JP2017139109A - Battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery system capable of predicting the state of a coating formed on a negative electrode with good accuracy.SOLUTION: A battery system 1 provided according to the present invention comprises: a secondary battery 20 including a positive electrode 30, a negative electrode 40 and a nonaqueous electrolyte; and a sensor 10 disposed between the positive electrode 30 and the negative electrode 40, which acquires a physical value showing the influence that a coating has on the degradation of the secondary battery 20 when the coating is formed on the negative electrode 40. The sensor 10 preferably includes e.g. a counter electrode 12 made of the same material as that of the positive electrode 30, an action electrode 14 made of the same material as that of the negative electrode 40, and a separator 16 interposed between the counter electrode 12 and the action electrode 14.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a battery system that predicts the state of a film formed on an electrode of a secondary battery.

  Non-aqueous electrolyte secondary batteries represented by lithium secondary batteries are lighter and have higher energy density than existing batteries. Therefore, so-called portable power sources such as personal computers and portable terminals, power sources for vehicle driving, and residential use It is used as a power storage device. In recent years, non-aqueous electrolyte secondary batteries have a high output for driving vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV) that charge and discharge at a high capacity and high rate. It is particularly preferably used as a power source.

  In this type of non-aqueous electrolyte secondary battery, a positive electrode including a positive electrode active material layer and a negative electrode including a negative electrode active material layer are disposed to face each other via a separator, and are accommodated in a battery case together with a non-aqueous electrolyte containing an electrolyte. Has been. In general, the non-aqueous electrolyte is impregnated in the positive electrode active material layer, the negative electrode active material layer, and the separator. And charging / discharging can be implement | achieved by making electrolyte ion come and go between positive / negative active material layers, and positive / negative active material occlude and discharge | release electrolyte ions.

Japanese Patent Laying-Open No. 2015-219980

  In this type of secondary battery, it is known that, for example, the battery capacity decreases with the use (deterioration) of the secondary battery. Therefore, by predicting the deterioration of the secondary battery, charging / discharging is controlled under conditions where the deterioration is difficult to occur to measure the extension of the battery life or to ensure the safety of the battery. For example, Patent Document 1 discloses a prediction function derived from the relationship between the growth of a film formed on the electrode surface of a secondary battery and the decrease in the film precursor component in the electrolyte, and the usage state of the secondary battery. Thus, a secondary battery monitoring device that predicts a change in battery capacity with time is disclosed.

The prediction function of Patent Document 1 employs a specific capacity deterioration model, and is based on the assumption that the coating that is a deterioration factor grows in proportion to the square root of the battery usage time. Here, the film actually formed on the electrode differs in the form of the film depending on the usage form of the battery, and may affect the deterioration state of the battery. For example, the state of the formed film or the like may differ between when charging / discharging at a high rate and when charging / discharging at a low rate. However, in the method of Patent Document 1, since capacity deterioration is predicted based only on the coating amount, there is a possibility that the deterioration prediction value and the actual battery deterioration state may deviate.
The present invention has been created to solve the above-described conventional problems, and a purpose thereof is a battery capable of accurately predicting a state (for example, electrochemical characteristics) of a film formed on a negative electrode. Is to provide a system.

  The invention disclosed herein is a secondary battery including a positive electrode, a negative electrode, and an electrolyte, and is disposed between the positive electrode and the negative electrode, and the coating is formed on the secondary battery when the coating is formed on the negative electrode. A battery system comprising: a sensor that acquires a physical property value indicating an influence on deterioration of the battery.

  According to the above configuration, the sensor is disposed in the secondary battery, and the physical property value indicating the influence of the film formed on the negative electrode by the sensor on the deterioration of the secondary battery (for example, ionic conductivity of the electrolyte, film resistance, etc.) ) Can be obtained. Thereby, for example, it is possible to predict a coating state that accurately reflects the actual battery usage history. This can be useful, for example, to more accurately reflect actual battery usage history to predict battery degradation.

  In a preferred aspect of the battery system disclosed herein, the physical property value is preferably the ionic conductivity of the electrolyte in the coating. The sensor is preferably composed of a counter electrode made of the same material as the positive electrode, a working electrode made of the same material as the negative electrode, and a separator interposed between the counter electrode and the working electrode. The negative electrode is preferably a carbon-based material, and the working electrode is preferably highly oriented pyrolytic graphite. In the sensor, the area of the counter electrode or the working electrode is preferably 1/100 or less of the area of the positive electrode or the negative electrode. For example, the sensor preferably has a dimension of at least one of the electrodes smaller than 10 mm × 10 mm. Moreover, it is preferable that the said sensor is arrange | positioned in the site | part which becomes the highest temperature in the use condition of the said secondary battery.

It is sectional drawing which shows typically the structure of the battery system which concerns on one Embodiment. It is a schematic diagram explaining the structure of the sensor which concerns on one Embodiment. It is a flowchart which shows the manufacturing method of the battery system which concerns on one Embodiment. It is a graph which shows the resistance increase rate of the sensor film which concerns on one Embodiment, and the limiting current rate which suppresses Li precipitation.

  Hereinafter, a battery system according to the present invention will be described based on preferred embodiments with appropriate reference to the drawings. Note that matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention (for example, a secondary battery structure that does not characterize the present invention) are based on prior art in this field. It can be grasped as a design matter of a person skilled in the art. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. In addition, dimensional relationships (length, width, thickness, etc.) in the drawings shown below do not necessarily reflect actual dimensional relationships. Furthermore, the expression “T to Y” indicating a range means “T or more and Y or less”.

  In this specification, “non-aqueous electrolyte secondary battery” refers to the use of electrolyte ions (lithium ions in the case of lithium ion batteries) as charge carriers, and repetitive charge / discharge is realized as the charge carriers move between the positive and negative electrodes. Secondary battery. A secondary battery generally referred to as a lithium ion battery, a lithium polymer battery, or the like is a typical example included in the nonaqueous electrolyte secondary battery in this specification. In this specification, the “active material” refers to a material that can reversibly occlude and release chemical species (for example, lithium ions) serving as charge carriers. Therefore, the case where the nonaqueous electrolyte secondary battery disclosed herein is a lithium ion battery will be described in detail below.

[Battery system]
FIG. 1 is a schematic cross-sectional view showing a configuration of a battery system 1 as a preferred embodiment. The battery system 1 includes a secondary battery 20 and a sensor 10. FIG. 2 is a conceptual diagram illustrating the configuration and arrangement of the sensor 10. FIG. 3 is a flowchart showing a method for manufacturing the battery system 1. Hereinafter, each part of the battery system 1 will be described in detail together with the manufacturing method of the battery system 1.

[Secondary battery]
The secondary battery 20 essentially includes a positive electrode 30, a negative electrode 40, and an electrolyte (not shown). Typically, a separator 50 that insulates between the positive electrode 30 and the negative electrode 40 may be interposed. And these positive electrode 30, the negative electrode 40, and the separator 50 are accommodated in the battery case 60 with electrolyte. As will be described later, the electrolyte is typically dissolved or dispersed in a non-aqueous solvent to constitute a non-aqueous electrolyte. The non-aqueous electrolyte is impregnated in the positive electrode 30, the negative electrode 40, and the separator 50. The electrolyte typically travels between the positive electrode 30 and the negative electrode 40 in a non-aqueous solvent in the form of electrolyte ions. Thereby, charging / discharging of the secondary battery 20 is implement | achieved.

[Positive electrode]
The positive electrode 30 typically includes a long (which may be strip-shaped) positive electrode current collector 32 and a positive electrode active material layer 34 held on the surface of the positive electrode current collector 32. The positive electrode current collector 32 is typically provided with a current collector exposed portion 36 in a strip shape along one end portion along the longitudinal direction, and a strip shape is formed in a portion other than the current collector exposed portion 36. Is provided with a positive electrode active material layer 34. The positive electrode active material layer 34 may be provided on both surfaces of the positive electrode current collector 32 or may be provided only on one of the surfaces. As the positive electrode current collector 32, a conductive material made of a metal having good conductivity (for example, aluminum, nickel, etc.) is suitable. This positive electrode active material layer 34 includes at least a positive electrode active material, and has a porous structure so that it can be impregnated with a nonaqueous electrolytic solution.

Although it does not restrict | limit especially as a positive electrode active material, It is a material which can occlude and discharge | release lithium ion which is electrolyte ion, Comprising: For example, the lithium containing compound (For example, lithium transition) containing a lithium element and 1 type, or 2 or more types of transition metal elements Metal composite oxide) can be preferably used. This lithium transition metal oxide is, for example, in the form of powder, lithium nickel composite oxide (for example, LiNiO ₂ ), lithium cobalt composite oxide (for example, LiCoO ₂ ), lithium manganese composite oxide (for example, LiMn ₂ O ₄ ), or And a ternary lithium-containing composite oxide such as lithium nickel cobalt manganese composite oxide (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ). In order to realize desired battery performance, various metal elements may be added to these active materials.

  In the positive electrode active material layer 34, in addition to the positive electrode active material, a conductive material that imparts conductivity to the positive electrode active material layer 34 and the constituent materials of these positive electrode active material layers are mutually connected to the current collector 32. A binder to be bonded and an optional additive which can be used as necessary as a constituent component of the positive electrode active material layer in a general lithium ion battery. Examples of the conductive material include various carbon blacks (for example, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, etc.), activated carbon, graphite, carbon having a primary particle diameter of about 3 to 500 nm. Carbon materials such as fibers can be suitably used. As the binder, for example, a halogenated vinyl resin such as polyvinylidene fluoride (PVdF), or a polyalkylene oxide such as polyethylene oxide (PEO) can be preferably used.

  The proportion of the positive electrode active material in the entire positive electrode active material layer 34 is suitably about 60% by mass or more from the viewpoint of realizing a high energy density, and is usually preferably about 70% by mass or more. 85 mass% or more is especially preferable. The proportion of the positive electrode active material can be determined in consideration of the necessary conductive material and the amount of binder, and can be, for example, 95% by mass or less. When using a conductive material, from the viewpoint of achieving both high output characteristics and energy density, the proportion of the conductive material in the entire positive electrode active material layer can be, for example, about 1% by mass or more, usually about It is preferable to set it as 2 mass% or more, for example, 4 mass% or more. An excessive conductive material is not preferable because it reduces the amount of the active material, and the conductive material can be, for example, 20% by mass or less, and is usually about 15% by mass or less, for example, 10% by mass or less. . When using a binder, the proportion of the binder in the entire positive electrode active material layer is, for example, about 0.5% by mass or more, and usually about 1% by mass or more from the viewpoint of suitably maintaining mechanical strength and shape. For example, it is preferably 10% by mass or less, and usually 5% by mass or less.

Further, the average thickness (per one surface) of the positive electrode active material layer 34 is not particularly limited, but may be, for example, 20 μm or more, typically 50 μm or more, and 200 μm or less, typically 100 μm or less. The mass (weight per unit area) of the positive electrode active material layer 34 provided per unit area of the positive electrode current collector 32 is 3 mg / cm ² or more (for example, 5 mg) per side of the positive electrode current collector 32 from the viewpoint of realizing a high energy density. / Cm ² or more, typically 7 mg / cm ² or more). From the viewpoint of realizing excellent output characteristics, the positive electrode current collector 32 may be 100 mg / cm ² or less per side (for example, 70 mg / cm ² or less, typically 50 mg / cm ² or less). Further, the density of the positive electrode active material layer 34 is, for example, 1.0 g / cm ³ or more (typically 2.0 g / cm ³ or more) and 4.5 g / cm ³ or less (for example, 4.0 g / cm ³ ). ³ or less).

[Negative electrode]
The long negative electrode 40 is typically provided with a current collector exposed portion 46 at one end along the longitudinal direction of the long negative electrode current collector 42, and a portion other than the current collector exposed portion 46. Is provided with a negative electrode active material layer 44. The negative electrode current collector exposed portion 46 is typically provided long along one end portion in the width direction of the negative electrode current collector 42. The negative electrode active material layer 44 may be provided on both surfaces of the negative electrode current collector 42 or may be provided only on one of the surfaces. The negative electrode current collector 42 is preferably composed of a conductive material made of a metal having good conductivity (for example, copper, nickel, etc.). The negative electrode active material layer 44 includes at least a negative electrode active material, and has a porous structure so that it can be impregnated with a nonaqueous electrolytic solution.

  In addition, although it does not restrict | limit especially here as a negative electrode active material, 1 type (s) or 2 or more types can be employ | adopted as the various materials known to be usable as a negative electrode active material of a lithium ion battery. Preferred examples include graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), carbon-based materials such as carbon nanotubes, oxide materials such as lithium titanate (LTO), and SixC. Examples thereof include Si-based alloy materials or materials obtained by combining these materials. Among these, from the viewpoint of energy density, graphite-based materials such as natural graphite (graphite) and artificial graphite can be preferably used. These negative electrode active materials may be in the form of a powder, for example, in the form of a film. As such a graphite-based material, a material in which amorphous carbon is disposed on at least a part of the surface can be preferably used. More preferably, almost all of the surface of the granular carbon is covered with an amorphous carbon film.

  In addition to the negative electrode active material, the negative electrode active material layer 44 may include one or more materials that can be used as a constituent component of the negative electrode active material layer 44 in a general lithium ion battery as necessary. May be contained. Examples of such materials include binders and various additives. As the binder, the same binder as that used for the negative electrode of a general lithium ion battery can be appropriately employed. For example, the same binder as in the positive electrode 30 can be used. As a preferred form, when the above aqueous solvent is used to form the negative electrode active material layer 44, water such as rubber such as styrene butadiene rubber (SBR), polyethylene oxide (PEO), vinyl acetate copolymer, etc. A water-soluble polymer material or a water-dispersible polymer material can be preferably used. In addition, various additives such as a conductive material, a thickener, and a dispersant can be used as appropriate. In the configuration using the conductive material, the same conductive material as that in the positive electrode 30 can be used. Examples of the thickener include cellulose polymers such as carboxymethyl cellulose (CMC), methyl cellulose (MC), and cellulose acetate phthalate (CAP).

  The proportion of the negative electrode active material in the entire negative electrode active material layer 44 is suitably about 50% by mass or more, usually 90% by mass or more, preferably 95% by mass or more, and the upper limit is, for example, 99% It can be made into the mass% or less. Thereby, a high energy density is realizable. When using a binder, the ratio of the binder to the whole negative electrode active material layer 44 can be, for example, about 0.5% by mass or more, and preferably about 0.5% by mass or more. The upper limit of the binder can be 10% by mass or less, and is usually preferably about 0.5% by mass or less. When using a conductive material, the ratio of the conductive material in the entire negative electrode active material layer can be set to, for example, about 0.5% by mass or more from the viewpoint of achieving both high output characteristics and energy density. Usually, it is preferably about 1% by mass or more, for example, 2% by mass or more. For example, the upper limit of the conductive material is preferably 99% by mass or less. The conductive material is often used when the conductivity of the negative electrode active material is not so good. Therefore, this conductive material may be included as a part of the ratio of the negative electrode active material (in place of the negative electrode active material), for example. Thereby, the mechanical strength (shape retention) of the negative electrode active material layer 44 can be suitably ensured, and good durability can be realized. When using a thickener, the ratio of the thickener to the whole negative electrode active material layer 44 can be made into about 1 mass%-10 mass%, for example, and can be about 1 mass%-5 mass% normally. It is preferable.

The mass (weight per unit area) of the negative electrode active material layer 44 provided per unit area of the negative electrode current collector 42 is 5 mg / cm ² per side of the negative electrode current collector 42 from the viewpoint of realizing high energy density and output density. It is good if it is above (typically 7 mg / cm ² or more) and about 20 mg / cm ² or less (typically 15 mg / cm ² or less). Further, the thickness per one side of the negative electrode active material layer 44 is, for example, 40 μm or more (typically 50 μm or more) and 100 μm or less (typically 80 μm or less). The density of the negative electrode active material layer 44 is, for example, 0.5 g / cm ³ or more (typically 1.0 g / cm ³ or more) and 2.0 g / cm ³ or less (typically 1.g / cm ³ or more). 5 g / cm ³ or less).

[Separator]
The separator 50 is a structural member that insulates the positive electrode 30 and the negative electrode 40, holds a non-aqueous electrolyte, and allows the non-aqueous electrolyte and charge carriers contained therein to pass therethrough. Such a separator 50 can be suitably constituted by a microporous resin sheet or a nonwoven fabric made of various materials. The separator 50 may be configured to have a shutdown function that softens and melts when the battery 20 reaches a predetermined temperature and blocks the passage of charge carriers. For example, a microporous sheet made of a polyolefin resin typified by polyethylene (PE) or polypropylene (PP) has a shutdown temperature of 80 ° C. to 140 ° C. (typically 110 ° C. to 140 ° C., for example, 120 ° C. to 135 ° C. ), The separator 50 is preferable.

The separator 50 is a heat resistant layer (HRL, not shown) composed of heat-resistant and insulating heat-resistant particles on one or both sides of the microporous resin sheet or the like as a base material. Can be provided. It is not particularly restricted but includes heat-resistant particles, for example, as the heat-resistant particles, for example, alumina _{(Al 2 O} 3), alumina hydrate (e.g. boehmite _{(Al 2 O 3 · H 2} O)), zirconia (ZrO ₂ ), ceria (CeO ₂ ), yttria (Y ₂ O ₃ ), mullite (Al ₆ O ₁₃ Si ₂ ), magnesia (MgO), silica (SiO ₂ ), titania (TiO ₂ ), magnesium hydroxide (Mg ( Fine powder having an average particle diameter of about 0.1 μm or more and 3 μm made of an inorganic metal compound such as OH) ₂ ) and magnesium carbonate (MgCO ₃ ) can be suitably used. These inorganic compounds may contain 1 type independently, and may contain 2 or more types in combination. Thereby, for example, even if the temperature of the flat wound electrode body is higher than the melting point of the separator 50 and the separator 50 contracts or breaks, it is possible to prevent the positive electrode 30 and the negative electrode 40 from being short-circuited. .

[Electrode body]
In the construction of the battery system 1, as shown in S1 of FIG. 3, first, the electrode body of the secondary battery 20 is constructed by making the positive electrode 30 and the negative electrode 40 prepared above face each other with a separator 50 therebetween. To do. At this time, as shown in FIG. 2, the sensor 10 is disposed in advance between the positive electrode 30 and the negative electrode 40. For example, it is preferable to configure a wound electrode body as shown in FIG. 1 for the secondary battery 20 used for charging and discharging a large capacity at a high rate. That is, a long positive electrode 30, a long negative electrode 40, and two long separators 50 are stacked from the bottom in the order of the separator 50, the negative electrode 40, the separator 50, and the positive electrode 30, and the width orthogonal to the longitudinal direction. Wind around the axis with the direction as the winding axis. At this time, for example, when the cross-sectional shape orthogonal to the winding axis is formed into an oval shape, a flat wound electrode body corresponding to the flat rectangular battery case 60 as illustrated in FIG. Can be built. Such a wound electrode body having an oval cross section may be formed by crushing and winding a wound electrode body wound in a cylindrical shape in one direction perpendicular to the winding axis. Alternatively, a flat wound electrode body may be formed by winding in a flat shape around a plate-shaped winding axis. The detailed shape of the flat wound electrode body can be appropriately shaped according to the shape of the battery case 60 to be used. The oval means a shape in which the short side portion of the rectangle is replaced with a semicircle having the short side as a diameter, and can include shapes that can be expressed as a track type, an oval type, a saddle type, or the like. .

  When the positive electrode 30, the negative electrode 40, and the separator 50 are stacked, the positive electrode current collector exposed portion 36 of the positive electrode 30 and the negative electrode current collector exposed portion 46 of the negative electrode 40 are seen from both sides in the width direction of the separator 50. The positive electrode 30 and the negative electrode 40 are overlapped with each other in the width direction so as to protrude to different sides. As a result, in the winding axis direction of the flat wound electrode body, the positive electrode current collector exposed portion 36 and the negative electrode current collector exposed portion 46 are respectively formed into the wound core portions (that is, the positive and negative active material layers 34 and 44 are It will protrude outward from the stacked part). As shown in FIG. 1, the positive electrode current collector exposed portion 36 and the negative electrode current collector exposed portion 46 are gathered together in the minor circle direction of the ellipse to form a current collector, thereby providing a highly efficient current collector. Electricity can be done.

  In addition, when predicting deterioration of the secondary battery 20 on the safety side, it is preferable that the sensor 10 is disposed at a portion where deterioration is more likely to proceed in the electrode body. From this point of view, for example, the sensor 10 is preferably arranged at a part that becomes the highest temperature as the secondary battery 20 is used. For example, it is preferable to be disposed near the center of the electrode body. When the electrode body is a wound electrode body, the sensor 10 is positioned so as to be located at the center of the flat surface of the wound electrode body on the start side of the long positive electrode 30 and the negative electrode 40 as shown in FIG. Is preferably arranged. When the electrode body is a flat wound electrode body, the sensor 10 is preferably arranged at the center of the flat surface of the electrode body and in the center in the thickness direction as shown in FIG.

[Sensor]
The sensor 10 can be various sensors that can acquire physical property values indicating the influence of the coating on the deterioration of the secondary battery 20 when a coating (not shown) is formed on the negative electrode 40. . Such physical property values may be, for example, electrochemical properties such as electrical conductivity and ionic conductivity of the coating, coating physical properties such as coating formation and coating thickness, and combinations thereof. Particularly preferred physical property values are the ionic conductivity (here, lithium ionic conductivity) and resistance characteristics of the electrolyte of the secondary battery in the thickness direction of the coating.

  It is known that when the secondary battery 20 is charged and discharged, an SEI film (Solid-Electrolyte Interface) is formed on the surface of the negative electrode 40. For example, when the negative electrode active material of the lithium ion secondary battery 20 is a carbon-based material, non-aqueous electrolysis is performed on the surface of the negative electrode to inactivate and stabilize the surface of the carbon-based material and suppress further decomposition of the electrolytic solution. A liquid-derived film is formed. If this film is formed excessively, for example, the battery capacity may be reduced and the resistance component may be increased, which may cause deterioration of the secondary battery 20. Therefore, if the formation state of the coating can be appropriately predicted, the deterioration of the battery based on the formation of the coating can be predicted with higher accuracy. Therefore, in the technique disclosed herein, the working electrode 14 and the counter electrode 12 corresponding to the negative electrode 40 and the positive electrode 30 are prepared, and the working electrode 14 and the counter electrode 12 are formed in the secondary battery 20. A sensor 10 (that is, a cell) is disposed. The working electrode 14 and the counter electrode 12 are preferably arranged so that the electrode plates are parallel between the positive electrode 30 and the negative electrode 40 of the actual secondary battery 20. The working electrode 14 and the counter electrode 12 can be insulated by the separator 16. Thereby, a sensor film corresponding to the film formed on the actual negative electrode 40 can be formed on the surface of the working electrode 14 of the cell as the secondary battery 20 is charged / discharged (used). The formation state of the sensor film can reflect the property of the film formed on the actual negative electrode 40. Therefore, the state of the film formed on the actual negative electrode 40 can be predicted with high accuracy by grasping the formation state of the sensor film from the physical property values.

  The counter electrode 12 and the working electrode 14 of the sensor 10 are each preferably composed of the same type of material (typically the same composition) as the positive electrode 30 and the negative electrode 40 of the actual secondary battery 20. Thereby, the sensor film formed on the sensor 10 can more accurately reflect the form of the film formed on the negative electrode 40 of the actual secondary battery 20. The counter electrode 12 can be composed of, for example, the positive electrode current collector described above and a positive electrode active material layer provided on one surface of the current collector. Moreover, the working electrode 14 can be comprised from said negative electrode collector and the negative electrode active material layer with which the single side | surface of this collector was equipped, for example. Conductive wires 12a and 14a can be connected to the counter electrode 12 and the working electrode 14, respectively, in order to obtain physical property values between the counter electrode and the working electrode. The conducting wire is not particularly limited, and for example, a silver wire coated with a fluororesin can be used. The separator 16 can be made of the same material as the separator 50 described above, for example. The counter electrode 12 and the working electrode 14 can be produced in the same manner as the positive electrode 30 and the negative electrode 40 described above.

  The dimensions of the counter electrode 12 and the working electrode 14 can be made smaller than the dimensions of the positive electrode 30 and the negative electrode 40 of the actual secondary battery 20 within a range in which handling is easy. The area of the counter electrode 12 and the working electrode 14 can be set to reflect the capacity ratio of the positive electrode 30 and the negative electrode 40 of the actual secondary battery 20, for example. Further, for example, the counter electrode 12 or the working electrode 14 can have an area of 1/100 or less of the actual area of the positive electrode 30 or the negative electrode 40, preferably 1/1000 or less, and preferably 1/10000 or less. Is more preferable. More specifically, the sensor 10 may have, for example, a negative electrode size of 10 mm × 10 mm or less or a size equal to or less than an area corresponding thereto (hereinafter the same), preferably 8 mm × 8 mm or less, More preferably, it is 5 mm × 5 mm or less. The shape of the cell is not limited to this square example, and may be any shape such as a rectangle, a circle, or an indefinite shape.

  When the negative electrode active material is a carbon-based material, the working electrode 14 (the active material layer of the working electrode 14) can also be configured using a carbon-based material. At this time, it is more preferable that the active material layer of the working electrode 14 be configured using particularly highly oriented pyrolytic graphite (HOPG). More specifically, it is particularly preferable that the surface of the working electrode 14 is constituted by a cleaved surface of HOPG. General graphite (for example, natural graphite) has a crystal structure in which basal planes having a carbon six-membered ring structure are stacked, but the orientation of the basal plane is not so high. On the other hand, highly oriented pyrolytic graphite has a crystal structure in which the flatness of the basal plane is enhanced, the crystallite size is large, and the degree of orientation is high. Therefore, the cleavage plane of highly oriented pyrolytic graphite is constituted by a very flat basal plane (that is, a graphene sheet), and the electron conductivity in the basal plane is remarkably enhanced. Note that since the electrode reaction is an electron transfer reaction at the interface between the electrode and the solution (here, a nonaqueous electrolyte solution), the electron behavior can be extremely sensitive to the surface state of the electrode. Therefore, the surface of the working electrode 14 is preferably composed of a HOPG cleaved surface because a highly controlled electrode surface can be realized that is smooth and extremely high in electron conductivity.

  As described above, when the surface of the working electrode 14 is formed of a HOPG cleavage surface, the surface area of the working electrode 14 can be significantly reduced due to its flatness. In comparison, the surface area of the counter electrode 12 becomes sufficiently large. Therefore, when the resistance between the counter electrode 12 and the working electrode 14 is measured when a sensor film is formed on the cell (sensor 10) formed of the counter electrode 12 and the working electrode 14, the counter electrode resistance occupying the entire resistance. Is sufficiently small. That is, when the resistance of the cell composed of the counter electrode 12 and the working electrode 14 is measured, the resistance component due to the counter electrode 12 is sufficiently suppressed, and the resistance component due to the sensor film can be extracted. Therefore, in a system using a lithium salt as an electrolyte, it is possible to extract a component relating to lithium ion conductivity of the sensor coating. Furthermore, by measuring the resistance between the counter electrode and the working electrode over time, it is possible to obtain the rate of change in resistance due to the sensor coating. This can be the rate of change of lithium ion conductivity for the sensor coating. From this, by the technique disclosed here, eventually, the change rate (resistance increase rate) of lithium ion conductivity about the film formed on the surface of the negative electrode of the secondary battery 20 is obtained instead. Can do.

The resistance measurement conditions between the counter electrode and the working electrode are not particularly limited. For example, it is preferable to measure the IV resistance by obtaining a current response when a predetermined voltage is applied between the counter electrode and the working electrode. As an example of the condition of the applied voltage, the following conditions can be given.
Measurement temperature: 25 ° C
Voltage amplitude: ± 150mV
Frequency: 100Hz

As HOPG, graphite with enhanced orientation can be used. This HOPG may be commercially available or may be prepared and prepared based on a known HOPG manufacturing method. HOPG may have a mosaic spread value (MS value) of about 5 ° or less, preferably about 1 ° or less, and more preferably about 0.5 ° or less. For example, after sticking a conductive adhesive tape or the like on the basal surface of the HOPG, it is possible to cleave and peel one to several layers of HOPG along the basal surface. Thereby, 1 layer-several layers of HOPG provided with a cleavage surface can be fixed to the surface of a conductive adhesive tape. This makes it possible to obtain a working electrode 14 having a conductive adhesive tape as a current collector (base material) and HOPG as an active material layer. At this time, the thickness of the HOPG layer on the conductive adhesive tape is not particularly limited, but may be, for example, about 10 to 40 μm (for example, about 30 μm). Further, the thickness of the conductive adhesive tape is not particularly limited, but for example, a thickness of about 50 to 150 μm (for example, about 100 μm) can be suitably used.
The thickness direction dimension of the counter electrode 12 is not particularly limited. For example, the total thickness of the aluminum foil as the positive electrode current collector and the positive electrode active material layer is set to about 20 to 80 μm (for example, about 50 μm). Can do.
Thus, the sensor 10 can have a small size and a simple configuration. Therefore, even when HOPG is used for the working electrode 14, it can be prepared at a low cost of, for example, 100 yen or less.

[Non-aqueous electrolyte]
As the nonaqueous electrolytic solution, typically, a support salt (for example, a lithium salt in a lithium ion battery) dissolved or dispersed in a nonaqueous solvent may be employed.
As the non-aqueous solvent, various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones used as an electrolytic solution in a general lithium ion battery can be used without particular limitation. Specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). In addition, monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyl difluoromethyl carbonate (F-DMC), trifluorodimethyl carbonate (TFDMC), methyl (2,2,2-trifluoroethyl) carbonate A non-aqueous solvent made of a cyclic or chain fluorinated carbonate such as (MTFEC) may be used. Such non-aqueous solvents can be used alone or in combination of two or more.

As the supporting salt, various types used for general lithium ion batteries can be appropriately selected and employed. For example, the use of lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N, LiCF ₃ SO ₃ is exemplified. Such supporting salts may be used singly or in combination of two or more. Such a supporting salt is preferably prepared so that the concentration in the non-aqueous electrolyte is within the range of 0.7 mol / L to 1.3 mol / L.

  This nonaqueous electrolytic solution may contain various additives as long as the characteristics of the secondary battery 20 are not impaired. As such an additive, as a film forming agent, an overcharge additive, etc., one or more of the battery input / output characteristics improvement, cycle characteristic improvement, initial charge / discharge efficiency improvement, safety improvement, etc. Can be used for purposes. Specific examples of such additives include film forming agents such as lithium bis (oxalato) borate (LiBOB), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and fluoroethylene carbonate (FEC); biphenyl (BP) And an overcharge additive comprising a compound capable of generating gas during overcharge, such as cyclohexylbenzene (CHB), an aromatic compound; a surfactant; a dispersant; a thickener; and an antifreeze agent. The concentration of these additives with respect to the entire non-aqueous electrolyte varies depending on the type of additive, but is usually about 0.1 mol / L or less (typically 0.005 mol / L to 0.05 mol) for the film forming agent. / L), it is typically about 6 mass% or less (typically 0.5 mass% to 4 mass%) with an overcharge additive.

  As shown in S <b> 2 of FIG. 3, the battery system 1 is assembled by housing the electrode body on which the sensor 10 is disposed in the battery case 60 together with the nonaqueous electrolytic solution. The positive electrode 30 and the negative electrode 40 may constitute a wound electrode body as described above. In the example of FIG. 1, the battery case 60 includes a rectangular case body having an opening for inserting a flat wound electrode body, and a sealing body that seals the opening of the case body. It is out. For example, various materials such as a metal made of aluminum and its alloy, iron and its alloy, a resin such as polyamide, and a laminate film can be suitably used. The case body (exterior case) is a thin square shape made of aluminum alloy and has a flat box shape (typically a rectangular parallelepiped shape) with a bottom having an open upper surface. The sealing body is provided with a positive electrode terminal 61 electrically connected to the positive electrode 30 of the wound electrode body and a negative electrode terminal 62 electrically connected to the negative electrode 40 of the wound electrode body. The wound electrode body is accommodated in the case body in a state of being fixed to the sealing body via the current collecting member. According to such a configuration, the accommodation position of the wound electrode body is stabilized and the possibility of breakage or the like is reduced, which is preferable.

  As shown in S3 of FIG. 3, the electrolyte seals the sealing body and the case body, and then, for example, a nonaqueous electrolytic solution is poured into the battery case from a liquid injection port (not shown) provided in the sealing body. It may be accommodated by liquid. The non-aqueous electrolyte may be injected while reducing the pressure in the battery case or after the pressure is reduced. After injecting the non-aqueous electrolyte, the non-aqueous electrolyte secondary battery can be prepared by sealing the injection port of the battery case 60 with a lid or the like. After injecting the non-aqueous electrolyte, it is preferable to stand for, for example, about 5 hours to 50 hours so that the non-aqueous electrolyte sufficiently penetrates into the wound electrode body. Then, the function as a battery is provided by performing an appropriate initial charging process.

When the sensor 10 is a cell composed of the working electrode 14 and the counter electrode 12, as shown in S4 to S5 in FIG. 3, for example, the initial charging process is a sensor for initially adjusting the potential of the sensor 10. It is preferable to perform battery initial charging for adjusting the potential of the secondary battery 20 after performing initial charging.
By performing the sensor initial charging, a coating film derived from the electrolytic solution can be suitably formed on the surface of the working electrode 14. The conditions of the sensor initial charge depend on the configuration of the sensor. For example, the following conditions are: temperature 25 ° C., voltage scanning speed 1 mV / sec, scanning voltage OCV (open circuit voltage) to 3.7 V). Illustrated.
In addition, by performing battery initial charging, a coating film derived from an electrolytic solution can be suitably formed on the surface of the negative electrode 40 of the secondary battery 20. The condition of the initial battery charging depends on the configuration of the secondary battery 20, but for example, the following condition: a temperature of 25 ° C., a voltage scanning speed of 1C and a constant current (CC) charge to 4.1V, and then rest for 5 minutes, And a 5 minute rest after a constant current (CC) discharge to 3.0V at 1C.

  Although not necessarily required for the secondary battery 20 after the initial charging process (S4 to S5), aging can be performed as shown in S6 of FIG. This makes it possible to detect cells (small short-circuited cells) that have a large voltage drop due to self-discharge, and avoid problems of quality variation and early capacity reduction when assembled batteries are used.

Hereinafter, the battery system disclosed herein and an example of confirming its use will be shown as specific examples. A prismatic two-piece body having a wound electrode body using Li _1.0 (Ni _1/3 Co _1/3 Mn _1/3 ) O ₂ as a positive electrode active material and natural graphite (average particle diameter 10 μm) as a negative electrode active material The next battery was built. As the non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) at a volume ratio of 3: 4: 3, and LiPF ₆ as a supporting salt is 1. What was dissolved at a concentration of 0 mol / L was used. In addition, the sensor was arrange | positioned in the state insulated with the separator between the positive electrode and negative electrode of this square secondary battery. The sensor has a configuration in which the same positive electrode active material as the secondary battery is used for the counter electrode, HOPG is used for the working electrode, and the counter electrode and the working electrode are insulated by a separator. The size of the counter electrode was a 3 mm square, and the size of the working electrode was a 4 mm square. The counter electrode and the working electrode were connected to wiring for sensor initial charging and IV resistance measurement (Ag wire coated with fluororesin) and extended outside the battery case of the secondary battery.

  This battery system is subjected to predetermined sensor initial charging and battery initial charging, and then is set to 3.0 V at a rate of 1.8 A (equivalent to 0.5 C) with respect to the secondary battery in an environment of 60 ° C. After the current (CC) discharge, the cycle was paused for 5 minutes, and the high-rate charge / discharge cycle after charging at a constant current (CC) to 4.1 V at a rate of 36 A (equivalent to 10 C) for 5 minutes was defined as 1 cycle. . 1C is a current value when the rated capacity is charged with constant current (or discharged) in one hour. At this time, the IV resistance between the counter electrode and the working electrode of the sensor before and during and after the cycle was measured. The IV resistance before the cycle is the initial resistance, the IV resistance during and after the cycle is the post-endurance resistance, and is formed on the surface of the working electrode of the sensor by the following formula: (post-endurance resistance) / (initial resistance). The rate of increase in resistance due to the sensor film was calculated. The results are shown below the graph in FIG. This resistance increase rate also represents the resistance increase rate of the negative electrode of the secondary battery, and also corresponds to the decrease rate of the lithium ion conductivity of the coating formed on the negative electrode. Thus, according to the technology disclosed herein, a physical property value that affects battery performance is obtained in a state that reflects the film properties of the film formed on the negative electrode surface alternatively through the sensor. Can do.

  An increase in the electrical resistance of the sensor film formed on the surface of the working electrode of the sensor means that the lithium ion conductivity is decreased in the film formed on the surface of the negative electrode in the secondary battery. That is, lithium ions are likely to aggregate on the surface of the negative electrode, increasing the resistance of the negative electrode, which can lead to the deposition of metal Li. Therefore, from the measured increase rate of lithium ion conductivity, it is possible to calculate a limit current rate at which metal Li does not precipitate on the negative electrode. Therefore, the result of calculating the limiting current rate is shown on the upper side of the graph of FIG. As described above, based on the result of predicting the state of the film formed on the negative electrode surface of the secondary battery based on the technology disclosed herein, control for suppressing the deposition of metal Li on the negative electrode is performed. May be. At this time, it is not necessary to control the current rate in accordance with the end-of-life performance of the secondary battery, and it is possible to employ an appropriate current rate according to the usage level of the secondary battery.

The above configuration is preferably applied to, for example, a battery system for a secondary battery that performs charge and discharge at a high rate (for example, a battery capacity of 20 Ah or more, typically 25 Ah or more, for example, 30 Ah or more). can do. Therefore, taking advantage of such characteristics, the technology disclosed herein includes secondary batteries for applications that require high energy density, high input / output density, cycle characteristics, and the like, and applications that require high reliability. It can be particularly preferably applied to a battery system. Examples of such applications include drive power supplies mounted on vehicles such as plug-in hybrid vehicles (PHV), hybrid vehicles (HV), and electric vehicles (EV). The secondary battery may typically be in the form of an assembled battery in which a plurality of secondary batteries are connected in series and / or in parallel.
Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. For example, the charge carrier is not limited to lithium ions, and may be, for example, sodium ions or other components. The technology described in the claims of the present application includes various modifications and changes of the specific examples illustrated above.

DESCRIPTION OF SYMBOLS 1 Battery system 10 Sensor 12 Counter electrode 14 Working electrode 20 Secondary battery 30 Positive electrode 40 Negative electrode 50 Separator

Claims (1)

A secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte;
A sensor that is disposed between the positive electrode and the negative electrode and obtains a physical property value indicating an influence of the coating on the deterioration of the secondary battery when the coating is formed on the negative electrode;
A battery system comprising:

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