JP2013057603A - Lithium secondary battery and deterioration detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a deterioration detection method of a lithium secondary battery which can simply and highly accurately detect a battery that easily deteriorates.SOLUTION: A deterioration detection method is for a lithium secondary battery to which a voltage stabilizing agent for maintaining constant battery voltage is added in non-aqueous electrolyte. The method includes: a first charging process for performing charging until the battery voltage reaches a predetermined first specified voltage; and a second charging process for performing charging by a charging rate lower than a charging rate of the first charging process. The second charging process measures a time when the battery voltage in charging reaches a predetermined charging stop voltage, and estimates deterioration of the battery on the basis of the required reach time.

Description

  The present invention relates to a method for detecting deterioration of a lithium secondary battery, and more particularly, to a method for detecting deterioration of a lithium secondary battery that can easily and accurately detect a battery that is likely to deteriorate.

  In recent years, lithium secondary batteries have been used as in-vehicle power supplies or personal computers and portable terminals. In particular, a lithium secondary battery that is lightweight and has a high energy density is gaining importance as a high-output power supply for vehicles.

Lithium secondary batteries are known to deteriorate in performance when the battery voltage becomes too high, and the battery voltage is monitored to detect such deterioration. For example, the battery voltage (open terminal voltage) at the time of charging is detected, the number of times when the voltage becomes a specified voltage or more is counted, and if the number is large, it is determined that the battery has deteriorated. By receiving such deterioration determination and taking appropriate measures such as lowering the charging voltage, it is possible to suppress the rapid deterioration of the battery and extend the battery life. For example, Patent Document 1 is cited as a conventional technique related to this type of charging process.

JP 2009-089516 A

  By the way, a lithium secondary battery used as a power source of a vehicle such as an automobile (for example, a hybrid vehicle or an electric vehicle using a lithium secondary battery as a power source and another power source having a different operating principle such as an internal combustion engine) It is desirable that the lithium secondary battery mounted on the battery has a large capacity as a driving power source. However, such a large-capacity type lithium secondary battery tends to be uneven in temperature and reaction in the battery due to an increase in size. Therefore, a local increase in voltage occurs during charging, and a part of the battery may be exposed to a high voltage state, which may cause deterioration of the battery. Since such a local voltage increase cannot be detected by the cell terminal voltage, there has been a problem that battery deterioration cannot be reliably prevented. The present invention solves the above problems.

  The method for detecting deterioration of a lithium secondary battery provided by the present invention is a method for detecting deterioration of a lithium secondary battery in which a voltage stabilizer that keeps the battery voltage constant is added to a non-aqueous electrolyte. The deterioration detection method includes a first charging step of charging the lithium secondary battery until the voltage of the battery reaches a predetermined first specified voltage. Moreover, after reaching | attaining said 1st regulation voltage, the 2nd charge process of charging with a charge rate lower than the charge rate of the said 1st charge process is included. In the second charging step, the time until the battery voltage at the time of charging reaches a preset charge stop voltage is measured, and the deterioration of the battery is estimated based on the arrival time.

  In the present specification, the “voltage stabilizer” refers to an additive having a function of keeping the battery voltage constant, and typically refers to a redox additive having a redox ability. When the battery voltage reaches a predetermined voltage during charging, such an additive is oxidized on the surface of the positive electrode to generate an oxidation product. When the oxidation product moves to the negative electrode side and is reduced on the negative electrode surface, the additive is regenerated. The reaction of such additives is performed reversibly, during which the battery voltage is kept approximately constant.

  In the deterioration detection method of the present invention, after charging the lithium secondary battery to which the voltage stabilizer is added until the voltage of the battery reaches a predetermined first specified voltage (first charging step), the first charging is performed. Charging is performed at a charging rate lower than the charging rate of the process (second charging process). At this time, if the battery temperature is uniform and the battery voltage is uniform, the voltage stabilizer will function properly when the battery voltage rises to the specified voltage. And the battery voltage is kept constant until the end of charging. On the other hand, if the temperature and reaction in the battery are uneven and the voltage in the battery is not uniform, a local increase in voltage occurs during charging, and a part of the battery is exposed to a high voltage state. Stabilizer decomposes. As a result, the voltage holding function of the voltage stabilizer is lost, and the battery voltage increases with time. According to the present invention, by grasping the transition (increase degree) of the battery voltage, it is possible to detect a local voltage increase in the battery and estimate a battery that is likely to deteriorate in the future.

  In a preferable aspect of the deterioration detection method disclosed herein, when the battery voltage at the time of charging reaches a preset charging stop voltage within a predetermined time, it is estimated that the deterioration of the battery is large. On the other hand, when the battery voltage does not reach the charge stop voltage within a predetermined time, the battery voltage at the time when the predetermined time has passed is grasped, and the battery has a degradability when the battery voltage exceeds a predetermined threshold. Estimated to be large. With this configuration, it is possible to accurately detect a battery that is likely to deteriorate in the future.

  The voltage stabilizer used in the present invention may be any additive having a function of keeping the above-described battery voltage constant. For example, 1,4-dimethoxy-2-fluorobenzene, 1,3-dimethoxy-5-chlorobenzene, 3,5-dimethoxy-1-fluorobenzene, 1,2-dimethoxy-4-fluorobenzene, 1,2-dimethoxy At least one aromatic compound selected from the group consisting of -4-bromobenzene and 2,5-dimethoxy-1-bromobenzene can be used. Since the above materials have an appropriate oxidation-reduction potential, when a voltage stabilizer comprising the material is added to the non-aqueous electrolyte, the above voltage is within a range that does not greatly exceed the decomposition potential of the non-aqueous electrolyte. This is preferable in that the stabilizer can function.

  Although it does not restrict | limit especially as a charge rate in the said 2nd charge process, Usually, it is appropriate to set it as 0.5 C or less, for example, it is preferable to set it as 0.2 C or less. If the charging rate in the second charging step is too high, the voltage stabilizer may not be able to hold the voltage and decomposed, and the above-described deterioration detection charging process may not be performed properly. On the other hand, if the charging rate is too low, it takes a lot of time to charge, so the deterioration detection process may not be performed quickly. From the viewpoint of promptly detecting deterioration, the charging rate is approximately 0.05C or higher. In addition, 1C here is defined as the amount of current that can be discharged in 1 hour from the battery capacity predicted from the theoretical capacity of the positive electrode.

  The charge stop voltage in the second charging step can be set to a voltage value such that the positive electrode potential (vs Li / Li +) is higher than the oxidation-reduction potential of the voltage stabilizer and lower than the decomposition potential of the voltage stabilizer. The deterioration detection process described above may not be performed properly if it is either higher or lower than this range. In a preferred embodiment, the charge stop voltage in the second charging step is 3.6V to 4.4V. Further, the predetermined time in the second charging step may be long enough to appropriately predict the battery deterioration from the behavior of the battery voltage during charging, and may vary depending on the charging rate. For example, when the charging rate is 0.1 C, approximately 40 to 100 minutes is appropriate, and preferably 50 to 70 minutes (for example, 60 minutes). In a preferred aspect, in the second charging step, the charging rate is 0.08 C to 0.2 C, the charging stop voltage is 3.9 V to 4.1 V, and the predetermined time is 50 minutes to 70 minutes. It is.

The first specified voltage in the first charging step can be set to a voltage value such that the positive electrode potential (vs Li / Li +) is lower than the oxidation-reduction potential of the voltage stabilizer. There are cases in which the deterioration detection process cannot be performed properly if it is either higher or lower than this range. In a preferred embodiment, the first specified voltage in the first charging step is 3.0V to 3.5V.

  A preferable application target of the technology disclosed herein is a relatively large capacity type lithium secondary battery having a rated capacity of 10 Ah or more. For example, the lithium secondary battery has a rated capacity of 20 Ah or more (for example, 20 Ah or more, typically 50 Ah or less), and further, 30 Ah or more (for example, 30 Ah or more, typically 100 Ah or less). Is exemplified. Such a large-capacity type lithium secondary battery is likely to have uneven temperature and reaction in the battery due to an increase in size, and a local voltage increase is likely to occur in the battery. Is particularly useful.

  In addition, according to the present invention, a lithium secondary battery system that can suitably execute the deterioration detection method disclosed herein is provided. That is, a lithium secondary battery system that detects deterioration of a lithium secondary battery in which a voltage stabilizer that keeps the battery voltage constant is added to a non-aqueous electrolyte, and the lithium secondary battery is under a predetermined condition. Charging means for charging, voltage measuring means for measuring the battery voltage of the lithium secondary battery charged by the charging means, and a control device electrically connected to each of the charging means and the voltage measuring means With. The charging means includes: a first charging process for charging the lithium secondary battery until a voltage of the battery reaches a predetermined first specified voltage; and the first charging after the first specified voltage is reached. The second charging process is performed in which charging is performed at a charging rate lower than the charging rate of the process. When the second charging process of the lithium secondary battery is performed by the charging unit, the control device waits until the battery voltage measured by the voltage measuring unit reaches a preset charging stop voltage. And the deterioration of the battery is estimated based on the arrival time. According to such a lithium secondary battery system, the above-described deterioration detection method can be suitably implemented.

  In a preferred aspect of the lithium secondary battery system disclosed herein, the control device has a deterioration property of the battery when the battery voltage reaches a charge stop voltage within a predetermined time in the second charging process. It is configured to be estimated to be large. Further, in a preferred aspect, when the battery voltage does not reach the charge stop voltage within a predetermined time in the second charging process, the control device grasps the battery voltage at the time when the predetermined time has passed, When the battery voltage exceeds a predetermined threshold value, the battery is estimated to have a large deterioration property. According to such a lithium secondary battery system, the above-described deterioration detection method can be suitably implemented.

It is a schematic diagram which shows an example of the structure of the lithium secondary battery used for one Embodiment of this invention. It is a schematic diagram which shows an example of the structure of the wound electrode body used for one Embodiment of this invention. It is a graph which shows the relationship between a battery voltage and charging time. It is a graph which shows the relationship between a battery voltage and charging time. It is a graph which shows the relationship between a battery voltage and charging time. It is a block diagram which shows an example of the lithium secondary battery system used for one Embodiment of this invention. It is a figure which shows the processing flow of the lithium secondary battery system used for one Embodiment of this invention. It is a side view of the vehicle carrying a lithium secondary battery system.

  Embodiments according to the present invention will be described below with reference to the drawings. In the following drawings, members / parts having the same action are described with the same reference numerals. Note that the dimensional relationship (length, width, thickness, etc.) in each drawing does not reflect the actual dimensional relationship. Further, matters other than the matters specifically mentioned in the present specification and matters necessary for the implementation of the present invention (for example, the configuration and manufacturing method of the electrode body including the positive electrode and the negative electrode, the configuration and manufacturing method of the separator and the electrolytic solution) General techniques relating to the construction of lithium secondary batteries and other batteries, etc.) can be grasped as design matters for those skilled in the art based on the prior art in this field.

  Hereinafter, a method for detecting deterioration of a lithium secondary battery according to an embodiment of the present invention will be described in the order of the configuration of the target lithium secondary battery and the method for detecting deterioration.

<Lithium secondary battery>
A lithium secondary battery 100 (hereinafter referred to as “battery” as appropriate) targeted by the capacity recovery method of the present embodiment includes, for example, a long positive electrode sheet 10 and a long negative electrode as shown in FIG. The electrode body (winding electrode body) 80 in a form in which the sheet 20 is wound flatly through the long separator 40 can accommodate the wound electrode body 80 together with the non-aqueous electrolyte 90 ( It has a configuration accommodated in a case 50 of a flat box shape.

  The case 50 includes a flat rectangular parallelepiped case main body 52 having an open upper end, and a lid 54 that closes the opening. As a material constituting the case 50, a metal material such as aluminum or steel is preferably used (in this embodiment, aluminum). Or the case 50 formed by shape | molding resin materials, such as a polyphenylene sulfide (PPS) and a polyimide resin, may be sufficient. On the upper surface of the case 50 (that is, the lid body 54), a positive electrode terminal 70 that is electrically connected to the positive electrode of the wound electrode body 80 and a negative electrode terminal 72 that is electrically connected to the negative electrode 20 of the electrode body 80 are provided. Yes. In the case 50, a flat wound electrode body 80 is accommodated together with a non-aqueous electrolyte (not shown).

  The wound electrode body 80 according to the present embodiment is the same as the wound electrode body of a normal lithium secondary battery, and as shown in FIG. ) Sheet structure.

<Positive electrode sheet>
The positive electrode sheet 10 has a structure in which a positive electrode active material layer 14 containing a positive electrode active material is held on both surfaces of a foil-like positive electrode current collector 12 in the form of a long sheet. However, the positive electrode active material layer 14 is not attached to one side edge (the left side edge portion in the drawing) along the widthwise end of the positive electrode sheet 10, and the positive electrode current collector 12 is exposed with a certain width. The positive electrode active material layer non-formed part 16 is formed. For the positive electrode current collector 12, an aluminum foil or other metal foil suitable for the positive electrode is preferably used.

As the positive electrode active material, one type or two or more types of materials conventionally used in lithium secondary batteries can be used without any particular limitation. Preferred applications of the technology disclosed herein include lithium and transition metals such as lithium nickel oxide (eg, LiNiO ₂ ), lithium cobalt oxide (eg, LiCoO ₂ ), and lithium manganese oxide (eg, LiMn ₂ O ₄ ). And a positive electrode active material mainly containing an oxide (lithium transition metal oxide) containing the element as a constituent metal element. Alternatively, a phosphate compound having an olivine type crystal structure such as LiFePO ₄ may be used.

  In addition to the positive electrode active material, the positive electrode active material layer 14 can contain one or two or more materials that can be used as a constituent component of the positive electrode active material layer in a general lithium secondary battery, if necessary. An example of such a material is a conductive material. As the conductive material, carbon materials such as carbon powder (for example, acetylene black (AB)) and carbon fiber are preferably used. Alternatively, conductive metal powder such as nickel powder may be used. In addition, examples of a material that can be used as a component of the positive electrode active material layer include various polymer materials (for example, polyvinylidene fluoride (PVDF)) that can function as a binder of the positive electrode active material.

<Negative electrode sheet>
Similarly to the positive electrode sheet 10, the negative electrode sheet 20 has a structure in which a negative electrode active material layer 24 containing a negative electrode active material is held on both surfaces of a long sheet-like foil-shaped negative electrode current collector 22. However, the negative electrode active material layer 24 is not attached to one side edge (the right side edge portion in the drawing) along the widthwise edge of the negative electrode sheet 20, and the negative electrode current collector 22 is exposed with a certain width. The negative electrode active material layer non-forming part 26 is formed. For the negative electrode current collector 22, a copper foil or other metal foil suitable for the negative electrode is preferably used. As the negative electrode active material, one or more of materials conventionally used in lithium secondary batteries can be used without any particular limitation. Preferable examples include carbon materials such as graphite carbon and amorphous carbon.

  In addition to the negative electrode active material, the negative electrode active material layer 24 can contain one or two or more materials that can be used as a constituent component of the negative electrode active material layer in a general lithium secondary battery, if necessary. Examples of such materials are polymer materials (eg, PVDF, styrene butadiene rubber (SBR)) that can function as a binder for the negative electrode active material, and function as a thickener for the paste for forming the negative electrode active material layer. Examples thereof include a polymer material to be obtained (for example, carboxymethyl cellulose (CMC)).

<Separator>
As the separator 40 disposed between the positive and negative electrode sheets 10 and 20, various porous sheets similar to those of a general lithium secondary battery provided with a wound electrode body can be used. Preferable examples include porous resin sheets (films, nonwoven fabrics, etc.) made of polyolefin resins such as polyethylene (PE) and polypropylene (PP). Such a porous resin sheet may have a single layer structure, or may have a two or more layers structure (for example, a three-layer structure in which PE layers are laminated on both sides of a PP layer).

<Winded electrode body>
In producing the wound electrode body 80, the positive electrode sheet 10 and the negative electrode sheet 20 are laminated via the separator 40. At this time, the positive electrode sheet 10 and the negative electrode sheet 20 are placed so that the positive electrode active material layer non-formation part of the positive electrode sheet 10 and the negative electrode active material layer non-formation part of the negative electrode sheet 20 protrude from both sides of the separator 40 in the width direction. Laminate slightly shifted in the width direction. The laminated body thus stacked is wound, and then the obtained wound body is crushed from the side surface direction and ablated, whereby a flat wound electrode body 80 can be produced.

  A wound core portion 82 (that is, the positive electrode active material layer 14 of the positive electrode sheet 10, the negative electrode active material layer 24 of the negative electrode sheet 20, and the separator 40) is densely laminated at the center portion in the winding axis direction of the wound electrode body 80. Part) is formed. Further, the electrode active material layer non-formed portions 16 and 26 of the positive electrode sheet 10 and the negative electrode sheet 20 protrude outward from the wound core portion 82 at both ends of the wound electrode body 80 in the winding axis direction. . A positive electrode lead terminal 74 and a negative electrode lead terminal 76 are provided on the protruding portion 16 (that is, the non-formed portion of the positive electrode active material layer 14) 16 and the protruding portion 26 (that is, the non-formed portion of the negative electrode active material layer 24) 26, respectively. Attached and electrically connected to the positive terminal 70 and the negative terminal 72 described above.

<Non-aqueous electrolyte>
Then, the wound electrode body 80 is accommodated in the main body 52 from the upper end opening of the case main body 52, and an appropriate nonaqueous electrolytic solution 90 is disposed (injected) in the case main body 52. Such a non-aqueous electrolyte typically has a composition in which a supporting salt is contained in a suitable non-aqueous solvent. As said non-aqueous solvent, ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC) etc. can be used, for example. Further, as the supporting salt, for _{example, LiPF 6, LiBF 4, LiAsF} 6, LiCF 3 can be preferably used a lithium salt of SO ₃ and the like.

  Thereafter, the opening is sealed by welding or the like with the lid 54, and the assembly of the lithium secondary battery 100 according to the present embodiment is completed. The sealing process of the case 50 and the placement (injection) process of the electrolytic solution may be the same as the method used in the manufacture of the conventional lithium secondary battery, and do not characterize the present invention. In this way, the construction of the lithium secondary battery 100 according to this embodiment is completed.

  A preferable application target of the technology disclosed herein is a relatively large capacity type lithium secondary battery 100 having a rated capacity of 10 Ah or more. For example, the lithium secondary battery has a rated capacity of 20 Ah or more (for example, 20 Ah or more, typically 50 Ah or less), and further, 30 Ah or more (for example, 30 Ah or more, typically 100 Ah or less). Is exemplified. Such a large-capacity type lithium secondary battery 100 tends to have non-uniform temperatures and reactions in the battery due to an increase in size, and a local increase in voltage tends to occur in the battery. Therefore, the deterioration detection method according to the present invention that can detect a local voltage increase in the battery can be particularly preferably applied to the large capacity type lithium secondary battery as described above.

<Deterioration detection method>
The method for detecting deterioration of a lithium secondary battery disclosed herein is a method for detecting deterioration of a lithium secondary battery in which a voltage stabilizer for keeping the battery voltage constant is added to a non-aqueous electrolyte, A first charging step for charging the battery until the voltage of the battery reaches a predetermined first specified voltage, and after reaching the first specified voltage, charging at a charging rate lower than the charging rate of the first charging step And a second charging step. Then, the battery voltage when the lithium secondary battery is charged in the second charging step is monitored, and the battery deterioration (the degree of battery deterioration in the future) is estimated according to the behavior of the battery voltage at that time. Hereinafter, the charging process in the deterioration detection method of the present embodiment is referred to as a deterioration detection process.

<Voltage stabilizer>
The voltage stabilizer used in the deterioration detection process can be used without particular limitation as long as it is an additive having a function of keeping the battery voltage constant. The voltage stabilizer is preferably a redox additive having redox ability, for example. When the additive reaches a predetermined voltage during charging, the additive is oxidized on the surface of the positive electrode to generate an oxidation product. When the oxidation product moves to the negative electrode side and is reduced on the negative electrode surface, the additive is regenerated. The reaction of such additives is performed reversibly, while the battery voltage is kept constant. As the additive (voltage stabilizer) that can be used in this configuration, at least one substance selected from the group consisting of aromatic compounds, heterocyclic complexes, radical compounds, Ce compounds, and metallocene complexes is preferably used.

  For example, the aromatic compounds include 1,4-dimethoxy-2-fluorobenzene, 1,3-dimethoxy-5-chlorobenzene, 3,5-dimethoxy-1-fluorobenzene, 1,2-dimethoxy-4-fluorobenzene. 1,2-dimethoxy-4-bromobenzene, 2,5-dimethoxy-1-bromobenzene, and the like. Of these, use of 1,4-dimethoxy-2-fluorobenzene is preferred. Two or more of these may be used in combination. Since the above materials have an appropriate oxidation-reduction potential, when a voltage stabilizer comprising the material is added to the non-aqueous electrolyte, the above voltage is within a range that does not greatly exceed the decomposition potential of the non-aqueous electrolyte. This is preferable in that the stabilizer can function.

  Heterocyclic complexes include TEMP (2,2,6,6-tetramethyl-1-piperidinyloxy, free radical), 4-hydroxy-TEMPO, 4-amino-TEMPO, 4-cyano-TEMPO, 4-carboxy-TEMPO. 4- (2-bromoacetamide) -TEMPO, 4- (2-iodoacetamide) -TEMPO, 3-hydroxy-TEMPO, 3-amino-TEMPO, 3-cyano-TEMPO, 3- (2-bromoacetamide) -TEMPO, 3, -(2-Iodoacetamide) -TEMPO, proxyl, β-hydroxy-proxyl, β- (2-bromoacetamide) -proxyl, β- (2-iodoacetamide) -proxyl and the like are exemplified. Two or more of these may be used in combination.

  Examples of the radical compound include tris (4-fluorophenyl) amine, tris (4-trifluoromethylphenyl) amine, tris (2,4,6-trifluorophenyl) amine, and tris (4-methyl-2,3,5). , 6-tetrafluorophenyl) amine, tris (2,3,5,6-tetrafluorophenyl) amine, tris (2,3,4,5,6-pentafluorophenyl) amine, tris (4-trifluoromethyl) -2,3,5,6-tetrafluorophenyl) amine, tris (2,6-difluoro-4-bromophenyl) amine, tris (2,4,6-tribromophenyl) amine, tris (2,4,4) Examples include triphenylamine compounds such as 6-trichlorophenyl) amine. Two or more of these may be used in combination.

Examples of the Ce compound include cerium salts such as Ce (NH ₄ ) ₂ (NO ₃ ) ₅ .

Examples of the metallocene complex include Fe (5-Cl-1,10-phenanthroline) ₃ X ₂ (wherein X is an anionic molecule), Ru (phenanthroline) ₃ X ₂ (where X in the formula Is an anionic molecule)), and the like. Two or more of these may be used in combination. The above materials are preferable in that the reversibility of the reaction is good, and thus when the voltage stabilizer made of the material is added to the non-aqueous electrolyte, the function of keeping the battery voltage constant can be appropriately exhibited.

  The concentration of the voltage stabilizer in the electrolyte solution is not particularly limited as long as it is a concentration that can stably exhibit the voltage holding function described above. For example, the concentration of the voltage stabilizer can be about 0.005 mol / L to 0.05 mol / L, usually about 0.008 mol / L to 0.03 mol / L, and particularly 0.009 mol / L. It is preferable to set the concentration to ˜0.02 mol / L (for example, about 0.01 mol / L). If the concentration of the voltage stabilizer is too low, the voltage holding function described above may not be stably exhibited. On the other hand, if the concentration of the voltage stabilizer is too high, the voltage stabilizer functions as a resistance component of the battery. , Battery performance may decrease (typically electrical resistance increases).

  The first specified voltage in the first charging step can be set to a voltage value such that the positive electrode potential is lower than the oxidation-reduction potential of the voltage stabilizer. Preferably, the voltage value is set to a potential that is 0.1 V or more lower than the oxidation-reduction potential of the voltage stabilizer. For example, when the above-mentioned 1,4-dimethoxy-2-fluorobenzene is used as a voltage stabilizer, the first specified voltage is approximately in the range of 3.0 V to 3.5 V (preferably 3.2 V to 3.5 V). Can be set. There are cases in which the deterioration detection process cannot be performed properly if it is either higher or lower than this range. The charging rate in the first charging step is not particularly limited, and is usually about 0.8C to 2.0C, preferably about 0.8C to 1.2C.

  In the method for detecting deterioration of a lithium secondary battery disclosed herein, a lithium secondary battery to which a voltage stabilizer is added is charged until the voltage of the battery reaches a predetermined first specified voltage (first charging step). ). Then, after reaching the first specified voltage, the charging process is performed at a charging rate lower than the charging rate of the first charging step (second charging step). In this second charging step, the battery voltage during charging is monitored. Then, a time until the battery voltage at the time of charging reaches a preset charging stop voltage is measured, and the deterioration of the battery is estimated based on the arrival time. Specifically, when the battery voltage reaches a preset charge stop voltage within a predetermined time, it is estimated that the battery is highly degradable. On the other hand, when the battery voltage does not reach the charge stop voltage within a predetermined time, the battery voltage at the time when the predetermined time has passed is grasped, and when the battery voltage exceeds a predetermined threshold, the battery is highly deteriorated. presume.

3, 4, and 5 show changes in battery voltage when the above-described deterioration inspection process (second charging process) is performed on various batteries having different battery deterioration states. As shown in the figures, the battery voltage during charging of the lithium secondary battery, gradually increase from the first predetermined voltages V ₁ with the progress of the charging process. At this time, if there is no unevenness in temperature and reaction in the battery and the voltage in the battery is uniform, as shown in L3 of FIG. 5, the voltage stabilizer functions when the battery voltage rises to a predetermined voltage. After that, the battery voltage stabilizes, and the battery voltage is kept constant until the end of charging. The portion where the battery voltage is constant in L3 in FIG. 5 indicates that the voltage stabilizer is functioning properly. On the other hand, if the temperature and reaction in the battery are uneven and the voltage in the battery is not uniform, a local increase in voltage occurs during charging, and a part of the battery is exposed to a high voltage state. Stabilizer decomposes. As a result, as shown in L1 of FIG. 3 and L2 of FIG. 4, the voltage holding function of the voltage stabilizer is lost, and the battery voltage increases with the passage of time. According to this configuration, by grasping the transition (increase degree) of the battery voltage, it is possible to detect a local voltage increase in the battery and estimate a battery that is likely to deteriorate in the future.

From the above knowledge, in the second charging step of the present embodiment, charging is performed at a charging rate lower than the charging rate of the first charging step, and the battery voltage at this time is monitored. Then, as shown in FIG. 3, when it reaches the charge stop voltage Va battery voltage predetermined for the predetermined time T _2, the deterioration of the battery is estimated as "large". Meanwhile, as shown in Fig. 4 and 5, when the battery voltage does not reach within a predetermined time T ₂ to the charge stop voltages Va, grasp the battery voltage V ₂ at which said predetermined constant-time T ₂ has elapsed, the battery If the voltage V ₂ exceeds Vb (estimated criteria of degradation) the predetermined threshold, the deterioration of the battery is estimated as "large" (Fig. 4). On the other hand, if the battery voltage V ₂ does not exceed the predetermined threshold value Vb, the deterioration of the battery is estimated as "small" (Figure 5).

At this time, the battery degradability may be estimated stepwise by preparing a plurality of threshold values (degradation estimation criteria) Vb corresponding to the battery degradability. That is, using a plurality of threshold Vb, as the battery voltage V ₂ at the predetermined time T ₂ has elapsed is greater degradation of the battery may be estimated to be large. Also, when it reaches the predetermined time T in ₂ to charge stop voltage Va, it may be estimated to be greater deterioration of the battery as compared with the case where the charge stop voltage Va does not reach the predetermined time T _2.

  Although it does not restrict | limit especially as a charge rate in the said 2nd charge process, Usually, it is appropriate to set it as 0.5 C or less, for example, it is preferable to set it as 0.2 C or less. If the charging rate in the second charging step is too high, the voltage stabilizer may not be able to hold the voltage and decomposed, and the above-described deterioration detection charging process may not be performed properly. On the other hand, if the charging rate is too low, it takes a lot of time to charge, so the deterioration detection process may not be performed quickly. From the viewpoint of promptly detecting deterioration, the charging rate is approximately 0.05C or higher. In addition, 1C here is defined as the amount of current that can be discharged in 1 hour from the battery capacity predicted from the theoretical capacity of the positive electrode.

  The charge stop voltage in the second charging step can be set to a voltage value such that the positive electrode potential is higher than the redox potential of the voltage stabilizer and lower than the decomposition potential of the voltage stabilizer. Preferably, the voltage value is set such that the positive electrode potential is 0.1 V or more higher than the redox potential of the voltage stabilizer and 0.1 V or more lower than the decomposition potential of the voltage stabilizer. For example, when the above-mentioned 1,4-dimethoxy-2-fluorobenzene is used as a voltage stabilizer, the charge stop voltage is generally 3.6 V to 4.4 V (preferably 3.8 V to 4.2 V, particularly preferably 3 .9V to 4.1V). The deterioration detection process described above may not be performed properly if it is either higher or lower than this range. Further, the predetermined time in the second charging step may be long enough to appropriately predict the battery deterioration from the behavior of the battery voltage during charging, and may vary depending on the charging rate. For example, when the charging rate is 0.1 C, approximately 40 to 100 minutes is appropriate, and preferably 50 to 70 minutes (for example, 60 minutes).

  The charging process in the degradation detection method disclosed here can be performed using an appropriate charging device (for example, a charging circuit). The charging device that can be used for the charging process is not particularly limited as long as it is a conventional charging device that can charge a lithium secondary battery, and various circuit configurations can be employed. The temperature of the charging treatment is not particularly limited, but it is usually appropriate to set the temperature to about 0 ° C. to 40 ° C., for example, preferably about 20 ° C. to 30 ° C.

<Lithium secondary battery system>
FIG. 6 is a block diagram showing an example of a lithium secondary battery system 1000 including a deterioration inspection apparatus that embodies the above-described lithium secondary battery deterioration detection process. As shown in FIG. 6, the lithium secondary battery system 1000 includes an electronic control that controls the operation of the lithium secondary battery 100, a load 110 connected to the lithium secondary battery 100, and the lithium secondary battery 100 connected to the load 110. The apparatus 120 and the voltage measurement part 130 which measures the battery voltage of this battery are provided. Since the lithium secondary battery 100 is the same as that described above, a detailed description thereof will be omitted.

  The load 110 may include a power consuming device that consumes the power stored in the lithium secondary battery 100 and a power supply device (charging means) that can charge the battery 100. The power supply device provided in the load 110 is not particularly limited as long as it is a power supply device that can charge a conventional lithium secondary battery, and various circuit configurations can be adopted. An electronic control device 120 is electrically connected to the power supply device provided in the load 110. The power supply unit (charging means) performs a first charging process for charging the lithium secondary battery 100 until the voltage of the battery 100 reaches a predetermined first specified voltage in response to a drive signal from the electronic control unit 120. It is comprised so that it may perform (1st charge process). In addition, the power supply unit (charging means) is configured to perform a second charging process in which charging is performed at a charging rate lower than the charging rate of the first charging process after reaching the first specified voltage (first). 2 charging step).

  The voltage measuring unit 130 is configured to measure the battery voltage (typically, the open terminal voltage of the battery) of the lithium secondary battery that is charged by the power supply device (charging means) of the load 110. The voltage measuring unit 130 can be arbitrarily selected from those conventionally used in a general lithium secondary battery system. For example, the voltage measurement unit 130 may be a circuit that is connected between terminals of the lithium ion secondary battery 100 and measures a voltage between the terminals. The voltage measuring unit 130 may be configured using an analog-digital converter that converts the measured voltage into a digital signal and outputs the digital signal to the electronic control unit 120. The measurement result of the battery voltage measured by the voltage measurement unit 130 is sent to the electronic control unit 120 as an output of the voltage measurement unit 130.

  The electronic control unit 120 is configured to control the operation of the lithium secondary battery 100 connected to the load 110, and drives and controls the load 110 based on predetermined information. A typical configuration of the electronic control unit 120 includes at least a ROM (Read Only Memory) storing a program for performing such control, a CPU (Central Processing Unit) capable of executing the program, an input / output port, and the like. Is included. Various signals from a current sensor, a temperature sensor, and the like (not shown), a signal (output) from the voltage measurement unit 130, and the like are input to the electronic control device 120 via an input port. Further, the electronic control device 120 outputs a drive signal to the load 110 (power consumption machine and power supply machine) via the output port.

  The electronic control device 120 includes a deterioration estimating unit that estimates the deterioration of the battery based on the measured value of the battery voltage measured by the voltage measuring unit 130. The measurement result of the battery voltage measured by the voltage measurement unit 130 is sent from the voltage measurement unit 130 to the deterioration estimation unit. The deterioration estimation unit monitors the battery voltage sent from the voltage measurement unit 130, and estimates the deterioration of the battery according to the behavior of the battery voltage at that time. Specifically, the electronic control device (deterioration estimation unit) 120 is a battery measured by the voltage measuring unit 130 when the second charging process of the lithium secondary battery is performed by the power supply unit (charging unit) of the load 110. The time until the voltage reaches a preset charge stop voltage is measured, and the deterioration of the battery is estimated based on the arrival time. Specifically, the electronic control unit (deterioration estimation unit) is configured to estimate that the battery deterioration is large when the battery voltage reaches the charge stop voltage within a predetermined time in the second charging process. Yes. In addition, when the battery voltage does not reach the charge stop voltage within a predetermined time in the second charging process, the electronic control device (deterioration estimation unit) grasps the battery voltage at the time when the predetermined time has passed, and the battery voltage When the battery exceeds a predetermined threshold, the battery is assumed to be highly degradable.

  The operation of the lithium secondary battery system 1000 configured as described above will be described. FIG. 7 is a flowchart illustrating an example of a processing routine executed by the deterioration estimation unit of the electronic control device 120 according to the present embodiment. This processing routine is executed when the deterioration of the lithium secondary battery 100 is detected.

When the processing routine shown in FIG. 7 is executed, the electronic control unit 120 first drives and controls the load 110 to charge the lithium secondary battery 100 (step S10; first charging process). The charging rate at this time is preferably 0.8C to 2.0C, for example 1.0C. Then, in step S11, and monitors the battery voltage Vx measured by the voltage measuring unit 130, determines whether the battery voltage Vx has reached the first predetermined voltage V _1. When the battery voltage Vx does not reach a first predetermined voltage _{V 1} (the case of "YES"), to continue the first charging process returns to step S10. On the other hand, (the case of "NO") if the battery voltage Vx reaches a first predetermined voltage V _1, followed by performing the low rate charging process in step S20 (the second charging process). The first predetermined voltages _{V 1} may be set in advance, for example, 3.5 V.

  In the low rate charging process of step S20, the load 110 is driven and charged at a low rate. The charging rate at this time is preferably 0.08C to 0.2C, for example, 0.1C. In step S21, the battery voltage Vx measured by the voltage measuring unit 130 is monitored to determine whether or not the battery voltage Vx has reached the charge stop voltage Va. When the battery voltage Vx reaches the charge stop voltage Va (in the case of “YES”, refer to FIG. 3), the process proceeds to step S22 to drive and control the load 110 and stop the low rate charge. Then, it is estimated that the battery deterioration is “large” (step S23). The charge stop voltage Va may be set in advance, for example, 4.0V.

On the other hand, (the case of "NO") if the battery voltage Vx does not reach the charge stop voltage Va at step S21, the process proceeds to step S24, the charging time Tx determines whether reaches the predetermined time T _2. ( "NO") if the charging time Tx does not reach the predetermined time T _2), to continue the low-rate charging returns to step S20. On the other hand, (the case of "YES") if the charging time Tx has reached the predetermined time _{T 2,} drives and controls the load 110 proceeds to step S25, stops the low-rate charging. Note that the predetermined time T ₂ may be set in advance, for example, 60 minutes.

After stopping the charging at step S25, then, when the user stops the charging at step S26 (i.e. time point the predetermined time T ₂ has elapsed) Check battery voltage V _2. Then, the battery voltage V ₂ to determine whether more than a predetermined threshold value Vb in step S27. When the battery voltage _{V 2} exceeds the threshold value Vb in step S27 ( "YES", see FIG. 4), the deterioration of the battery is estimated as "large" (step S28). On the other hand, (the case of "NO", see FIG. 5) when the battery voltage V ₂ does not exceed the threshold value Vb, the deterioration of the battery is estimated as "small" (Step S29). The threshold value Vb may be set in advance, for example, 3.7V.

  In this way, by subjecting the lithium secondary battery to which the voltage stabilizer has been added to the low-rate charging process, it is possible to accurately detect a battery that is likely to deteriorate in the future.

  The electronic control unit 120 may output the estimation result estimated by the deterioration estimation unit to a display unit (not shown). In the display unit, in response to the estimation result, for example, a display prompting battery replacement can be displayed.

  Moreover, the electronic control apparatus 120 may include a control unit (not shown) that controls charging / discharging of the battery based on the estimation result estimated by the deterioration estimation unit. The control unit drives and controls the load 110 (power consumption machine and power supply machine) so that the battery state is kept good based on at least the estimation result estimated by the deterioration estimation unit. Such control is, for example, for setting the maximum allowable input / output of the battery 100 based on the estimation result estimated by the deterioration estimation unit, and driving and controlling the load 110 within the set maximum input / output range. possible. For example, the maximum input / output may be set to be smaller as the deterioration of the battery estimated by the deterioration estimation unit is larger, and the maximum input / output may be set to be larger as the deterioration of the battery is smaller. According to this configuration, the maximum allowable input / output of the battery is appropriately set according to the future deterioration of the battery, so that overload to the battery can be prevented and further deterioration of the battery is suppressed. can do.

  As described above, in the lithium secondary battery system 1000 according to the present embodiment, a battery that is likely to deteriorate in the future is obtained by a simple configuration in which a voltage stabilizer is added to the non-aqueous electrolyte and charging is performed at a low rate. Simple and highly accurate detection is possible.

  The lithium secondary battery system 1000 disclosed herein has performance suitable as a battery mounted on a vehicle. Therefore, according to the present invention, as shown in FIG. 8, there is provided a vehicle 1 including any lithium secondary battery system 1000 disclosed herein. In particular, a vehicle (for example, an automobile) including the lithium secondary battery system 1000 as a power source (typically, a power source of a hybrid vehicle or an electric vehicle) is provided.

  Hereinafter, although the test example regarding this invention is demonstrated, it is not intending to limit this invention to what is shown to the following test examples.

<Preparation of positive electrode sheet>
LiFePO ₄ powder was used as the positive electrode active material. First, positive electrode active material powder, AB as a conductive material, and PVDF as a binder are mixed in N-methylpyrrolidone (NMP) so that the mass ratio of these materials is 85: 5: 10. An active material layer paste was prepared. This positive electrode active material layer paste is applied to both sides of a long sheet-like positive electrode current collector (aluminum foil having a thickness of about 20 μm) and dried to provide a positive electrode active material layer on both surfaces of the positive electrode current collector. The obtained positive electrode sheet was produced.

<Preparation of negative electrode sheet>
As the negative electrode active material, graphite powder was used. First, negative electrode active material powder, SBR as a binder, and CMC as a thickener are mixed in water so that the mass ratio of these materials is 95: 2.5: 2.5. A layer paste was prepared. This negative electrode active material layer paste is applied to one side of a long sheet-like negative electrode current collector (copper foil having a thickness of about 15 μm) and dried to provide a negative electrode active material layer on both sides of the negative electrode current collector. The obtained negative electrode sheet was produced.

<Production of lithium secondary battery>
Next, the positive electrode sheet and the two negative electrode sheets are alternately stacked so that the positive electrode active material layer and the negative electrode active material layer face each other, and two separators (PE on both sides of the PP layer) A three-layer structure in which layers were stacked was used.) To insert an electrode body. This electrode body was inserted into a laminate bag together with a non-aqueous electrolyte to construct a test lithium secondary battery (laminate cell). As a non-aqueous electrolyte, a mixed solvent containing EC and EMC at a volume ratio of 5: 5 contains LiPF ₆ as a supporting salt at a concentration of about 1 mol / liter, and 1,4 as a voltage stabilizer. A non-aqueous electrolyte solution containing -dimethoxy-2-fluorobenzene at a concentration of about 0.01 mol / L was used. Thus, the test lithium secondary battery 100 in which the voltage stabilizer was added to the non-aqueous electrolyte was assembled.

<Measurement of initial cell capacity>
The initial cell capacity of the test lithium secondary battery obtained as described above was measured by the following procedures 1 to 3 at a temperature of 25 ° C. and a voltage range of 2.5 V to 4.1 V.
Procedure 1: After reaching 4.1V by 1 / 3C constant current charge, perform constant voltage charge until the final current value is 1/10 of the initial current value or until the total charge time is 4 hours Charged.
Procedure 2: Discharged to 2.5 V by 1/3 C constant current discharge.
Procedure 3: The charging / discharging operations of Procedures 1 and 2 were repeated three times, and the discharge capacity in the third constant current discharge was defined as the initial cell capacity. In this test lithium secondary battery, the initial cell capacity is about 200 mAh.

<Charge / discharge test>
After the measurement of the initial cell capacity, a test lithium secondary battery was placed in a thermostat at 60 ° C., and a charge / discharge test was performed to give a charge / discharge pattern simulating actual use conditions. In this example, six test lithium secondary batteries (samples 1 to 6) were prepared, and different charge / discharge patterns were provided. Specifically, (1) mode; charge, discharge, pause (2) charge rate; 1 / 3C, 3C, 10C (3) seconds; 1 second, 3 seconds, 5 seconds, one level each The selection was repeated 100 times, and the arrangement was used as the charge / discharge pattern. The charge / discharge test was conducted by repeating this charge / discharge pattern 2000 times.

<Measurement of intermediate cell capacity>
After the charge / discharge test, the intermediate cell capacity of the test lithium secondary battery was measured by the same method as the measurement of the initial cell capacity described above.

<Deterioration inspection process>
After the measurement of the intermediate cell capacity, the deterioration test process for the test lithium secondary battery was performed according to the following procedures 1-3.
Procedure 1: Charged to 3.5 V by constant current charging at 1 C (first charging step).
Procedure 2: After Procedure 1, the battery was charged by constant current charging at 0.1 C (second charging step).
Procedure 3: The battery voltage at the time of charging in Procedure 2 was monitored, and either the termination condition of (1) the battery voltage reached 4.0 V or (2) 60 minutes passed from the start of charging was satisfied. Charging was stopped at that time.
As a result, in samples 1 to 4, charging was stopped under time conditions, and the battery voltages at the time of charging stop were 3.58V, 3.56V, 3.91V, 3.93V in the order of samples 1-4. On the other hand, in Samples 5 and 6, charging was stopped under voltage conditions. The transition of the battery voltage of samples 1, 3 and 5 is shown in FIGS. 5, 4 and 3, respectively.

<Durability test>
After the deterioration inspection process, the test lithium secondary battery was placed in a constant temperature bath at 60 ° C., the charge amount was adjusted so as to be half of the intermediate cell capacity, and left for 20 days to make a durability test.

<Measurement of final cell capacity>
After the durability test, the final cell capacity of the test lithium secondary battery was measured by the same method as the measurement of the initial cell capacity described above. Then, the capacity retention ratio (= “final cell capacity / intermediate cell capacity” × 100) was calculated from the intermediate cell capacity before the endurance test and the final cell capacity after the endurance test. The results are shown in Table 1.

  As is clear from Table 1, the batteries according to Samples 5 and 6 that stopped charging under the voltage condition during the deterioration inspection process had a capacity retention rate of less than 80%, and the capacity deterioration after the durability test was large. On the other hand, the batteries according to Samples 1 to 4 that stopped charging under the time condition during the deterioration inspection process had a higher capacity retention rate than Samples 5 and 6, and had less capacity deterioration after the durability test. Moreover, from the comparison of samples 1 to 4, the capacity deterioration after the durability test was larger as the voltage at the time of stopping charging was higher in the deterioration inspection process. From this, it can be seen that the larger the rate of voltage increase in the degradation inspection process, the greater the degradation of capacity in the subsequent durability test. From the above results, the battery to which the voltage stabilizer is added is charged at a low rate, and the higher the battery voltage rise rate at that time, the higher the possibility of future capacity degradation (the battery Large).

  As mentioned above, although this invention was demonstrated in detail, the said embodiment is only an illustration and what changed and modified the above-mentioned specific example is included in the invention disclosed here.

DESCRIPTION OF SYMBOLS 1 Vehicle 10 Positive electrode sheet 12 Positive electrode collector 14 Positive electrode active material layer 16 Positive electrode active material layer non-formation part 20 Negative electrode sheet 22 Negative electrode current collector 24 Negative electrode active material layer 26 Negative electrode active material layer non-formation part 40 Separator 50 Battery case 52 Case body 54 Lid 70 Positive electrode terminal 72 Negative electrode terminal 74 Positive electrode lead terminal 76 Negative electrode lead terminal 80 Winding electrode body 82 Winding core portion 90 Non-aqueous electrolyte 100 Lithium secondary battery 110 Load 120 Electronic controller 130 Voltage measuring unit 1000 Lithium secondary battery system

Claims (14)

A method for detecting deterioration of a lithium secondary battery in which a voltage stabilizer for keeping a battery voltage constant is added to a non-aqueous electrolyte,
A first charging step of charging the lithium secondary battery until the voltage of the battery reaches a predetermined first specified voltage;
A second charging step of charging at a charging rate lower than the charging rate of the first charging step after reaching the first specified voltage;
Here, in the second charging step, the time until the battery voltage at the time of charging reaches a preset charging stop voltage is measured, and the deterioration of the battery is estimated based on the arrival time. Secondary battery deterioration detection method.   The deterioration detection method according to claim 1, wherein, in the second charging step, when the battery voltage reaches a charge stop voltage within a predetermined time, it is estimated that the deterioration of the battery is large.   In the second charging step, when the battery voltage does not reach the charge stop voltage within a predetermined time, the battery voltage at the time when the predetermined time has elapsed is grasped, and when the battery voltage exceeds a predetermined threshold, The deterioration detection method according to claim 1, wherein the deterioration of the battery is estimated to be large.   The deterioration detection method according to any one of claims 1 to 3, wherein a charging rate in the second charging step is 0.05C to 0.5C.   The deterioration detection according to any one of claims 1 to 4, wherein the charge stop voltage in the second charging step is set to a voltage value such that a positive electrode potential is higher than an oxidation-reduction potential of the voltage stabilizer. Method.   The deterioration detection method according to any one of claims 1 to 5, wherein a charge stop voltage in the second charging step is 3.6V to 4.4V.   The deterioration detection method according to any one of claims 1 to 6, wherein the predetermined time in the second charging step is 40 minutes to 100 minutes.   The deterioration according to any one of claims 1 to 7, wherein the first specified voltage in the first charging step is set to a voltage value such that a positive electrode potential is lower than an oxidation-reduction potential of the voltage stabilizer. Detection method.   The deterioration detection method according to claim 1, wherein a first specified voltage in the first charging step is 3.0V to 3.5V.   Examples of the voltage stabilizer include 1,4-dimethoxy-2-fluorobenzene, 1,3-dimethoxy-5-chlorobenzene, 3,5-dimethoxy-1-fluorobenzene, 1,2-dimethoxy-4-fluorobenzene, 1 10. At least one aromatic compound selected from the group consisting of 1,2-dimethoxy-4-bromobenzene and 2,5-dimethoxy-1-bromobenzene is used. Degradation detection method.   In the second charging step, the charging rate is 0.08C to 0.2C, the charging stop voltage is 3.9V to 4.1V, and the predetermined time is 50 minutes to 70 minutes. The deterioration detection method according to any one of 1 to 10. A lithium secondary battery system that detects deterioration of a lithium secondary battery in which a voltage stabilizer that keeps the battery voltage constant is added to the non-aqueous electrolyte,
Charging means for charging the lithium secondary battery;
Voltage measuring means for measuring a battery voltage of the lithium secondary battery being charged by the charging means;
A control device electrically connected to each of the charging means and the voltage measuring means,
The charging means includes: a first charging process for charging the lithium secondary battery until a voltage of the battery reaches a predetermined first specified voltage; and after the first specified voltage is reached, the first charging is performed. Configured to perform a second charging process for charging at a charging rate lower than the charging rate of the process,
Here, when the second charging process of the lithium secondary battery is performed by the charging unit, the control device until the battery voltage measured by the voltage measuring unit reaches a preset charging stop voltage. A lithium secondary battery system configured to measure time and to estimate the deterioration of the battery based on the arrival time.   13. The control device according to claim 12, wherein the control device is configured to estimate that the battery is highly degradable when the battery voltage reaches a charge stop voltage within a predetermined time in the second charging process. Lithium secondary battery system.   In the second charging process, when the battery voltage does not reach the charge stop voltage within a predetermined time, the control device grasps the battery voltage at the time when the predetermined time has passed, and the battery voltage reaches a predetermined threshold value. 14. The lithium secondary battery system according to claim 12, wherein the lithium secondary battery system is configured to estimate that the deterioration of the battery is large when exceeding the limit.

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