JP2012018775A - Lithium ion secondary battery and battery pack - Google Patents

Abstract

Provided is a lithium ion secondary battery that prevents overcharging due to variations in SOC of single cells when charging an assembled battery.
A lithium ion secondary battery provided by the present invention includes a positive electrode, a negative electrode, and an electrolytic solution. The positive electrode is a positive electrode active material layer formed on a current collector, and has a main positive electrode active material having a predetermined redox potential as a main component, and a high potential positive electrode having a higher redox potential than the main positive electrode active material A positive electrode active material layer including an active material is provided.
[Selection] Figure 4

Description

  The present invention relates to a lithium ion secondary battery. The present invention also relates to an assembled battery in which a plurality of lithium ion secondary batteries are electrically connected to each other.

  Lithium ion secondary batteries that are charged and discharged by moving lithium ions back and forth between the positive electrode and the negative electrode are light and high energy density can be obtained. Therefore, they are preferable for on-vehicle power supplies or power supplies for personal computers and portable terminals. It is becoming increasingly important to be used.

In an assembled battery in which such lithium ion secondary batteries (unit cells) are connected to each other (typically in series), each unit cell is used when each unit cell is constructed or used as an assembled battery. There may be variations in the SOC (State of charge) of the battery. When an assembled battery having a variation in SOC between the single cells is charged, it is necessary to stop the charging of the entire assembled battery when one of the single cells constituting the assembled battery is fully charged. If all the cells are fully charged without stopping charging, some cells may be overcharged, causing problems such as decomposition reaction at the positive electrode in the overcharged cells. Because. On the other hand, when the charging is stopped, other unit cells are still charged, but are not fully charged, and there is a possibility that the usable capacity is insufficient. Thus, the case where the capability as an assembled battery cannot be exhibited to the maximum by the variation of SOC of each single battery may generate | occur | produce.
In order to cope with such a problem, Patent Documents 1 to 8 are cited as conventional techniques. For example, Patent Document 1 describes a technique for detecting the voltage of each unit cell and charging or discharging a unit cell whose voltage difference from a reference voltage is equal to or greater than a threshold value to equalize the voltage. ing.

JP 2009-038876 A Japanese Unexamined Patent Publication No. 2000-0787768 Japanese Patent Laid-Open No. 09-017447 JP 05-335034 A JP 2007-048612 A JP-A-11-213987 JP 2007-294654 A JP 2009-142071 A

However, although the technique described in Patent Document 1 can prevent overcharge due to the variation in the SOC of the unit cells, the device configuration for that is complicated. For this reason, what can implement | achieve the same objective with a simpler structure was calculated | required.
Therefore, the present invention has been created to solve the above-described conventional problems, and the purpose of the present invention is to prevent the overcharge associated with the variation in the SOC of the unit cell when charging the assembled battery. It is to provide a battery. Another object is to provide an assembled battery including the lithium ion secondary battery.

  In order to achieve the above object, the present invention provides a lithium ion secondary battery including a positive electrode, a negative electrode, and an electrolytic solution. In the lithium ion secondary battery disclosed herein, the positive electrode is a current collector and a positive electrode active material layer formed on the current collector, and has a predetermined redox potential as a main component A positive electrode active material layer including an active material and a high potential positive electrode active material having a higher redox potential than the main positive electrode active material is provided.

In the present specification, the “positive electrode active material” refers to a positive electrode side capable of reversibly occluding and releasing (typically inserting and removing) chemical species (here, lithium ions) that serve as charge carriers in a secondary battery. The active material.
In this specification, the “negative electrode active material” means a negative electrode side capable of reversibly occluding and releasing (typically inserting and removing) chemical species (here, lithium ions) which are charge carriers in a secondary battery. The active material.
Furthermore, in this specification, “SOC” refers to the state of charge of a lithium ion secondary battery, which is determined based on the main positive electrode active material and the main negative electrode active material. The SOC is 100% when the potential difference becomes maximum (battery upper limit voltage), and the SOC when the potential difference between the main positive electrode active material and the main negative electrode active material becomes minimum (battery lower limit voltage) is 0%.

The lithium ion secondary battery provided by the present invention includes a main positive electrode active material as a main component in a positive electrode active material layer formed on a positive electrode current collector, and a higher redox potential than the main positive electrode active material. And a high potential positive electrode active material.
Thus, the positive electrode active material layer contains a high-potential positive electrode active material having a higher oxidation-reduction potential than the main positive electrode active material, so that the positive electrode made of only the main positive electrode active material is contained in the lithium ion secondary battery. It is possible to provide a voltage flat portion (region where voltage fluctuation during charging is extremely small) higher than the upper limit voltage (that is, SOC 100%). For this reason, even when the lithium ion secondary battery is charged, after the release of lithium ions from the main cathode active material having a predetermined redox potential is completed and the upper limit voltage is reached, further charging is performed. The high-potential positive electrode active material reacts (lithium ions are released), and the increase in the voltage of the lithium ion secondary battery is suppressed at the voltage flat portion by the high-potential positive electrode active material and does not overcharge. Thereby, the upper limit voltage abnormality (problems such as heat generation accompanying the decomposition of the positive electrode that may occur due to overcharging) can be prevented in advance.
Therefore, a plurality of lithium ion secondary batteries of the present invention are electrically connected (typically in series) to each other (typically 10 or more, preferably about 10 to 30, for example, 20). When a battery is constructed, even if there is a variation in the SOC of each secondary battery, it is possible to prevent the occurrence of problems due to overcharging during charging and to correct the variation in the SOC of each secondary battery. Thus, the state of charge can be the same, that is, all the lithium ion secondary batteries can be aligned to a predetermined SOC (typically 70% to 100%). Further, the correction of the SOC variation is performed by including a high-potential positive electrode active material in the positive electrode active material layer in each battery, so that the configuration is simpler than in the past.

In a preferred aspect of the lithium ion secondary battery disclosed herein, the high potential positive electrode active material is at least 0.2 V (for example, about 0.2 V to 1.0 V) higher redox than the main positive electrode active material. It has a potential.
According to such a configuration, when the lithium ion secondary battery is further charged after the release of lithium ions from the main positive electrode active material is completed and reaches 100%, an upper limit voltage abnormality (can occur due to overcharge). (Problems such as heat generation associated with the decomposition of the positive electrode) can be effectively prevented.

In a preferred aspect of the lithium ion secondary battery disclosed herein, the positive electrode active material layer includes 5 to 25 parts by mass of the high potential positive electrode active material per 100 parts by mass of the main positive electrode active material. To do.
According to this configuration, it is possible to sufficiently ensure the capacity of the lithium ion secondary battery at a predetermined SOC (typically 70% to 100%) and effectively prevent an upper limit voltage abnormality due to overcharging.

In a preferred aspect of the lithium ion secondary battery disclosed herein, the main positive electrode active material is an olivine type lithium-containing oxide, and the high potential positive electrode active material constitutes the main positive electrode active material. The olivine-type lithium-containing oxide has a higher redox potential than the olivine-type lithium-containing oxide.
According to such a configuration, the olivine-type lithium-containing oxide has a stable structure even after the release of lithium ions is completed, so that an upper limit voltage abnormality due to overcharging can be more effectively prevented.

In a preferred aspect of the lithium ion secondary battery disclosed herein, the negative electrode is a current collector and a negative electrode active material layer formed on the current collector, and a predetermined redox as a main component A negative electrode active material layer including a main negative electrode active material having a potential and a high potential negative electrode active material having a higher oxidation-reduction potential than the main negative electrode active material is provided.
Thus, the negative electrode active material layer contains a high-potential negative electrode active material having a higher oxidation-reduction potential than the main negative electrode active material, so that the lithium ion secondary battery has a negative electrode composed only of the main negative electrode active material. It is possible to provide a voltage flat portion (region in which voltage fluctuation during charging is extremely small) lower than the lower limit voltage (that is, SOC 0%). For this reason, even when the lithium ion secondary battery is discharged, even after the discharge of lithium ions from the main negative electrode active material having a predetermined redox potential is completed and the lower limit voltage is reached, further discharge is performed. Since the high-potential negative electrode active material reacts, the voltage drop of the lithium ion secondary battery is suppressed at the voltage flat portion by the high-potential negative electrode active material and does not cause overdischarge. Thereby, the lower limit voltage abnormality (problems such as capacity deterioration accompanying the decomposition of the negative electrode that may occur due to overdischarge) can be prevented in advance.
Therefore, when an assembled battery is constructed by electrically connecting a plurality of the lithium ion secondary batteries to each other (typically in series), even if there is a variation in SOC in each secondary battery, Prevents over-discharge and corrects the SOC variation of each secondary battery to equalize the state of charge, that is, equalize the SOC between each lithium ion secondary battery.

In a preferred embodiment of the lithium ion secondary battery disclosed herein, the main negative electrode active material or the high potential negative electrode active material has a D ₅₀ (D50) in a particle size distribution measured based on a laser diffraction method or a light scattering method. It is characterized by being lithium titanate having a median diameter (larger than 1 μm (typically 1 μm to 10 μm, for example, 3 μm to 7 μm)).
According to such a configuration, lithium titanate having a D ₅₀ (median diameter) in the above range exhibits a low resistance value, and therefore can be preferably used as a negative electrode active material from the viewpoint of reducing the resistance of the lithium ion secondary battery.

In a preferred aspect of the lithium ion secondary battery disclosed herein, the electrolytic solution includes a redox shuttle agent having a higher oxidation-reduction potential than the main positive electrode active material.
According to this configuration, when the SOC of the lithium ion secondary battery is further charged exceeding 100%, the redox shuttle agent can react to suppress an increase in voltage, so that an upper limit voltage abnormality (decomposition of the positive electrode) Can be more effectively prevented.

  In addition, according to the present invention, an assembled battery in which a plurality of lithium ion secondary batteries disclosed herein are combined is provided. The assembled battery provided by the present invention can prevent overcharging associated with variation in SOC of each unit cell during charging. Therefore, the assembled battery can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile including an electric motor such as a hybrid vehicle, an electric vehicle, and a fuel cell vehicle.

It is a perspective view which shows typically the external shape of the lithium ion secondary battery which concerns on one Embodiment. It is a longitudinal cross-sectional view which follows the II-II line | wire in FIG. It is a perspective view showing typically an assembled battery concerning one embodiment. It is a graph which shows the change of the voltage at the time of charging / discharging of the lithium ion secondary battery which concerns on one Embodiment. It is a graph which shows the change of the voltage at the time of charging / discharging of the lithium ion secondary battery which concerns on other one Embodiment. It is a graph which shows the change of the voltage at the time of charging / discharging of the lithium ion secondary battery which concerns on other one Embodiment. It is a graph which shows the change of the voltage at the time of charging / discharging of the conventional lithium ion secondary battery. It is a graph which shows the relationship between the resistance of a lithium ion secondary battery, and D50 particle size of lithium titanate.

  Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than matters specifically mentioned in the present specification and necessary for carrying out 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 secondary battery provided by the present invention is a positive electrode active material layer formed on a current collector as described above, and has a main positive electrode active material having a predetermined redox potential as a main component, It is characterized by including a positive electrode including a positive electrode active material layer including a high potential positive electrode active material having a higher oxidation-reduction potential than the positive electrode active material.

  The positive electrode provided in the lithium ion secondary battery disclosed herein can have the same configuration as the conventional one except that the positive electrode active material that characterizes the present invention is provided. As a positive electrode current collector constituting such a positive electrode, a conductive member made of a metal having good conductivity is preferably used, like the current collector used for the positive electrode of a conventional lithium ion secondary battery. For example, aluminum or an alloy containing aluminum as a main component can be used. The shape of the positive electrode current collector may vary depending on the shape of the lithium ion secondary battery, and is not particularly limited, and may be various forms such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape.

  Next, a material constituting the positive electrode active material layer formed on the surface of the positive electrode current collector will be described. The surface of the positive electrode current collector has a positive electrode active material layer containing at least a main positive electrode active material and a high potential positive electrode active material. Furthermore, the positive electrode active material layer may contain a conductive material, a binder (binder), and the like as necessary.

The main positive electrode active material contained in the positive electrode active material layer formed on the positive electrode of the lithium ion secondary battery disclosed herein is not particularly limited as long as it is a material capable of inserting and extracting lithium. For example, as a suitable example, an olivine type lithium-containing oxide represented by the general formula LiMPO ₄ (M is at least one element of Co, Ni, Mn, Fe; for example, LiFePO ₄ , LiMnPO ₄ ) (typically Is olivine type lithium phosphate). Alternatively, a composite oxide containing lithium and at least one transition metal element can be given. Examples of the composite oxide include cobalt lithium composite oxide (LiCoO ₂ ), nickel lithium composite oxide (LiNiO ₂ ), manganese lithium composite oxide (LiMn ₂ O ₄ ), or nickel / cobalt-based LiNi _x. Co _1-x O ₂ (0 <x <1), cobalt-manganese LiCo _x Mn _1-x O ₂ (0 <x <1), nickel-manganese LiNi _x Mn _1-x O ₂ (0 <X <1) or LiNi _x Mn _2−x O ₄ (0 <x <2), a so-called binary lithium-containing composite oxide containing two kinds of transition metal elements, or a transition metal element Examples include ternary lithium-containing composite oxides such as nickel, cobalt, and manganese containing three types.

  Further, the high potential positive electrode active material contained in the positive electrode active material layer formed on the positive electrode of the lithium ion secondary battery disclosed herein is the same material as the main positive electrode active material, and the positive electrode active material layer includes Examples thereof include those having a higher redox potential than a predetermined redox potential (depending on the positive electrode active material) of the main positive electrode active material contained. A preferred example is an olivine-type lithium-containing oxide.

The high-potential positive electrode active material has a redox potential that is at least 0.2 V (for example, about 0.2 V to 1.0 V) higher than the redox potential of the main positive electrode active material at 100% SOC of a lithium ion secondary battery. Is preferred. If it is less than 0.2 V, if the lithium ion secondary battery continues to be charged after reaching the upper limit voltage (full charge, SOC 100%), it immediately reaches the redox potential of the high potential positive electrode active material. There is a possibility that the upper limit voltage abnormality due to overcharging cannot be effectively prevented.
The amount of the high-potential positive electrode active material contained in the positive electrode active material layer is appropriately determined, but is about 5 to 25 parts by mass (more preferably about 10 to 15 parts by mass) with respect to 100 parts by mass of the main positive electrode active material. Is preferred. If the high-potential positive electrode active material is less than 5 parts by mass with respect to 100 parts by mass of the main positive electrode active material, the upper limit voltage abnormality due to overcharging cannot be effectively prevented. On the other hand, if the amount is more than 25 parts by mass, sufficient capacity cannot be obtained at a predetermined SOC (typically 70% to 100%) of the lithium ion secondary battery.

  Moreover, when a conductive material is included in the positive electrode active material layer formed on the positive electrode of the lithium ion secondary battery disclosed herein, the conductive material is conventionally used in this type of lithium ion secondary battery. As long as it is, it is not limited to a specific conductive material. For example, carbon black such as acetylene black and ketjen black, and other (such as graphite) powdery carbon materials can be used.

  Furthermore, as a binder (binder) contained in the positive electrode active material layer formed on the positive electrode of the lithium ion secondary battery disclosed herein, for example, an aqueous liquid is used as a composition for forming the positive electrode active material layer. When using a composition (typically a composition prepared in the form of a paste or slurry, hereinafter referred to as a positive electrode active material layer forming paste), a polymer material that dissolves or disperses in water can be preferably used. . For example, polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC) and the like can be mentioned. Alternatively, when a solvent-based liquid composition (positive electrode active material layer forming paste) is used, a polymer that dissolves in an organic solvent (nonaqueous solvent) such as polyvinylidene fluoride (PVDF) or polyvinylidene chloride (PVDC). Materials can be used. In addition, the polymer material illustrated above may be used as a thickener and other additives in the above composition in addition to being used as a binder.

  Here, the “aqueous liquid composition” is a concept indicating a composition using water or a mixed solvent mainly containing water as a dispersion medium of the active material. As a solvent other than water constituting such a mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used. The “solvent-based liquid composition” is a concept indicating a composition in which a dispersion medium of an active material is mainly an organic solvent. As the organic solvent, for example, N-methylpyrrolidone (NMP) can be used.

  The positive electrode of the lithium ion secondary battery disclosed here can be suitably manufactured, for example, generally by the following procedure. A paste for forming a positive electrode active material layer is prepared by dispersing the above-described main positive electrode active material, high potential positive electrode active material, conductive material, binder material soluble in an organic solvent, and the like in an organic solvent. The prepared paste is applied to a sheet-like positive electrode current collector, dried, and then compressed (pressed) to form a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. The positive electrode (positive electrode sheet) provided can be produced. In addition, as a method of applying the positive electrode active material layer forming paste to the positive electrode current collector, a technique similar to a conventionally known method can be appropriately employed, and the detailed description is not given because it does not characterize the present invention. Omitted.

In the lithium ion secondary battery constructed using the positive electrode, the positive electrode active material layer formed on the positive electrode current collector includes at least a main positive electrode active material and a high potential positive electrode active material. For this reason, as shown in FIG. 4, even when the lithium ion secondary battery is charged to 100% SOC (upper limit voltage) and further charged, the high potential positive electrode active material reacts (desorbs lithium). A voltage flat portion with very little voltage fluctuation appears, so the voltage of the lithium ion secondary battery does not rise above the voltage of the voltage flat portion due to the reaction of the high potential positive electrode active material, and there is a problem with overcharge It is possible to prevent the voltage from rising to an abnormal voltage.
On the other hand, in a lithium ion secondary battery having a conventional configuration (not including a high potential positive electrode active material), as shown in FIG. 7, there is no voltage flat portion having a voltage higher than the SOC 100% voltage (upper limit voltage). When the battery is charged to exceed SOC 100%, the voltage rises rapidly and a problem associated with overcharging occurs.
As described above, an assembled battery in which a plurality of lithium ion secondary batteries constructed using the positive electrode are connected to each other (typically in series) is charged even if there is a variation in SOC in each secondary battery. In this case, it is possible to prevent overcharge, and to correct the variation in SOC of each secondary battery so as to make it a predetermined state of charge (SOC).

The main negative electrode active material contained in the negative electrode active material layer formed in the negative electrode of the lithium ion secondary battery disclosed herein may be any material that can occlude and release lithium, such as graphite. Carbon materials; oxide materials such as lithium titanate (Li ₄ Ti ₅ O ₁₂ , LTO) and iron oxide (Fe ₂ O ₃ ); tin (Sn), aluminum (Al), zinc (Zn), silicon (Si Or a metal material composed of a metal alloy mainly composed of these metal elements. For example, graphite particles can be preferably used.

Further, a high potential negative electrode active material may be mixed in the negative electrode active material layer in order to prevent a lower limit voltage abnormality during discharge of the lithium ion secondary battery. The high potential negative electrode active material is the same material as the main negative electrode active material, and is higher than a predetermined oxidation-reduction potential (depending on the main negative electrode active material) of the main negative electrode active material contained in the negative electrode active material layer. Those having an oxidation-reduction potential can be mentioned. When graphite particles are used as the main negative electrode active material, for example, lithium titanate can be preferably used. At this time, the lithium titanate has a D ₅₀ (median diameter) of 1 μm larger (typically 1 μm to 10 μm (for example, 3 μm) in a particle size distribution measured by a particle size distribution measuring apparatus based on a laser diffraction method or a light scattering method. Since the lithium titanate in the above range exhibits low resistance, it can be preferably used from the viewpoint of reducing battery resistance.
The amount of the high-potential negative electrode active material contained in the negative electrode active material layer is appropriately determined, but is about 5 to 25 parts by mass (more preferably about 10 to 15 parts by mass) with respect to 100 parts by mass of the main negative electrode active material. Is preferred. If the high-potential negative electrode active material is less than 5 parts by mass with respect to 100 parts by mass of the main negative electrode active material, the lower limit voltage abnormality due to overdischarge cannot be effectively prevented. On the other hand, if the amount is more than 25 parts by mass, sufficient capacity cannot be obtained at a predetermined SOC (typically 70% to 100%) of the lithium ion secondary battery.

In the negative electrode active material layer of the lithium ion secondary battery disclosed herein, in addition to the main negative electrode active material (and a high potential negative electrode active material as necessary), Two or more kinds of materials can be contained as required. As such a material, various materials that can function as a binder as listed as a constituent material of the positive electrode active material layer can be similarly used.
The negative electrode is a paste-like composition (hereinafter referred to as “the negative electrode active material”) and a binder or the like dispersed in an appropriate solvent (water, organic solvent, etc.) similar to the conventional one. A negative electrode active material layer forming paste) is prepared. The prepared negative electrode active material layer forming paste is applied to the negative electrode current collector, dried, and then compressed (pressed) to form the negative electrode current collector and the negative electrode active material formed on the negative electrode current collector A negative electrode (negative electrode sheet) provided with a layer can be produced.

The lithium ion secondary battery constructed using the negative electrode including the main negative electrode active material and the high potential negative electrode active material was discharged to SOC 0% (lower limit voltage) as shown in FIG. Even in the case of further discharge later, the high potential negative electrode active material reacts (lithium desorption reaction), and a voltage flat portion with extremely small voltage fluctuation appears. Therefore, the voltage of the lithium ion secondary battery is It is possible to prevent a drop to an abnormal voltage that does not drop from the voltage of the voltage flat portion due to the reaction of the high potential negative electrode active material and causes a problem associated with overdischarge.
On the other hand, in the conventional lithium ion secondary battery (not including the high potential negative electrode active material), as shown in FIG. 7, there is no voltage flat portion having a voltage lower than the SOC 0% voltage (lower limit voltage). When the discharge exceeds SOC 0%, the voltage suddenly drops and a problem associated with overdischarge occurs.
As described above, each of the assembled batteries formed by connecting a plurality of lithium ion secondary batteries (typically in series) to each other, constructed using a negative electrode including the main negative electrode active material and the high potential negative electrode active material, Even if there is a variation in SOC in the secondary battery, overdischarge can be prevented during discharge, and the discharge state can be made uniform by correcting the variation in SOC of each secondary battery.

The electrolytic solution contained in the lithium ion secondary battery disclosed herein has a composition in which a lithium salt that can function as an electrolyte is contained in an appropriate nonaqueous solvent (organic solvent). As the electrolyte, a lithium salt conventionally used in lithium ion secondary batteries can be appropriately selected and used. An example of such a lithium salt is LiPF ₆ . Examples of the non-aqueous solvent include carbonates such as ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and propylene carbonate (PC). Such non-aqueous solvents can be used alone or in combination of two or more. Instead of the electrolytic solution, a solid electrolyte (all solid polymer electrolyte) or a gel electrolyte (polymer gel electrolyte) may be used.

  In addition, a redox shuttle agent (shuttle additive) may be mixed with the electrolytic solution in order to prevent an upper limit voltage abnormality during charging of the lithium ion secondary battery. The redox shuttle agent is a compound having a function of preventing the battery voltage (potential difference between positive and negative electrodes) from becoming a predetermined value or more due to the redox shuttle agent itself. Examples of the redox shuttle agent include compounds having a higher redox potential than a predetermined redox potential of the main positive electrode active material (which varies depending on the main positive electrode active material). For example, aromatic compounds such as 1,2-dimethoxy-4-fluorobenzene and 2,4-difluoroanisole; heterocyclic complexes; radical compounds such as nitroxyl radical compounds; Ce compounds such as cerium nitrate; metallocenes such as ferrocene complexes A complex etc. are mentioned.

The redox shuttle agent preferably has an oxidation-reduction potential that is at least 0.2 V (for example, approximately 0.2 V to 1.0 V) higher than the oxidation-reduction potential of the main positive electrode active material at 100% SOC of the lithium ion secondary battery. If the voltage is lower than 0.2V, if the lithium ion secondary battery is fully charged (SOC 100%) and then continues to be charged, the redox shuttle agent will reach the oxidation-reduction potential immediately. There is a risk that the upper limit voltage abnormality due to the above cannot be effectively prevented.
Moreover, although the quantity of the red oxs shuttle agent contained in electrolyte solution is determined suitably, it is preferable to mix about 0.01-0.3 mol / L of red sx shuttle agents with electrolyte solution.

The lithium ion secondary battery constructed using the above-described electrolyte solution containing the redox shuttle agent is an oxidation of the redox shuttle agent itself even when the lithium ion secondary battery is further charged after being charged to 100% SOC. Since the reduction reaction prevents the battery voltage from exceeding a predetermined value, it is possible to prevent an increase to an abnormal voltage that causes a problem associated with overcharging.
As described above, an assembled battery formed by connecting a plurality of lithium ion secondary batteries constructed using the above electrolyte solution to each other (typically in series) is charged even if there is a variation in SOC in each secondary battery. In this case, it is possible to prevent overcharge and to correct a variation in SOC of each secondary battery so that a predetermined state of charge can be made uniform.

Hereinabove, the positive electrode, the negative electrode, and the electrolytic solution of the lithium ion secondary battery disclosed herein have been described in detail. As a particularly preferred embodiment, the lithium ion secondary battery is constructed using a negative electrode including the positive electrode and the main negative electrode active material and a high potential negative electrode active material. As shown in FIG. 6, the lithium ion secondary battery having such a configuration has a voltage flat part higher than the upper limit voltage (SOC 100%) and a voltage flat part lower than the lower limit voltage (SOC 0%). It is possible to prevent an increase to an abnormal voltage that causes a problem associated with overcharge and a decrease to an abnormal voltage that causes a problem associated with overdischarge. Therefore, an assembled battery in which a plurality of lithium ion secondary batteries are connected to each other prevents overcharge during charging and prevents overdischarge during discharge to improve the performance of each secondary battery. It can be used to its full potential. Furthermore, overcharge can be effectively prevented by using an electrolytic solution containing the redox shuttle agent.
Even if a lithium ion secondary battery is constructed using an electrolyte containing the redox shuttle agent and a negative electrode containing the main negative electrode active material and a high potential negative electrode active material, the positive electrode and the main negative electrode active material An effect similar to that of a lithium ion secondary battery constructed using a negative electrode containing a potential negative electrode active material can be obtained.

Hereinafter, although one form of a lithium ion secondary battery provided with the said positive electrode is demonstrated, referring drawings, it is not intending to limit this invention to this embodiment. That is, as long as the positive electrode according to the present embodiment is employed, the shape (outer shape and size) of the lithium ion secondary battery to be constructed is not particularly limited. In the following embodiment, a rectangular battery will be described.
In addition, 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. Moreover, the dimensional relationship (length, width, thickness, etc.) in each drawing does not necessarily reflect the actual dimensional relationship.

FIG. 1 is a perspective view schematically showing a lithium ion secondary battery according to an embodiment. FIG. 2 is a longitudinal sectional view taken along line II-II in FIG.
In the lithium ion secondary battery 10 according to the present embodiment, a positive electrode (positive electrode sheet) 66 in which a main positive electrode active material and a high potential positive electrode active material are included in the positive electrode active material layer 64 is used as the positive electrode (positive electrode sheet) 66. ing. As shown in FIGS. 1 and 2, a lithium ion secondary battery 10 is a battery having an electrode body 50 and a square shape (typically a flat rectangular parallelepiped shape) that accommodates the electrode body 50 and an appropriate electrolytic solution. Case 15 is provided.

  The case 15 includes a box-shaped case main body 30 in which one of the narrow surfaces in the flat rectangular parallelepiped shape is an opening 20, and the opening 20 is attached (for example, welded) to the opening 20. And a lid 25 for closing. The lid body 25 is formed in a rectangular shape that matches the shape of the opening 20 of the case body 30. Further, the lid body 25 is provided with a positive terminal 60 and a negative terminal 80 for external connection, respectively, and some of these terminals 60 and 70 protrude from the lid body 25 toward the outside of the case 15. It is formed to do. Similarly to the case of the conventional lithium ion secondary battery, the lid 25 is provided with a safety valve 40 for discharging the gas generated inside the case 15 to the outside of the case 15 when the battery is abnormal. .

  As shown in FIG. 2, the lithium ion secondary battery 10 includes a wound electrode body 50 in the same manner as a normal lithium ion secondary battery. The electrode body 50 is accommodated in the case main body 30 in a posture in which the winding axis is laid down (that is, in the direction in which the opening 20 is positioned in the lateral direction with respect to the winding axis). The electrode body 50 includes a positive electrode sheet (positive electrode) 66 having a positive electrode active material layer 64 formed on the surface of a long sheet-like positive electrode current collector 62 and a negative electrode active material on the surface of a long sheet-like negative electrode current collector 72. The negative electrode sheet (negative electrode) 76 on which the material layer 74 is formed is overlapped with two long separator sheets 80 and wound, and the resulting electrode body 50 is flattened by crushing and ablating from the side surface direction. It is formed into a shape.

  Further, in the wound positive electrode sheet 66, the positive electrode current collector 62 is exposed without forming the positive electrode active material layer 64 at one end portion along the longitudinal direction, while the negative electrode is wound. Also in the sheet 76, the negative electrode current collector 72 is exposed at one end portion along the longitudinal direction without forming the negative electrode active material layer 74. A positive electrode terminal 60 is joined to the exposed end of the positive electrode current collector 62, and is electrically connected to the positive electrode sheet 66 of the wound electrode body 50 formed in the flat shape. Similarly, the negative electrode terminal 70 is joined to the exposed end portion of the negative electrode current collector 72 and is electrically connected to the negative electrode sheet 76. The positive and negative electrode terminals 60 and 70 and the positive and negative electrode current collectors 62 and 72 can be joined by, for example, ultrasonic welding, resistance welding, or the like. The positive electrode sheet 66 and the negative electrode sheet 76 are produced as described above.

The positive electrode sheet 66 and the negative electrode sheet 76 produced above are stacked and wound together with two separators (for example, porous polyolefin resin) 80, and the wound electrode body 50 obtained is rolled into the case body 30 with its winding shaft lying sideways. And an electrolytic solution such as a mixed solvent of EC and DMC (for example, a mass ratio of 1: 1) containing an appropriate amount of a supporting salt (for example, a lithium salt such as LiPF ₆ ) (for example, a concentration of 1 M). After the injection, the lithium ion secondary battery 10 of the present embodiment can be constructed by mounting the lid 25 on the opening 20 and sealing (for example, laser welding).
As the negative electrode sheet 76, a negative electrode (negative electrode sheet) 76 in which the negative electrode active material layer 74 includes a main negative electrode active material and a high potential negative electrode active material may be used. Moreover, you may use what mixed the said Red X shuttle agent in electrolyte solution.

  Next, a configuration example of a battery pack including a plurality of the single cells, with the lithium ion secondary battery 10 having such a configuration as a single cell, will be described. As shown in FIG. 3, this assembled battery 100 includes a plurality of (typically 10 or more, preferably about 10 to 30, for example, 20) lithium ion secondary batteries (unit cells) 10 respectively. The positive surfaces 60 and the negative electrodes 70 are inverted one by one so as to be alternately arranged, and the wide surfaces of the case 15 are arranged in the facing direction (stacking direction). A cooling plate 110 having a predetermined shape is sandwiched between the arranged cells 10. The cooling plate 110 functions as a heat dissipating member for efficiently dissipating the heat generated in each unit cell 10 during use, and preferably a cooling fluid (typically air) between the unit cells 10. ) (For example, a shape in which a plurality of parallel grooves extending vertically from one side of the rectangular cooling plate to the opposite side are provided on the surface). A cooling plate made of metal having good thermal conductivity or lightweight and hard polypropylene or other synthetic resin is suitable.

As shown in FIG. 3, a pair of end plates (restraint plates) 120 and 120 are arranged at both ends of the unit cell 10 and the cooling plate 110 arranged as described above. One or a plurality of sheet-like spacer members 150 as length adjusting means may be sandwiched between the cooling plate 110 and the end plate 120. The cell 10, the cooling plate 110 and the spacer member 150 arranged in the above manner are applied with a predetermined restraining pressure in the stacking direction by a fastening restraint band 130 attached so as to bridge between both end plates. It is restrained. More specifically, as shown in FIG. 3, by tightening and fixing the end portion of the restraining band 130 to the end plate 120 with screws 155, the unit cell or the like is applied with a predetermined restraining pressure in the arrangement direction. It is restrained by. Thereby, restraint pressure is also applied to the wound electrode body 50 housed in the battery case 15 of each unit cell 10.
In addition, between the adjacent unit cells 10, one positive electrode terminal 60 and the other negative electrode terminal 70 are electrically connected by a connection member (bus bar) 140. Thus, the assembled battery 100 of the desired voltage is constructed | assembled by connecting each cell 10 in series.

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

<Test Example 1: Performance evaluation of battery pack>
[Production of assembled battery]
[Sample 1-1]
LiFePO ₄ as the main cathode active material, acetylene black (AB) as the conductive material, and PVDF as the binder are weighed so that the mass ratio is 85: 5: 10, and these materials are used as the solvent NMP. A paste for forming a positive electrode active material layer was prepared by dispersing. The paste was applied onto an aluminum foil having a thickness of 15 μm and subjected to a treatment by a roll press to produce a positive electrode sheet A in which a positive electrode active material layer was formed on the aluminum foil.
On the other hand, a natural graphite-based carbon material (graphite) having a D ₅₀ particle size of 12 μm (based on the laser diffraction method) as the main negative electrode active material, SBR as the binder, and carboxymethyl cellulose (CMC) as the thickener The weight ratio was 95: 2.5: 2.5, and these materials were dispersed in ion-exchanged water to prepare a negative electrode active material layer forming paste. The paste was applied on a copper foil having a thickness of 10 μm and subjected to a treatment by a roll press to prepare a negative electrode sheet A in which a negative electrode active material layer was formed on the copper foil. The amount of the paste applied was adjusted so that the ratio between the theoretical capacity of the positive electrode and the theoretical capacity of the negative electrode was 1 (positive electrode): 1.5 (negative electrode).
As the electrolytic solution, an electrolytic solution A in which 1 mol / L LiPF ₆ was dissolved in a mixed solvent of EC and EMC in a volume ratio of 1: 1 was used.
The obtained positive electrode sheet A and negative electrode sheet A were rolled together with two separator sheets (polypropylene / polyethylene composite porous membrane), and the obtained wound electrode body was cylindrical with the above electrolyte A. And a lithium ion secondary battery according to Sample 1-1 was produced.
For the lithium ion secondary battery according to Sample 1-1, each charging upper limit voltage ( The battery was charged up to (see Table 1). That is, the charging was performed until the final current value during constant voltage charging was 1/10 of the initial current value. After the charging, six batteries according to Sample 1-1 were connected in series to produce an assembled battery according to Sample 1-1.

[Sample 1-2]
The mass ratio of graphite having a D ₅₀ particle size of 12 μm as the main negative electrode active material and lithium titanate (Li ₄ Ti ₅ O ₁₂ ) having a D ₅₀ particle size of 3 μm as the high potential negative electrode active material is 90:10. The mixture was weighed to obtain a mixture of negative electrode active materials.
The negative electrode active material mixture, SBR as a binder, and CMC as a thickener are weighed so that the mass ratio is 95: 2.5: 2.5. A paste for forming a negative electrode active material layer was prepared by dispersing. The paste was applied on a copper foil having a thickness of 10 μm, and a roll press treatment was performed to prepare a negative electrode sheet B in which a negative electrode active material layer was formed on the copper foil. The amount of paste applied was adjusted so that the ratio between the theoretical capacity of the positive electrode and the theoretical capacity of the negative electrode was 1 (positive electrode): 1.5 (negative electrode). Other than using the obtained negative electrode sheet B, a lithium ion secondary battery according to Sample 1-2 was manufactured in the same manner as Sample 1-1, and six batteries according to Sample 1-2 were connected in series. An assembled battery according to Sample 1-2 was produced.

[Sample 1-3]
As an electrolytic solution, 1 mol / L LiPF ₆ and 0.01 mol / L 1,2-dimethoxy-4-fluorobenzene as a redox shuttle agent were dissolved in a 1: 1 mixed solvent of EC and EMC in a volume ratio. A lithium ion secondary battery according to Sample 1-3 was produced in the same manner as Sample 1-1 except that Electrolyte B was used, and six batteries according to Sample 1-3 were connected in series. An assembled battery according to 3 was produced.

[Sample 1-4]
LiFePO ₄ as the main positive electrode active material and LiFe _0.5 Mn _0.5 PO ₄ as the high potential positive electrode active material were weighed so as to have a mass ratio of 90:10 to obtain a mixture of positive electrode active materials.
The positive electrode active material was weighed so that the mass ratio of the mixture of the positive electrode active material, AB as the conductive material, and PVDF as the binder was 85: 5: 10, and these materials were dispersed in the solvent NMP. A layer forming paste was prepared. The paste was applied on an aluminum foil having a thickness of 15 μm and subjected to a treatment by a roll press to prepare a positive electrode sheet B in which a positive electrode active material layer was formed on the aluminum foil. The amount of paste applied was adjusted so that the ratio between the theoretical capacity of the positive electrode and the theoretical capacity of the negative electrode was 1 (positive electrode): 1.5 (negative electrode). Except for using the obtained positive electrode sheet B, a lithium ion secondary battery according to Sample 1-4 was manufactured in the same manner as Sample 1-1, and six batteries according to Sample 1-4 were connected in series. An assembled battery according to Sample 1-4 was produced.

[Sample 1-5]
A lithium ion secondary battery according to Sample 1-5 was fabricated in the same manner as Sample 1-1 except that electrolyte solution B was used instead of electrolyte solution A, and negative electrode sheet B was used instead of negative electrode sheet A. Then, six batteries according to Sample 1-5 were connected in series to produce an assembled battery according to Sample 1-5.

[Sample 1-6]
A lithium ion secondary battery according to Sample 1-6 was prepared in the same manner as Sample 1-1 except that positive electrode sheet B was used instead of positive electrode sheet A, and negative electrode sheet B was used instead of negative electrode sheet A. Then, six batteries according to Sample 1-6 were connected in series to produce an assembled battery according to Sample 1-6.

[Charge / discharge cycle test]
Six types of assembled batteries from Sample 1-1 to Sample 1-6 were installed in the thermostatic layer (25 ° C.), respectively, and the positive electrode and the sixth lithium ion secondary battery of the first lithium ion secondary battery of each assembled battery A terminal was connected to the negative electrode of the battery. And charging / discharging was repeated 500 cycles with respect to each assembled battery, and the presence or absence of voltage abnormality generation | occurrence | production was confirmed after 500 cycles. The charge / discharge condition of one cycle is that each lithium ion secondary battery is CCCV charged (constant current constant voltage charge) to the upper limit voltage at 1 C (that is, charged until all lithium ion secondary batteries of the assembled battery reach the upper limit voltage). After that, each lithium ion secondary battery was subjected to CC discharge (constant current discharge) at 1 C to the lower limit voltage (that is, discharged until all lithium ion secondary batteries of the assembled battery reached the lower limit voltage). . Table 1 shows the upper limit voltage and the lower limit voltage of each lithium ion secondary battery. Further, the discharge capacity retention ratio (%) was calculated from the discharge capacity at the 500th cycle relative to the discharge capacity at the first cycle. The results are shown in Table 1.
In addition, when abnormality (opening of a safety valve, etc.) was confirmed during charging of the assembled battery, it was determined that the upper limit voltage was abnormal. On the other hand, when any lithium ion secondary battery fell below the lower limit voltage by 0.3 V or more during discharge of the assembled battery, it was determined that the lower limit voltage was abnormal.

  As shown in Table 1, in the assembled batteries according to Sample 1-4 and Sample 1-6, the occurrence of the upper limit voltage abnormality was not confirmed because the positive electrode contained the high potential positive electrode active material. In the assembled batteries according to Sample 1-3 and Sample 1-5, since the redox shuttle agent was included in the electrolyte, the occurrence of the upper limit voltage abnormality was not confirmed. In the assembled batteries according to Sample 1-2, Sample 1-5, and Sample 1-6, since the high-potential negative electrode active material was contained in the negative electrode, occurrence of the lower limit voltage abnormality was not confirmed. Moreover, in the assembled batteries according to Sample 1-5 and Sample 1-6, it was confirmed that the discharge capacity maintenance rate was as high as 95% and the performance degradation of the entire assembled battery was prevented. From the above, the assembled battery in which lithium ion secondary batteries manufactured (constructed) using a positive electrode including a high-potential positive electrode active material and a negative electrode including a high-potential negative electrode active material are connected to each other in series is most excellent. It could be confirmed.

<Test Example 2: Resistance test of lithium ion secondary battery>
In Sample 1-2, Sample 1-5, and Sample 1-6, lithium titanate with a D ₅₀ particle size of 3 μm was used. How does resistance change depending on the D ₅₀ particle size of lithium titanate? It was measured. The following samples 2-1 to 2-6 were prepared.

Sample 2-1: A lithium ion secondary battery according to Sample 2-1 was constructed in the same manner as Sample 1-2, except that D ₅₀ based on laser diffraction was used and lithium titanate having a particle size of 0.1 μm was used. did.
Sample 2-2: in addition to the _{D 50} particle size based on the laser diffraction method using lithium titanate of 0.15μm, similarly to the sample 1-2, construct a lithium ion secondary battery according to Sample 2-2 did.
Sample 2-3: in addition to the D ₅₀ particle size based on the laser diffraction method using lithium titanate of 0.5μm, in the same manner as Sample 1-2, construct a lithium ion secondary battery according to Sample 2-3 did.
Sample 2-4: using lithium titanate of D ₅₀ particle size is 3μm based on laser diffraction method, in the same manner as Sample 1-2, was constructed lithium ion secondary battery according to Sample 2-4.
Sample 2-5: in addition to the D ₅₀ particle size based on the laser diffraction method using lithium titanate of 5.5μm, in the same manner as Sample 1-2, construct a lithium ion secondary battery according to Sample 2-5 did.
Sample 2-6: in addition to the D ₅₀ particle size based on the laser diffraction method using lithium titanate of 7μm, in the same manner as Sample 1-2, was constructed lithium ion secondary battery according to Sample 2-6.

The resistance (Ω) of the six types of lithium ion secondary batteries of Sample 2-1 to Sample 2-6 was measured. Resistance measurement was performed as follows. After charging the lithium ion secondary battery to the upper limit voltage, the SOC was adjusted to 50% by CC discharging 50% of the battery capacity. Then charge and discharge 0.5C charge, 0.5C discharge, 1.0C charge, 1.0C discharge, 2.0C charge and 2.0C discharge for 10 seconds each and read the voltage fluctuation range for each 10 seconds. It was. Using the relationship of resistance = voltage fluctuation width / current value, a first-order approximation of the voltage fluctuation width with respect to the current value was performed, and the slope was defined as resistance. The result is shown in FIG. In FIG. 8, the vertical axis represents the resistance (Ω) of the lithium ion secondary battery, and the horizontal axis represents the D ₅₀ particle size (μm) of lithium titanate.
As shown in FIG. 8, the resistance of the lithium ion secondary battery when D ₅₀ particle size greater than 1 [mu] m, as compared to the D ₅₀ particle size is less than 1 [mu] m, it was confirmed that the smaller. Therefore, from the viewpoint of reducing the resistance of the lithium ion secondary battery, it was confirmed that lithium titanate having a D ₅₀ particle size larger than 1 μm can be preferably used.

  As mentioned above, although this invention was demonstrated by suitable embodiment, such description is not a limitation matter and of course various modifications are possible. For example, by stacking a plurality of batteries each having a bipolar electrode having a positive electrode active material layer formed on one side of a current collector and a negative electrode active material layer formed on the other side, the batteries are connected in series. The present invention can also be applied to a bipolar battery (assembled battery).

  The assembled battery formed by connecting a plurality of lithium ion secondary batteries according to the present invention is capable of outputting a large current and is excellent in safety by preventing overcharge due to the variation in SOC of each battery as described above. In particular, it can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile. That is, a vehicle (typically equipped with an electric motor such as an automobile, in particular, a hybrid automobile, an electric automobile, or a fuel cell automobile) provided with a battery pack in which a plurality of lithium ion secondary batteries according to the present invention are connected to each other. Car).

DESCRIPTION OF SYMBOLS 10 Lithium ion secondary battery 15 Battery case 20 Opening part 25 Cover body 30 Case main body 40 Safety valve 50 Winding electrode body 60 Positive electrode terminal 62 Positive electrode current collector 64 Positive electrode active material layer 66 Positive electrode sheet 70 Negative electrode terminal 72 Negative electrode current collector 74 Negative electrode active material layer 76 Negative electrode sheet 80 Separator sheet 100 Battery pack 110 Cooling plate 120 End plate 130 Restraint band 140 Connecting member (bus bar)
150 Spacer member 155 Screw

Claims (8)

A lithium ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte solution,
The positive electrode is a current collector, a positive electrode active material layer formed on the current collector, and a main positive electrode active material having a predetermined redox potential as a main component, and a redox than the main positive electrode active material A lithium ion secondary battery comprising a positive electrode active material layer including a high potential positive electrode active material having a high potential.   The lithium ion secondary battery according to claim 1, wherein the high potential positive electrode active material has a redox potential that is at least 0.2 V higher than the main positive electrode active material.   The lithium ion secondary battery according to claim 1, wherein the positive electrode active material layer includes 5 to 25 parts by mass of the high potential positive electrode active material per 100 parts by mass of the main positive electrode active material.   The main positive electrode active material is an olivine-type lithium-containing oxide, and the high-potential positive electrode active material has an oxidation-reduction potential higher than that of the olivine-type lithium-containing oxide constituting the main positive electrode active material. The lithium ion secondary battery according to claim 1, wherein the lithium ion secondary battery is a contained oxide.   The negative electrode is a current collector, a negative electrode active material layer formed on the current collector, and a main negative electrode active material having a predetermined redox potential as a main component, and a redox than the main negative electrode active material The lithium ion secondary battery according to any one of claims 1 to 4, further comprising a negative electrode active material layer including a high potential negative electrode active material having a high potential. The main negative electrode active material or the high potential negative electrode active material is lithium titanate having a D ₅₀ (median diameter) of more than 1 μm in a particle size distribution measured based on a laser diffraction method or a light scattering method. Item 6. A lithium ion secondary battery according to Item 5.   The lithium ion secondary battery according to claim 1, wherein the electrolytic solution contains a redox shuttle agent having a higher oxidation-reduction potential than the main positive electrode active material. The assembled battery which combined multiple lithium ion secondary batteries in any one of Claim 1 to 7.

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