JP2009211956A - Lithium-ion battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium-ion battery in which durability with respect to high-rate discharge is improved effectively. <P>SOLUTION: The lithium ion battery 10 is equipped with a wound electrode body 30, and positive and negative electrode terminals are connected respectively to one end and the other end of its winding direction. An electrolytic solution holding amount per unit volume of a wound core part 31, wound by superimposing an active material layer of positive, and negative electrode sheets out of the electrode body 30 and a separator is constituted to become more in the center part 312 of a winding axial direction than on one-end side (positive electrode terminal side) 313 and on the other-end side (negative electrode terminal side) 311. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a lithium ion battery, and more particularly to a lithium ion battery with improved durability against repeated high-rate discharge.

Lithium ion batteries that are charged and discharged by the movement of lithium ions between the positive electrode and the negative electrode are lightweight and can provide high output. An increase is expected. For example, Patent Document 1 is cited as a prior art document regarding a lithium ion battery.
JP 2002-231316 A

  By the way, some uses of lithium ion batteries are assumed to be used 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) It is a typical example of a lithium ion battery in which such a use mode is assumed. However, even though conventional conventional lithium ion batteries exhibit relatively high durability against charge / discharge cycles at a low rate, performance degradation (increase in internal resistance) occurs in charge / discharge patterns that repeat high-rate discharge. Etc.).

  Patent Document 1 describes a technique for suppressing an increase in internal resistance due to the progress of a charge / discharge cycle by using a negative electrode having a composition obtained by adding a conductive material to a carbon material having a specific structure and an electrolyte solution having a predetermined concentration. However, even with such a technique, it has not been possible to sufficiently improve the durability against a charge / discharge pattern that repeats high-rate discharge (for example, rapid discharge at a level required in a lithium ion battery for a vehicle power source).

  Accordingly, an object of the present invention is to provide a lithium ion battery in which durability against high rate discharge is more effectively improved.

  In the conventional lithium ion battery having a wound electrode body, the present inventor continuously discharges and charges at a high rate for a short time (pulse form) as expected in a lithium ion battery for a vehicle power source. We noticed that there was a unique phenomenon that the internal resistance markedly increased when repeated. Therefore, the effect of repetition of such high-rate pulse discharge on the lithium ion battery was analyzed in detail. As a result, in a lithium ion battery that repeats high-rate pulse discharge, the concentration of lithium salt in the electrolyte that has permeated the wound electrode body varies depending on the location. More specifically, the lithium in the central portion in the axial direction of the wound electrode body It was newly found that the salt concentration is lower than both ends (the lithium salt concentration is greatly reduced compared to the initial state). If there is such a bias in the lithium salt concentration (which can also be grasped as the lithium ion concentration; hereinafter referred to as “Li concentration”), the battery reaction becomes relatively slow in the portion where the Li concentration is relatively low. Therefore, the high-rate discharge performance as the whole battery is lowered. Further, since the battery reaction concentrates on the portion where the Li concentration is high, the deterioration of the portion is promoted. Any of these events can be a factor of reducing the durability (degrading the performance) of the lithium ion battery against a charge / discharge pattern (high rate charge / discharge cycle) that repeats a high rate discharge.

  Based on this knowledge, the present invention improves the durability of a lithium ion battery against high-rate charge / discharge cycles by a new approach of eliminating or mitigating the unevenness (unevenness) of the Li concentration.

  The lithium ion battery provided by the present invention is a wound electrode in which a positive and negative electrode sheet having an active material layer on a long sheet-shaped current collector is wound in the longitudinal direction via a long sheet-shaped separator. The body and the electrolytic solution are housed in a container. A positive terminal is connected to one end of the electrode body in the winding axis direction, and a negative terminal is connected to the other end. The electrode body includes an electrolyte solution holding amount per unit volume of the wound core portion in which the active material layer of the positive and negative electrode sheets and the separator are wound in the electrode body (hereinafter simply referred to as “ Electrolytic solution holding amount ") may be referred to as the one end side (that is, the side where the positive electrode terminal is connected to the electrode body; hereinafter referred to as the" positive electrode terminal side "). ) And the other end side (that is, the side where the negative electrode terminal is connected to the electrode body; hereinafter, also referred to as the “negative electrode terminal side”).

  As described above, in the conventional lithium ion battery, the fluctuation range of the Li concentration when the high-rate charge / discharge cycle is applied at the axially central portion and both end portions (one end side and the other end side) of the wound core portion. There was a difference. That is, the variation (decrease) in the Li concentration was larger in the center than at both ends. According to the lithium ion battery of the present invention having the above configuration, more electrolytic solution can be included in the central portion of the wound core portion than at both ends. In other words, more lithium salts (lithium ions) can be stocked in the center than at both ends. If the absolute amount of the lithium salt in the central portion increases, the variation (decrease) width of the Li concentration when a predetermined amount of the lithium salt is lost becomes small. Therefore, according to the configuration of the present invention, the fluctuation range of the Li concentration in the central portion is reduced, and thereby the difference in the Li concentration fluctuation width between the central portion and both ends (and thus the difference in Li concentration after the fluctuation, that is, the Li concentration). Concentration deviation) can be eliminated or alleviated. This can improve the durability of the lithium ion battery against high-rate charge / discharge cycles. That is, according to the lithium ion battery having the above-described configuration, deterioration of battery performance (for example, increase in internal resistance) can be suppressed even in a usage mode in which high-rate discharge is repeated. Any of the lithium ion batteries disclosed herein can be preferably used for applications that require durability against high-rate discharge 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).

  In the lithium ion battery disclosed herein, various configurations such that the amount of electrolytic solution retained in the central portion of the wound core portion is greater than that of both end portions as described above can be employed alone or in appropriate combination. .

  For example, as at least one of the positive and negative electrode sheets (for example, the negative electrode sheet), the porosity of the active material layer of the electrode sheet constitutes the central portion (the central portion of the wound core portion of the electrode sheet). A portion configured to be higher than at least one of the one end side (positive electrode terminal side) and the other end side (negative electrode terminal side) can be employed in the portion, that is, the central portion of the width of the active material layer. . The electrode sheet may be configured such that the porosity of the active material layer in the central portion is higher than both the one end side and the other end side. By using the electrode sheet having such a configuration, it is possible to easily realize a wound electrode body configured such that the amount of electrolytic solution retained in the center portion is larger than that of both end portions and a lithium ion battery including the electrode body. . Therefore, the present invention provides, as another aspect, an electrode sheet (typically a negative electrode sheet) for a lithium ion battery having a wound electrode body, and having an active material layer on a long sheet-shaped current collector. And the electrode sheet for lithium ion batteries comprised so that the porosity in the center part of the width | variety of the said active material layer might become higher than the both ends of this active material layer is provided. The electrode sheet can be suitably used as a component (component) of any lithium ion battery disclosed herein.

  Moreover, what was comprised so that the porosity in the said center part may become higher as at least one of the said one end side and the said other end side as said separator can be employ | adopted. The separator comprised so that the porosity of the center part may become higher than any of the said one end side and the said other end side may be sufficient. By using the separator having such a configuration, it is possible to easily realize a wound electrode body that is configured such that the amount of electrolytic solution retained in the center portion is larger than that of both end portions, and a lithium ion battery including the electrode body. Therefore, the present invention provides, as another aspect, a separator for a lithium ion battery including a wound electrode body, which has a long sheet shape, and has a void ratio at the center portion of the width higher than both end portions. Provided is a lithium ion battery separator. The separator having such a configuration can be suitably used as a component (part) of any lithium ion battery disclosed herein.

  In a preferable aspect of the lithium ion battery disclosed herein, the separator has a thickness of the central portion larger than at least one (typically both) of the one end side and the other end side. Contrary to the thickness tendency of the separator, the thickness of the central portion of the active material layer facing the separator is smaller than at least one (typically both) of the one end side and the other end side. And the porosity of this separator is higher than the porosity of the said active material layer at least in the said center part (preferably over the whole axial length of the said winding core part).

  According to the electrode sheet and separator having an active material layer having a thickness tendency, the cross-sectional area As of the separator and the cross-sectional area Aa of the active material layer occupy the cross-section of the electrode body (cross-section perpendicular to the winding axis) in the central portion. An electrode body in which the ratio (As / Aa) is larger than the above-described area ratio in the cross section of at least one of the one end side and the other end side (typically both) can be suitably formed. Therefore, it is possible to easily realize a wound electrode body that is configured such that the amount of electrolytic solution retained in the central portion is larger than that of both end portions, and a lithium ion battery including the electrode body. In general, the active material expands or contracts somewhat as lithium ions enter and exit (insertion / desorption), and this may cause an action of pushing out the electrolyte solution (pumping action) from the active material layer, particularly in a high-rate charge / discharge cycle. However, according to the above configuration, since the thickness of the active material layer in the central portion is small (that is, the amount of active material is small), the pumping action can be reduced in the central portion. Therefore, coupled with the fact that more electrolyte solution is held at the center of the electrode body (winding core portion) than at both ends, the amount of electrolyte solution retained in the electrode body is biased by high-rate charge / discharge cycles or the like. (Typically, the amount of electrolyte retained in the central portion is significantly lower than that at both ends) can be alleviated or eliminated. This can further enhance the durability against the high rate charge / discharge cycle.

  The fluctuation range of the Li concentration when the high rate charge / discharge cycle is performed is typically larger on the one end side (positive electrode terminal side) than on the other end side (negative electrode terminal side) of the wound core portion. In a preferable aspect of the lithium ion battery disclosed herein, the amount of electrolyte solution retained per unit volume of the wound core portion is larger on the one end side than on the other end side (that is, the electrolyte solution). The holding amount increases in order of the negative electrode terminal side, the positive electrode terminal side, and the central portion). This can alleviate the unevenness of the Li concentration. In order to realize the above configuration, for example, it is preferable to employ an electrode sheet (positive electrode sheet and / or negative electrode sheet) in which the porosity of the active material layer increases in order of the negative electrode terminal side, the positive electrode terminal side, and the central portion. it can. Moreover, you may use the separator sheet from which the porosity becomes large in order of the negative electrode terminal side, the positive electrode terminal side, and the center part.

  The extent to which the amount of electrolyte solution retained in the central portion is larger than that at both end portions can be appropriately set in consideration of the assumed usage mode, target durability, and the like. As an example, a configuration in which the electrolyte holding amount per unit volume on the other end side is 1 and the electrolyte holding amount in the central portion is approximately 1.1 to 2 can be preferably adopted. For example, when the winding core part is divided into three parts of the one end side, the central part, and the other end side so that the axial lengths are equal to each other, the axial lengths of the respective parts are The electrolyte retention amount at the center may be configured such that the electrolyte retention amount at the other end portion is 1, and the electrolyte retention amount at the central portion is approximately 1.1-2.

  As another example, it is possible to preferably employ a configuration in which the electrolyte solution holding amount per unit volume on the other end side is 1, and the electrolyte solution holding amount on the one end side is approximately 1 to 1.5. For example, when the winding core part is divided into three parts of the one end side, the central part, and the other end side so that the axial lengths are equal to each other, the axial lengths of the respective parts are The electrolyte retention amount at the center may be configured such that the electrolyte retention amount at the other end side is 1, and the electrolyte retention amount at the one end portion is approximately 1 to 1.5.

  Any of the lithium ion batteries disclosed herein has performance suitable as a battery mounted on a vehicle (for example, light weight and high output can be obtained), and is particularly excellent in durability against high-rate charge / discharge. obtain. Therefore, according to this invention, the vehicle provided with one of the lithium ion batteries disclosed here 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.

  As a preferable application object of the technology disclosed herein, lithium ions that can be used in a charge / discharge cycle including a high-rate discharge of 50 A or more (for example, 50 A to 250 A), or even 100 A or more (for example, 100 A to 200 A). Batteries: Large capacity type with a theoretical capacity of 1 Ah or more (and 3 Ah or more), and used in a charge / discharge cycle including high-rate discharge of 10 C or more (for example, 10 C to 50 C) or 20 C or more (for example, 20 C to 40 C). Examples are lithium ion batteries that are assumed to be used.

  Further, as a preferable application target of the technology disclosed herein, when the electrode body is viewed from the side of the winding axis, the size of the projection surface of the winding core portion is about the winding axis direction (lateral direction in FIG. 3). A lithium ion battery having a size of 5 cm or more (typically 5 cm to 25 cm, for example, 7 cm to 20 cm) can be given. In this way, in a lithium ion battery having a relatively long (large) axial length of the wound core portion, the Li concentration is likely to be biased due to high-rate charge / discharge depending on the conventional configuration. Therefore, the present invention is applied. Is particularly beneficial.

  The technology disclosed herein can be preferably applied to a lithium ion battery including an electrode body in which positive and negative electrode sheets and a separator are wound flatly. For example, when viewed from the normal direction of the flat surface (lateral direction of the winding axis), the size of the projection surface of the winding core portion is 5 cm or more (typically 5 cm to 25 cm, for example, 7 cm to 7 cm). 20 cm) and 5 cm or more (typically 5 cm to 25 cm, for example, 7 cm to 20 cm) in the height direction (vertical direction in FIG. 3). In this way, in the lithium ion battery having a relatively long axial length of the wound core portion and a large height (large size), a bias of Li concentration due to high-rate charge / discharge tends to occur depending on the conventional configuration. It is particularly beneficial to apply the invention.

  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 lithium ion battery according to the present invention can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile. Therefore, for example, as schematically shown in FIG. 7, the present invention is a vehicle (typically a battery that includes such a battery 10 (which may be in the form of an assembled battery formed by connecting a plurality of such batteries 10 in series) as a power source. In particular, an automobile (in particular, a car equipped with an electric motor such as a hybrid car or an electric car) 1 is provided.

  Although it is not intended to be particularly limited, in the following, a flatly wound electrode body (wound electrode body) and a nonaqueous electrolyte solution are accommodated in a flat box-shaped (cuboid shape) container. The present invention will be described in detail by taking a lithium ion battery as an example. Moreover, in the following drawings, the same code | symbol is attached | subjected to the member and site | part which show | plays the same effect | action, and the overlapping description may be abbreviate | omitted or simplified.

<Example 1>
A schematic configuration of a lithium ion battery according to an embodiment of the present invention is shown in FIGS. In this lithium ion battery 10, an electrode body (winding electrode body) 30 in which a long positive electrode sheet 32 and a negative electrode sheet 34 are wound flatly via a long sheet-like separator 35 is not shown. It has the structure accommodated in the container 11 of the shape (flat box shape) which can accommodate this winding electrode body 30 with a nonaqueous electrolyte.

  The container 11 includes a bottomed square cylindrical casing 12 having an opening at one end, and a lid 13 attached to the opening and closing the opening. As a material constituting the container 11, a metal material such as aluminum or steel is preferably used. Or the container 11 formed by shape | molding resin materials, such as PPS (polyphenylene sulfide) and a polyimide resin, may be sufficient. For example, the container 11 in which the housing 12 and the lid 13 are both made of aluminum can be preferably used.

  The flat wound electrode body 30 according to the present embodiment is the same as the wound electrode body of a normal lithium ion battery except for the configuration of the active material layer (negative electrode active material layer) provided in the negative electrode sheet described later. In addition, a long sheet-like positive electrode sheet 32 and a negative electrode sheet 34 are typically laminated together with two long sheet-like separators (separator sheets) 35 and wound in the longitudinal direction (typically substantially circular). And then the resulting wound body is crushed from the lateral direction and ablated. In this manner, instead of a mode in which the laminate of sheets is rolled and then flattened, the laminate may be wound into a flat shape (substantially oval, elliptical, etc.) from the beginning.

  Each of the positive electrode sheet 32 and the negative electrode sheet 34 has a configuration in which an active material layer is formed on a long sheet-like current collector. The active material layer is formed in a band-like region excluding one end in the width direction of the current collector (one end along the longitudinal direction). That is, one end in the width direction is a portion where the active material layer is not formed (active material layer non-formed portion). The positive and negative electrode sheets 32 and 34 and the separator sheet 35 are obtained by overlapping the active material layers of both electrode sheets, and the active material layer non-formation part of the positive electrode sheet and the active material layer non-formation part of the negative electrode sheet The positive and negative electrode sheets 32 and 34 are wound in a state where they are laminated with their positions slightly shifted in the width direction so as to protrude from one end and the other end of the electrode. As a result, at the one end and the other end of the wound electrode body 30 in the winding axis direction, the active material layer non-formed portion of the positive electrode sheet 32 is the wound core portion 31 (that is, the active material layers of both electrode sheets 32 and 34). A portion 32A that protrudes outward from the portion where the separator and the separator are closely wound) and a portion 34A where the active material layer non-forming portion of the negative electrode sheet 34 protrudes outward from the wound core portion 31 are formed. Has been. One ends of a positive terminal 14 and a negative terminal 16 for external connection are connected to the protruding portions 32A and 34A. The other ends of the electrode terminals 14 and 16 are drawn out of the container 11 (lid body 13).

  The wound electrode body 30 is configured so that the central portion in the axial direction of the wound core portion 31 has a larger amount of electrolyte solution retained per unit deposition than both the positive electrode terminal side and the negative electrode terminal side. . In this example, the porosity of the active material layer of the negative electrode sheet 34 is made different between a part in the width direction of the active material layer (the axial direction of the wound core part) and the other part (specifically, The above configuration is realized by the fact that the porosity in the central portion 312 of the width of the negative electrode active material layer is higher than both end portions 311 and 313. In the present embodiment, the configuration (porosity and thickness) of the positive electrode sheet 32 and the separator sheet 35 and the thickness of the negative electrode active material layer are substantially constant at least within the range of the axial length of the wound core portion. The configuration of the negative electrode sheet 34 will be described in detail later.

  As the material and the member constituting the wound electrode body 30, the same electrode body as that provided in a conventional lithium ion battery can be used.

  For example, as the positive electrode current collector, a long sheet-like member (metal foil) made of a highly conductive metal is preferably used. In particular, a positive electrode current collector formed using an aluminum material such as aluminum (Al) or an aluminum alloy (an alloy containing Al as a main component) is preferable. For example, an aluminum foil having a thickness of about 5 μm to 30 μm (preferably 10 μm to 30 μm, for example, 15 μm) can be preferably used as the positive electrode current collector. As an example, an aluminum foil having a thickness of about 2 m to 4 m (for example, 2.7 m) and a width of about 8 cm to 15 cm (for example, 12 cm) having the above thickness can be preferably used as a current collector.

As the positive electrode active material (typically in particulate form), a layered oxide-based positive electrode active material, a spinel-structured oxide-based positive electrode active material, and the like used for a general lithium ion battery can be preferably used. As a typical example of such a positive electrode active material, lithium and a transition metal element such as lithium nickel oxide (for example, LiNiO ₂ ), lithium cobalt oxide (for example, LiCoO ₂ ), and lithium manganese oxide (for example, LiMn ₂ O ₄ ) are used. Examples thereof include a positive electrode active material having an oxide (lithium transition metal oxide) containing as a constituent metal element as a main component (can be a positive electrode active material substantially made of a lithium transition metal oxide).

  Here, “lithium nickel oxide” means an oxide having Li and Ni as constituent metal elements, and at least one other metal element in addition to Li and Ni (that is, a transition metal element other than Li and Ni, and Also included are oxides that contain less than Ni (or typical metal elements) in terms of the amount of Ni (in terms of the number of atoms. If two or more metal elements other than Li and Ni are included, the total amount of them is less than Ni). That means The metal element is selected from the group consisting of, for example, Co, Al, Mn, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce. Or one or more elements. The same applies to lithium cobalt oxide and lithium manganese oxide.

  As such a lithium transition metal oxide (typically in a particulate form), for example, a lithium transition metal oxide powder (hereinafter sometimes referred to as an active material powder) prepared and provided by a conventionally known method is used. It can be used as it is. For example, a lithium transition metal oxide powder substantially composed of secondary particles having an average particle size in the range of about 1 μm to 25 μm (typically about 2 μm to 15 μm) is used as the positive electrode in the technology disclosed herein. It can preferably be employed as an active material.

  The positive electrode active material layer preferably contains a conductive material in addition to the positive electrode active material. As the conductive material, a carbon material such as carbon powder or carbon fiber is preferably used. Alternatively, conductive metal powder such as nickel powder may be used. Among these, only 1 type may be used and 2 or more types may be used together. As the carbon powder, various carbon blacks (for example, acetylene black, furnace black, ketjen black), graphite powder, and the like can be used. Of these, acetylene black can be preferably employed. For example, it is preferable to use a granular conductive material (for example, a granular carbon material such as acetylene black) in which the average particle size of constituent particles (typically primary particles) is in the range of about 10 nm to 200 nm (for example, about 20 nm to 100 nm). .

  In addition, the positive electrode active material layer can contain one or two or more materials that can be used as components of the positive electrode active material layer in a general lithium ion battery, if necessary. Examples of such a material include various polymer materials that can function as a binder (binder) of the above constituent components.

  Although not particularly limited, the ratio of the positive electrode active material to the entire positive electrode active material layer (typically approximately the same as the ratio of the positive electrode active material to the solid content of the positive electrode active material composition) is approximately 50. It is preferably at least mass% (typically 50 to 95 mass%), more preferably about 75 to 90 mass%. In the positive electrode active material layer having a composition containing a conductive material, the proportion of the conductive material in the active material layer can be, for example, about 3 to 25% by mass, and preferably about 3 to 15% by mass. In this case, the proportion of the positive electrode active material in the active material layer is suitably about 80 to 95% by mass (for example, 85 to 95% by mass).

  Further, in a composition containing a positive electrode active material layer forming component (for example, a polymer material) other than the positive electrode active material and the conductive material, the total content ratio of these arbitrary components (ratio to the total positive electrode active material layer forming component) is about 7 It is preferable to set it as mass% or less, and it is more preferable to set it as about 5 mass% or less (for example, about 1-5 mass%). The total content of the above optional components may be about 3% by mass or less (for example, about 1 to 3% by mass).

  As a method for forming the positive electrode active material layer, a composition (positive electrode active material composition) in which a positive electrode active material (typically in a particulate form) and other positive electrode active material layer components are dispersed in an appropriate solvent (preferably an aqueous solvent). ) Is preferably applied to one side or both sides (here, both sides) of the positive electrode current collector in a band shape and dried. Although not particularly limited, the solid content concentration of the positive electrode active material composition (nonvolatile content, that is, the ratio of the active material layer forming component) can be, for example, about 40 to 60% by mass. After drying the positive electrode active material composition, an appropriate press treatment (for example, various conventionally known press methods such as a roll press method and a flat plate press method can be employed) is performed as necessary. The thickness and density of the material layer 35 can be adjusted as appropriate.

  As the separator sheet 35 that is used while being overlapped with the positive electrode sheet 32 and the negative electrode sheet 34, various porous sheets can be used as in the case of a separator of a conventional lithium ion battery including a wound electrode body. As the separators 50A and 50B used while being superimposed on the positive and negative electrode sheets, 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 layers are laminated on both sides of a PP layer). For example, a porous separator sheet made of a synthetic resin (for example, made of polyolefin such as polyethylene) having a length of 2 m to 4 m (for example, 3.1 m), a width of 8 cm to 12 cm (for example, 10 cm), and a thickness of about 5 μm to 30 μm (for example, 20 μm) Can be preferably used.

  Although it does not specifically limit, as a property of a preferable porous sheet (typically porous resin sheet), an average pore diameter is about 0.001 micrometer-30 micrometers, and thickness is 5 micrometers-100 micrometers (more preferably 10 micrometers-30 micrometers). ) Is an example of a porous resin sheet. The porosity (porosity) of the porous sheet can be, for example, about 20 to 90% by volume (preferably 30 to 80% by volume).

  As the negative electrode current collector, a long sheet-like member (metal foil) made of a highly conductive metal is preferably used. In particular, a positive electrode current collector made of a copper material such as copper or a copper alloy (an alloy containing copper as a main component) is preferable. For example, a copper foil having a thickness of about 5 μm to 30 μm (preferably 10 μm to 30 μm, for example, 15 μm) can be preferably used as the negative electrode current collector. As an example, a copper foil having a thickness of 2 m to 4 m (for example, 2.9 m) and a width of about 8 cm to 15 cm (for example, 12 cm) having the above thickness can be preferably used as the negative electrode current collector.

  As the negative electrode active material, a carbon material containing a graphite structure (layered structure) at least in part can be suitably used. Any carbon material such as so-called graphitic (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), or a combination of these can be used. It is. For example, natural graphite, mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), etc. can be used. As the negative electrode active material, for example, a particulate carbon material (graphite particles or the like) having an average particle diameter of about 5 μm to 50 μm can be preferably used.

  In addition to the negative electrode active material, the negative electrode active material layer can contain one or two or more materials that can be used as a constituent component of the negative electrode active material layer in a general lithium ion battery, if necessary. Examples of such a material include various polymer materials that can function as a binder (binder) of the above constituent components. Moreover, the negative electrode active material layer containing the same electrically conductive material as the positive electrode side may be sufficient.

  Although not particularly limited, the ratio of the negative electrode active material to the entire negative electrode active material layer can be, for example, about 60% by mass or more (typically about 60 to 99.5% by mass), and about 70%. It is preferable to set it as -99 mass%, and it is more preferable to set it as about 80-98 mass%. In the negative electrode active material layer having the composition containing the polymer material as described above, the ratio of the polymer material in the entire active material layer can be, for example, approximately 0.5 to 10% by mass, and approximately 2 to 7% by mass. It is preferable that

  As a method for forming the negative electrode active material layer, a negative electrode active material composition in which a negative electrode active material (typically in particulate form) and other negative electrode active material layer components are dispersed in a suitable solvent (preferably an aqueous solvent) is used. A method of applying a belt-like shape on one side or both sides (here, both sides) of the electrical conductor and drying can be preferably employed. Although it does not specifically limit, the solid content concentration of a negative electrode active material composition can be about 40-60 mass%, for example. After drying, the thickness, porosity, density, and the like of the negative electrode active material layer can be appropriately adjusted by performing an appropriate press treatment as necessary.

  FIG. 4 is a schematic cross-sectional view showing an enlarged part of a cross section along the winding axis of the wound electrode body 30 according to the present embodiment, which is formed on the negative electrode current collector 342 and one side thereof. The negative electrode active material layer 344 and the separator sheet 35 facing the active material layer 344 are shown. As described above, in the negative electrode active material layer 344 according to this example, the porosity of the negative electrode active material layer 344 in the axial central portion 312 of the wound core portion 31 is higher than the porosity of both end portions 311 and 313. It is comprised so that it may become. The level of the porosity between the central portion 312 and both end portions 311 and 313 of the negative electrode active material layer 344 can be roughly grasped as a relationship that reverses the density of these portions. That is, a portion having a relatively high porosity corresponds to a portion having a relatively low density.

  In order to form the negative electrode active material layer having such a configuration, for example, when the negative electrode active material composition is applied to the negative electrode current collector 342, the application amounts (in terms of solid content) of both end portions 311, 313 rather than the central portion 312 are set. Keep a lot. Therefore, in a state where the applied negative electrode active material composition is dried (uncompressed state), the thickness of the negative electrode active material layer is larger at both end portions 311 and 313 than at the center portion 312. When this is pressed so that the whole negative electrode active material layer has substantially the same thickness, both end portions 311 and 313 are compressed more than the central portion 312, and as a result, the porosity of the central portion 312 is higher than that of both end portions 311 and 313. A high negative electrode active material layer 344 can be formed.

  Alternatively, the above-described configuration may be realized by coating a plurality of types of negative electrode active material compositions (typically by coating in a strip shape along the longitudinal direction of the current collector). For example, since the filling efficiency generally decreases as the particle size of the particles increases (the porosity increases), two types of negative electrode active material compositions having different average particle sizes of the negative electrode active material particles are prepared. A composition having a relatively large average particle size of the negative electrode active material particles is applied to the central portion, and a composition having a relatively small average particle size is applied to both ends. Thereby, the negative electrode active material layer whose porosity of the center part is higher than both end parts can be formed.

  In addition, as a method of making the porosity different between the central portion 312 and the both end portions 311 and 313, a method of making the drying conditions of the negative electrode active material composition different between these portions, and a negative electrode active material composition having different solid content concentrations For example, a method of separately coating a material, a method of using two types of negative electrode active material compositions for negative electrode active material particles having different particle size distributions, and the like can be employed alone or in appropriate combination.

  Regarding the relationship between the negative electrode terminal side 311 and the positive electrode terminal side 313, it is preferable that the porosity of the negative electrode terminal side 311 is higher than that of the positive electrode terminal side 313 as shown in FIG. 4. This is because, as shown in the test results in the comparative example described later, the decrease in the Li concentration (particularly, the Li concentration of the electrolyte held in the negative electrode sheet 34, see FIG. 9) due to the severe high-rate charge / discharge cycle is This is because the central portion 312 is larger than both the end portions 311 and 313, and the negative terminal side 313 tends to have a larger reduction width in comparison between the negative terminal side 311 and the positive terminal side 313. The negative electrode active material layer having a void ratio that increases in the order of the central portion 312, the positive electrode terminal side 313, and the negative electrode terminal side 311 can be obtained by, for example, any one of the above-described methods ( The method can be formed by applying a method of varying the porosity of the material layer.

  The degree to which the porosity is different between the central portion 312 and the both end portions 311 and 313 can be appropriately set in consideration of the usage mode assumed for the lithium ion battery, the target durability, and the like. For example, assuming that the porosity (for example, 40%) of the negative electrode active material layer 344 on the negative electrode terminal side 311 is 1, the porosity of the central portion 312 is about 1.1 to 1.5 (for example, about 1.35, for example). A configuration in which the porosity of the side 311 is about 54% if the porosity is 40% can be preferably employed. Further, assuming that the porosity (for example, 40%) of the negative electrode active material layer 344 on the negative electrode terminal side 311 is 1, the porosity on the positive electrode terminal side 313 is approximately 1 to 1.5 (however, the porosity of the central portion 312 is equal to or It is preferable to employ a configuration that is smaller than the porosity, for example, about 1.31, or about 52% if the porosity on the negative electrode terminal side 311 is 40%.

  The porosity of the negative electrode active material layer 344 may be varied (continuously) with a gradation between a portion where the porosity is high and a portion where the porosity is low, or may be varied stepwise (discontinuously). Also good. According to the negative electrode active material layer (and the negative electrode having the active material layer) in which the change in porosity is given gradation, the deviation of the Li concentration can be alleviated better. The aspect in which the porosity changes stepwise can be preferably adopted from the viewpoints of manufacturability and quality stability.

The wound electrode body 30 having such a configuration is accommodated in the housing 12, and an appropriate nonaqueous electrolytic solution is disposed (injected) into the housing 12. As the electrolytic solution, the same non-aqueous electrolytic solution conventionally used for lithium ion batteries can be used without particular limitation. Such a nonaqueous electrolytic solution typically has a composition in which a supporting salt is contained in a suitable nonaqueous solvent. Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), 1,2-dimethoxyethane, 1,2 One or more selected from the group consisting of -diethoxyethane, tetrahydrofuran, 1,3-dioxolane and the like can be used. Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) _{3 and the} like. A lithium salt can be preferably used. For example, a mixed solvent containing EC, DMC, and EMC at a mass ratio of 30.94: 25.15: 31.75 contains lithium hexafluorophosphate (LiPF ₆ ) as a supporting salt at a concentration of about 1 mol / liter. The electrolyte solution etc. which were made can be used preferably.

  The opening of the housing 12 is sealed by welding or the like between the housing and the lid body 13 corresponding thereto, and the construction (assembly) of the lithium ion battery 10 according to the present embodiment is completed. 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. . Thereafter, the battery is conditioned (initial charge / discharge). You may perform processes, such as degassing and a quality inspection, as needed.

  As shown in FIG. 4, the battery 10 according to this example is configured such that the porosity of the negative electrode active material layer 344 in the central portion 312 is larger than both the positive electrode terminal side 313 and the negative electrode terminal side 311. As a result, the negative electrode active material layer 344 (and thus the wound core portion 31) has an amount of electrolyte stocked per unit area of the central portion 312 (and hence the amount of lithium salt) from which of both end portions 311 and 313. Is also configured to increase. Therefore, even when a high-rate charge / discharge cycle (for example, a charge / discharge pattern that repeats a high-rate discharge of 100 A or more and / or 20 C or more as in a comparative example described later) performed under severe conditions is performed, the axis of the electrode body It is possible to mitigate an event in which a difference in the lithium salt concentration occurs depending on the direction position, and to suppress the deviation of the Li concentration relative to the axial direction. Further, as described above, more electrolytic solution is stored in the central portion 312 than at both end portions 311 and 313. Therefore, there is a difference in the amount of decrease in the electrolytic solution depending on the axial position of the electrode body due to the high rate charge / discharge. It is possible to mitigate the events that occur and to suppress the unevenness of the electrolyte amount. Therefore, according to the lithium ion battery 10 which concerns on a present Example, the outstanding durability with respect to high-rate charge / discharge can be implement | achieved.

  In addition, the relationship of the electrolytic solution holding amount here (relative degree between the central portion 312 and both end portions 311 and 313, etc.) refers to a relationship when the lithium ion battery is in a stable state, and this relationship is always the same. It is not required to satisfy. For example, it may be configured such that the above relationship can be realized when starting to use the battery or when the battery has not been used for a certain period (for example, about 6 hours or more). For example, a part of the electrolytic solution or the lithium salt moves from the central portion 312 of the electrode body 30 to the both end portions 311 and 313 or the electrodes from the both end portions 311 and 313 by being temporarily used in a high rate charge / discharge cycle or the like. Even if it moves to the outside of the body 30, if the continuation of such severe high-rate charging / discharging stops (for example, the battery is not used), the Li concentration of each part of the electrode body is made uniform by diffusion or the like, and each part of the electrode body An action of replenishing (recovering) the electrolyte holding amount to the initial state (equilibrium state before the high-rate charge / discharge cycle) by the capillary phenomenon or the like works. This makes it possible to prepare for the next high rate charge / discharge. Therefore, according to any of the lithium ion batteries disclosed herein, it is caused by a severe high-rate charge / discharge cycle by being configured such that the electrolyte holding amount in the central portion of the wound core portion is larger than both ends. As a result, the unevenness of Li concentration can be reduced or eliminated, and the effect can be maintained over a long period of time.

<Comparative example>
In order to show the technical significance of adopting the configuration according to the present invention more clearly, as a comparative example, the amount of electrolyte retained in the central part of the wound electrode body (wound core part) is made larger than both ends. Therefore, a lithium ion battery in which no intentional measures were taken was prepared. The lithium ion battery according to this comparative example was subjected to a cycle test (high-rate deterioration acceleration test) with a strict high-rate charge / discharge pattern, and then the change caused in the battery was examined. The influence (change) of the charge / discharge pattern on the lithium ion battery will be specifically described with reference to the obtained results.

  A lithium ion battery according to the comparative example was produced as follows.

That is, lithium nickelate powder (positive electrode active material) represented by LiNiO ₂ , acetylene black (conductive material) having an average particle diameter of 48 nm and carboxymethyl cellulose (CMC) have a mass ratio of 87: 10: 3. And it mixed with ion-exchange water so that solid content concentration might be about 45 mass%, and the aqueous active material composition (positive electrode active material composition) was prepared. As the positive electrode current collector 32, a long aluminum foil having a length of 4469 mm, a width of 86.8 mm, and a thickness of 15 μm was used. One end of the positive electrode current collector 32 is left in the width direction (positive electrode protruding portion 32A), and the positive electrode active material composition is 70.9 mm wide on both sides in the other region (corresponding to the axial length of the wound core portion). And dried with a hot air dryer. The coating amount of the positive electrode active material composition was adjusted so as to be about 11.9 mg / cm ² (solid content basis) for both surfaces. After drying, the positive electrode active material layer was pressed so that the density was about 2.5. The coating, drying, and pressing were performed so that the thickness of the active material layer was substantially constant (uniform) at any position in the width direction of the positive electrode active material layer. When the porosity of the positive electrode active material layer after pressing was calculated from the basis weight and thickness, it was about 49.6%.

Further, natural graphite (powder), styrene butadiene rubber (SBR), and CMC are mixed with ion-exchanged water so that the mass ratio of these materials is 98: 1: 1 and the solid content concentration is 45 mass%. Thus, an aqueous active material composition (negative electrode active material composition) was prepared. As the negative electrode current collector 34, a long copper foil having a length of 4652 mm, a width of 91.5 mm, and a thickness of 10 μm was used. One end of the negative electrode current collector 34 is left in the width direction (negative electrode protruding portion 34A), and the negative electrode active material composition is applied to both sides of the negative electrode current collector 34 in a strip shape having a width of 76.2 cm. Dried. The coating amount of the negative electrode active material composition was adjusted so as to be about 8 mg / cm ² (solid content basis) on both sides. In a state where the negative electrode active material composition was dried (uncompressed state), the density of the negative electrode active material layer was about 1.2 g / cm ³ . This was pressed so that the density of the negative electrode active material layer was about 1.3 g / cm ^3, and the coating, drying, and pressing were performed at any position in the width direction of the negative electrode active material layer. Was made substantially constant (uniform). When the porosity of the negative electrode active material layer after pressing was calculated from the basis weight and thickness, it was about 40%.

  As the separator sheet, two porous polyethylene sheets having a length of 4929 mm, a width of 82.5 mm, and a thickness of 20 μm (porosity of about 42%) were used. These separator sheets and the positive electrode sheet 32 and the negative electrode sheet 34 obtained above are stacked so that the protruding portions 32A and 34A protrude from both sides in the width direction and wound in the longitudinal direction (the number of winding times: About 33 times), the wound body was crushed from the side to obtain a flat wound electrode body 30. The axial length of the wound core portion 31 of the electrode body 30 was 9 cm as described above, and the height of the wound core portion 31 was 10 cm.

  At one end of the electrode body 30 in the flat direction, at one end in the winding axis direction of the electrode body 12, the positive electrode sheet 32 constituting the positive electrode protruding portion 32A is gathered in the radial direction and the positive electrode terminal 14 made of aluminum is welded. At the other end of the electrode body 30 in the winding axis direction, the negative electrode sheet 34 constituting the negative electrode protruding portion 34A was gathered in the radial direction and the copper negative electrode terminal 16 was welded.

As the container 11, a container having a flat box shape with a height of 9.2 cm, a width of 11 cm, and a thickness of 1.35 cm was used. The container 11 includes a bottomed square cylindrical casing 12 and a lid 13 attached to the opening to close the opening. Both the case 12 and the lid 13 are made of aluminum. As shown in FIG. 2, the wound electrode body 30 is accommodated in the container 11, and the mixed solvent containing EC, DMC, and EMC at a mass ratio of 30.94: 25.15: 31.75 is used as a supporting salt. After injecting an electrolytic solution containing lithium hexafluorophosphate (LiPF ₆ ) at a concentration of about 1 mol / liter, the container 11 is hermetically sealed by welding the joint between the housing 12 and the lid 13. did. In this way, the lithium ion battery 10 according to the comparative example was assembled. Thereafter, an initial charge / discharge treatment (conditioning) was performed by a conventional method to obtain a lithium ion battery according to a comparative example. The theoretical capacity of this lithium ion battery is 5 Ah.

  The lithium ion battery thus obtained was given a severe charge / discharge pattern that repeated high-rate pulse discharge for 10 seconds at 150 A (corresponding to a discharge time rate of 30 C), thereby causing changes in the lithium ion battery. Was analyzed. More specifically, after charging the lithium ion battery according to the comparative example at a rate of 1C to SOC (state of charge) 60% in a room temperature (about 25 ° C.) environment, the following (1) to (4) The charge / discharge pattern was repeated 2500 times continuously.

[Charge / discharge cycle conditions]
(1) Discharge at 150 A for 10 seconds.

  (2) Pause for 5 seconds.

  (3) CC-CV charge at 40 A for 120 seconds (constant voltage charge until constant charge is 120 seconds after constant current charge to 3.72 V at 40 A).

  (4) Pause for 5 seconds.

  After completion of the charge / discharge cycle, the container is quickly cut to take out the wound electrode body, and as shown in FIG. 3, the wound core portion 31 of the electrode body 30 has the same axial length. It was divided into three parts: one end side (negative electrode terminal side) portion 311, a central portion 312, and the other end side (positive electrode terminal side) portion 313. And the positive electrode sheet located in the upper part (U1 shown in FIG. 3), middle part (same M1), and lower part (same L1) in the 20th turn of the wound electrode body 30 in the center of the axial length of the negative electrode terminal side part 311. 32, a negative electrode sheet 34 and a separator sheet 35 were cut out from the sample having a diameter of 1 cm. The same applies to the upper, middle, and lower portions (U2, M2, and L2) at the center of the axial length of the central portion 312 and the upper, middle, and lower portions (U3, M3, and L3) at the center of the axial length of the positive terminal portion 313. A sample was cut out.

Positive electrode sheet pieces (a total of three samples) collected from the upper, middle, and lower parts of the negative electrode terminal side portion 311 were collected, and the electrolyte contained in these samples was extracted with γ-butyrolactone. EC in the extract was quantified by GC-MS (gas chromatograph mass spectrometer) and Li (LiPF ₆ ) was quantified by ¹⁹ F-NMR analysis. From the results, the total amount of electrolyte contained in the three samples was determined. The amount [mg] and the Li concentration [mol / liter] of the electrolyte were calculated. In the same manner, the amount of the electrolyte solution (sample) was also obtained for the negative electrode sheet piece and the separator sheet piece collected from the negative electrode terminal side portion 311 and the positive electrode sheet piece, the negative electrode sheet piece and the separator sheet piece collected from the central portion 312 and the positive electrode terminal side portion 313. The total amount of 3 sheets) and the Li concentration were determined. The results are shown in Tables 1 and 2.

  As can be seen from these results, for any of the positive electrode sheet 32, the negative electrode sheet 34, and the separator sheet 35, the Li concentration of the sample collected from the central portion 312 is any of the negative electrode terminal side portion 311 and the positive electrode terminal side portion 313. Was significantly lower. This is because the concentration of Li concentration observed in the above comparative example is adopted by adopting a configuration in which more lithium salt (electrolytic solution) can be stocked at the center of the electrode body (winding core portion) than at both ends. It is suggested that can be effectively mitigated or eliminated.

  Further, when comparing the Li concentration between the negative electrode terminal side portion 311 and the positive electrode terminal side portion 313, the positive electrode terminal side portion 313 is clearly lower for the positive electrode sheet 32 and the negative electrode sheet 34, and the positive electrode terminal side portion also for the separator sheet 35. 313 was slightly lower, and therefore, the positive electrode terminal side portion 313 showed a larger decrease in the Li concentration than the negative electrode terminal side portion 311 as a whole of the wound core portion 31. This is because the retained amount of the electrolytic solution increases in the order of the negative electrode terminal side portion 311, the positive electrode terminal side portion 313, and the central portion 312, thereby making it possible to more effectively alleviate or eliminate the uneven Li concentration. It suggests.

  8 to 10 schematically show the deviation of the Li concentration with respect to the axial direction of the wound core portion 31 after the high-rate charge / discharge cycle in order to facilitate understanding of the present invention. FIG. 8 shows an uneven Li concentration in the wound core portion 31, FIG. 9 shows an uneven Li concentration in the electrolytic solution held on the negative electrode sheet 34, and FIG. 10 shows an Li concentration in the electrolytic solution held on the separator sheet 35. It represents the concentration bias. In these drawings, the line representing the Li concentration is not intended to accurately reflect the Li concentration in each part, but shows a general tendency in an easy-to-understand manner.

<Example 2>
The lithium ion battery according to this example has the same configuration as that of the lithium ion battery 10 according to Example 1 except for the negative electrode active material layer 344 and the separator 35. FIG. 5 is a schematic cross-sectional view showing an enlarged part of a cross section along the winding axis of the wound electrode body 30 according to the present embodiment, which is formed on the negative electrode current collector 342 and one side thereof. The negative electrode active material layer 344 and the separator sheet 35 facing the active material layer 344 are shown. In the present embodiment, the porosity (also referred to as porosity or porosity) of the separator sheet 35 is different between the central portion 312 and the both end portions 311 and 313. That is, the separator sheet 35 is configured such that the void ratio is higher in the central portion 312 than in the both end portions 311 and 313. The porosity of the positive electrode terminal side 313 and the negative electrode terminal side 311 of the separator sheet 35 is substantially the same.

  According to the wound core portion 31 of the electrode body 30 constructed using the separator sheet 35 having such a configuration, more electrolytic solution (lithium salt) than any of both end portions 311 and 313 per unit area of the central portion 312. Can be stocked. Therefore, similarly to Example 1, it is possible to suppress the deviation of the Li concentration and the amount of the electrolyte even with respect to the high rate charge / discharge cycle performed under severe conditions. Therefore, according to the lithium ion battery 10 which concerns on a present Example, the outstanding durability with respect to high-rate charge / discharge can be implement | achieved.

  The method for manufacturing the separator sheet 35 in which the porosity of the central portion 312 is higher than that of both end portions 311 and 313 is not particularly limited. For example, a method for producing a porous polyolefin resin sheet is known in which a polyolefin resin sheet (film) having no holes is first formed, and the holes are formed by pulling the resin sheet while being heated. In the above, by making the heating temperature different between the central portion and both end portions (heating the central portion to a higher temperature), the porosity of the central portion can be made higher than that of the both end portions. Alternatively, the amount of tension at the center may be greater than at both ends.

  From the result of the comparative example, for example, assuming that the porosity (for example, 42%) on the negative electrode terminal side 311 of the separator sheet 35 is 1, the porosity of the central portion 312 is about 1.1 to 2 (for example, about 1.6). A configuration in which the porosity of the negative electrode terminal side 311 is about 67% when the porosity is 42% can be preferably employed. Further, assuming that the porosity (for example, 42%) on the negative electrode terminal side 311 of the separator sheet 35 is 1, the porosity on the positive electrode terminal side 313 is approximately 1 to 1.5 (however, the porosity is equal to or equal to the porosity of the central portion 312) It is preferable to employ a configuration that is smaller than the rate, for example, approximately 1, that is, about the same as the porosity of the negative electrode terminal side 311).

  As shown in the results of the comparative example (Table 1), the deviation of Li concentration due to the high-rate charge / discharge cycle is particularly remarkable in the negative electrode sheet 32. Therefore, according to an embodiment in which the porosity (electrolytic solution holding amount) of the negative electrode active material layer 344 is higher at the central portion 312 than at both end portions 311 and 313 as in the first embodiment, the above Li concentration deviation is more effective. (E.g., more quickly) can be eliminated or mitigated.

  On the other hand, the preferable range that can be adopted as the porosity of the negative electrode active material layer 344 is easily restricted due to consideration of the strength of the active material layer 344 and the efficiency of the battery reaction. Compared with the layer 344, it can be adjusted in a wider range. Therefore, according to the embodiment in which the porosity (electrolyte holding amount) of the separator sheet 35 is higher at the central portion 312 than at both end portions 311 and 313 as in the present embodiment, the degree to which the porosity is different at these portions. The advantage of being able to select from a wider range is obtained.

  The lithium ion battery disclosed herein may have a configuration in which Example 1 and Example 2 are combined. For example, as the separator sheet 35 in the first embodiment, the separator sheet 35 having a higher porosity in the central portion 312 than the both end portions 311 and 313 as in the second embodiment can be used. According to such a configuration, since both the negative electrode sheet 34 and the separator sheet 35 are configured to be able to hold more electrolyte solution than the both end portions 311 and 313 in the central portion 312, the electrolyte solution holding amount of these portions Can be adjusted more easily.

<Example 3>
The structure of the main part of the lithium ion battery according to this example is shown in FIG. FIG. 6 is a schematic cross-sectional view showing an enlarged part of a cross section along the winding axis of the wound electrode body 30 according to the present embodiment, and is opposed to the separator sheet 35 and one surface thereof. The negative electrode active material layer 344 and the negative electrode current collector 342 that holds the negative electrode active material layer 344, the positive electrode active material layer 324 that faces the other surface of the separator sheet 35, and the positive electrode current collector 322 that holds the positive electrode active material layer 322 are illustrated. Other configurations are the same as those of the lithium ion battery 10 according to the first embodiment.

  The separator sheet 35 (for example, a porous polyolefin sheet having a porosity of 45%) is configured such that the thickness gradually increases from both end portions 311 and 313 toward the central portion 312. On the other hand, contrary to the thickness tendency of the separator sheet 35, the negative electrode active material layer 344 (for example, the porosity is 40%) and the positive electrode active material layer 324 (for example, the porosity is 40%) , 313, the thickness gradually increases (that is, the cross-sectional shape is complementary to the cross-sectional shape of the separator sheet 35). The porosity (density) of each of the separator sheet 35, the negative electrode active material layer 344, and the positive electrode active material layer 324 is approximately the same at the central portion 312 and both end portions 311, 313.

  According to such a configuration, by thinning the low porosity active material layers 324 and 344 in the central portion 312 while thickening the high porosity separator sheet, by reversing this relationship at both end portions 311 and 313, It is possible to easily realize the wound electrode body 30 configured such that the electrolytic solution holding amount of the central portion 312 is larger than both end portions 311 and 313. In addition, since the thickness of the active material layers 324 and 344 is smaller in the central portion 312, than the both end portions 311 and 313, the pumping action associated with the entry and exit of lithium ions in the central portion 312 can be reduced. Therefore, according to the configuration of the present embodiment, combined with the above-described configuration, it is possible to effectively alleviate or eliminate the unevenness of the electrolyte holding amount due to the high rate charge / discharge cycle or the like.

  From the result of the comparative example, for example, assuming that the thickness (for example, 20 μm) at the width center of the negative electrode terminal side 311 of the separator sheet 35 is 1, the thickness at the width center of the central portion 312 is about 1.1 to 2 (for example, about 1). A configuration such that the thickness of the negative electrode terminal side 311 is about 32 μm is preferable. Further, assuming that the thickness (for example, 20 μm) at the width center of the negative electrode terminal side 311 of the separator sheet 35 is 1, the thickness at the width center of the positive electrode terminal side 313 is approximately 1 to 1.5 (however, equivalent to the thickness of the center portion 312 or It is preferable to employ a configuration that is smaller than the thickness (for example, approximately 1, that is, approximately equal to the thickness of the negative electrode terminal 311).

  At least one of the separator sheet 35, the negative electrode active material layer 344, and the positive electrode active material layer 324 (for example, the separator sheet 35 and the negative electrode active material layer 344) has a higher porosity in the central portion 312 than the both end portions 311 and 313. You may be comprised so that it may become. This makes it possible to more easily adjust the amount of electrolyte retained in each part. For example, the separator sheet 35 configured such that the thickness of the central portion 312 is larger than both end portions 311 and 313 and the porosity of the central portion 312 is higher than both end portions 311 and 313 can be preferably used. The method for manufacturing the separator sheet 35 having such a configuration is not particularly limited. For example, a polyolefin-based resin sheet (film) having no holes is first formed, and the holes are formed by pulling the resin sheet while being heated, so that the thickness and porosity of each part in the width direction are substantially constant. A polyolefin resin sheet is obtained. Then, by compressing both end portions 311 and 313 in the width direction of the resin sheet, the thickness and void ratio of the both end portions 311 and 313 can be made smaller than the central portion 312.

  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 lithium ion battery which concerns on one Example. It is the II-II sectional view taken on the line of FIG. It is a top view which shows typically the electrode body of the lithium ion battery which concerns on one Example. It is an expanded sectional view which shows the principal part of the lithium ion battery which concerns on one Example. It is an expanded sectional view which shows the principal part of the lithium ion battery which concerns on one Example. It is an expanded sectional view which shows the principal part of the lithium ion battery which concerns on one Example. It is a side view which shows typically the vehicle (automobile) provided with the lithium ion battery of this invention. It is typical explanatory drawing which shows the bias | inclination tendency of Li concentration in the conventional lithium ion battery about the whole winding core part. It is typical explanatory drawing which shows the bias | inclination tendency of Li density | concentration in the conventional lithium ion battery about a negative electrode sheet. It is typical explanatory drawing which shows the bias | inclination tendency of Li density | concentration in the conventional lithium ion battery about a separator sheet.

Explanation of symbols

1: Vehicle (car)
DESCRIPTION OF SYMBOLS 11: Container 12: Housing | casing 13: Lid body 14: Positive electrode terminal 16: Negative electrode terminal 30: Winding electrode body 31: Winding core part 311: Negative electrode terminal side (negative electrode terminal side part, other end side, both ends)
312: Central part (central part)
313: Positive terminal side (positive terminal side, one end, both ends)
32: Positive electrode sheet 322: Positive electrode current collector 324: Positive electrode active material layer 34: Negative electrode sheet 342: Negative electrode current collector 344: Negative electrode active material layer 35: Separator sheet (separator)

Claims (9)

A lithium ion battery in which an electrode body and an electrolytic solution are housed in a container,
The electrode body is a wound electrode body in which a positive and negative electrode sheet having an active material layer on a long sheet-shaped current collector is wound in a longitudinal direction via a long sheet-shaped separator. A positive electrode terminal is connected to one end in the rotational axis direction, and a negative electrode terminal is connected to the other end,
The electrode body has an electrolyte solution holding amount per unit volume of a wound core portion wound by overlapping the active material layer of the positive and negative electrode sheets and the separator in the electrode body in the winding axis direction. The lithium ion battery is configured to be larger in the central portion than the one end side and the other end side.   At least one of the positive and negative electrode sheets is configured such that the porosity of the active material layer of the electrode sheet is higher than at least one of the one end side and the other end side in the central portion. Item 6. The battery according to Item 1.   3. The battery according to claim 1, wherein the separator is configured to have a void ratio higher than at least one of the one end side and the other end side in the central portion. The separator has a thickness larger than at least one of the one end side and the other end side in the central portion,
The active material layer facing the separator has a thickness smaller than at least one of the one end side and the other end side in the central portion contrary to the thickness tendency of the separator, and
The battery according to any one of claims 1 to 3, wherein a porosity of the separator is larger than a porosity of the active material layer at least in the central portion.   The said electrode body is comprised so that the electrolyte solution holding | maintenance amount per unit volume of the said winding core part may be larger in the said one end side than the said other end side. Battery.   The said electrode body is comprised so that the electrolyte solution holding amount per unit volume of the said other end side may be 1, and the electrolyte solution holding amount of the said center part will be 1.1-2. The battery according to any one of the above.   The said electrode body is comprised so that the electrolyte solution holding | maintenance amount per unit volume of the said other end side may be set to 1, and the electrolyte solution holding | maintenance amount of the said one end side will be 1-1.5. The battery according to any one of the above.   The battery according to claim 1, which is used as a power source for a vehicle.   A vehicle comprising the battery according to any one of claims 1 to 8.

Images