the binder include polyvinylidene fluoride (PVDF), fluorine-based rubber, styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), acrylic rubber (ACM), and the like.
  • the protective layer 12 may contain a predetermined amount of a conductive agent and a binder.
  • a conductive agent include carbon materials such as graphite.
  • the binder include polyvinylidene fluoride (PVDF), fluorine rubber, styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), and acrylic rubber (ACM).
  • the current collector 10 can be made of, for example, a copper foil or a copper alloy foil.
  • the protective layer 12 since the protective layer 12 includes a metal oxide capable of inserting and extracting lithium ions, it also functions as an active material layer. However, since the metal oxide contained in the protective layer 12 is generally made of a material having lower conductivity and smaller capacity than the carbon material contained in the active material layer 11, The protective layer 12 is distinguished from the layer 11.
  • Table 3 shows a lithium non-aqueous solvent using a mixed solvent of ethylene carbonate (EC) and fluorinated carboxylic acid ester (FMP) (mass ratio 1: 1) and having the negative electrode 2 having the structure shown in FIG. Results of measurement of cycle characteristics (capacity retention ratio) and the amount of Li on the negative electrode surface when an ion secondary battery (batteries 7 and 8) was prepared and the end-of-charge voltage was changed to 4.2 to 4.3 V Is shown.
  • the batteries 5 and 6 shown in Table 2 are listed for comparison.
  • the negative electrode 2 used for the batteries 5 and 6 has a structure in which an active material layer 11 made of artificial graphite (C) is formed on the current collector 10, and the positive electrode active material used for the batteries 7 and 8 is Same as batteries 5 and 6.
  • the protective layer 12 made of LTO formed on the surface of the active material layer 11 contains the metal (Mn 2+ ) eluted from the positive electrode active material and the active material layer 11. This is thought to be because the reaction with the occluded lithium (Li + ) was suppressed.
  • FIG. 4B the decrease in lithium (Li + ) occluded in the active material layer 11 is suppressed, and even when the end-of-charge voltage is increased to 4.2 V or more, the capacity retention rate is reduced. It is thought that the decrease could be suppressed.
  • LTO has the property of occluding and releasing lithium, like the carbon material (C), and therefore, lithium (Li + ) is also occluded in the protective layer 12.
  • the crystal structure of LTO has a spinel structure, and the activation energy of lithium is lower than that of the layered crystal carbon material (C). Therefore, even if metal (Mn 2+ ) is deposited on the surface of the protective layer 12, it is difficult to bond with lithium (Li + ) occluded in the protective layer 12, so that the metal (Mn 2+ ) and lithium (Li + ) It is thought that the reaction with was able to be suppressed.
  • the negative electrode 2 As described above, in the lithium ion secondary battery including the nonaqueous electrolyte including the solute composed of the lithium salt and the nonaqueous solvent composed of the fluorinated carboxylic acid ester represented by the above formula (1), the negative electrode 2
  • the active material layer 11 made of a carbon material formed on the current collector 10 and the protective layer 12 formed on the active material layer 11 and containing a metal oxide capable of inserting and extracting lithium ions.
  • the metal oxide is made of a material whose activation energy of lithium is lower than that of the carbon material constituting the active material layer 11, and typically, lithium titanate is preferably used.
  • the present invention is particularly effective when the positive electrode 1 having a positive electrode active material layer made of a lithium-containing metal oxide containing Mn or Fe is used. This is because the lithium-containing metal oxide containing Mn or Fe is likely to react with protons that are released from the non-aqueous solvent.
  • the thickness of the protective layer 12 is preferably in the range of 1 to 20 ⁇ m. If it is thinner than 1 ⁇ m, the effect of suppressing the reaction between the metal (Mn 2+ ) and lithium (Li + ) is not sufficiently exhibited. On the other hand, when it is thicker than 20 ⁇ m, LTO has a lower conductivity and a smaller capacity than a carbon material, leading to a decrease in discharge performance of the lithium ion battery.
  • the active material layer 11 and the protective layer 12 are formed on one surface of the current collector 10 in the above embodiment, the negative electrode 2 may be formed on both surfaces of the current collector 10.
  • the present invention is useful as a power source for driving automobiles, electric motorcycles, electric playground equipment and the like.

Landscapes

  • Chemical & Material Sciences (AREA)
  • General Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Composite Materials (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Inorganic Chemistry (AREA)
  • Battery Electrode And Active Subsutance (AREA)
  • Secondary Cells (AREA)

Abstract

The purpose of the present invention is to provide a lithium-ion secondary battery which exhibits a small decline in cycle properties even when a charging final voltage is increased to 4.2V or higher. The present invention is a lithium-ion secondary battery equipped with a positive electrode (1), a negative electrode (2), a separator (3), and a nonaqueous electrolyte, wherein: the negative electrode (2) is provided with an active material layer (11) comprising a carbon material and formed on a current collector (10), and a protective layer (12) containing a metal oxide capable of absorbing and discharging lithium ions, and formed on the active material layer (11); and the nonaqueous electrolyte contains a solute comprising a lithium salt, and a nonaqueous solvent comprising a fluorinated carboxylic acid ester represented by this formula. CFxH3-x-CH2-C(=O)-OR (1≤x≤3; R represents an alkyl group)

Description

リチウムイオン二次電池Lithium ion secondary battery
　本発明は、充電終止電圧の設定電圧の高いリチウムイオン二次電池に関する。 The present invention relates to a lithium ion secondary battery having a high set voltage for the end-of-charge voltage.
　リチウムイオン二次電池は、携帯用電子機器や通信機器などの駆動電源として利用が広がっている。一般に、リチウムイオン二次電池では、負極に、リチウムの吸蔵・放出が可能な炭素材料を用い、正極には、ＬｉＭｎＯ２などの遷移金属とリチウムの複合酸化物を活物質として用いており、これによって高出力、高容量の二次電池を実現している。 Lithium ion secondary batteries are widely used as drive power sources for portable electronic devices and communication devices. In general, in a lithium ion secondary battery, a carbon material capable of inserting and extracting lithium is used for a negative electrode, and a composite oxide of a transition metal such as LiMnO 2 and lithium is used as an active material for a positive electrode. High power and high capacity secondary batteries have been realized.
　代表的なリチウムイオン二次電池は、正極及び負極をセパレータを介して捲回された電極群が、非水電解質とともに、電池ケース内に収容された構成からなる。 A typical lithium ion secondary battery has a configuration in which an electrode group in which a positive electrode and a negative electrode are wound through a separator is housed in a battery case together with a nonaqueous electrolyte.
　ここで、非水電解質は、エチレンカーボネート（ＥＣ）、ジメチルカーボネート（ＤＭＣ）、ジエチルカーボネート（ＤＥＣ）等の炭酸エステルからなる非水溶媒に、ＬｉＰＦ６、ＬｉＢＦ４等のリチウム塩からなる溶質を溶解したものが用いられている。 Here, the nonaqueous electrolyte dissolves a solute composed of a lithium salt such as LiPF 6 or LiBF 4 in a nonaqueous solvent composed of a carbonate such as ethylene carbonate (EC), dimethyl carbonate (DMC), or diethyl carbonate (DEC). Is used.
　しかしながら、従来の炭酸エステルからなる非水溶媒は、耐酸化性が低いため、非水溶媒が分解し、正極上に被膜が形成され、これにより、内部抵抗の増大を招き、サイクル特性が低下するという問題がある。 However, since the conventional non-aqueous solvent comprising a carbonate ester has low oxidation resistance, the non-aqueous solvent is decomposed and a film is formed on the positive electrode, thereby increasing internal resistance and reducing cycle characteristics. There is a problem.
　そこで、特許文献１には、非水溶媒に、フッ素化カルボン酸エステルを含む非水溶媒を用いることが記載されている。このフッ素化カルボン酸エステルを含む非水溶媒は、耐酸化性が高いため、分解されにくい。そのため、正極上の被膜形成に起因するサイクル特性の低下を抑制することができる。 Therefore, Patent Document 1 describes that a nonaqueous solvent containing a fluorinated carboxylic acid ester is used as the nonaqueous solvent. The non-aqueous solvent containing the fluorinated carboxylic acid ester is highly resistant to oxidation and thus is not easily decomposed. For this reason, it is possible to suppress a decrease in cycle characteristics due to film formation on the positive electrode.
特開２０１０－６２１３２号公報JP 2010-62132 A
　一般に、リチウムイオン二次電池の充電終止電圧は、４．１～４．２Ｖに設定されているが、充電終止電圧を４．２Ｖ以上に高めることができれば、リチウムイオン二次電池の容量を増加させることができる。 Generally, the end-of-charge voltage of a lithium ion secondary battery is set to 4.1 to 4.2V. If the end-of-charge voltage can be increased to 4.2V or more, the capacity of the lithium ion secondary battery is increased. Can be made.
　しかしながら、本願発明者等が、フッ素化カルボン酸エステルを含む非水溶媒を用いて作製したリチウムイオン二次電池に対して、充電終止電圧を４．２Ｖ以上に高めて、その特性を評価したところ、サイクル特性が低下することが分かった。 However, the inventors of the present application have evaluated the characteristics of a lithium ion secondary battery produced using a nonaqueous solvent containing a fluorinated carboxylic acid ester by increasing the end-of-charge voltage to 4.2 V or higher. It was found that the cycle characteristics deteriorated.
　このサイクル特性の低下は、非水溶媒の耐酸化性とは異なる、フッ素化カルボン酸エステルに固有の別の要因で生じた課題と考えられる。 This decrease in cycle characteristics is considered to be caused by another factor inherent to the fluorinated carboxylic acid ester, which is different from the oxidation resistance of the non-aqueous solvent.
　本発明は、かかる課題に鑑みなされたもので、その主な目的は、充電終止電圧を４．２Ｖ以上に高めても、サイクル特性の低下の少ないリチウムイオン二次電池を提供することにある。 The present invention has been made in view of such a problem, and a main object thereof is to provide a lithium ion secondary battery with little deterioration in cycle characteristics even when the end-of-charge voltage is increased to 4.2 V or higher.
　本発明に係るリチウムイオン二次電池は、正極、負極、セパレータ、及び非水電解質を備えたリチウムイオン二次電池であって、負極は、集電体上に形成された炭素材料からなる負極活物質と、負極活物質上に形成された、リチウムイオンを吸蔵・放出可能な金属酸化物を含む保護層とを備え、非水電解質は、リチウム塩からなる溶質と、以下の式に示したフッ素化カルボン酸エステルからなる非水溶媒とを含む。 A lithium ion secondary battery according to the present invention is a lithium ion secondary battery including a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte, and the negative electrode is a negative electrode active material made of a carbon material formed on a current collector. And a protective layer containing a metal oxide capable of occluding and releasing lithium ions formed on the negative electrode active material. The nonaqueous electrolyte includes a solute composed of a lithium salt and fluorine represented by the following formula: And a non-aqueous solvent comprising a carboxylic acid ester.
　　ＣＦｘＨ３－ｘ－ＣＨ２－Ｃ（＝Ｏ）－ＯＲ（１≦ｘ≦３；Ｒはアルキル基）
　ここで、上記金属酸化物は、チタン酸リチウムからなることが好ましい。 CF x H 3-x —CH 2 —C (═O) —OR (1 ≦ x ≦ 3; R is an alkyl group)
Here, the metal oxide is preferably made of lithium titanate.
　本発明によれば、充電終止電圧を４．２Ｖ以上に高めても、サイクル特性の低下の少ないリチウムイオン二次電池を提供することができる。 According to the present invention, it is possible to provide a lithium ion secondary battery with little deterioration in cycle characteristics even when the end-of-charge voltage is increased to 4.2 V or higher.
（ａ）、（ｂ）は、負極表面に正極活物質から溶出した金属が析出したときの状態を説明した断面図である。(A), (b) is sectional drawing explaining the state when the metal eluted from the positive electrode active material deposited on the negative electrode surface. 本発明の一実施形態におけるリチウムイオン二次電池の構成を示した断面図である。It is sectional drawing which showed the structure of the lithium ion secondary battery in one Embodiment of this invention. 本発明の一実施形態における負極の構成を示した断面図である。It is sectional drawing which showed the structure of the negative electrode in one Embodiment of this invention. （ａ）、（ｂ）は、本発明における負極表面に正極活物質から溶出した金属が析出したときの状態を説明した断面図である。(A), (b) is sectional drawing explaining the state when the metal eluted from the positive electrode active material deposited on the negative electrode surface in this invention.
　本発明を説明する前に、本発明を想到するに至った経緯をまず説明する。 Before explaining the present invention, the background to the idea of the present invention will be described first.
　表１は、非水溶媒に、エチレンカーボネート（ＥＣ）とジメチルカーボネート（ＤＭＣ）との混合溶媒（質量比１：１）、及び、エチレンカーボネート（ＥＣ）とフッ素化カルボン酸エステルとの混合溶媒（質量比１：１）をそれぞれ用いてリチウムイオン二次電池（電池１～電池６）を作製して、充電終止電圧を４．１～４．４Ｖに変えたときの、サイクル特性（容量維持率）を測定した結果を示したものである。ここで、フッ素化カルボン酸エステルとして、フルオロメチルプロピオネート（３，３，３－トリフルオロプロピオン酸メチル　ＣＡＳ：１８８３０－４４－９；ＦＭＰ）を用いた。 Table 1 shows a mixed solvent (mass ratio 1: 1) of ethylene carbonate (EC) and dimethyl carbonate (DMC) and a mixed solvent of ethylene carbonate (EC) and a fluorinated carboxylic acid ester (non-aqueous solvent). Cycle characteristics (capacity retention rate) when lithium ion secondary batteries (battery 1 to battery 6) were prepared using mass ratios 1: 1) and the end-of-charge voltage was changed to 4.1 to 4.4V. ) Shows the measurement results. Here, fluoromethyl propionate (methyl 3,3,3-trifluoropropionate CAS: 18830-44-9; FMP) was used as the fluorinated carboxylic acid ester.
　ここで、作製したリチウムイオン二次電池は、正極活物質にＬｉＮｉ０．５Ｍｎ０．５Ｏ２を、負極活物質に炭素材料として人造黒鉛を、非水電解質にＬｉＰＦ６をそれぞれ用いた。 Here, in the manufactured lithium ion secondary battery, LiNi 0.5 Mn 0.5 O 2 was used as the positive electrode active material, artificial graphite as the carbon material was used as the negative electrode active material, and LiPF 6 was used as the nonaqueous electrolyte.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　また、サイクル特性は、次のようにして評価した。まず、２５℃の環境下で、０．２Ｃで充電終止電圧（４．１～４．４Ｖ）まで定電流充電した後、終止電流０．０５Ｃまで定電圧充電し、その後、０．２Ｃで２．５Ｖまで定電流放電した。この充放電を１００サイクル行い、１サイクル目の放電容量に対する１００サイクル後の放電容量の比率（容量維持率）を求めて、サイクル特性を評価した。 In addition, the cycle characteristics were evaluated as follows. First, in an environment of 25 ° C., after constant current charging at 0.2 C to the end-of-charge voltage (4.1 to 4.4 V), constant-voltage charging to the end current of 0.05 C, and then at 2 C at 2 C . Constant current discharge to 5V. This charging / discharging was performed 100 cycles, and the ratio of the discharge capacity after 100 cycles to the discharge capacity at the first cycle (capacity maintenance ratio) was determined to evaluate the cycle characteristics.
　表１に示すように、ジメチルカーボネートを含む非水溶媒（ＥＣ／ＤＭＣ）を用いた電池１～３では、充電終止電圧を４．１Ｖから４．４Ｖに上げても、容量維持率が約３．８％しか低下していないのに対し、フッ素化カルボン酸エステルを含む非水溶媒（ＥＣ／ＦＭＰ）を用いた電池４～６では、充電終止電圧を４．１Ｖから４．４Ｖに上げると、容量維持率が約２４％も低下していることが分かる。 As shown in Table 1, in the batteries 1 to 3 using the non-aqueous solvent (EC / DMC) containing dimethyl carbonate, the capacity retention ratio is about 3 even when the end-of-charge voltage is increased from 4.1 V to 4.4 V. On the other hand, in batteries 4 to 6 using non-aqueous solvents (EC / FMP) containing fluorinated carboxylic acid esters, the end-of-charge voltage is increased from 4.1 V to 4.4 V. It can be seen that the capacity retention rate has decreased by about 24%.
　本発明者等は、フッ素化カルボン酸エステルを含む非水溶媒（ＥＣ／ＦＭＰ）を用いた場合、充電終止電圧を４．１Ｖから４．４Ｖに上げると容量維持率が大幅に低下する理由を以下のように考えた。 When the non-aqueous solvent (EC / FMP) containing the fluorinated carboxylic acid ester is used, the present inventors have raised the reason why the capacity maintenance ratio is greatly reduced when the end-of-charge voltage is increased from 4.1 V to 4.4 V. I thought as follows.
　電池４～６で用いたフッ素化カルボン酸エステルは、以下の式（１）で表される構造を持つ。 The fluorinated carboxylic acid ester used in the batteries 4 to 6 has a structure represented by the following formula (1).
　　ＣＦxＨ3-x－ＣＨ2－Ｃ(＝Ｏ)－ＯＲ(１≦ｘ≦３；Ｒはアルキル基)　　（１）
　上記構造において、Ｃ（＝Ｏ）と結合しているＨ２（プロトン）は、電気陰性度の高いＦ基を有するＣと隣り合っており、電荷が引き寄せられる一方、反対側のカルボニル基が共役構造となり電子が非局在化するため、プロトンが脱離した状態で安定化する。そのため、充電終止電圧を４．１Ｖ以上にすると、非水溶媒からプロトンが離脱しやすくなる。 CF x H 3-x —CH 2 —C (═O) —OR (1 ≦ x ≦ 3; R is an alkyl group) (1)
In the above structure, H 2 (proton) bonded to C (═O) is adjacent to C having an F group with high electronegativity, and the charge is attracted, while the opposite carbonyl group is conjugated. Since it becomes a structure and electrons are delocalized, it is stabilized in a state where protons are desorbed. Therefore, when the end-of-charge voltage is set to 4.1 V or more, protons are easily released from the nonaqueous solvent.
　非水溶媒から離脱したプロトンは、正極活物質（ＬｉＮｉ０．５Ｍｎ０．５Ｏ２）と反応して、正極活物質から金属（例えば、Ｍｎ２＋）の溶出が加速される。そして、図１（ａ）に示すように、正極活物質から溶出した金属（Ｍｎ２＋）は、負極の集電体１０上に形成された活物質層１１表面に析出し、図１（ｂ）に示すように、活物質層１１表面に被膜２０が形成される。そして、被膜２０中の金属（Ｍｎ２＋）は、活物質層１１中に吸蔵されたリチウム（Ｌｉ＋）と結合することによって、活物質層１１中のリチウム（Ｌｉ＋）が減少する。これにより、フッ素化カルボン酸エステルを含む非水溶媒（ＥＣ／ＦＭＰ）を用いたリチウムイオン二次電池では、充電終止電圧を４．２Ｖ以上に上げると容量維持率が大幅に低下すると考えられる。 Protons released from the nonaqueous solvent react with the positive electrode active material (LiNi 0.5 Mn 0.5 O 2 ), and the elution of metal (for example, Mn 2+ ) from the positive electrode active material is accelerated. As shown in FIG. 1A, the metal (Mn 2+ ) eluted from the positive electrode active material is deposited on the surface of the active material layer 11 formed on the current collector 10 of the negative electrode, and FIG. As shown in FIG. 2, a film 20 is formed on the surface of the active material layer 11. The metal in the coating 20 (Mn 2+) by binding with lithium occluded in the active material layer 11 (Li +), lithium in the active material layer 11 (Li +) is decreased. As a result, in a lithium ion secondary battery using a non-aqueous solvent (EC / FMP) containing a fluorinated carboxylic acid ester, it is considered that the capacity retention rate is significantly lowered when the end-of-charge voltage is increased to 4.2 V or higher.
　この考えを検証するために、サイクル特性の評価を行った電池を分解して、負極表面の被膜２０内に存在するＬｉ量を測定した。ここで、Ｌｉ量は、以下のような方法で測定した。まず、電池を２．５Ｖまで放電した状態で分解し、取り出した負極とＬｉ金属を組み合わせたセルを作製した。このセルを、０．０１Ｃで１．５Ｖまで充電した後、セルを再度分解して負極を取り出した。取り出した負極に、酸を添加してすべて溶解させ、ＩＣＰ－ＭＳ（誘導結合プラズマ質量分析）法を用いて、残存するＬｉ量を測定した。その結果を表２に示す。 In order to verify this idea, the battery whose cycle characteristics were evaluated was disassembled, and the amount of Li present in the coating 20 on the negative electrode surface was measured. Here, the amount of Li was measured by the following method. First, the battery was disassembled in a state where the battery was discharged to 2.5 V, and a cell in which the extracted negative electrode and Li metal were combined was produced. After this cell was charged to 1.5 V at 0.01 C, the cell was again disassembled and the negative electrode was taken out. An acid was added to the extracted negative electrode to dissolve it, and the amount of remaining Li was measured using an ICP-MS (inductively coupled plasma mass spectrometry) method. The results are shown in Table 2.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　表２に示すように、ジメチルカーボネートを含む非水溶媒（ＥＣ／ＤＭＣ）を用いた電池１～３では、充電終止電圧を４．１Ｖから４．３Ｖに上げても、負極表面のＬｉ量は殆ど増加していないのに対し、フッ素化カルボン酸エステルを含む非水溶媒（ＥＣ／ＦＭＰ）を用いた電池４～６では、充電終止電圧を電圧を４．１Ｖから４．３Ｖに上げると、負極表面のＬｉ量が大幅に増加しているのが分かる。このＬｉ量の増加は、非水溶媒からプロトンが離脱したことに起因して、正極活物質から溶出した金属（Ｍｎ２＋）によって、負極活物質中に吸蔵されたリチウム（Ｌｉ＋）が被膜２０中に吸い上げられたことによるものと考えられる。 As shown in Table 2, in the batteries 1 to 3 using a non-aqueous solvent (EC / DMC) containing dimethyl carbonate, the amount of Li on the negative electrode surface was increased even when the end-of-charge voltage was increased from 4.1 V to 4.3 V. On the other hand, in the batteries 4 to 6 using the non-aqueous solvent (EC / FMP) containing the fluorinated carboxylic acid ester, when the end-of-charge voltage is increased from 4.1 V to 4.3 V, the voltage is hardly increased. It can be seen that the amount of Li on the negative electrode surface is greatly increased. This increase in the amount of Li is due to the release of protons from the non-aqueous solvent, so that the lithium (Li + ) occluded in the negative electrode active material by the metal (Mn 2+ ) eluted from the positive electrode active material is coated with the film 20. This is thought to be due to being sucked inside.
　本発明者等は、このような知見から、正極活物質から溶出した金属（Ｍｎ２＋）と負極活物質中に吸蔵されたリチウム（Ｌｉ＋）との反応を抑制することができれば、充電終止電圧を４．２Ｖ以上に上げても、サイクル特性（容量維持率）の低下を抑制できると考え、本発明を想到するに至った。 From these findings, the present inventors have been able to suppress the reaction between the metal (Mn 2+ ) eluted from the positive electrode active material and the lithium (Li + ) occluded in the negative electrode active material. Even if the voltage is increased to 4.2 V or higher, it is considered that the decrease in cycle characteristics (capacity maintenance ratio) can be suppressed, and the present invention has been conceived.
　以下、本発明の実施形態を図面に基づいて詳細に説明する。なお、本発明は、以下の実施形態に限定されるものではない。また、本発明の効果を奏する範囲を逸脱しない範囲で、適宜変更は可能である。さらに、他の実施形態との組み合わせも可能である。 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to the following embodiment. Moreover, it can change suitably in the range which does not deviate from the range which has the effect of this invention. Furthermore, combinations with other embodiments are possible.
　図２は、本発明の一実施形態におけるリチウムイオン二次電池１００の構成を示した断面図である。 FIG. 2 is a cross-sectional view showing the configuration of the lithium ion secondary battery 100 in one embodiment of the present invention.
　図２に示すように、正極１と負極２とがセパレータ３を介して捲回された電極群４が、非水電解質（不図示）とともに、円筒形の電池ケース７に収容されている。正極１は、正極リード５を介して正極端子を兼ねる封口体８に接合され、負極２は、負極リード６を介して負極端子を兼ねる電池ケース７の底部に接合されている。そして、電池ケース７の開口部は、ガスケット９を介して、封口体８で封口されている。 As shown in FIG. 2, an electrode group 4 in which a positive electrode 1 and a negative electrode 2 are wound through a separator 3 is accommodated in a cylindrical battery case 7 together with a nonaqueous electrolyte (not shown). The positive electrode 1 is joined to a sealing body 8 that also serves as a positive electrode terminal via a positive electrode lead 5, and the negative electrode 2 is joined to the bottom of a battery case 7 that also serves as a negative electrode terminal via a negative electrode lead 6. The opening of the battery case 7 is sealed with a sealing body 8 via a gasket 9.
　なお、本発明におけるリチウムイオン二次電池１００は、後述する非水電解質の材料、及び負極２の構成を除き、リチウムイオン二次電池を構成する他の構成要素については、特に制限はなく、通常使用される部材等を用いることができる。 The lithium ion secondary battery 100 according to the present invention is not particularly limited with respect to the other components constituting the lithium ion secondary battery, except for the non-aqueous electrolyte material described later and the configuration of the negative electrode 2. The member used etc. can be used.
　また、本発明におけるリチウムイオン二次電池１００は、円筒形二次電池に限定されず、例えば、角形二次電池等であってもよい。また、電極群４は、正極１と負極２とがセパレータ３を介して積層されたものであってもよい。 Further, the lithium ion secondary battery 100 in the present invention is not limited to a cylindrical secondary battery, and may be, for example, a square secondary battery. Further, the electrode group 4 may be one in which the positive electrode 1 and the negative electrode 2 are laminated via the separator 3.
　本発明における非水電解質は、フッ素化カルボン酸エステルを含む非水溶媒に、ＬｉＰＦ６、ＬｉＢＦ４等のリチウム塩からなる溶質を溶解したものからなる。ここで、フッ素化カルボン酸エステルは、上記式（１）に示す構造のものからなる。また、非水溶媒には、エチレンカーボネート（ＥＣ）等の他の溶媒を含んだ混合溶媒であってもよい。その場合、混合溶媒におけるフッ素化カルボン酸エステルと他の溶媒との混合比は、本発明の効果を奏する範囲内で、適宜決めることができる。 The non-aqueous electrolyte in the present invention is formed by dissolving a solute composed of a lithium salt such as LiPF 6 or LiBF 4 in a non-aqueous solvent containing a fluorinated carboxylic acid ester. Here, the fluorinated carboxylic acid ester has a structure represented by the above formula (1). Further, the non-aqueous solvent may be a mixed solvent containing other solvents such as ethylene carbonate (EC). In that case, the mixing ratio of the fluorinated carboxylic acid ester and the other solvent in the mixed solvent can be appropriately determined within the range where the effects of the present invention are exhibited.
　図３は、本実施形態における負極２の構成を示した断面図である。 FIG. 3 is a cross-sectional view showing the configuration of the negative electrode 2 in the present embodiment.
　図３に示すように、負極２は、集電体１０と、集電体１０の上に形成された活物質を含む活物質層１１と、活物質層１１の上に形成された、リチウムイオンを吸蔵・放出可能な金属酸化物を含む保護層１２とを備えている。 As shown in FIG. 3, the negative electrode 2 includes a current collector 10, an active material layer 11 containing an active material formed on the current collector 10, and lithium ions formed on the active material layer 11. And a protective layer 12 containing a metal oxide capable of occluding and releasing.
　ここで、活物質層１１に含まれる活物質は炭素材料からなり、例えば、黒鉛、カーボンブラック、アセチレンブラック、炭素繊維等が挙げられる。また、保護層１２に含まれる金属酸化物は、例えば、チタン酸リチウム（ＬｉxＴｉyＯz:ＬＴＯ）の他、酸化モリブデン等が挙げられる。 Here, the active material contained in the active material layer 11 is made of a carbon material, and examples thereof include graphite, carbon black, acetylene black, and carbon fiber. Examples of the metal oxide contained in the protective layer 12 include molybdenum oxide in addition to lithium titanate (LixTiyOz: LTO).
　なお、活物質層１１には、所定量の結着剤が含まれていてもよい。結着剤としては、ポリフッ化ビニリデン（ＰＶＤＦ）、フッ素系ゴム、スチレンブタジエンゴム（ＳＢＲ）、ニトリルブタジエンゴム（ＮＢＲ）、アクリルゴム（ＡＣＭ）等が挙げられる。 Note that the active material layer 11 may contain a predetermined amount of a binder. Examples of the binder include polyvinylidene fluoride (PVDF), fluorine-based rubber, styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), acrylic rubber (ACM), and the like.
　また、保護層１２には、所定量の導電剤及び結着剤が含まれていてもよい。導電剤としては、黒鉛等の炭素材料が挙げられる。また結着剤としては、ポリフッ化ビニリデン（ＰＶＤＦ）、フッ素系ゴム、スチレンブタジエンゴム（ＳＢＲ）、ニトリルブタジエンゴム（ＮＢＲ）、アクリルゴム（ＡＣＭ）等が挙げられる。 Further, the protective layer 12 may contain a predetermined amount of a conductive agent and a binder. Examples of the conductive agent include carbon materials such as graphite. Examples of the binder include polyvinylidene fluoride (PVDF), fluorine rubber, styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), and acrylic rubber (ACM).
　また、集電体１０は、例えば、銅箔または銅合金箔を用いることができる。 Moreover, the current collector 10 can be made of, for example, a copper foil or a copper alloy foil.
　なお、本実施形態において、保護層１２は、リチウムイオンを吸蔵・放出可能な金属酸化物を含むため、活物質層としても機能する。しかし、保護層１２に含まれる金属酸化物は、一般に、活物質層１１に含まれる炭素材料に比べて導電性が低く、容量も小さい材料で構成されていることから、便宜的に、活物質層１１と区別して、保護層１２と呼んでいる。 In the present embodiment, since the protective layer 12 includes a metal oxide capable of inserting and extracting lithium ions, it also functions as an active material layer. However, since the metal oxide contained in the protective layer 12 is generally made of a material having lower conductivity and smaller capacity than the carbon material contained in the active material layer 11, The protective layer 12 is distinguished from the layer 11.
　表３は、非水溶媒に、エチレンカーボネート（ＥＣ）とフッ素化カルボン酸エステル（ＦＭＰ）との混合溶媒（質量比１：１）を用い、図３に示した構造の負極２を備えたリチウムイオン二次電池（電池７、８）を作製して、充電終止電圧を４．２～４．３Ｖに変えたときの、サイクル特性（容量維持率）、及び負極表面のＬｉ量を測定した結果を示したものである。なお、表３には、表２に示した電池５、６を比較のために載せている。ここで、電池５、６に使用した負極２は、集電体１０上に人造黒鉛（Ｃ）からなる活物質層１１を形成した構造からなり、電池７、８に使用した正極活物質は、電池５、６と同じである。 Table 3 shows a lithium non-aqueous solvent using a mixed solvent of ethylene carbonate (EC) and fluorinated carboxylic acid ester (FMP) (mass ratio 1: 1) and having the negative electrode 2 having the structure shown in FIG. Results of measurement of cycle characteristics (capacity retention ratio) and the amount of Li on the negative electrode surface when an ion secondary battery (batteries 7 and 8) was prepared and the end-of-charge voltage was changed to 4.2 to 4.3 V Is shown. In Table 3, the batteries 5 and 6 shown in Table 2 are listed for comparison. Here, the negative electrode 2 used for the batteries 5 and 6 has a structure in which an active material layer 11 made of artificial graphite (C) is formed on the current collector 10, and the positive electrode active material used for the batteries 7 and 8 is Same as batteries 5 and 6.
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　表３に示すように、集電体１０上に人造黒鉛（Ｃ）からなる活物質層１１を形成した構造の負極２を用いた電池５、６では、容量維持率が低下し、負極表面のＬｉ量が増加しているのに対し、集電体１０上に人造黒鉛（Ｃ）からなる活物質層１１とチタン酸リチウム（ＬＴＯ）からなる保護層１２を形成した構造の負極２を用いた電池７、８では、容量維持率の低下が抑制され、かつ、負極表面のＬｉ量も少ないことが分かる。 As shown in Table 3, in the batteries 5 and 6 using the negative electrode 2 having a structure in which the active material layer 11 made of artificial graphite (C) is formed on the current collector 10, the capacity retention rate decreases, and the negative electrode surface While the amount of Li increased, the negative electrode 2 having a structure in which an active material layer 11 made of artificial graphite (C) and a protective layer 12 made of lithium titanate (LTO) were formed on the current collector 10 was used. In the batteries 7 and 8, it can be seen that the decrease in capacity retention rate is suppressed and the amount of Li on the negative electrode surface is small.
　これは、図４（ａ）に示すように、活物質層１１の表面に形成されたＬＴＯからなる保護層１２が、正極活物質から溶出した金属（Ｍｎ２＋）と、活物質層１１中に吸蔵されたリチウム（Ｌｉ＋）との反応を抑制したためと考えられる。その結果、図４（ｂ）に示すように、活物質層１１中に吸蔵されたリチウム（Ｌｉ＋）の減少が抑制され、充電終止電圧を４．２Ｖ以上に上げても、容量維持率の低下を抑制することができたと考えられる。 As shown in FIG. 4A, this is because the protective layer 12 made of LTO formed on the surface of the active material layer 11 contains the metal (Mn 2+ ) eluted from the positive electrode active material and the active material layer 11. This is thought to be because the reaction with the occluded lithium (Li + ) was suppressed. As a result, as shown in FIG. 4B, the decrease in lithium (Li + ) occluded in the active material layer 11 is suppressed, and even when the end-of-charge voltage is increased to 4.2 V or more, the capacity retention rate is reduced. It is thought that the decrease could be suppressed.
　ＬＴＯからなる保護層１２が、金属（Ｍｎ２＋）とリチウム（Ｌｉ＋）との反応を抑制する効果は、次のような理由によるものと推察される。 The effect that the protective layer 12 made of LTO suppresses the reaction between metal (Mn 2+ ) and lithium (Li + ) is presumed to be due to the following reason.
　すなわち、ＬＴＯは、炭素材料（Ｃ）と同様に、リチウムを吸蔵、放出する性質を有するため、保護層１２中にもリチウム（Ｌｉ＋）が吸蔵されている。しかし、ＬＴＯの結晶構造は、スピネル構造を有し、層状結晶の炭素材料（Ｃ）に比べて、リチウムの活性化エネルギーが低い。そのため、保護層１２の表面に金属（Ｍｎ２＋）が析出しても、保護層１２中に吸蔵されているリチウム（Ｌｉ＋）と結合しにくいため、金属（Ｍｎ２＋）とリチウム（Ｌｉ＋）との反応を抑制することができたと考えられる。 That is, LTO has the property of occluding and releasing lithium, like the carbon material (C), and therefore, lithium (Li + ) is also occluded in the protective layer 12. However, the crystal structure of LTO has a spinel structure, and the activation energy of lithium is lower than that of the layered crystal carbon material (C). Therefore, even if metal (Mn 2+ ) is deposited on the surface of the protective layer 12, it is difficult to bond with lithium (Li + ) occluded in the protective layer 12, so that the metal (Mn 2+ ) and lithium (Li + ) It is thought that the reaction with was able to be suppressed.
　以上、説明したように、リチウム塩からなる溶質と、上記式（１）に示したフッ素化カルボン酸エステルからなる非水溶媒とを含む非水電解質を備えたリチウムイオン二次電池において、負極２を、集電体１０上に形成された炭素材料からなる活物質層１１と、活物質層１１上に形成された、リチウムイオンを吸蔵・放出可能な金属酸化物を含む保護層１２とを備えた構成にすることによって、充電終止電圧を４．２Ｖ以上に高めても、サイクル特性の低下の少ないリチウムイオン二次電池を実現することができる。 As described above, in the lithium ion secondary battery including the nonaqueous electrolyte including the solute composed of the lithium salt and the nonaqueous solvent composed of the fluorinated carboxylic acid ester represented by the above formula (1), the negative electrode 2 The active material layer 11 made of a carbon material formed on the current collector 10 and the protective layer 12 formed on the active material layer 11 and containing a metal oxide capable of inserting and extracting lithium ions. With this configuration, it is possible to realize a lithium ion secondary battery with little deterioration in cycle characteristics even when the end-of-charge voltage is increased to 4.2 V or higher.
　ここで、金属酸化物は、活物質層１１を構成する炭素材料に比べて、リチウムの活性化エネルギーが低い材料からなり、代表的には、チタン酸リチウムを用いることが好ましい。 Here, the metal oxide is made of a material whose activation energy of lithium is lower than that of the carbon material constituting the active material layer 11, and typically, lithium titanate is preferably used.
　また、本発明は、ＭｎまたはＦｅを含むリチウム含有金属酸化物からなる正極活物質層を備えた正極１を用いた場合に、特にその効果が発揮される。ＭｎまたはＦｅを含むリチウム含有金属酸化物は、非水溶媒から離脱したプロトンと反応しやすいからである。 The present invention is particularly effective when the positive electrode 1 having a positive electrode active material layer made of a lithium-containing metal oxide containing Mn or Fe is used. This is because the lithium-containing metal oxide containing Mn or Fe is likely to react with protons that are released from the non-aqueous solvent.
　また、保護層１２の厚みは、１～２０μｍの範囲にあることが好ましい。１μｍより薄いと、金属（Ｍｎ２＋）とリチウム（Ｌｉ＋）との反応を抑制する効果が十分に発揮されない。また、２０μｍより厚いと、ＬＴＯは、炭素材料に比べて、導電性が低く、容量も小さいため、リチウムイオン電池の放電性能の低下を招く。 The thickness of the protective layer 12 is preferably in the range of 1 to 20 μm. If it is thinner than 1 μm, the effect of suppressing the reaction between the metal (Mn 2+ ) and lithium (Li + ) is not sufficiently exhibited. On the other hand, when it is thicker than 20 μm, LTO has a lower conductivity and a smaller capacity than a carbon material, leading to a decrease in discharge performance of the lithium ion battery.
　以上、本発明を好適な実施形態により説明してきたが、こうした記述は限定事項ではなく、もちろん、種々の改変が可能である。例えば、上記実施形態においては、負極２は、集電体１０の片面に活物質層１１及び保護層１２を形成したが、集電体１０の両面に形成してもよい。 As mentioned above, although this invention has been demonstrated by suitable embodiment, such description is not a limitation matter and of course various modifications are possible. For example, although the active material layer 11 and the protective layer 12 are formed on one surface of the current collector 10 in the above embodiment, the negative electrode 2 may be formed on both surfaces of the current collector 10.
　本発明は、自動車、電動バイク又は電動遊具等の駆動用電源として有用である。 The present invention is useful as a power source for driving automobiles, electric motorcycles, electric playground equipment and the like.
　１　　　正極 
　２　　　負極 
　３　　　セパレータ 
　４　　　電極群 
　５　　　正極リード 
　６　　　負極リード 
　７　　　電池ケース 
　８　　　封口体 
　９　　　ガスケット 
　１０　　集電体 
　１１　　活物質層 
　１２　　保護層 
　２０　　被膜 
　１００　リチウムイオン二次電池 1 Positive electrode
2 Negative electrode
3 Separator
4 Electrode group
5 Positive lead
6 Negative lead
7 Battery case
8 Sealing body
9 Gasket
10 Current collector
11 Active material layer
12 Protective layer
20 coating
100 Lithium ion secondary battery

Claims (7)

  1. 　正極、負極、セパレータ、及び非水電解質を備えたリチウムイオン二次電池であって、
    　前記負極は、
    　　集電体上に形成された炭素材料からなる活物質層と、
    　　前記活物質層上に形成された、リチウムイオンを吸蔵・放出可能な金属酸化物を含む保護層と
    を備え、
    　前記非水電解質は、リチウム塩からなる溶質と、下式に示したフッ素化カルボン酸エステルからなる非水溶媒とを含む、リチウムイオン二次電池。
    　　ＣＦｘＨ３－ｘ－ＣＨ２－Ｃ（＝Ｏ）－ＯＲ（１≦ｘ≦３；Ｒはアルキル基）     A lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte,
    The negative electrode is
    An active material layer made of a carbon material formed on a current collector;
    A protective layer including a metal oxide capable of inserting and extracting lithium ions formed on the active material layer,
    The non-aqueous electrolyte is a lithium ion secondary battery including a solute composed of a lithium salt and a non-aqueous solvent composed of a fluorinated carboxylic acid ester represented by the following formula.
    CF x H 3-x —CH 2 —C (═O) —OR (1 ≦ x ≦ 3; R is an alkyl group)
  2. 　前記金属酸化物は、前記活物質層を構成する炭素材料に比べて、リチウムの活性化エネルギーが低い材料からなる、請求項１に記載のリチウムイオン二次電池。 2. The lithium ion secondary battery according to claim 1, wherein the metal oxide is made of a material having a lower activation energy of lithium than a carbon material constituting the active material layer.
  3. 　前記金属酸化物は、チタン酸リチウムからなる、請求項２に記載のリチウムイオン二次電池。 The lithium ion secondary battery according to claim 2, wherein the metal oxide is made of lithium titanate.
  4. 　前記正極は、ＭｎまたはＦｅを含むリチウム含有金属酸化物からなる正極活物質層を備えている、請求項１に記載のリチウムイオン二次電池。 The lithium ion secondary battery according to claim 1, wherein the positive electrode includes a positive electrode active material layer made of a lithium-containing metal oxide containing Mn or Fe.
  5. 　前記保護層の厚みは、１～２０μｍの範囲にある、請求項１に記載のリチウムイオン二次電池。 The lithium ion secondary battery according to claim 1, wherein the thickness of the protective layer is in the range of 1 to 20 µm.
  6. 　前記非水溶媒は、エチレンカーボネートをさらに含む混合溶媒からなる、請求項１に記載のリチウムイオン二次電池。 The lithium ion secondary battery according to claim 1, wherein the non-aqueous solvent is a mixed solvent further containing ethylene carbonate.
  7. 　前記リチウムイオン二次電池の充電終止電圧は、４．２Ｖ以上に設定されている、請求項１に記載のリチウムイオン二次電池。 The lithium ion secondary battery according to claim 1, wherein a charge end voltage of the lithium ion secondary battery is set to 4.2 V or more.
PCT/JP2012/006716 2011-12-14 2012-10-19 Lithium-ion secondary battery WO2013088622A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2011-273415 2011-12-14
JP2011273415 2011-12-14

Publications (1)

Publication Number Publication Date
WO2013088622A1 true WO2013088622A1 (en) 2013-06-20

Family

ID=48612105

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2012/006716 WO2013088622A1 (en) 2011-12-14 2012-10-19 Lithium-ion secondary battery

Country Status (1)

Country Link
WO (1) WO2013088622A1 (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103762335A (en) * 2013-12-30 2014-04-30 曙鹏科技（深圳）有限公司 Lithium titanate electrode plate and lithium ion battery
WO2015004841A1 (en) * 2013-07-08 2015-01-15 パナソニックＩｐマネジメント株式会社 Nonaqueous electrolyte secondary battery
WO2023025067A1 (en) * 2021-08-27 2023-03-02 深圳市原速光电科技有限公司 Electrode protective layer, and preparation method therefor and use thereof

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH11120992A (en) * 1997-10-08 1999-04-30 Ricoh Co Ltd Nonaqueous electrolyte secondary battery
JP2006294469A (en) * 2005-04-12 2006-10-26 Matsushita Electric Ind Co Ltd Nonaqueous electrolyte secondary battery
JP2009289414A (en) * 2007-02-20 2009-12-10 Sanyo Electric Co Ltd Nonaqueous electrolyte for secondary battery and the nonaqueous electrolyte secondary battery

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH11120992A (en) * 1997-10-08 1999-04-30 Ricoh Co Ltd Nonaqueous electrolyte secondary battery
JP2006294469A (en) * 2005-04-12 2006-10-26 Matsushita Electric Ind Co Ltd Nonaqueous electrolyte secondary battery
JP2009289414A (en) * 2007-02-20 2009-12-10 Sanyo Electric Co Ltd Nonaqueous electrolyte for secondary battery and the nonaqueous electrolyte secondary battery

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015004841A1 (en) * 2013-07-08 2015-01-15 パナソニックＩｐマネジメント株式会社 Nonaqueous electrolyte secondary battery
CN105122533A (en) * 2013-07-08 2015-12-02 松下电器产业株式会社 Nonaqueous electrolyte secondary battery
CN103762335A (en) * 2013-12-30 2014-04-30 曙鹏科技（深圳）有限公司 Lithium titanate electrode plate and lithium ion battery
WO2023025067A1 (en) * 2021-08-27 2023-03-02 深圳市原速光电科技有限公司 Electrode protective layer, and preparation method therefor and use thereof

Similar Documents

Publication Publication Date Title
JP6070540B2 (en) Secondary battery and electrolyte
JP6656717B2 (en) Non-aqueous electrolyte additive, non-aqueous electrolyte containing the same, and lithium secondary battery including the same
JP4936440B2 (en) Non-aqueous secondary battery
WO2012066878A1 (en) Non-aqueous electrolyte secondary battery
WO2010131401A1 (en) Electrode for lithium ion secondary battery, and lithium ion secondary battery
WO2015115051A1 (en) Nonaqueous-electrolyte secondary-battery negative electrode
KR20160072220A (en) Non-aqueous electrolyte secondary battery
US10541445B2 (en) Non-aqueous electrolyte solution for lithium secondary battery and lithium secondary battery comprising the same
WO2015079664A1 (en) Positive electrode for non-aqueous electrolyte secondary battery
JP2017535017A (en) Negative electrode active material for lithium secondary battery, method for producing the same, negative electrode for lithium secondary battery including the same, and lithium secondary battery
WO2015004841A1 (en) Nonaqueous electrolyte secondary battery
WO2015037367A1 (en) Nonaqueous-electrolyte secondary battery
JP2011071100A (en) Positive electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery using the same
KR20160038339A (en) Negative active material for rechargeable lithium battery, method for preparing same, and rechargeable lithium battery comprising same
US10026992B2 (en) Additive for non-aqueous electrolyte, non-aqueous electrolyte comprising the same, and lithium secondary battery comprising the same
JP2011060481A (en) Nonaqueous electrolyte secondary battery
JP7029676B2 (en) Method for manufacturing negative electrode for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery and negative electrode for non-aqueous electrolyte secondary battery
JP2004171907A (en) Lithium secondary battery
JP2009110942A (en) Nonaqueous secondary battery and apparatus using the same
JP2011192541A (en) Nonaqueous secondary battery
JP2014049287A (en) Nonaqueous electrolyte secondary battery and nonaqueous electrolyte secondary battery stack
JP6572882B2 (en) Positive electrode for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery
WO2013088622A1 (en) Lithium-ion secondary battery
JP2020071944A (en) Nonaqueous electrolyte lithium ion secondary battery
JP2007265758A (en) Nonaqueous secondary battery and its usage

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 12856734

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 12856734

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: JP