JP2014082084A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery capable of improving cycle characteristics.SOLUTION: A lithium ion secondary battery comprises: a positive electrode having a positive electrode collector and a positive electrode active material layer formed on the surface of the positive electrode collector; a negative electrode having a negative electrode collector and a negative electrode active material layer formed on the surface of the negative electrode collector; and a nonaqueous electrolyte. In the positive electrode, a negative electrode coating material layer containing transition metal and/or a sulfide of transition metal is formed in an active material layer non-formed part, where the positive electrode active material layer is not formed, on the surface of the positive electrode collector.

Description

  The present invention relates to a lithium ion secondary battery.

  A lithium ion secondary battery is a secondary battery having a high charge / discharge capacity and capable of high output. At present, lithium ion secondary batteries are mainly used as a power source for portable electronic devices, and further expected as a power source for electric vehicles that are expected to be widely used in the future. Therefore, an even higher capacity lithium ion secondary battery is desired. There is also a need for a lithium ion secondary battery with high capacity and good cycle characteristics.

  A lithium ion secondary battery is composed of a positive electrode, a negative electrode, and an electrolytic solution. The positive electrode includes a current collector and a positive electrode active material layer including a positive electrode active material formed on a surface of the current collector, for example, a metal composite oxide of lithium and a transition metal. The negative electrode includes a current collector and a negative electrode active material layer including a negative electrode active material capable of inserting and extracting lithium ions formed on the surface of the current collector. Carbon materials such as graphite are widely used as the negative electrode active material. In recent years, the use of silicon or silicon oxide instead of carbon materials has been studied.

  When the lithium ion secondary battery is charged / discharged, insertion / extraction of lithium ions is performed between the positive electrode active material and the negative electrode active material through the electrolytic solution. At that time, the electrolytic solution is partially reduced and decomposed, and the decomposition product covers the surface of the negative electrode active material to form a film. This film is a film in which lithium ions can easily pass but electrons cannot easily pass through, and it is said to be a solid electrolyte interface film (SEI: Solid Electrolyte Interface). The solid electrolyte interface coating covers the surface of the negative electrode active material, thereby preventing direct contact between the electrolytic solution and the negative electrode active material, thereby suppressing degradation of the electrolytic solution. Therefore, when SEI is formed on the surface of the negative electrode active material, the lithium ion secondary battery has improved cycle characteristics. However, since this film is difficult to pass electrons, it is assumed that it becomes a resistance component.

  For example, Patent Document 1 discloses a form in which a metal layer covers at least a part of the surface of the negative electrode active material particles. In the embodiment, the metal layer is formed by an electrolytic plating method. It is described that if the surface of the negative electrode active material particles located on the outermost layer is coated with a metal layer, the decomposition reaction of the electrolyte and the like is effectively suppressed.

JP 2010-140885 A

  The inventors of the present invention have studied to easily form a coating that can suppress degradation of the electrolytic solution and hardly become a resistance component on at least a part of the negative electrode active material layer.

  The present invention has been made in view of such circumstances. Lithium which can suppress degradation and degradation of the electrolytic solution and which is difficult to become a resistance component can be easily formed on the negative electrode active material layer to improve cycle characteristics. An object is to provide an ion secondary battery.

  As a result of intensive studies by the present inventors, it has been found that a material layer capable of covering the negative electrode is formed on the positive electrode, and a film containing the constituent components of the material layer can be formed on the negative electrode by charging and discharging.

  That is, the lithium ion secondary battery of the present invention includes a positive electrode current collector, a positive electrode having a positive electrode active material layer formed on the surface of the positive electrode current collector, a negative electrode current collector, and a surface of the negative electrode current collector. A negative electrode having a negative electrode active material layer formed on the non-aqueous electrolyte, and a positive electrode is an active material layer on which no positive electrode active material layer is formed on the surface of the positive electrode current collector A negative electrode coating material layer containing a transition metal and / or a transition metal sulfide is formed in the portion.

  The transition metal is preferably at least one selected from the group consisting of Zn, Sn, Cu, Ni, Ti, and Mo.

  The negative electrode active material layer contains a negative electrode active material, and when the negative electrode active material is 100 parts by mass, the transition metal and / or transition metal sulfide is preferably 1 part by mass or less.

  The negative electrode active material layer preferably contains a negative electrode active material made of a carbon-based material.

  After at least initial charge / discharge using the lithium ion secondary battery, a film containing at least a transition metal that is a constituent component of the negative electrode coating material layer is formed on at least a part of the surface of the negative electrode active material layer. Yes.

  Another lithium ion secondary battery of the present invention includes a first positive electrode current collector, a first positive electrode having a positive electrode active material layer formed on a surface of the first positive electrode current collector, and a second positive electrode current collector. Body, a second positive electrode having a negative electrode coating material layer containing a transition metal and / or transition metal sulfide formed on the surface of the second positive electrode current collector, a negative electrode current collector, and a negative electrode current collector It has the negative electrode which has the negative electrode active material layer formed in the surface, and a non-aqueous electrolyte, It is characterized by the above-mentioned.

  In the lithium ion secondary battery of the present invention, by forming a negative electrode coating material layer containing a transition metal and / or transition metal sulfide on the positive electrode, at least a part of the negative electrode active material layer is at least partly after the first charge / discharge. A film containing a transition metal that is a constituent component of the negative electrode coating material layer is formed.

  In the lithium ion secondary battery of the present invention, the transition metal that is a constituent component of the negative electrode coating material layer is eluted by charge and discharge. In addition, the non-aqueous electrolyte is partially reduced and decomposed, and the decomposition products are also eluted. In the lithium ion secondary battery of the present invention, in the negative electrode, a film containing a transition metal, which is a component of the negative electrode coating material layer, and a decomposition product of the non-aqueous electrolyte is formed. This film is selectively deposited on the surface of the negative electrode active material located on the surface of the negative electrode active material layer. By forming a film on the negative electrode active material, it is possible to prevent direct contact between the electrolytic solution and the negative electrode active material, and to suppress further degradation of the electrolytic solution. Moreover, the transition metal which is a structural component of the negative electrode coating material layer is contained in this coating film. The transition metal contained in the coating traps the elution ions of metal components such as Mn eluted from the positive electrode active material of the lithium ion secondary battery, so that the negative electrode is prevented from being deteriorated by the elution ions from the positive electrode active material. I can do it. Therefore, the cycle characteristics of the lithium ion secondary battery of the present invention are improved.

It is a schematic diagram explaining the positive electrode for lithium ion secondary batteries of 1st Embodiment. It is a schematic diagram explaining the positive electrode for lithium ion secondary batteries of 2nd Embodiment. It is a schematic diagram explaining the lithium ion secondary battery of 3rd Embodiment. It is a figure which shows the EDX (energy dispersive X-ray spectroscopy: Energy Dispersive X-ray Spectroscopy) spectrum of the negative electrode active material layer after the first charge / discharge of Test Example 1. 6 is a diagram showing an EDX spectrum of a negative electrode active material layer after charge / discharge in Test Example 2. FIG. 4 is a diagram showing an EDX spectrum of a negative electrode active material layer after charge / discharge in Test Example 3. FIG.

<Lithium ion secondary battery>
The lithium ion secondary battery of this invention has a positive electrode, a negative electrode, and a non-aqueous electrolyte.

  The positive electrode includes a positive electrode current collector, a positive electrode active material layer formed on the surface of the positive electrode current collector, and an active material layer unformed portion where the positive electrode active material layer is not formed on the surface of the positive electrode current collector. And a negative electrode coating material layer formed.

  The current collector refers to a chemically inert electronic high conductor that keeps a current flowing through an electrode during discharge or charging of a lithium ion secondary battery. Examples of the material used for the current collector include metal materials such as stainless steel, titanium, nickel, aluminum, and copper, or conductive resins. The current collector can take the form of a foil, a sheet, a film, or the like. Therefore, metal foils, such as copper foil, nickel foil, aluminum foil, stainless steel foil, can be used suitably as a collector. The film thickness of the current collector is preferably 1 μm to 200 μm. The surface of the current collector may be oxidized, and the surface of the current collector may be covered with another metal, metal oxide, carbon, or the like.

  As the positive electrode current collector, aluminum foil and stainless steel foil are preferably used.

  The positive electrode active material layer includes a positive electrode active material, a binder, and, if necessary, a conductive additive.

  A lithium-containing compound is suitable as the positive electrode active material. For example, lithium-containing metal composite oxides such as lithium cobalt composite oxide, lithium nickel composite oxide, and lithium manganese composite oxide can be used. Other metal compounds or polymer materials can also be used as the positive electrode active material. Examples of the other metal compound include oxides such as titanium oxide, vanadium oxide, and manganese dioxide, or disulfides such as titanium sulfide and molybdenum sulfide. Examples of the polymer material include conductive polymers such as polyaniline and polythiophene and organic compounds having a quinone structure.

In particular, the positive electrode active material has a general formula: Li _x Co _p Ni _q Mn _r O ₂ (0.8 <x <1.5, p + q + r = 1, 0 <p <1, 0 ≦ q <1, 0 ≦ r < It is preferable that the composite metal oxide represented by 1) is included. Since the composite metal oxide is excellent in thermal stability and low in cost, by including the composite metal oxide, an inexpensive lithium ion secondary battery with good thermal stability can be obtained.

Examples of the composite metal oxide include LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiCoO ₂ , LiNi _0.8 Co _0.2 O ₂ can be used. Among them, LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ is preferable from the viewpoint of thermal stability.

  The binder plays a role of connecting the positive electrode active material and the conductive additive to the current collector. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, and alkoxysilyl group-containing resins. Can be used.

  The conductive assistant is added to increase the conductivity of the electrode. Carbon black, graphite, acetylene black (AB), Ketjen black (KB), vapor grown carbon fiber (Vapor Carbon Carbon Fiber: VGCF), or nickel flakes, which are metal fine particles, as a conductive auxiliary agent, Copper flakes and the like can be added alone or in combination of two or more. The amount of the conductive aid used is not particularly limited, but can be, for example, about 1 to 30 parts by mass with respect to 100 parts by mass of the positive electrode active material.

  The positive electrode active material layer is prepared by preparing a composition for forming a positive electrode active material layer containing a positive electrode active material, a binder and, if necessary, a conductive additive, and adding a suitable solvent to the above composition to make a paste. Thus, it can be formed after being applied to the surface of the positive electrode current collector and then dried and compressed as necessary to increase the electrode density.

  As a method for applying the composition for forming a positive electrode active material layer, conventionally known methods such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, and a curtain coating method can be used.

  As a solvent for adjusting the viscosity, N-methyl-2-pyrrolidone (NMP), methanol, methyl isobutyl ketone (MIBK) and the like can be used.

  The negative electrode coating material layer includes a transition metal or a transition metal sulfide. These transition metals or sulfides of transition metals are not particularly limited as long as they can be eluted as ions during charge / discharge. Although it is possible to use Mn or Fe as the transition metal, if there is a concern that the transition metal elutes again from the coating formed on the negative electrode, Zn or Sn is used rather than using Mn or Fe as the transition metal. It is preferable to use at least one selected from the group consisting of Cu, Ni, Ti and Mo. In particular, the negative electrode coating material layer preferably contains at least one selected from ZnS, Cu and Mo.

  The method for forming the negative electrode coating material layer in the active material layer non-formed part where the positive electrode active material layer is not formed on the surface of the positive electrode current collector is not particularly limited. The negative electrode coating material layer may be formed before the positive electrode active material layer is formed, or may be formed after the positive electrode active material layer is formed. As a method for forming the negative electrode coating material layer, a vacuum deposition method, a sputtering method, a chemical vapor deposition method (CVD method), a coating method, or the like can be used.

  In particular, the method for forming the negative electrode coating material layer is preferably a sputtering method. If the negative electrode coating material layer is formed by sputtering, it is not necessary to include a binder component or the like in the negative electrode coating material layer as compared with the coating method, so that a homogeneous and highly adhesive film can be formed. In addition, if a sputtering method is used, a film having higher adhesion can be formed as compared with a vacuum deposition method or a CVD method.

  FIG. 1 shows a schematic diagram for explaining the positive electrode of the first embodiment in which a negative electrode coating material layer is formed on the surface of the positive electrode current collector where the active material layer is not formed. In FIG. 1, a positive electrode active material layer 2 and a negative electrode coating material layer 3 are formed adjacent to each other on one surface of a positive electrode current collector 1.

  Moreover, the schematic diagram explaining the positive electrode of 2nd Embodiment is shown in FIG. In FIG. 2, the positive electrode active material layer 2 is formed on one surface of the positive electrode current collector 1, and the negative electrode coating material layer 3 is formed on the other surface of the positive electrode current collector 1.

  The negative electrode coating material layer is a material for forming a coating film containing its constituent components mainly on the surface of the negative electrode active material after charging and discharging of the lithium ion secondary battery. Therefore, when the negative electrode active material is 100 parts by mass, the transition metal and / or transition metal sulfide is preferably 1 part by mass or less.

  If the amount of transition metal and / or transition metal sulfide is more than 1 part by mass when the negative electrode active material is 100 parts by mass, the thickness of the coating formed on the surface of the negative electrode active material increases and resistance to lithium ion migration. Is unfavorable because of the high.

  Basically, the proportion of the negative electrode active material in the negative electrode active material layer is large. Therefore, strictly speaking, depending on the content ratio of the negative electrode active material in the negative electrode active material layer, when the negative electrode active material layer is formed with a thickness of 50 μm to 200 μm, the negative electrode coating material layer has a thickness of 100 nm to 400 nm as a guide. May be formed.

  The negative electrode has a negative electrode current collector and a negative electrode active material layer formed on the surface of the negative electrode current collector.

  As the negative electrode current collector, the same current collector as described for the positive electrode current collector can be used. In particular, a copper foil is suitably used for the negative electrode current collector.

  The negative electrode active material layer includes a negative electrode active material, a binder, and, if necessary, a conductive additive.

  As the negative electrode active material, a carbon-based material that can occlude and release lithium, an element that can be alloyed with lithium, an elemental compound that has an element that can be alloyed with lithium, or a polymer material can be used.

  Examples of the carbon-based material include non-graphitizable carbon, artificial graphite, coke, graphite, glassy carbon, organic polymer compound fired body, carbon fiber, activated carbon, or carbon black. Here, the organic polymer compound fired body refers to a material obtained by firing and carbonizing a polymer material such as phenols and furans at an appropriate temperature.

  Elements that can be alloyed with lithium are Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si, Ge, Sn. , Pb, Sb, Bi. Among them, the element capable of alloying lithium is preferably silicon (Si) or tin (Sn).

Examples of elemental compounds having elements that can be alloyed with lithium include ZnLiAl, AlSb, SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , _{CaSi 2, CrSi 2, Cu 5} Si, FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O, SiO v (0 <v ≦ 2), SnO _w (0 <w ≦ 2), SnSiO ₃ , LiSiO or LiSnO can be used. The elemental compound having an element capable of alloying with lithium is preferably a silicon compound or a tin compound. The silicon compound is preferably SiO _x (0.5 ≦ x ≦ 1.5). For the tin compound, for example, a tin alloy (Cu—Sn alloy, Co—Sn alloy, etc.) can be used.

  As the polymer material, polyacetylene, polypyrrole, or the like can be used.

  The negative electrode active material is preferably made of a carbon-based material. When a lithium ion secondary battery is used at high voltage and high temperature, a metal component such as Mn contained in the positive electrode active material or a component such as Al in the positive electrode current collector may be eluted. The eluted Mn and Al enter the layer where the original Li ions of the carbon-based material as the negative electrode active material are inserted, and Li ions cannot be inserted between the layers. In the present invention, a film containing a transition metal component is formed on the surface of the negative electrode active material. This transition metal component easily adsorbs eluted Mn and Al. Therefore, in the lithium ion secondary battery of this invention, it can suppress that Mn and Al enter into the interlayer of a carbonaceous material. Therefore, when the negative electrode active material is a carbon-based material, the effect of the coating that improves the cycle characteristics of the lithium ion secondary battery is noticeable.

  As the negative electrode binder and the conductive additive, the same materials as those for the positive electrode can be used.

  As the non-aqueous electrolyte, a non-aqueous electrolyte that can be used for a lithium ion secondary battery can be used. The nonaqueous electrolytic solution includes a solvent and an electrolyte dissolved in the solvent.

  As the solvent, for example, cyclic esters, chain esters, and ethers can be used. Examples of cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of chain esters that can be used include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. As ethers, for example, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane can be used.

As the electrolyte dissolved in the electrolytic solution, for example, a lithium salt such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ can be used. As the electrolyte, LiPF ₆ and LiBF ₄ are particularly preferable.

As the non-aqueous electrolyte, for example, a lithium salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO _{3 is} added in a solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, dimethyl carbonate and the like to 0.5 mol / l to 1.7 mol. A solution dissolved at a concentration of about 1 / l can be used.

  Another lithium ion secondary battery of the present invention includes a first positive electrode current collector, a first positive electrode having a positive electrode active material layer formed on a surface of the first positive electrode current collector, and a second positive electrode current collector. Body, a second positive electrode having a negative electrode coating material layer containing a transition metal and / or transition metal sulfide formed on the surface of the second positive electrode current collector, a negative electrode current collector, and a negative electrode current collector It has the negative electrode which has the negative electrode active material layer formed in the surface, and a non-aqueous electrolyte, It is characterized by the above-mentioned.

  The structure of this other lithium ion secondary battery is characterized by having a second positive electrode having a negative electrode coating material layer not having a positive electrode active material layer, in addition to the first positive electrode having a positive electrode active material layer. This lithium ion secondary battery is referred to as a third embodiment. FIG. 3 shows a schematic diagram for explaining a lithium ion secondary battery of the third embodiment.

  The lithium ion secondary battery shown in FIG. 3 includes a first positive electrode 60 in which the positive electrode active material layer 2 is formed on two surfaces of the positive electrode current collector 1, and a negative electrode active material layer 5 on one surface of the negative electrode current collector 4. The negative electrode 70 is formed, and the second positive electrode 80 having the negative electrode coating material layer 3 formed on the entire surface of the second positive electrode current collector 11. Although not shown in FIG. 3, in the lithium ion secondary battery of the third embodiment, a plurality of first positive electrodes 60 and negative electrodes 70 are alternately stacked, and one or a plurality of second positive electrodes 80 are provided at the outermost peripheral portion. Or it arrange | positions between lamination | stacking of a positive electrode and a negative electrode. In the third embodiment, a film can be formed on the surfaces of the plurality of negative electrodes 70 after charge and discharge.

  A separator is sandwiched between the positive electrode and the negative electrode described above to form an electrode body. Lithium ion secondary battery in which a non-aqueous electrolyte is impregnated in the electrode body after connecting between the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal leading to the outside using a current collecting lead or the like It is good to do.

  The shape of the lithium ion secondary battery is not particularly limited, and various shapes such as a cylindrical shape, a square shape, a coin shape, and a laminate shape can be employed.

  After at least initial charge / discharge using the above-described lithium ion secondary battery, a film containing at least the constituent components of the negative electrode coating material layer is formed at least in part on the surface of the negative electrode active material layer.

  The coating contains at least a transition metal that is a constituent component of the negative electrode coating material layer. The coating contains a decomposition product of the nonaqueous electrolytic solution in addition to the transition metal. The component of this film can be measured using, for example, EDX (Energy Dispersive X-ray Spectroscopy).

  This coating is formed on at least a part of the surface of the negative electrode active material layer. This film is selectively deposited on the surface of the negative electrode active material located on the surface of the negative electrode active material layer. By forming a film on the negative electrode active material, it is possible to prevent direct contact between the electrolytic solution and the negative electrode active material, and to suppress further degradation of the electrolytic solution. Moreover, the transition metal which is a structural component of the negative electrode coating material layer is contained in this coating film. The transition metal contained in the coating traps the elution ions of metal components such as Mn eluted from the positive electrode active material of the lithium ion secondary battery, so that the negative electrode is prevented from being deteriorated by the elution ions from the positive electrode active material. I can do it.

  The coating preferably has a thickness of 1 nm to 50 nm. If the film has a thickness of 1 nm or more, the negative electrode can be protected. If the film is thicker than 50 nm, the resistance to movement of lithium ions increases, which is not preferable.

  The lithium ion secondary battery of the present invention described above can be suitably used not only in the field of portable devices such as mobile phones and notebook computers, and information-related devices, but also in the field of stationary and automobiles.

  As mentioned above, although embodiment of the lithium ion secondary battery of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

  Hereinafter, the present invention will be described in more detail with reference to examples.

<Production of laminated lithium-ion secondary battery>
(Test Example 1)
An aluminum foil having a thickness of 20 μm was prepared as a positive electrode current collector. The aluminum foil was put in a sputtering apparatus, and ZnS was sputtered on one surface thereof to form a ZnS layer having a thickness of 100 nm.

A positive electrode active material layer was formed on the back surface of an aluminum foil having a ZnS layer formed on one side as follows. First, LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ as a positive electrode active material, acetylene black as a conductive additive, 88 parts by mass and 6 parts by mass, respectively, and polyvinylidene fluoride (PVDF) 6 as a binder A part by mass was mixed, and the mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to prepare a slurry.

The slurry was placed on the surface of the aluminum foil on which the ZnS layer was not formed, and applied using a doctor blade so that the slurry became a film. The obtained sheet was dried at 80 ° C. for 20 minutes to volatilize and remove NMP, and then the aluminum foil on which the ZnS layer was formed and the coating on the aluminum foil were tightly bonded with a roll press. . At this time, the electrode density was set to 2.3 g / cm ² . The joined product was heated with a vacuum dryer at 120 ° C. for 6 hours, cut into a predetermined shape (rectangular shape of 25 mm × 30 mm), and formed into a positive electrode having a thickness of about 50 μm.

  The negative electrode was produced as follows. 97 parts by mass of graphite powder, 1 part by mass of acetylene black as a conductive additive, 1 part by mass of styrene-butadiene rubber (SBR) and 1 part by mass of carboxymethylcellulose (CMC) as a binder are mixed, and this mixture is mixed. A slurry was prepared by dispersing in an appropriate amount of ion-exchanged water. This slurry was applied to a copper foil having a thickness of 20 μm as a negative electrode current collector so as to form a film using a doctor blade, and the current collector coated with the slurry was dried and pressed. It was heated with a vacuum dryer for a time, cut into a predetermined shape (rectangular shape of 25 mm × 30 mm), and a negative electrode having a thickness of about 45 μm was obtained.

A laminate type lithium ion secondary battery was manufactured using the positive electrode and the negative electrode. Specifically, a rectangular sheet (27 × 32 mm, thickness 25 μm) made of polypropylene resin as a separator was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed, and then an electrolyte solution was injected into the bag-like laminated film. As an electrolytic solution, a solution obtained by dissolving 1 mol of LiPF ₆ in a solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at EC: DEC = 3: 7 (volume ratio) was used. Thereafter, the remaining one side was sealed to obtain a laminate type lithium ion secondary battery in which the four sides were hermetically sealed and the electrode plate group and the electrolyte were sealed. Note that the positive electrode and the negative electrode have a tab that can be electrically connected to the outside, and a part of the tab extends to the outside of the laminated lithium ion secondary battery. Through the above steps, a laminate type lithium ion secondary battery of Test Example 1 was produced.

  In the laminate type lithium ion secondary battery of Test Example 1, when the negative electrode active material was 100 parts by mass, the ZnS layer was 1 part by mass.

(Test Example 2)
An aluminum foil having a thickness of 20 μm was prepared as a positive electrode current collector. The aluminum foil was put in a sputtering apparatus, and Cu was sputtered on one surface to form a Cu layer having a thickness of 100 nm.

  A laminated lithium ion secondary battery of Test Example 2 was produced in the same manner as in Test Example 1 except that the aluminum foil on which the Cu layer was formed was used as a positive electrode current collector.

  In the laminated lithium ion secondary battery of Test Example 2, when the negative electrode active material was 100 parts by mass, the Cu layer was 5 parts by mass.

(Test Example 3)
An aluminum foil having a thickness of 20 μm was prepared as a positive electrode current collector. The aluminum foil was put in a sputtering apparatus, and Mo was sputtered on one surface thereof to form a Mo layer having a thickness of 100 nm.

  A laminated lithium ion secondary battery of Test Example 3 was produced in the same manner as in Test Example 1 except that the aluminum foil on which the Mo layer was formed was used as a positive electrode current collector.

  In the laminated lithium ion secondary battery of Test Example 1, when the negative electrode active material was 100 parts by mass, the Mo layer was 5 parts by mass.

(Test Example 4)
A laminated lithium ion secondary battery of Test Example 4 was prepared in the same manner as in Test Example 1 except that an aluminum foil having a thickness of 20 μm was prepared as the positive electrode current collector, and that aluminum foil was used as the positive electrode current collector. .

<Confirmation of coating>
The laminated lithium ion secondary batteries of Test Example 1, Test Example 2 and Test Example 3 were charged and discharged under the following conditions.

  At the time of charging, CCCV charging (constant current constant voltage charging) was performed at 55 ° C. at a 1C rate and a voltage of 4.5V. The voltage was held for 1 hour. When discharging, CC discharge (constant current discharge) was performed at a voltage of 3.0 V and a 1 C rate.

  After the charge / discharge operation, each battery was disassembled, the negative electrode active material layer was separated from the negative electrode current collector, and measurement was performed at an acceleration voltage of 15 kV using an EDX apparatus (energy dispersive X-ray spectrometer). The EDX spectra of the measurement results of Test Example 1, Test Example 2, and Test Example 3 are shown in FIGS. 4, 5, and 6, respectively.

  From the EDX spectrum shown in FIG. 4, it was found that Zn, S, F and P were detected. From this, it was confirmed that the negative electrode active material layer of Test Example 1 was formed with a film having Zn, S, F, and P components. The film thickness of this film was 50 nm. The film thickness was measured by cross-sectional SEM observation.

  From the EDX spectrum shown in FIG. 5, it was found that Cu and F were detected. From this, it was confirmed that a film having Cu and F components was formed on the negative electrode active material layer of Test Example 2. The film thickness of this coating was 200 nm.

  From the EDX spectrum shown in FIG. 6, it was found that Mo, P, and F were detected. From this, it was confirmed that a film having Mo, P and F components was formed on the negative electrode active material layer of Test Example 3. The film thickness of this coating was 200 nm.

<Cycle characteristic evaluation>
The cycle characteristics of the laminated lithium ion secondary batteries of Test Example 1 and Test Example 4 were evaluated. As an evaluation of the cycle characteristics, a cycle test in which charging and discharging were repeated under the following conditions was performed, and the discharge capacity of each cycle was measured. At the time of charging, CCCV charging (constant current constant voltage charging) was performed at 55 ° C. at a 1C rate and a voltage of 4.5V. CV charging was held at a voltage of 4.5V for 1 hour. When discharging, CC discharge (constant current discharge) was performed at 3.0 V and 1 C rate. This charging / discharging was made into 1 cycle, and the cycle test was done to 25 cycles. Before and after the cycle test, the capacity when the current rate is 0.33C is measured, the capacity when the current rate is 0.33C before the cycle test is the initial capacity, and the capacity when the current rate is 0.33C after the cycle test is the capacity after the cycle. The capacity maintenance rate was calculated as The capacity retention rate (%) was obtained by the following formula.
Capacity retention rate (%) = (capacity after cycle / initial capacity) × 100
The results are shown in Table 1.

  From Table 1, the capacity retention rate of the laminate type lithium ion secondary battery of Test Example 1 was significantly improved as compared with the laminate type lithium ion secondary battery of Test Example 4. Here, it was found that the initial capacity of the laminate type lithium ion secondary battery of Test Example 1 was lower than that of the laminate type lithium ion secondary battery of Test Example 4. When the conductivity of the negative electrode of Test Example 1 and the conductivity of the negative electrode of Test Example 4 were measured, the conductivity of the negative electrode of Test Example 1 and the conductivity of the negative electrode of Test Example 4 were equivalent. Therefore, the initial capacity of Test Example 1 should be equivalent to the initial capacity of Test Example 4, but this decrease in initial capacity is caused by the fact that Zn is a substance that occludes Li, so that Li is occluded by Zn for the first time. It was judged that the result was an irreversible capacity. The setting of the initial capacity can be optimized by the thickness of the negative electrode coating material layer and the capacity design of the positive and negative electrodes.

  1: positive electrode current collector, 2: positive electrode active material layer, 3: negative electrode coating material layer, 4: negative electrode current collector, 5: negative electrode active material layer, 11: second positive electrode current collector, 60: first positive electrode , 70: negative electrode, 80: second positive electrode.

Claims (6)

A positive electrode having a positive electrode current collector and a positive electrode active material layer formed on the surface of the positive electrode current collector;
A negative electrode having a negative electrode current collector and a negative electrode active material layer formed on the surface of the negative electrode current collector;
A non-aqueous electrolyte,
Have
In the positive electrode, a negative electrode coating material layer containing a transition metal and / or a transition metal sulfide is formed on the surface of the positive electrode current collector in an active material layer non-formed portion where the positive electrode active material layer is not formed. Lithium ion secondary battery characterized by being made. A first positive electrode having a first positive electrode current collector and a positive electrode active material layer formed on the surface of the first positive electrode current collector;
A second positive electrode having a second positive electrode current collector and a negative electrode coating material layer containing a transition metal and / or a transition metal sulfide formed on the surface of the second positive electrode current collector;
A negative electrode having a negative electrode current collector and a negative electrode active material layer formed on the surface of the negative electrode current collector;
A non-aqueous electrolyte,
A lithium ion secondary battery comprising:   The lithium ion secondary battery according to claim 1 or 2, wherein the transition metal is at least one selected from the group consisting of Zn, Sn, Cu, Ni, Ti, and Mo.   The negative electrode active material layer contains a negative electrode active material, and when the negative electrode active material is 100 parts by mass, the transition metal and / or sulfide of the transition metal is 1 part by mass or less. 4. The lithium ion secondary battery according to claim 3.   The lithium ion secondary battery according to claim 1, wherein the negative electrode active material layer contains a negative electrode active material made of a carbon-based material.   After performing at least initial charge / discharge using the lithium ion secondary battery according to any one of claims 1 to 5, at least part of the surface of the negative electrode active material layer has at least the negative electrode coating material layer. A lithium ion secondary battery in which a film containing a transition metal as a constituent is formed.