JP5218808B2 - Lithium ion battery - Google Patents

Lithium ion battery Download PDF

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JP5218808B2
JP5218808B2 JP2007153823A JP2007153823A JP5218808B2 JP 5218808 B2 JP5218808 B2 JP 5218808B2 JP 2007153823 A JP2007153823 A JP 2007153823A JP 2007153823 A JP2007153823 A JP 2007153823A JP 5218808 B2 JP5218808 B2 JP 5218808B2
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lithium ion
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JP2008305746A (en
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真典 伊藤
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トヨタ自動車株式会社
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion cell with durability against high rate electric discharge improved, and an anode for the cell. <P>SOLUTION: The lithium ion cell is provided with an anode 40 with an anode active material layer 45 retained at an anode collector 42 made of conductive metal. The anode active material layer 45 contains a first active material layer 451 mainly composed of a carbon material (such as graphite) as a first anode active material, and a second active material layer 452 mainly composed of a second anode active material (such as a lithium titanium oxide) having a higher electropositive potential than the above carbon material, provided between the anode collector 42 and the first active material layer 451. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a lithium ion battery, and more particularly to a lithium ion battery exhibiting good durability against high rate discharge.

  A lithium secondary battery (typically a lithium ion battery) that is charged and discharged as lithium ions move between the positive electrode and the negative electrode is lightweight and provides high output. The demand for mobile terminals is expected to increase further in the future. Patent Documents 1 to 3 are cited as prior art documents relating to lithium secondary batteries.

JP-A-2005-050806 JP 2005-174924 A JP 2007-026913 A

  In one typical configuration of a lithium ion battery, a negative electrode having a configuration in which a material (negative electrode active material) capable of reversibly occluding and releasing lithium ions (charge carriers) is held in a negative electrode current collector is used. As the negative electrode active material, a carbon material (graphite or the like) having a graphite structure at least partially is preferably used. Further, as the negative electrode current collector, a metal material having good conductivity such as copper is preferably used.

  By the way, some uses of a lithium ion battery are assumed to be used over a long period in a mode in which high-rate discharge (rapid discharge) is repeated. A lithium ion battery used as a power source for a vehicle (for example, a lithium ion battery mounted on a hybrid vehicle that uses a lithium ion battery and another power source having different operating principles such as an internal combustion engine as a power source) This is a typical example of a lithium ion battery in which such a usage mode is assumed. It would be useful to provide a technique for improving the durability of lithium ion batteries against repeated high-rate discharges (that is, suppressing deterioration of battery performance).

  Accordingly, the present invention provides a lithium ion battery comprising a negative electrode having a configuration in which a carbon material as a negative electrode active material is held on a negative electrode current collector made of a conductive metal, and having improved durability against high-rate discharge The purpose is to provide. Moreover, an object of this invention is to provide the negative electrode for lithium ion batteries suitable as a component of this lithium ion battery.

  The present inventor has found that the above-described deterioration in battery performance due to high-rate discharge is caused by the fact that a part of the negative electrode is locally overdischarged when discharge is continuously performed at a high current density. It was thought that the potential of the negative electrode in the discharge portion was locally increased, and this promoted the reaction between the negative electrode current collector and the electrolyte. And, in order to suppress such a local increase in negative electrode potential, a material mainly having a potential more noble than the carbon material between the layer mainly composed of the carbon material as the negative electrode active material and the negative electrode current collector is mainly used. The present invention has been completed by finding that the above-mentioned problems can be solved by interposing a layer to be interposed.

The lithium ion battery provided by the present invention includes a negative electrode having a configuration in which a negative electrode current collector made of conductive metal holds a negative electrode active material layer. The negative electrode active material layer includes a first active material layer mainly composed of a carbon material as a first negative electrode active material, and a second active material layer mainly composed of a second negative electrode active material. Here, the second active material layer is a layer mainly composed of a second negative electrode active material having a nobler potential than the carbon material, and is between the negative electrode current collector and the first active material layer. Is provided.
According to the lithium ion battery including the negative electrode having such a configuration, it is possible to suppress deterioration in battery performance (for example, reduction in battery capacity due to a charge / discharge cycle with high rate discharge) even in a usage mode in which high rate discharge is repeated. Therefore, any of the lithium ion batteries disclosed herein can be preferably used for applications that are assumed to be discharged at a high rate and other various applications. In particular, it is suitable for use as a power source of a vehicle such as an automobile (typically, a hybrid vehicle or an electric vehicle).

  A suitable example of the conductive metal constituting the negative electrode current collector is copper (Cu). In other words, a copper-made negative electrode current collector can be preferably used. Moreover, as said carbon material (1st negative electrode active material), the carbon material which has a graphite structure in at least one part is preferable, for example, graphite can be used preferably.

  As the second negative electrode active material, a material capable of reversibly occluding and releasing lithium ions and capable of performing the occlusion and release at a noble (higher) potential than the carbon material can be used. . A suitable example of such a material is lithium titanium oxide. By using lithium titanium oxide as the second negative electrode active material, a lithium ion battery with particularly good durability against high-rate discharge (for example, battery capacity maintenance rate with respect to charge / discharge cycles involving high-rate discharge) can be realized.

  The ratio of the thickness of the second active material layer to the total thickness of the first active material layer and the second active material layer is, for example, approximately 35% or less (typically approximately 1% to 35%). ). If the thickness ratio of the second active material layer is too large, the initial battery performance (for example, initial discharge capacity) may tend to decrease.

  Any of the lithium ion batteries disclosed herein has performance (for example, light weight and high output) suitable as a battery mounted on a vehicle, and can be particularly excellent in durability against high-rate discharge. . Therefore, according to the present invention, a vehicle including any of the lithium ion batteries disclosed herein is provided. In particular, a vehicle (for example, an automobile) including the lithium ion battery as a power source (typically, a power source of a hybrid vehicle or an electric vehicle) is preferable.

  Moreover, according to this invention, the negative electrode for lithium ion batteries is provided. The negative electrode includes a negative electrode current collector made of a conductive metal and a negative electrode active material layer held by the negative electrode current collector. The negative electrode active material layer includes a first active material layer mainly composed of a carbon material as a first negative electrode active material, and a second active material layer mainly composed of a second negative electrode active material. Here, the second active material layer is a layer mainly composed of a second negative electrode active material having a nobler potential than the carbon material, and is between the negative electrode current collector and the first active material layer. Provided. The negative electrode having such a configuration is suitable as a negative electrode provided in any of the lithium ion batteries disclosed herein.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  The technique disclosed here is that a carbon material (typically, a carbon material having a graphite structure at least partially, such as graphite) as a negative electrode active material is made of a conductive metal (typically copper). The present invention can be widely applied to a negative electrode configured to be held by a negative electrode current collector, a lithium ion battery including the negative electrode, and a vehicle equipped with the lithium ion battery. The outer shape of the lithium ion battery is not particularly limited, and may be, for example, a rectangular parallelepiped shape, a flat shape, a cylindrical shape, or the like.

As the negative electrode current collector constituting the negative electrode, a conductive member made of a metal material having good conductivity (eg, copper, nickel, aluminum, iron, stainless steel, etc.) is preferably used. The technology disclosed herein is particularly a negative electrode current collector (typically substantially copper) (made of copper or an alloy (copper alloy) containing copper as a main component). It can be preferably applied to a negative electrode provided with a negative electrode current collector comprising:
The shape of the negative electrode current collector is not particularly limited because it can vary depending on the shape of the lithium ion battery constructed using the obtained negative electrode, for example, a rod shape, a plate shape, a sheet shape, a foil shape, a mesh shape, etc. It can be in various forms. The current collector itself in various forms may be produced by any conventionally known method in the field of lithium ion batteries, and does not characterize the present invention. The technology disclosed herein can be preferably applied to a lithium ion battery including a negative electrode in a form in which a negative electrode active material is held on, for example, a sheet-shaped or foil-shaped negative electrode current collector. As a preferable embodiment of such a lithium ion battery, a lithium ion battery including a wound electrode body can be given.

  In the negative electrode disclosed herein, the negative electrode current collector includes a first active material layer mainly composed of the first negative electrode active material and a second active material layer mainly composed of the second negative electrode active material. A negative electrode active material layer (typically, a negative electrode active material layer composed of the first active material layer and the second active material layer) is held. The number of the first active material layers and the second active material layers included in the negative electrode active material layer may be one layer or two or more, respectively, but at least the first active material layer and the negative electrode in the lowest layer (most negative electrode current collector side) A second active material layer is provided between the current collector. In other words, the second active material layer is first provided on the surface of the negative electrode current collector, and at least one first active material layer is provided thereon. Further, one or more first active material layers and / or second active material layers may be laminated thereon. Usually, a negative electrode active material layer having a structure including a first active material layer and a second active material layer one by one is preferable. According to such a configuration, since the second negative electrode active material is concentrated in the vicinity of the surface of the negative electrode current collector, the effect of suppressing the potential increase on the surface of the current collector (and the effect of increasing durability against high-rate discharge) Can be efficiently exhibited.

  As the first negative electrode active material, a carbon material capable of occluding and releasing lithium ions (in other words, capable of functioning as an active material) is used. Any carbon material of a so-called graphitic material (graphite), a non-graphitizable carbon material (hard carbon), a graphitizable carbon material (soft carbon), or a combination of these materials is preferably used. obtain. It is preferable to use a particulate carbon material (carbon particles) containing a graphite structure (layered structure) at least partially. For example, natural graphite, mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), etc. can be used.

  As the first negative electrode active material (typically carbon particles, preferably graphite particles such as spherical graphite), for example, a carbon material having an average particle diameter of about 50 μm or less (typically 5 μm to 50 μm) is used. Can do. Carbon particles having an average particle size of about 20 μm or less (typically 5 μm to 20 μm) are preferable, and carbon particles having an average particle size of about 15 μm or less (typically 5 μm to 15 μm) are particularly preferable. Thus, carbon particles having a relatively small particle size have a large surface area per unit volume, and thus can be a negative electrode active material more suitable for rapid charge / discharge (for example, high rate discharge). Therefore, a lithium ion battery using such a negative electrode active material can be suitable as, for example, a lithium ion battery mounted on a vehicle (particularly, a lithium ion battery used as a power source for a vehicle).

  On the other hand, as the second negative electrode active material, a material capable of occluding and releasing lithium ions and having a nobler potential than the carbon material (typically graphite) as the first negative electrode active material, in other words, A material having a higher electrode potential than the one negative electrode active material is used. By disposing the second negative electrode active material on the surface of the negative electrode current collector, even when the desorption of lithium ions from the first negative electrode active material locally proceeds excessively, the surface of the negative electrode current collector It is possible to mitigate an event in which the potential of N is increased locally. For example, a (noble) material whose electrode potential is about 0.1 V or more higher than the first negative electrode active material can be preferably used as the second negative electrode active material, and is about 0.3 V or more (for example, about 0.5 V or more). Even better results can be achieved by using higher materials. Further, it is preferable to use a second negative electrode active material whose electrode potential is lower than that of the negative electrode current collector itself (preferably about 0.5 V or more, more preferably 1 V or more).

  The second negative electrode active material is preferably selected so as to exhibit an effect of suppressing an increase in potential (vs. Li) of the negative electrode current collector surface to about 2 V or less (more preferably about 1 V) or less. From such a viewpoint, a material having an electrode potential (vs. Li) of about 2 V or less (typically about 0.5 V to 2 V) is preferable. For example, the electrode potential (vs. Li) is about 1 V or less (typically about v). A material of about 0.5V to 1V) can be preferably used. It is preferable to use a material having excellent high rate characteristics as the second negative electrode active material, whereby the effect of suppressing the potential increase can be more appropriately exhibited. In addition, by using a material with less structural expansion and contraction associated with charge and discharge as the second negative electrode active material, it is possible to suppress collapse of the conductive network and realize better durability. Since the second active material layer mainly composed of the second negative electrode active material is provided as the first layer of the negative electrode active material layer (that is, on the surface of the negative electrode current collector), by selecting a material having such a small expansion and contraction. The effect can be exhibited particularly well.

Specific examples of the second negative electrode active material in the technology disclosed herein include lithium titanium oxide, lithium titanium sulfide, lithium sulfide, molybdenum sulfide (typically MoS 2 ), iron sulfide, and metal nitride. It is done. Of these, only one kind may be used, or two or more kinds may be used in combination in the same or different second active material layers. Here, the “lithium titanium oxide” refers to an oxide containing at least lithium and titanium as constituent metal elements. In addition to an oxide in which the constituent metal element is composed only of lithium and titanium, at least one kind other than lithium and titanium is used. It is meant to include an oxide containing a metal element in a smaller proportion than titanium. Such an oxide is sometimes referred to as a lithium-titanium composite oxide, and a typical example includes a compound composed of lithium, titanium, and oxygen. Similarly, “lithium titanium sulfide” refers to a sulfide (composite sulfide) containing at least lithium and titanium as constituent metal elements, and a typical example includes a compound composed of lithium, titanium, and sulfur. The “iron sulfide” refers to a sulfide containing at least iron as a constituent metal element. In addition to a compound composed of iron and sulfur such as FeS and FeS 2 , lithium is further contained in addition to iron and sulfur. It is a concept including a compound (complex sulfide), for example, a compound represented by the following formula: Li x FeS 2 (wherein x is a number satisfying 0 <x <2). As a typical example of the metal nitride, a nitride containing lithium and a transition metal element as a constituent metal element (that is, lithium transition metal nitride), for example, Li x Co y N (wherein x is 0 < x <4, and y in the formula is preferably a number satisfying 0 <y <0.5.).
Among these, as the second negative electrode active material, the following formula (1):
Li 4 + x Ti 5 O 12 (1);
Lithium titanium oxide (composite oxide) represented by can be preferably employed. A preferable range of x in the above formula (1) is -1 ≦ x ≦ 3, preferably 0 ≦ x ≦ 3, for example, 0 ≦ x ≦ 2.

  A particulate material can be preferably used as the second negative electrode active material. For example, a second negative electrode active material having an average primary particle size of about 1 μm or less (more preferably about 0.5 μm or less) is used. Use is preferred. As described above, the second negative electrode active material having a relatively small particle size has a large surface area per unit volume, and thus has a high diffusion rate of lithium ions, and can be a negative electrode active material suitable for more rapid charge / discharge (for example, high rate discharge). . Therefore, the effect of suppressing the local voltage increase of the negative electrode current collector is sufficiently exhibited, and durability against high-rate discharge (for example, capacity retention rate) can be further improved. Note that particles having a particle size of 0.1 μm or less are preferably cut because it is difficult to collect current.

  The second active material layer mainly composed of the second negative electrode active material is, for example, a liquid in which the second negative electrode active material (preferably particulate, for example, lithium titanium oxide particles) is dispersed in an appropriate solvent. By applying (typically applying) a composition (typically a paste or slurry-like composition) to the negative electrode current collector, and drying the composition (second active material layer forming composition) Preferably it can be made. As the solvent (that is, a dispersion medium such as the second negative electrode active material), any of water, an organic solvent, and a mixed solvent thereof can be used. In applying the composition for forming the second active material layer to the negative electrode current collector (preferably in the form of foil or sheet), a technique similar to a conventionally known method can be appropriately employed. For example, a predetermined amount of the above composition may be applied in a layered manner to the surface of the current collector using a suitable coating device (slit coater, die coater, comma coater, etc.).

In addition to the second negative electrode active material and the solvent, the second active material layer forming composition may be one or two types that can be blended in a composition used for forming a negative electrode active material layer in a general lithium ion battery. The above materials can be contained as needed. An example of such a material is a conductive material (conductivity imparting material). Examples of the conductive material include carbon powders such as various carbon blacks (acetylene black, furnace black, ketjen black, etc.) and graphite powder, and carbon fibers obtained by a vapor phase method such as VGCF (registered trademark). One or two or more selected from conductive metal powders such as nickel powder, etc. may be used.
Other examples of materials that can be contained in the composition as necessary include a binder (binder) and a fluidity modifier. For example, fluorine-containing polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP); styrene butadiene rubber (SBR), acrylic rubber (for example, , Rubber having (meth) acrylic acid ester as main constituent monomer), fluorine rubber (for example, vinylidene fluoride rubber, tetrafluoroethylene-propylene copolymer rubber), polybutadiene, ethylene-propylene-diene copolymer Rubbers such as coalesced (EPDM) and sulfonated EPDM; acrylic resins (for example, resins having (meth) acrylic acid ester as a main constituent monomer, polyacrylic acid, etc.); carboxymethylcellulose (CMC), diacetylcellulose, Hydroxypropyl cell One or two or more polymer materials appropriately selected from various polymers such as cellulose-based polymers such as cellulose; polyvinyl alcohol; polyalkylene oxides such as polyethylene oxide; and the like, and the binder and / or fluidity modifier (typical Can be suitably used as a viscosity modifier, such as a thickener.

Although not particularly limited, the solid content concentration of the second active material layer forming composition (nonvolatile content, that is, the ratio of the second active material layer forming component in the composition) is, for example, about 40 to 60% by mass. It is appropriate to set the degree. The ratio of the second negative electrode active material to the solid content (second active material layer forming component) of the composition is, for example, about 60% by mass or more (typically about 60 to 99% by mass). It is preferably about 70 to 97% by mass, more preferably about 80 to 95% by mass.
In the composition for forming the second active material layer having the composition containing the conductive material as described above, the ratio of the conductive material in the solid content can be, for example, about 0.5 to 30% by mass, It is preferable to set it as 20 mass%, and it is more preferable to set it as about 5-18 mass%. By making the usage-amount of an electroconductive material into the said range, the desired electroconductivity improvement effect can be acquired, suppressing the excessive influence on other battery performance (for example, initial stage battery capacity). For example, even when a lithium ion battery is stored under high temperature conditions, the decomposition of the nonaqueous electrolyte on the surface of the conductive material can be suppressed to a low level.
Further, in the composition for forming the second active material layer having the composition containing the polymer material as described above, the ratio of the polymer material to the solid content can be, for example, about 0.5 to 10% by mass. It is preferable to set it as 2-7 mass%. By setting the use ratio of the polymer material within the above range, sufficient adhesive strength can be ensured while suppressing an excessive influence on other battery performance (for example, initial internal resistance).

  In addition, the first active material layer mainly composed of the first negative electrode active material is a first negative electrode active material (preferably carbon particles such as spherical graphite), for example, in the same manner as the formation of the second active material layer described above. Preferably, the liquid composition (the composition for forming the first active material layer) in which the particles are dispersed in an appropriate solvent is applied to a negative electrode current collector having a second active material layer on the surface and dried. Can be made. As the solvent (that is, a dispersion medium such as the first negative electrode active material), any of water, an organic solvent, and a mixed solvent thereof can be used. This composition for forming a first active material layer is a kind that can be blended in a composition used for forming a negative electrode active material layer in a general lithium ion battery, similarly to the composition for forming a second active material layer described above. Or 2 or more types of materials can be contained as needed. For example, the first active material layer forming composition can contain the same conductive material and polymer material as examples of materials that can be contained in the second active material layer forming composition, if necessary.

Although not particularly limited, it is appropriate that the solid content concentration of the first active material layer forming composition is, for example, about 40 to 60% by mass. Further, the ratio of the first negative electrode active material to the solid content (first active material layer forming component) of the composition is, for example, about 60% by mass or more (typically about 60 to 99.5% by mass). It is preferably about 70 to 99% by mass, more preferably about 80 to 98% by mass.
In the composition for forming the first active material layer having the composition containing the conductive material as described above, the ratio of the conductive material in the solid content can be set to, for example, about 0.5 to 30% by mass. It is preferably 20% by mass (more preferably about 1 to 18% by mass). By setting the use ratio of the conductive material within the above range, it is possible to obtain a desired conductivity improvement effect while suppressing an excessive influence on other battery performance (for example, initial battery capacity). For example, even when a lithium ion battery is stored under high temperature conditions, the decomposition of the nonaqueous electrolyte on the surface of the conductive material can be suppressed to a low level.
Further, in the first active material layer forming composition having the composition containing the polymer material as described above, the ratio of the polymer material to the solid content can be, for example, about 0.5 to 10% by mass, It is preferable to set it as 2-7 mass%. By setting the use ratio of the polymer material in the above range, sufficient adhesive strength can be ensured while suppressing an excessive influence on other battery performance (for example, internal resistance).

The application amount of the first and second active material layer forming compositions is not particularly limited, and can be set to an appropriate amount according to the shape and target performance of the negative electrode and the battery. For example, when producing a negative electrode used for the construction of a lithium ion battery having a wound electrode body as described above, a foil-shaped current collector (for example, a metal foil (copper having a thickness of about 10 to 30 μm) Foil etc.) can be preferably used. The total coating amount of the first active material layer and the second active material amount formed after drying (that is, the total coating amount in terms of solid content) is formed on the surface of It is good to apply | coat so that it may become about 5-20 mg / cm < 2 > per unit area of a collector. When the composition is applied to both sides of the current collector (that is, a negative electrode active material layer is provided on both sides of the current collector), the coating amount may be set so that the total amount of both surfaces falls within the above range. . Alternatively, the composition may be applied only to one side of the current collector. Usually, the aspect which apply | coats the said composition to both surfaces of a collector can be employ | adopted preferably. After the application, the negative electrode active material layer can be formed by drying the applied product by an appropriate drying means and pressing it as necessary. As a pressing method, various conventionally known pressing methods such as a roll pressing method and a flat plate pressing method can be appropriately employed. For example, the composition for forming the second active material layer is applied to the surface of the negative electrode current collector and dried to form the second active material layer, and then the first active material layer is formed on the second active material layer. The composition may be applied and dried (if necessary, pressing may be performed after the formation of the second active material layer and before the formation of the first active material layer and / or after the formation of the first active material layer. ), A negative electrode active material layer having a two-layer structure in which the second active material layer and the first active material layer are laminated in this order on the surface of the negative electrode current collector is obtained.

  About the negative electrode active material layer provided on any one side of the negative electrode current collector, the total thickness of the first active material layer and the second active material layer (typically the same as the total thickness of the negative electrode active material layer) .)) (The total thickness of the second active material layers when two or more second active material layers are included) can be, for example, about 50% or less, for example, about 35%. The following (for example, about 10 to 30%) is preferable. The lower limit of the thickness ratio of the second active material layer is not particularly limited as long as the effect of improving the durability against high-rate discharge is realized, but it is usually preferably about 1% or more, and about 5% or more. More preferably. For example, a negative electrode active material layer having a two-layer structure in which a second active material layer and a first active material layer are laminated in this order on both surfaces of the negative electrode current collector is formed, and the second active material layer occupying the negative electrode active material layer. A negative electrode in which the thickness ratio of the material layer is about 5 to 35% (more preferably about 10 to 30%) is preferable. In the negative electrode active material layer including two or more second active material layers per side, the thickness ratio of the layer provided at the bottom of the second active material layers (that is, on the surface of the negative electrode current collector) is The total thickness of the two or more second active material layers and the first active material layer (typically the total thickness of the negative electrode active material layer) is about 1% or more (more preferably about 5% or more). It is preferable that

  The ratio of the first negative electrode active material (carbon material) and the second negative electrode active material (for example, lithium titanium oxide) contained in the negative electrode active material layer is, for example, the total mass of the first negative electrode active material and the second negative electrode active material Can be set such that the mass of the second negative electrode active material is about 1 to 50% by mass, and the ratio is preferably about 5 to 35% by mass. Further, in the negative electrode active material layer including two or more second active material layers per side, the second negative electrode active material included in the layer provided on the surface of the negative electrode current collector among the two or more second active material layers. The mass ratio of the substance is preferably about 1% by mass or more (more preferably about 5% by mass or more) with respect to the total mass of the first negative electrode active material and the second negative electrode active material.

  In one exemplary embodiment of the technology disclosed herein, the first active material layer and the surface of the negative electrode current collector are within a range including at least the entire region where the first active material layer is formed in the negative electrode current collector. A second active material layer is formed so as to be separated from each other. Further, the second active material layer may be formed so as to extend to a range where the first active material layer is not formed. Usually, the region in which the second active material layer is formed and the region in which the first active material layer is formed substantially coincide with each other, or the outer edge of the region in which the first active material layer is formed is the second active material. These active material layer formation regions are preferably set so as to be slightly inside the outer edge of the layer formation region.

  The lithium ion battery that can be provided by the present invention can be configured in substantially the same manner as a conventional secondary battery of this type except that the negative electrode having the above-described configuration is used. In such a lithium ion battery, a positive electrode active material (a material capable of reversibly occluding and releasing lithium ions) is typically retained in any of the negative electrodes disclosed herein and a positive electrode current collector made of an appropriate material. A positive electrode having the above structure, a porous sheet-like separator separating the positive and negative electrodes, and a nonaqueous electrolyte disposed between the positive and negative electrodes. There is no particular limitation on the structure (for example, a metal casing or laminate film structure) and size of the battery outer container, or the structure of the electrode body (for example, a wound structure or a laminated structure) having positive and negative electrodes as main components. .

For example, as the positive electrode active material (typically in particulate form), a layered structure oxide-based positive electrode active material, a spinel-structured oxide-based positive electrode active material, or the like used in a general lithium ion battery is preferably used. Can do. As a typical example of such a positive electrode active material, lithium and a transition metal element such as lithium cobalt oxide (for example, LiCoO 2 ), lithium nickel oxide (for example, LiNiO 2 ), and lithium manganese oxide (for example, LiMn 2 O 4 ) are used. A positive electrode active material mainly containing an oxide containing a constituent metal element (lithium transition metal oxide) can be given.
Here, “lithium cobalt oxide” means an oxide having lithium and cobalt as constituent metal elements, and at least one other metal element in addition to lithium and cobalt (that is, a transition metal element other than lithium and cobalt and Also includes oxides containing less than cobalt (or typical metal elements) in terms of the number of atoms (in terms of the number of atoms. If two or more kinds of metal elements other than lithium and cobalt are included, the total amount thereof is less than cobalt). The same applies to lithium nickel oxide and lithium manganese oxide. Therefore, for example, an oxide having a composition in which less than 50% by number of sites in cobalt in LiCoO 2 is replaced with any one selected from Ni and Mn (for example, the following formula: LiCo 1-xy Ni x Mn y O 2 (compound represented by x + y <0.5); is included in the concept of lithium cobalt oxide. Also, an oxide having a composition in which less than 50% by number of sites in nickel in LiNiO 2 is replaced with Al (for example, represented by the following formula: LiNi 1-x Al x O 2 (x <0.5); Compound) or an oxide having a composition in which the site is replaced with any one selected from Mn and Al (for example, LiNi 1-xy Mn x Al y O 2 (x + y <0.5) Is included in the concept of lithium nickel oxide. In addition, an oxide having a composition in which less than 50% by number of manganese sites in LiMn 2 O 4 is replaced with Co (for example, the following formula; LiMn 2−x Co x O 4 (x <1); Are included in the concept of lithium manganese oxide. The technology disclosed herein can be preferably applied to, for example, a lithium ion battery including a positive electrode active material mainly composed of lithium cobalt oxide or lithium nickel oxide.

  The technology disclosed herein is a lithium ion battery constructed using a positive electrode having such a positive electrode active material and the negative electrode, and the lower limit of the expected operating voltage (that is, normal operating voltage) is between the electrodes. The voltage (inter-terminal voltage) of about 2.5V to 3V (for example, 3V, 2.8V, etc.) can be preferably applied. The upper limit of the operating voltage may vary depending on the type of the positive electrode active material, but for example, a lithium ion battery having a positive electrode active material mainly composed of lithium cobalt oxide or lithium nickel oxide is usually about 4V to 4.2V. Degree. The present invention relates to a lithium ion battery that is scheduled to be charged / discharged between the lower limit voltage and the upper limit voltage under normal (normal) use conditions (at least used for such an intention) and the battery. It can apply preferably to the negative electrode to comprise. In particular, it is suitable for applications that are expected to be discharged with a large current of 5 A or more (further 10 A or more, for example, about 10 A to 1000 A). In addition, the technique disclosed here can be applied to a lithium ion battery that is not intended for use in performing such high-rate discharge and a negative electrode that constitutes the battery, and can contribute to further improvement in durability.

The positive electrode in the technology disclosed herein typically has a configuration in which a layer containing such a positive electrode active material as a main component (positive electrode active material layer) is held by a positive electrode current collector. As the positive electrode current collector, a conductive member made of a metal having good conductivity is preferably used. In particular, it is preferable to use a positive electrode current collector made of aluminum (Al) or an alloy containing aluminum as a main component (aluminum alloy).
The shape of the positive electrode current collector is not particularly limited because it can vary depending on the shape of the lithium ion battery constructed using the obtained positive electrode, similarly to the negative electrode current collector described above. The technology disclosed herein is applied to, for example, a lithium ion battery including a positive electrode in a form in which a positive electrode active material layer is held on a sheet-shaped or foil-shaped current collector (for example, a lithium ion battery including a wound electrode body). It can be preferably applied.

The positive electrode active material layer is formed by, for example, a liquid composition (typically a paste or slurry composition) in which a positive electrode active material (preferably in the form of particles, for example, lithium cobalt oxide particles) is dispersed in an appropriate solvent. It can preferably be produced by applying to a positive electrode current collector and drying the composition (composition for forming a positive electrode active material layer). As the solvent (dispersion medium such as positive electrode active material particles), any of water, organic solvents, and mixed solvents thereof can be used.
In addition to the positive electrode active material and the solvent, the positive electrode active material layer forming composition is one or more materials that can be blended in a composition used for forming a positive electrode active material layer in a general lithium ion battery. Can be contained as required. For example, the same conductive materials and polymer materials (binders and / or fluidity modifiers) exemplified as materials that can be contained in the second active material layer forming composition, if necessary, for forming the positive electrode active material layer It can be contained in the composition.

  Although not particularly limited, the solid content concentration of the positive electrode active material layer forming composition (nonvolatile content, that is, the proportion of the positive electrode active material layer forming component in the composition) is, for example, about 40 to 60% by mass. It is appropriate to do. The content ratio of the positive electrode active material in the solid content (positive electrode active material layer forming component) is preferably at least about 50% by mass, for example, about 75 to 99% by mass. Usually, it is appropriate to set this ratio to about 78 to 95% by mass. In the composition containing the conductive material, for example, the ratio of the positive electrode active material to the positive electrode active material layer forming component is about 78 to 95% by mass, and the ratio of the conductive material is about 3 to 20% by mass (more preferably 5 to 18%). Mass%) is preferred. By setting the use ratio of the conductive material in the above range, it is possible to obtain a desired conductivity improvement effect while suppressing an excessive influence on other battery performance (for example, battery capacity). For example, even when a lithium ion battery is stored under high temperature conditions, the decomposition of the nonaqueous electrolyte on the surface of the conductive material can be suppressed to a low level. In the composition containing the polymer component as described above, the ratio of the polymer component to the positive electrode active material layer forming component is preferably about 2 to 7% by mass. By setting the use ratio of the polymer material in the above range, sufficient adhesive strength can be ensured while suppressing an excessive influence on other battery performance (for example, internal resistance).

  In applying (typically applying) such a composition for forming a positive electrode active material layer to a positive electrode current collector (preferably a foil or sheet), a technique similar to a conventionally known method is appropriately employed. be able to. For example, a predetermined amount of the above composition may be applied in a layered manner to the surface of the current collector using a suitable coating device (slit coater, die coater, comma coater, etc.). After the application, the applied material is dried by an appropriate drying means, and pressed as necessary to form a positive electrode active material layer.

A typical example of the non-aqueous electrolyte used in the lithium ion battery disclosed herein is a liquid electrolyte containing a non-aqueous solvent and a lithium salt (supporting salt) that can be dissolved in the solvent. It may be a solid (gel) electrolyte in which a polymer is added to the liquid electrolyte.
As the non-aqueous solvent, aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones, and lactones can be used. For example, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, Generally lithium ion batteries such as 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, acetonitrile, propionitrile, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, γ-butyrolactone, etc. 1 type, or 2 or more types selected from the non-aqueous solvent known as what can be used for these electrolytes can be used. Moreover, you may contain additives, such as vinylene carbonate (VC) and ethylene sulfite (ES), for example in the density | concentration of about 0.5-10 mass% as needed.

Examples of the supporting salt include LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiN (CF 3 SO 2 ) 2 , LiN (C 2 F 5 SO 2 ). One, two or more lithium salts selected from 2 , LiC (CF 3 SO 2 ) 3 , LiB [(OCO) 2 ] 2 , and the like can be used.
In addition, the density | concentration of the support salt in the said nonaqueous electrolyte is not restrict | limited in particular, For example, it can be made to be the same as that of the electrolyte used with the conventional lithium ion battery. Usually, a nonaqueous electrolyte containing an appropriate lithium compound (supporting salt) at a concentration of about 0.1 mol / L to 5 mol / L (for example, about 0.8 mol / L to 1.5 mol / L) is preferably used. be able to.

Hereinafter, an embodiment of a negative electrode for a lithium ion battery that can be provided by the present invention and a lithium ion battery including the negative electrode will be described with reference to the drawings.
As shown in FIGS. 1 to 4, the lithium ion battery 10 according to the present embodiment includes a housing (outer container) 12 made of metal (resin or laminate film is also suitable). A long sheet-like positive electrode (positive electrode sheet) 30, a separator 50A, a negative electrode (negative electrode sheet) 40, and a separator 50B are stacked in this order in the housing 12, and then wound (in this embodiment, rolled into a flat shape). The wound electrode body 20 configured in this manner is accommodated.

  The positive electrode 30 includes a long positive electrode current collector 32 and a positive electrode active material layer 35 formed on the surface thereof. As the positive electrode current collector 32, a sheet material (typically a metal foil such as an aluminum foil) made of a metal such as aluminum, nickel, or titanium can be used. The positive electrode active material layer 35 may be obtained by applying a suitable composition for forming a positive electrode active material layer as described above to the positive electrode current collector 32. Typically, the composition is applied to the surfaces of both sides of the positive electrode current collector 32. Since such a coated material contains a solvent, the coated material is then dried in an appropriate temperature range (typically 70 to 200 ° C.) that does not denature the positive electrode active material. Thereby, the positive electrode active material layer 35 can be formed in the desired site | part of the surface of the both sides of the positive electrode collector 32 (FIG. 2). Moreover, the thickness and density of the positive electrode active material layer 35 can be appropriately adjusted by performing an appropriate press process (for example, a roll press process) as necessary.

  On the other hand, the negative electrode 40 includes a long negative electrode current collector 42 and a negative electrode active material layer 45 formed on the surface of the negative electrode current collector. The negative electrode active material layer 45 includes a first active material layer 451 mainly composed of a carbon material (for example, spherical graphite) as a first negative electrode active material, and a second negative electrode active material (for example, having a noble potential than the carbon material). And a second active material layer 452 provided between the negative electrode current collector 42 and the first active material layer 451 (FIGS. 2 and 3). As the negative electrode current collector 42, a sheet material (typically a metal foil such as a copper foil) made of a metal such as copper can be used. Similarly to the positive electrode side, the negative electrode active material layer 45 is coated on the surfaces of both sides of the negative electrode current collector 45 with a suitable first active material layer forming composition and second active material layer forming composition as described above. Then, it may be obtained by drying at an appropriate temperature and adjusting the thickness and density by applying an appropriate press treatment (for example, roll press treatment) as necessary. In FIG. 2, in order to facilitate understanding of the present invention, a part of the first active material layer 451 is removed from a part of the negative electrode 40 (lower left part in the figure), and the second active material layer 452 below the part is removed. In reality, the first active material layer 451 is formed in substantially the same range as the second active material layer 452 including this portion.

  As the separators 50 </ b> A and 50 </ b> B that are used while being overlapped with the positive electrode 30 and the negative electrode 40, various porous sheets that are known to be usable for separators of lithium ion batteries including a nonaqueous electrolyte can be used. . For example, a porous resin sheet (film) made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP) can be suitably used. Such a porous resin sheet may have a single-layer structure or a multilayer structure of two or more layers (for example, a three-layer structure in which PE is laminated on both sides of PP). Although it does not specifically limit, as a property of a preferable porous sheet (typically porous resin sheet), an average pore diameter is about 0.0005-30 micrometers (more preferably 0.001-15 micrometers), and thickness is. The porous resin sheet which is about 5-100 micrometers (more preferably 10-30 micrometers) is illustrated. The porosity of the porous sheet may be, for example, about 20 to 90% by volume (preferably 30 to 80% by volume).

  As shown in FIG. 2, a portion where the positive electrode active material layer forming composition is not applied to one end portion along the longitudinal direction of the positive electrode sheet 30, and thus the positive electrode active material layer 35 is not formed (active material layer). (Unformed part) is provided. In addition, the first and second active material layer forming compositions are not applied to one end portion along the longitudinal direction of the negative electrode sheet 40, and thus the portion where the negative electrode active material layer 45 is not formed (active material layer not yet formed). Forming portion). When the positive and negative electrode sheets 30 and 40 are overlapped with the two separators 50A and 50B, the active material layers 35 and 45 are overlapped and the active material layer non-formed portion of the positive electrode sheet and the active material layer of the negative electrode sheet are not formed. The positive and negative electrode sheets 30 and 40 are slightly shifted and overlapped so that the portions are separately arranged at one end and the other end along the longitudinal direction. In this state, a total of four sheets 30, 40, 50A, 50B are wound, and then the obtained wound body is crushed from the side surface direction and crushed to obtain the flat wound electrode body 20.

Next, the obtained wound electrode body 20 is accommodated in the housing 12 (FIG. 4), and the positive electrode active material layer unformed portion and the negative electrode active material layer unformed portion are partly outside the housing 12. The external connection positive terminal 14 and the external connection negative terminal 16 are electrically connected to each other.
Then, an appropriate nonaqueous electrolyte (for example, a liquid nonaqueous electrolyte (electrolyte) in which a suitable amount of a lithium salt such as LiPF 6 is contained in a mixed solvent of diethyl carbonate and ethylene carbonate) is disposed in the housing 12 ( Then, the opening of the housing 12 is sealed by welding or the like between the housing and the corresponding lid member 13 to complete the construction (assembly) of the lithium ion battery 10 according to the present embodiment. In addition, the sealing process of the housing | casing 12 and the arrangement | positioning (injection) process of electrolyte solution can be performed similarly to the method currently performed by manufacture of the conventional lithium ion battery, and do not characterize this invention. .

  As described above, the lithium ion battery including the lithium ion battery according to the present invention or the negative electrode according to the present invention has little deterioration in battery performance (for example, a decrease in battery capacity) even in a usage mode in which high rate discharge is repeated. Therefore, such a lithium ion battery can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile. Therefore, as schematically shown in FIG. 6, the present invention provides a power source for the lithium ion battery 10 according to the present invention (which may be in the form of an assembled battery formed by connecting a plurality of the lithium ion batteries in series). A vehicle (typically an automobile, particularly an automobile equipped with an electric motor such as a hybrid vehicle, an electric vehicle, etc.) 1 is provided.

  In practicing the present invention, it is not necessary to clarify the reason why a lithium ion battery excellent in durability against high-rate discharge is realized by using the negative electrode having the above-described configuration, but the following may be considered as one factor. . That is, the present inventor has found that the performance deterioration of the lithium ion battery due to high rate discharge is caused by partial discharge of the negative electrode locally when the discharge is continuously performed at a high current density. It was considered that this was due to the fact that the potential of the overdischarge portion was locally increased, and this promoted the reaction between the negative electrode current collector and the electrolyte. For example, when the potential of the current collector becomes too high beyond the potential range that the negative electrode current collector can experience when discharged in the range of the intended operating voltage due to the overdischarge, an electrolyte component (for example, , Such as reductive decomposition of the non-aqueous solvent contained in the electrolyte) and precipitation of the decomposition product on the negative electrode surface or the like.

  In addition to the carbon material as the first negative electrode active material, the negative electrode of the lithium ion battery disclosed herein is a second negative electrode active material having a noble potential than the carbon material (the release of lithium ions from the carbon material). It can be grasped as a material having a high potential. According to this configuration, the local potential increase of the negative electrode current collector can be suppressed (relieved) by the action of the second negative electrode active material, and as a result, durability against high-rate discharge is improved (reduction of battery deterioration). Is considered to be realized. The second negative electrode active material is disposed between the first negative electrode active material and the negative electrode current collector (that is, the second active material layer provided between the first active material layer and the negative electrode current collector). Since they are arranged in a concentrated manner, for example, compared to a mode in which the first negative electrode active material and the second negative electrode active material are mixed, a mechanism for suppressing the local potential increase by the second negative electrode active material (in other words, The effect of improving the durability of the battery can be more effectively exhibited.

  According to a preferred embodiment of the lithium ion battery or the negative electrode for the battery disclosed herein, a carbon material (typically graphite) having excellent performance is used as the first negative electrode active material, and the potential is higher than that of the carbon material. However, by using a noble material as the second negative electrode active material, it is possible to improve the performance after durability while ensuring desired initial performance (for example, initial battery capacity). Further, by arranging the second active material so as to be concentrated on the negative electrode current collector side with respect to the first negative electrode active material, even with a relatively small amount of the second negative electrode active material (for example, the total thickness of the negative electrode active material layer) The thickness of the second negative electrode active material layer occupying about 5 to 35%, preferably about 10 to 30%), a sufficient durability improvement effect can be realized. This can advantageously contribute to the reduction of the material cost and is advantageous in securing the initial performance.

  Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the specific examples.

<Example 1>
A positive electrode was produced as follows. That is, lithium cobalt oxide (LiCoO 2 ) powder as a positive electrode active material, acetylene black (AB) as a conductive material, and PVDF as a binder are mixed at a ratio of N: 90: 7: 3. -A paste-like composition for forming a positive electrode active material layer was prepared by mixing with methylpyrrolidone (NMP). This composition is applied to both sides of an aluminum foil having a thickness of about 15 μm as a positive electrode current collector and dried to form a positive electrode active material layer, and then the whole is pressed, cut into a predetermined width and elongated. A sheet was used. Thereafter, the positive electrode active material layer was scraped along the longitudinal direction with a predetermined width from one end in the width direction of the sheet to expose the surface of the positive electrode current collector. Thus, a sheet-like positive electrode (positive electrode sheet) was obtained.

Moreover, the negative electrode was produced as follows. That is, spherical natural graphite (average particle diameter 5 μm) as the first negative electrode active material, AB as the conductive material, and PVDF as the binder are NMP in a ratio of 94: 2: 4 of these materials. And a paste-like composition for forming a first active material layer was prepared. Moreover, lithium titanium oxide powder (average particle diameter 1 μm) having a composition represented by Li 4 Ti 5 O 12 as the second negative electrode active material (that is, a composition in which x is 0 in the above-described formula (1)), Then, AB as a conductive material and PVDF as a binder are mixed with NMP at a ratio of mass ratio of these materials of 87: 10: 3 to prepare a paste-like second active material layer forming composition. did. The second active material layer (lower layer) was formed by applying and drying the second active material layer forming composition on both surfaces of a copper foil having a thickness of about 15 μm as the negative electrode current collector. Furthermore, the first active material layer (upper layer) was formed by applying and drying the first active material layer forming composition from above the second active material layer. Thus, the negative electrode active material layer of the structure by which the 2nd active material layer and the 1st active material layer were laminated | stacked in this order on both surfaces of the said negative electrode collector was formed. Next, the whole was pressed and cut into a predetermined width to form a long sheet. Thereafter, the negative electrode active material layer was scraped along the longitudinal direction with a predetermined width from one end in the width direction of the sheet to expose the surface of the negative electrode current collector. In this way, a sheet-like negative electrode (negative electrode sheet) was obtained.
In this example, the thickness of the negative electrode active material layer provided in the finally formed negative electrode sheet is about 30 μm per side (the total thickness of the negative electrode sheet including the negative electrode current collector and the negative electrode active material layers provided on both sides thereof). The thickness ratio of the second active material layer (lower layer) in the thickness of the negative electrode active material layer is about 10% (that is, the thickness ratio of the first active material layer (upper layer) is about 75 μm). The coating amount of the second active material layer forming composition and the first active material layer forming composition and the press conditions were adjusted so that the ratio was about 90%.

  Using the positive electrode sheet and the negative electrode sheet thus obtained, a lithium ion battery 100 having the configuration shown in FIG. 5 was produced in the following procedure. The size of the lithium ion battery 100 is 14.5 mm in diameter and 50 mm in height (that is, AA type). In FIG. 5, members / parts having the same functions as those of the lithium ion battery 10 shown in FIGS. 1 to 4 are denoted by the same reference numerals, and redundant description may be omitted.

  The positive electrode sheet 30 and the negative electrode sheet 40 produced above and two separators (here, porous polypropylene sheets were used) 50A and 50B were overlapped and wound in a spiral shape. Also, the aluminum positive electrode lead plate 103 is attached to the exposed portion of the positive electrode current collector of the positive electrode sheet 30 by laser welding, and the negative electrode lead plate 104 made of copper is similarly attached to the exposed portion of the negative electrode current collector of the negative electrode sheet 40 by laser welding. It was. The wound electrode body 20 obtained in this manner was roughly inserted into a metal case (outer container) 102 having a bottomed cylindrical outer shape. After the insertion, a stainless sealing plate 106 was disposed so as to close the upper end opening of the case 102, and the positive electrode lead plate 103 was attached to the sealing plate 106 by laser welding. Further, the negative electrode lead plate 104 was attached to the center of the bottom surface of the case 12 which also served as the negative electrode terminal by laser welding. Note that a cap member 101 that also serves as a positive electrode terminal is spot-welded to the sealing plate 106 in advance. Further, the sealing plate 106 and the cap member 101 are electrically insulated from the case 102 by an insulating gasket 107 made of polypropylene resin disposed on the outer periphery thereof. A safety valve 108 is arranged between the sealing plate 106 and the cap member 101 so as to release the internal gas to the outside when an abnormality occurs in the lithium ion battery 100 and the battery internal pressure rises excessively. ing.

After the above operation, a liquid nonaqueous electrolyte (in this case, 2.3 mL) was injected into the case 102 from an electrolyte injection port (not shown), and the injection port was sealed. As the non-aqueous electrolyte (electrolytic solution), a supporting salt (here, LiPF 6 ) is dissolved at a concentration of 1 mol / L in a 3: 7 (volume ratio) mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC). We used what we did. In this way, a lithium ion battery according to this example was produced.

<Example 2>
In this example, the second active material layer forming composition and the first active material layer are formed so that the ratio of the thickness of the second active material layer (lower layer) to the thickness of the negative electrode active material layer is about 5%. The coating amount of the material layer forming composition was adjusted. Other points were the same as in Example 1, and a lithium ion battery according to Example 2 was produced.

<Example 3>
In this example, the composition for forming the second active material layer and the first active material layer are adjusted so that the ratio of the thickness of the second active material layer (lower layer) to the thickness of the negative electrode active material layer is about 30%. The coating amount of the material layer forming composition was adjusted. The lithium ion battery according to Example 3 was fabricated in the same manner as Example 1 with respect to other points.

<Example 4>
In this example, the composition for forming the second active material layer and the first active material layer are adjusted so that the ratio of the thickness of the second active material layer (lower layer) to the thickness of the negative electrode active material layer is about 40%. The coating amount of the material layer forming composition was adjusted. The lithium ion battery according to Example 4 was fabricated in the same manner as Example 1 with respect to other points.

<Example 5>
In this example, instead of Li 4 Ti 5 O 12 used in Examples 1 to 4, the composition represented by Li 6 Ti 5 O 12 (that is, the composition in which x is 2 in the above formula (1)) Lithium titanium oxide powder (average particle size 2.5 μm) was used as the second negative electrode active material. Other points were the same as in Example 1, and a lithium ion battery according to Example 5 was produced.

<Example 6>
In this example, the first active material layer-forming composition was directly applied to the surface of the negative electrode current collector without using the second active material layer-forming composition. A negative electrode active material layer composed of an active material layer was formed on both sides of the negative electrode current collector. The coating amount of the first active material layer forming composition was adjusted so that the thickness of the negative electrode active material layer (here, the same thickness as the first active material layer) was the same as in Example 1. Other points were the same as in Example 1, and a lithium ion battery according to Example 6 was produced.

[Performance evaluation test]
About the lithium ion battery obtained by Examples 1-6, the degree of the battery deterioration (here capacity reduction) with respect to the charging / discharging cycle at a high rate (here 10A) was evaluated. That is, each battery was charged to 4.1 V with a constant current of 10 A at room temperature (25 ° C.), and then discharged to 2.8 V with a constant current of 10 A. The battery capacity (initial discharge capacity) [mAh] at the time was measured. Subsequently, charging / discharging under the above conditions was performed until the 500th cycle, and the battery capacity (discharge capacity after 500 cycles) [mAh] at the 500th cycle discharge was measured. From these measured values, the retention rate (%) of the discharge capacity after 500 cycles with respect to the initial discharge capacity was calculated for each battery.
The results of the evaluation test are shown in Table 1 together with the thickness ratio of the second active material layer to the thickness of the negative electrode active material included in each battery (0% in Example 6 having no second active material layer). In Table 1, according to the thickness ratio of the second active material layer, the description order of Example 1 and Example 2 is shown upside down.

  As is clear from the results shown in Table 1, the lithium ion batteries according to Examples 1 to 5 in which the second active material layer is disposed between the first active material layer and the negative electrode current collector have the second active material layer. Compared to the battery according to Example 6 that does not have any, the capacity retention rate was improved (more specifically, 80% or more). In the batteries of Examples 1 to 3 and Example 5 in which the thickness ratio of the second active material layer is in the range of 5 to 35%, a high capacity retention rate of 95% or more is realized, and in particular, the thickness ratio of the second active material layer A capacity retention rate of 100% was achieved in the batteries of Examples 1, 3 and Example 5 with 10 to 30%. As a result, according to the batteries of Examples 1 to 3 and Example 5, although the initial discharge capacity was slightly reduced as compared with the battery of Example 6, a discharge capacity obviously higher than that of the battery of Example 6 was obtained after the endurance. Further, as can be seen from the comparison between Example 1 and Example 5, the same durability (capacity maintenance ratio) improvement effect was realized even when different types of second active material layers were used.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and changed the above-mentioned specific example is contained in the invention disclosed here.

It is a perspective view which shows typically the external shape of the lithium ion battery which concerns on one Embodiment. It is a partially broken top view which shows the positive / negative electrode and separator which comprise the wound electrode body which concerns on one Embodiment. It is the III-III sectional view taken on the line in FIG. It is the IV-IV sectional view taken on the line in FIG. It is sectional drawing which shows typically the shape of the AA type | mold lithium ion battery produced as one Example. It is a side view which shows typically the vehicle (automobile) provided with the lithium ion battery of this invention.

Explanation of symbols

1 Vehicle (Automobile)
DESCRIPTION OF SYMBOLS 10,100 Lithium ion battery 12 Case 20 Winding electrode body 30 Positive electrode 32 Positive electrode current collector 35 Positive electrode active material layer 40 Negative electrode sheet (negative electrode)
42 Negative electrode current collector 45 Negative electrode active material layer 451 First active material layer 452 Second active material layer 50A, 50B Separator

Claims (8)

  1. A lithium ion battery comprising a negative electrode configured to hold a negative electrode active material layer on a negative electrode current collector made of a conductive metal,
    The negative electrode active material layer is
    A first active material layer mainly composed of a carbon material as a first negative electrode active material;
    A second active material layer mainly composed of a second negative electrode active material provided between the negative electrode current collector and the first active material layer and having a more noble potential than the carbon material;
    Only including,
    The negative electrode current collector is made of copper,
    The carbon material is graphite;
    The second negative electrode active material is lithium titanium oxide,
    The lithium ion battery whose average particle diameter of the said carbon material is 20 micrometers or less .
  2. A lithium ion battery comprising a negative electrode configured to hold a negative electrode active material layer on a negative electrode current collector made of a conductive metal,
    The negative electrode active material layer is
    A first active material layer mainly composed of a carbon material as a first negative electrode active material;
    A second active material layer mainly composed of a second negative electrode active material provided between the negative electrode current collector and the first active material layer and having a more noble potential than the carbon material;
    Including
    The negative electrode current collector Ri copper der,
    The second negative electrode active material is lithium titanium oxide,
    The lithium ion battery whose average particle diameter of the said carbon material is 20 micrometers or less .
  3. A lithium ion battery comprising a negative electrode configured to hold a negative electrode active material layer on a negative electrode current collector made of a conductive metal,
    The negative electrode active material layer is
    A first active material layer mainly composed of a carbon material as a first negative electrode active material;
    A second active material layer mainly composed of a second negative electrode active material provided between the negative electrode current collector and the first active material layer and having a more noble potential than the carbon material;
    Including
    The carbon material Ri graphite der,
    The second negative electrode active material is lithium titanium oxide
    The lithium ion battery whose average particle diameter of the said carbon material is 20 micrometers or less .
  4. A lithium ion battery comprising a negative electrode configured to hold a negative electrode active material layer on a negative electrode current collector made of a conductive metal,
    The negative electrode active material layer is
    A first active material layer mainly composed of a carbon material as a first negative electrode active material;
    A second active material layer mainly composed of a second negative electrode active material provided between the negative electrode current collector and the first active material layer and having a more noble potential than the carbon material;
    Including
    The second negative active material Ri lithium titanium oxide der,
    The lithium ion battery whose average particle diameter of the said carbon material is 20 micrometers or less .
  5.   5. The ratio of the thickness of the second active material layer to the total thickness of the first active material layer and the second active material layer is 35% or less, according to claim 1. Lithium-ion battery.
  6.   The lithium ion battery according to any one of claims 1 to 5, which is used as a power source for a vehicle.
  7. The lithium ion battery according to any one of claims 1 to 6, wherein an average particle size of the second negative electrode active material is 1 µm or less.
  8. A vehicle comprising the lithium ion battery according to any one of claims 1 to 7.
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