Control Method of Battery System

Abstract

To suppress degradation of a non-aqueous electrolyte secondary battery.SOLUTION: The present invention relates to a method for controlling a battery system 100 having a non-aqueous electrolyte secondary battery 1, the non-aqueous electrolyte secondary battery 1 including a positive electrode active material and a negative electrode active material. The positive electrode active material is changed in the phase by charge or discharge of the non-aqueous electrolyte secondary battery 1 and charging or discharging is restricted so that the positive electrode active material is prevented from charging or discharging in a charge depth region P in which a phase change happens after a specific condition is satisfied.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for controlling a battery system.

Background Art

[0002] Japanese Unexamined Patent Application Publication No. 2013-196805 discloses a lithium-ion secondary battery system that, when it is detected or estimated that the start SOC or end SOC of the charge-discharge cycle of a lithium-ion secondary battery is a characteristic point that appears on the Q-dV / dQ curve, sets the start SOC or end SOC to an SOC that avoids the characteristic point appearing on the Q-dV / dQ curve. According to the lithium-ion secondary battery system disclosed in the same publication, it is said that the cycle characteristics of the lithium-ion secondary battery can be improved.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The inventor of the present invention intends to suppress the deterioration of a non-aqueous electrolyte secondary battery.

Means for Solving the Problems

[0005] The method for controlling a battery system disclosed herein is a method for controlling a battery system including a non-aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery includes a positive electrode active material and a negative electrode active material. The positive electrode active material undergoes a phase change by charge and discharge of the non-aqueous electrolyte secondary battery, and after reaching a specific condition, charge and discharge are not performed, or charge and discharge are restricted, in a charge depth region where a phase change occurs. According to such a battery system, the deterioration of the non-aqueous electrolyte secondary battery is suppressed.

Brief Description of the Drawings

[0006]

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MODE FOR CARRYING OUT THE INVENTION

[0007] Hereinafter, an embodiment of the technology disclosed herein will be described with reference to the drawings. The embodiments described herein are not, of course, intended to particularly limit the present invention. Each drawing is schematically drawn and does not necessarily reflect the actual object. Also, members and parts having the same function are appropriately given the same reference numerals, and duplicate explanations are appropriately omitted.

[0008] <Battery System 100> FIG. 1 is a schematic diagram showing a battery system 100. As shown in FIG. 1, the battery system 100 includes a non-aqueous electrolyte secondary battery 1 and a control device 70. The non-aqueous electrolyte secondary battery 1 may be plural or singular. From the viewpoint of adjusting the battery capacity, operating voltage, etc. according to an external load, it is preferable that a plurality of non-aqueous electrolyte secondary batteries 1 are used in the battery system 100. The plurality of non-aqueous electrolyte secondary batteries 1 may be connected in series, may be connected in parallel, or may be connected in a combination of series and parallel.

[0009] <Non-aqueous Electrolyte Secondary Battery 1> The non-aqueous electrolyte secondary battery 1 contains a positive electrode active material and a negative electrode active material. In this embodiment, a lithium-ion secondary battery is used as the non-aqueous electrolyte secondary battery 1. Hereinafter, an example of the non-aqueous electrolyte secondary battery 1 will be described.

[0010] FIG. 2 is a longitudinal sectional view schematically showing the internal structure of the non-aqueous electrolyte secondary battery 1. FIG. 3 is a perspective view schematically showing the electrode body 20 of the non-aqueous electrolyte secondary battery 1. As shown in FIG. 2, it includes a case 10, an electrode body 20, and a non-aqueous electrolyte (not shown).

[0011] The case 10 is a box-shaped container. In this embodiment, a rectangular case 10 is used. Inside the case 10, the electrode body 20 and the non-aqueous electrolyte are accommodated. For the case 10, for example, a metal material (such as aluminum) having a certain strength is used. A positive electrode terminal 12 and a negative electrode terminal 14 are attached to the case 10. The positive electrode terminal 12 and the negative electrode terminal 14 are connected to the electrode body 20 inside the case 10. Specifically, the positive electrode terminal 12 is connected to the positive electrode plate 30 (see FIG. 3) of the electrode body 20. Aluminum or the like is used for the positive electrode terminal 12. On the other hand, the negative electrode terminal 14 is connected to the negative electrode plate 40 (see FIG. 3) of the electrode body 20. Copper or the like is used for this negative electrode terminal 14.

[0012] The electrode body 20 is a power generation element of the non-aqueous electrolyte secondary battery 1. As shown in FIG. 3, the electrode body 20 includes a positive electrode plate 30, a negative electrode plate 40, and a separator 50. In this embodiment, the electrode body 20 is a wound electrode body. The wound electrode body is produced by laminating and winding the positive electrode plate 30, the negative electrode plate 40, and the separator 50. The structure of the electrode body 20 is not particularly limited, and it may be another conventionally known structure (such as a laminated electrode body).

[0013] The positive electrode plate 30 includes a positive electrode core 32 that is a conductive metal foil, and a positive electrode active material layer 34 formed on the surface of the positive electrode core 32. Aluminum or the like is used for the positive electrode core 32. The positive electrode active material layer 34 contains a positive electrode active material, a conductive material, a binder, and the like. As the conductive material, carbon materials such as acetylene black and graphite can be used. As the binder, resin materials such as polyvinylidene fluoride (PVdF) can be used.

[0014] In this embodiment, the positive electrode active material layer 34 contains a lithium composite oxide (hereinafter, also referred to as "high-Ni-containing lithium composite oxide") in which the nickel content with respect to metal atoms other than lithium is 70 mol% or more, as the positive electrode active material. By using the high-Ni-containing lithium composite oxide as the positive electrode active material, the non-aqueous electrolyte secondary battery 1 can be increased in capacity.

[0015] As the high-Ni-containing lithium composite oxide, a lithium nickel cobalt manganese-based composite oxide is preferable. In the lithium nickel cobalt manganese-based composite oxide, the nickel content with respect to metal atoms other than Li is 70 mol% or more as described above. In the lithium nickel cobalt manganese-based composite oxide, the nickel content with respect to metal atoms other than Li is preferably 80 mol% or more.

[0016] The type of the high-Ni-containing lithium composite oxide is not particularly limited as long as the Ni content relative to metal atoms other than lithium is 70 mol% or more. Examples of the high-Ni-containing lithium composite oxide include lithium nickel cobalt manganese-based composite oxides, lithium nickel cobalt aluminum-based composite oxides, and the like. As the high-Ni-containing lithium composite oxide, a lithium transition metal composite oxide represented by the following formula (I) is exemplified. Li a Ni 1-b A b O2 (I)

[0017] Here, a is 0.8 or more and 1.2 or less, and b is preferably less than 0.2. A is an element other than Ni, and preferably contains at least one of Co and Mn. Further, the molar ratio of the total of the Co content (mol) and the Mn content (mol) to the content (mol) of A is preferably 0.8 or more. At least one element selected from the group consisting of Al, Zr, B, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, Ti, and Si may be contained.

[0018] The positive electrode active material layer 34 may contain a surfactant. As the surfactant, known ones used in the positive electrode active material layer conventionally and those having properties equivalent to or better than those may be used. Specifically, as the surfactant, a cationic surfactant, an anionic surfactant, an amphoteric surfactant, a nonionic surfactant, or the like can be used. These may be used alone or in combination of two or more.

[0019] The negative electrode plate 40 includes a negative electrode core 42 which is a conductive metal foil, and a negative electrode active material layer 44 provided on the surface of the negative electrode core 42. Copper or the like is used for the negative electrode core 42. Further, the negative electrode active material layer 44 contains a negative electrode active material, a binder, a thickener, and the like. Examples of the negative electrode active material include carbon materials such as graphite, hard carbon, and soft carbon. Examples of the binder include resin materials such as styrene butadiene rubber (SBR). Examples of the thickener include resin materials such as carboxymethyl cellulose (CMC).

[0020] The separator 50 is an insulating sheet interposed between the positive electrode plate 30 and the negative electrode plate 40. As the separator 50, for example, resin materials such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide can be used. A heat-resistant layer containing an inorganic filler may be formed on the surface of the separator 50. Examples of the inorganic filler include inorganic oxides such as aluminum oxide, magnesium oxide, silicon oxide, and titanium oxide; nitrides such as aluminum nitride and silicon nitride; metal hydroxides such as calcium hydroxide, magnesium hydroxide, and aluminum hydroxide; and clay minerals such as mica, talc, boehmite, zeolite, apatite, and kaolin. The separator 50 may contain a binder for fixing the heat-resistant layer on the surface. As the binder, resin binders such as polyvinylidene fluoride (PVdF) and acrylic resins can be used.

[0021] The non-aqueous electrolyte typically contains a non-aqueous solvent and an electrolyte salt (in other words, a supporting salt). As the non-aqueous solvent, various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, lactones, etc. used in the electrolytes of common lithium-ion secondary batteries can be used without particular limitation. Among them, carbonates are preferred, and specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyl difluoromethyl carbonate (F-DMC), trifluorodimethyl carbonate (TFDMC), etc. Such non-aqueous solvents can be used alone or in appropriate combinations of two or more. As the electrolyte salt, for example, lithium salts such as LiPF6, LiBF4, lithium bis(fluorosulfonyl)imide (LiFSI), etc. can be used, and among them, LiPF6 can be preferably used. The non-aqueous electrolyte may contain various additives such as a film-forming agent such as an oxalato complex, vinylene carbonate (VC), a gas-generating agent such as biphenyl (BP), cyclohexylbenzene (CHB); a thickening agent; etc.

[0022] Incidentally, by repeatedly charging and discharging a non-aqueous electrolyte secondary battery, the capacity of the non-aqueous electrolyte secondary battery may decrease. The decrease in the capacity of the non-aqueous electrolyte secondary battery due to charging and discharging is also referred to as cycle degradation. Cycle degradation may proceed due to chemical reactions occurring among the positive electrode, negative electrode, and non-aqueous electrolyte during charging and discharging. For example, the positive electrode active material contained in the positive electrode active material layer may undergo a phase change due to the charging and discharging of the non-aqueous electrolyte secondary battery. The phase change of the positive electrode active material may occur when lithium is occluded or released from the positive electrode active material during charging and discharging. The phase change does not proceed at a constant rate during charging and discharging. For example, the ease of phase change may vary depending on the state of charge (SOC) during charging and discharging of the non-aqueous electrolyte secondary battery. When the state of charge of the non-aqueous electrolyte secondary battery is charged and discharged in the charge depth region where the phase change occurs (hereinafter, also referred to as the "phase change region"), the phase change of the positive electrode active material tends to proceed. Also, the charge depth at which the phase change is likely to occur may vary depending on the type of the positive electrode active material. By controlling the charging and discharging so that the state of charge of the non-aqueous electrolyte secondary battery does not reach the charge depth at which the phase change is likely to occur, the capacity degradation of the non-aqueous electrolyte secondary battery can be suppressed.

[0023] The control of charging and discharging can be executed after a specific condition is reached. The specific condition can be set based on the data acquired during the charging and discharging of the non-aqueous electrolyte secondary battery 1. In this embodiment, the condition is set by calculating and evaluating the damage caused by the phase change occurring in the positive electrode active material based on the data acquired during charging and discharging. Here, the charging and discharging of the non-aqueous electrolyte secondary battery 1 are controlled by the control device 70. Hereinafter, a method for controlling the charging and discharging of the non-aqueous electrolyte secondary battery 1 will be described in conjunction with the configuration of the control device 70.

[0024] FIG. 4 is a flowchart showing a flow executed by the control device 70 (see FIG. 1). The control device 70 controls the upper limit of the SOC during charging and discharging. In this embodiment, the upper limit SOC in the initial state is set to 100%. As shown in FIG. 4, the control device 70 includes a process S10 of detecting the charge and discharge capacity Q, a process S20 of detecting the charge depth region P where a phase change occurs, a process S30 of determining whether charging and discharging has occurred across the charge depth region P where a phase change occurs, a process S40 of calculating and storing the damage amount D, a process S50 of comparing the damage amount D with a threshold Th, and a process S60 of changing the upper limit SOC.

[0025] 〈Control Device 70〉 The control device 70 controls the charging and discharging of the non-aqueous electrolyte secondary battery 1. As shown in FIG. 1, the control device 70 controls the range of the SOC (charge depth) when the non-aqueous electrolyte secondary battery 1 is charged and discharged. The control device 70 is, for example, a microcomputer. The control device 70 includes, for example, an I / F, a CPU, a ROM, and a RAM. The control device 70 may be composed of a single computer or a plurality of computers.

[0026] The control device 70 includes a sensor 71. The sensor 71 includes a voltage sensor 71a, a current sensor 71b, and a temperature sensor 71c. The voltage sensor 71a detects the battery voltage of the non-aqueous electrolyte secondary battery 1. The current sensor 71b detects the charge and discharge current of the non-aqueous electrolyte secondary battery 1. The temperature sensor 71c detects the battery temperature of the non-aqueous electrolyte secondary battery 1. As the temperature sensor 71c, various elements for detecting temperature (such as a thermistor, etc.) can be used. The battery voltage, the charge and discharge current, and the battery temperature are acquired at predetermined intervals. The interval at which the battery voltage, the charge and discharge current, and the battery temperature are acquired can be set, for example, every 1 second to every 100 seconds. In this embodiment, the interval at which the battery voltage, the charge and discharge current, and the battery temperature are acquired is set to every 10 seconds. The interval at which the battery voltage, the charge and discharge current, and the battery temperature are acquired may be appropriately set according to the ROM and RAM capacities of the control device 70.

[0027] The control device 70 includes a charge-discharge capacity detection unit 72 and an SOC detection unit 73. In the charge-discharge capacity detection unit 72 and the SOC detection unit 73, the numerical values acquired by the voltage sensor 71a, the current sensor 71b, and the temperature sensor 71c are associated with time and used for estimating the charge-discharge capacity Q and the SOC.

[0028] The control device 70 includes a detection unit 74, a determination unit 75, a calculation unit 76, a storage unit 77, a comparison unit 78, and a control unit 79. Each of the units 72 to 79 included in the control device 70 may be realized by one or more processors or may be incorporated into a circuit.

[0029] <Process S10 for Detecting Charge-Discharge Capacity Q> In process S10 (see FIG. 4), the charge-discharge capacity detection unit 72 detects the charge-discharge capacity Q by integrating the current detected by the current sensor 71b. In conjunction with the detection of the charge-discharge capacity Q, the SOC may also be detected. The SOC detection unit 73 estimates the SOC based on, for example, the fully charged capacity stored in advance and the charge-discharge capacity Q. The SOC is calculated by the charge-discharge capacity Q with respect to the fully charged capacity (charge-discharge capacity Q / fully charged capacity). The SOC detection unit 73 may calculate from the relationship between the battery voltage and the SOC stored in advance. When the charge-discharge capacity Q is detected, subsequently, the voltage change amount dV / dQ with respect to the charge-discharge capacity is calculated.

[0030] <Process S20 for Detecting Charge Depth Region P Where Phase Change Occurs> In process S20 (see FIG. 4), the detection unit 74 detects the charge depth region (phase change region) P where a phase change occurs. In this embodiment, the detection unit 74 detects the voltage change amount dV / dQ with respect to the charge-discharge capacity Q. The charge depth region P where a phase change occurs is detected based on the voltage change amount dV / dQ with respect to the charge-discharge capacity Q. In this embodiment, the detection unit 74 detects the phase change region P based on the Q-dV / dQ curve showing the relationship between the charge-discharge capacity Q and the voltage change amount dV / dQ with respect to the charge-discharge capacity (hereinafter also simply referred to as "dV / dQ").

[0031] In the knowledge of the present inventors, when a high-Ni-containing lithium composite oxide is used as the positive electrode active material, a phase change may occur near the full charge capacity (for example, the depth of charge is 70% or more, and may be 80% or more). The occurrence of a phase change in the positive electrode active material during charge and discharge is detected based on the battery voltage and battery current detected by the sensor 71. In the knowledge of the present inventors, the phase change occurring in the positive electrode active material can be detected based on the Q-dV / dQ curve. During charging, when a phase change occurs in the positive electrode active material near the full charge capacity, dV / dQ becomes small. When a phase change occurs in the positive electrode active material, dV / dQ becomes maximum near the full charge capacity during charging. In addition, an inflection point appears where the change in dV / dQ with respect to the charge and discharge capacity Q becomes large. For example, by detecting the charge and discharge capacity Q when dV / dQ becomes equal to or less than the maximum value, the charge depth region where a phase change occurs in the positive electrode active material can be detected.

[0032] FIG. 5 is a graph showing a Q-dV / dQ curve. In FIG. 5, the Q-dV / dQ curves of the lithium ion secondary batteries of Examples 1 to 3 described later are shown together with the potential curve. As shown in FIG. 5, the full charge capacity of the non-aqueous electrolyte secondary battery 1 is about 200 Ah. In this embodiment, dV / dQ becomes maximum when the charge and discharge capacity Q is about 170 Ah. dV / dQ becomes minimum when the charge and discharge capacity Q is about 180 Ah. dV / dQ becomes equal to or less than the above maximum (dV / dQ when the charge and discharge capacity Q is about 170 Ah) when the charge and discharge capacity Q is about 190 Ah. At this time, the phase change region P is a region where the charge and discharge capacity Q is 170 Ah or more and 190 Ah or less (the depth of charge is 85% or more and 95% or less). The electrode is likely to be damaged when charged and discharged in the charge depth region P. Thus, the detection unit 74 detects the phase change region P based on the relationship between dV / dQ and the charge and discharge capacity Q. When the charge depth region P is detected, it is determined whether charging and discharging have occurred across the charge depth region P. Note that "charging and discharging across the charge depth region P" is not limited to the case where the charge and discharge capacity Q is charged from below the lower limit to above the upper limit of the phase change region P, or discharged from above the upper limit to below the lower limit of the phase change region P, but also includes the case where charging or discharging is performed without passing through the phase change region P.

[0033] If the charge-discharge current I is large, it may be difficult to accurately detect the charge depth region P due to the influence of overvoltage. The detection unit 74 may detect the charge depth region P based on parameters other than the voltage change amount dV / dQ. For example, the charge depth region P may be detected based on dV / dSOC.

[0034] FIG. 6 is a graph showing the SOC-dV / dSOC curve. dV / dSOC is the voltage change amount with respect to SOC. Similar to the Q-dV / dQ curve, the detection unit 74 may detect the phase change region P based on the SOC-dV / dSOC curve (see FIG. 6) showing the relationship between SOC and dV / dSOC. According to the findings of the present inventor, when the charge-discharge current I is large, the detection accuracy can be improved by detecting the charge depth region P based on the SOC-dV / dSOC curve. The detection of the voltage change amount dV / dQ is performed when the current value is below a certain value, and dV / dSOC may be substituted for current values above that. The detection unit 74 may, for example, detect the Q-dV / dQ curve when the charge-discharge current is less than 0.1C, and detect the SOC-dV / dSOC curve when the charge-discharge current I is 0.1C or more.

[0035] In addition, the charge depth at which the phase change occurs can be grasped in advance by tests or the like. In this case, the detection of the charge depth region P by the detection unit 74 does not necessarily have to be performed. However, the phase change region P may vary with the deterioration of the battery. In this case, the control device 70 may store, for example, data of the phase change region P corresponding to the deterioration of the battery (e.g., a decrease in the capacity retention rate). The control device 70 may be configured to be able to read the data of the phase change region P corresponding to the deterioration of the battery.

[0036] <Process S30 for determining whether charging and discharging has been performed in the charge depth region P where a phase change occurs> In process S30 (see FIG. 4), the determination unit 75 determines whether charging and discharging has occurred in the charge and discharge depth region P where a phase change occurs. If the charge and discharge capacity Q detected by the charge and discharge capacity detection unit 72 falls within the charge and discharge depth region P detected by the detection unit 74 (Yes), the process proceeds to process S40 (see FIG. 4), and the damage amount D is calculated. If the charge and discharge capacity Q does not fall within the charge and discharge depth region P (No), the process ends and the upper limit of the SOC during charge and discharge is not changed.

[0037] 〈Process S40 for calculating and storing damage amount D〉 In process S40, the calculation unit 76 calculates the damage amount D. The storage unit 77 stores the damage amount D. Here, the damage amount D is a quantification of the damage caused by charging and discharging in the charge and discharge depth region P described above. The damage to the positive electrode active material can accumulate due to charging and discharging in the charge and discharge depth region P and the progress of the phase change of the positive electrode active material.

[0038] In this embodiment, the calculation unit 76 calculates based on the charge and discharge current I and the battery temperature T when charging and discharging in the charge and discharge depth region P. The calculation unit 76 calculates the damage amount D based on a pre-stored map. The map is set so that the damage coefficient α is specified based on the charge and discharge current I and the battery temperature T. When charging and discharging does not occur in the charge and discharge depth region P, the damage coefficient α may be set to 0.

[0039] The map may be composed of a matrix with the charge and discharge current I on the vertical axis and the battery temperature T on the horizontal axis. The damage coefficient α at a specific charge and discharge current I and battery temperature T can be set in the map. According to the map, the damage coefficient α is specified based on the charge and discharge current I acquired by the current sensor 71b and the battery temperature T acquired by the temperature sensor 71c.

[0040] The map may store those preset by means of tests, simulations, theoretical calculations, etc. according to the composition of the positive electrode active material and the like. The setting of the map will be described later. Note that the configuration of the map is not limited to such a form. The map may be configured such that the damage coefficient α is specified based on other parameters detected or estimated by the control device 70, such as the battery voltage, SOC, charge-discharge capacity Q, etc. Further, a plurality of maps may be stored in the control device 70. For example, a plurality of maps may be stored in the control device 70 for each damage amount D. In this case, by using the map based on the accumulated damage amount D, the damage coefficient α at a specific charge-discharge current I and battery temperature T can be updated.

[0041] According to the trials of the present inventor, the damage to the positive electrode active material is smaller as the charge-discharge current I during charge-discharge is larger. As the charge-discharge current I is larger, the damage coefficient α becomes smaller, and as the charge-discharge current I is smaller, the damage coefficient α becomes larger. Further, the damage to the positive electrode active material is smaller as the battery temperature T during charge-discharge is lower. As the battery temperature T is smaller, the damage coefficient α becomes smaller, and as the battery temperature T is larger, the damage coefficient α becomes larger.

[0042] The damage amount D is stored in the storage unit 77. The stored damage amount D is the integration of the previously calculated damage coefficient α. The calculation unit 76 adds the currently calculated damage coefficient α to the damage amount D. When the currently calculated damage coefficient α is added to the damage amount D, subsequently, it is determined whether the damage amount D has become equal to or greater than the threshold Th. Note that to the currently stored damage amount D, a new damage coefficient α will be added when charging and discharging in the charge depth region P next time.

[0043] Note that the calculation of the damage amount D is not limited to the above-described form. The calculation of the damage amount D may be performed, regardless of the map, for example, by the number of times the charge depth region P is crossed during charge and discharge (for example, in this embodiment, the number of times the charge depth reaches 85% or more and 95% or less during charge and discharge). Thus, specific conditions for controlling charge and discharge may be set based on the number of times the charge depth region P is crossed during charge and discharge.

[0044] <Process S50 for Comparing Damage Amount D with Threshold Th> In process S50 (see FIG. 4), the comparison unit 78 compares the damage amount D with the threshold Th. If the damage amount D stored in process S40 is equal to or greater than the threshold Th (Yes), the process proceeds to process S60. If the damage amount D stored in process S40 is less than the threshold Th (No), the process ends and the upper limit of the SOC during charge and discharge is not changed.

[0045] Note that the threshold Th may be determined in advance by tests, simulations, theoretical calculations, etc. For example, the relationship between the damage amount D and the capacity retention rate may be obtained by tests, and the threshold Th may be determined as the damage amount at which the change rate of the capacity retention rate becomes large. Also, the threshold Th may be determined based on the relationship between the damage amount D and the resistance increase rate. The determined threshold Th is stored in the control device 70 and can be referred to by the comparison unit 78.

[0046] <Process S60 for Changing the Upper Limit SOC> In process S60 (see FIG. 4), the control unit 79 changes the upper limit SOC during charge and discharge. When the damage amount D exceeds the threshold Th, the control unit 79 restricts the use of the charge depth region (phase change region) P where a phase change occurs. The value of the upper limit SOC to be changed may be determined according to the composition of the positive electrode active material, etc. In this embodiment, the upper limit SOC is changed to 80% (charge and discharge capacity Q is 160 Ah). As shown in FIG. 5, in Examples 1 and 2, dV / dQ becomes maximum when the charge and discharge capacity Q is about 170 Ah, and the phase change of the positive electrode active material can proceed. By restricting the charge and discharge capacity Q to 160 Ah, the progress of the phase change of the positive electrode active material can be suppressed.

[0047] Thus, in the battery system 100, after a specific condition is reached (in this embodiment, after the amount of damage D becomes equal to or greater than the threshold value Th), charging and discharging are controlled so as not to charge and discharge in the depth-of-charge region (phase change region) P where a phase change occurs. As a result, the phase change of the positive electrode active material is suppressed, and the capacity of the non-aqueous electrolyte secondary battery is likely to be maintained. Also, the resistance of the non-aqueous electrolyte secondary battery is less likely to increase. Also, before the upper limit SOC is changed, the upper limit SOC is set high (100% in this embodiment). For this reason, a high-capacity battery system 100 is realized.

[0048] Also, the control of charging and discharging of the non-aqueous electrolyte secondary battery 1 is not limited to not charging and discharging in the phase change region P, and may be realized by restricting charging and discharging. For example, after charging and discharging are restricted, in normal use, the SOC is restricted so as not to exceed the changed upper limit SOC. When preset conditions such as an emergency are satisfied, charging and discharging may be controlled so as to charge and discharge beyond the upper limit SOC.

[0049] Note that the upper limit SOC may be gradually changed according to the integration of the amount of damage D. In other words, the limiting amount (the charge-discharge capacity Q, the upper limit SOC, etc. whose use is restricted) may be gradually changed with respect to the integrated value of the amount of damage D. For example, until the amount of damage D exceeds 80, the upper limit SOC may be set to 100%. As described above, when the amount of damage D exceeds 100, the upper limit SOC may be changed to 80%. In this case, the control unit 79 may control the upper limit SOC so that the upper limit SOC linearly changes from 100% to 80% until the amount of damage changes from 80 to 100, for example. The upper limit SOC is not limited to being linearly restricted, and may be controlled stepwise (for example, the upper limit SOC decreases by 5% every time the amount of damage D is integrated by 5). Thus, by gradually changing the limiting amount, it is easy to suppress the progress of the phase change of the positive electrode active material while reducing the influence on the usability of the battery system 100. Also, the user of the battery system 100 can easily cope with the restriction of charging and discharging.

[0050] Also, the use of the state of charge range P may be restricted when predetermined conditions are satisfied. For example, when the amount of damage D exceeds the threshold Th, the use may be restricted only in the low battery voltage range. The use of the state of charge range P may be restricted when the charge and discharge current I is low, and the use of the state of charge range P may not be restricted when the charge and discharge current I is high. According to the experiments of the present inventors, the lower the charge and discharge current I, the easier the phase change of the positive electrode active material progresses, and the higher the charge and discharge current I, the more difficult the phase change of the positive electrode active material progresses. In other words, the lower the charge and discharge current I, the greater the damage to the positive electrode active material, and the higher the charge and discharge current I, the smaller the damage to the positive electrode active material. Therefore, by restricting the use of the state of charge range P when the charge and discharge current I is low, the effect of suppressing the progress of the phase change of the positive electrode active material is significant. When the charge and discharge current I is high, the phase change of the positive electrode active material hardly progresses even if the use of the state of charge range P is not restricted. Although not particularly limited, it is preferable to restrict the use of the state of charge range P when the charge and discharge current I is less than 0.5C, and not to restrict the use of the state of charge range P when it is 0.5C or more. For example, when the battery system 100 is used as an in-vehicle battery, it may be restricted so that when the current is 0.5C or more, deceleration is performed by regenerative braking, and when it is less than 0.5C, deceleration is performed by hydraulic braking. Thereby, damage to the positive electrode active material can be minimized, and regenerative energy can be recovered to improve energy efficiency.

[0051] Hereinafter, embodiments of the present invention will be described, but the present invention is not intended to be limited to those shown in such embodiments.

[0052] <Preparation of Lithium-Ion Secondary Battery> A lithium nickel manganese cobalt composite oxide as a positive electrode active material layer, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed at a mass ratio of binder:AB:PVdF = 97.5:1.5:1.0. The molar ratio of nickel, cobalt, and manganese in the lithium nickel manganese cobalt composite oxide is nickel:cobalt:manganese = 80:10:10. An appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to the obtained mixture to adjust the positive electrode composite material slurry. The positive electrode composite material slurry was applied to both sides of a long aluminum foil and dried. Here, the coating amount of the positive electrode composite material slurry was adjusted so that the weight of the positive electrode active material layer after drying was about 390 mg per 10 cm 2 and it was applied. Then, the coating film was roll-pressed with a rolling roller to produce a positive electrode plate.

[0053] Graphite as a negative electrode active material layer, carboxymethyl cellulose (CMC) as a thickener, and styrene butadiene rubber (SBR) as a binder were mixed in ion-exchanged water at a mass ratio of graphite:CMC:SBR = 98.3:0.7:1.0 to prepare a negative electrode composite material slurry. The negative electrode composite material slurry was applied to both sides of a long copper foil and dried. Here, the coating amount of the negative electrode composite material slurry was adjusted so that the weight of the negative electrode active material layer after drying was about 255 mg per 10 cm 2 and it was applied. Then, the coating film was roll-pressed with a rolling roller to produce a negative electrode plate.

[0054] As a separator, one composed of polyethylene (PE) provided with aluminum oxide on the surface via polyvinylidene fluoride (PVdF) was prepared.

[0055] A mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1 was prepared. LiPF6 was dissolved in the mixed solvent to a concentration of 1.0 mol / L to prepare a non-aqueous electrolyte.

[0056] The positive electrode plate and the negative electrode plate were wound with a separator interposed therebetween to produce a wound electrode body. The electrode body was housed in a rectangular battery case together with the prepared non-aqueous electrolyte and hermetically sealed to obtain the lithium-ion secondary battery of Example 1. The upper limit voltage of the lithium-ion secondary battery of Example 1 was set to 4.2 V.

[0057] As the positive electrode active material, a lithium nickel manganese cobalt-based composite oxide having a molar ratio of nickel:cobalt:manganese of nickel:cobalt:manganese = 70:10:20 was used. The coating amount of the positive electrode mixture slurry was adjusted so that the weight of the positive electrode active material layer after drying was 425 mg per 10 cm 2 and it was coated. Except for the above, the lithium-ion secondary battery of Example 2 was obtained in the same manner as in Example 1. The upper limit voltage of the lithium-ion secondary battery of Example 2 was set to 4.25 V.

[0058] As the positive electrode active material, a lithium nickel manganese cobalt-based composite oxide having a molar ratio of nickel:cobalt:manganese of nickel:cobalt:manganese = 60:20:20 was used. The coating amount of the positive electrode mixture slurry was adjusted so that the weight of the positive electrode active material layer after drying was 440 mg per 10 cm 2 and it was coated. Except for the above, the lithium-ion secondary battery of Example 3 was obtained in the same manner as in Example 1. The upper limit voltage of the lithium-ion secondary battery of Example 3 was set to 4.25 V. The weights of the positive electrode active materials were set so that the capacities of the lithium-ion secondary batteries according to Examples 1 to 3 were the same.

[0059] 〈Measurement of initial resistance〉 The lithium-ion secondary batteries of Examples 1 to 3 were adjusted to a state of 50% SOC. Next, a current was passed at various current values in an environment of -10°C, and the battery voltage after 2 seconds was measured. Then, the passed current and the voltage change were linearly interpolated, and the resistance value (initial resistance) was calculated from the slope.

[0060] 〈Evaluation of capacity retention rate〉 Figures 7 and 8 are graphs showing the relationship between the number of cycles and the capacity retention rate. In Figure 7, the relationship between the number of cycles and the capacity retention rate for the lithium-ion secondary batteries of Example 1, Example 3, and Example 4 described later is shown. In Figure 8, the relationship between the number of cycles and the capacity retention rate for the lithium-ion secondary batteries of Example 2, Example 3, and Example 5 described later is shown.

[0061] For the lithium-ion secondary battery of Example 1, the capacity retention rate was evaluated. First, it was discharged at a current of 50 A until the battery voltage reached 3.0 V. Next, it was charged at a current of 50 A until the battery voltage reached 4.2 V. Then, it was discharged at a current of 50 A until the battery voltage reached 3.0 V. The capacity of the lithium-ion secondary battery for this test was defined as the initial capacity. For the lithium-ion secondary battery after the initial capacity measurement, charge and discharge between SOC 0 to 100% were performed 1000 cycles at a current of 50 A. Here, SOC 0% was set to the open circuit voltage (OCV) of 3.0 V, and SOC 100% was set to the OCV of 4.2 V. After 250 cycles, after 500 cycles, and after 1000 cycles, the battery capacity was obtained and taken as the capacity after durability. Using the initial capacity and the capacity after durability, the following formula (1): Capacity retention rate (%) = Capacity after durability / Initial capacity × 100 (1) Based on this, the capacity retention rate (%) in the cycle test was calculated. For the lithium-ion secondary batteries of Examples 2 and 3, the capacity retention rate was evaluated in the same manner as the lithium-ion secondary battery of Example 1, except that the upper limit battery voltage (battery voltage at SOC 100%) was 4.25 V.

[0062] Furthermore, for a lithium-ion secondary battery (Example 4) similar to Example 1, the initial resistance was measured, and a cycle test was conducted under the same conditions as above while comparing the damage amount D with the threshold value Th according to the flowchart shown in FIG. 4. Since the damage amount D became equal to or greater than the threshold value Th after 250 cycles, thereafter, the upper limit SOC was set to 80%, and charge and discharge between SOC 0 to 80% were performed up to 1000 cycles. Also, for a lithium-ion secondary battery (Example 5) similar to Example 2, the initial resistance was measured, and a cycle test was conducted under the same conditions as above while comparing the damage amount D with the threshold value Th according to the flowchart shown in FIG. 4. Since the damage amount D became equal to or greater than the threshold value Th after 500 cycles, thereafter, the upper limit SOC was set to 80%, and charge and discharge between SOC 0 to 80% were performed up to 1000 cycles. The results of the evaluation of the capacity retention rate are shown in FIGS. 7 and 8.

[0063] 〈Evaluation of Resistance Increase Rate〉 FIGS. 9 and 10 are graphs showing the relationship between the number of cycles and the resistance increase rate. In FIG. 9, the relationship between the number of cycles and the capacity retention rate for the lithium-ion secondary batteries of Example 1, Example 3, and Example 4 is shown. In FIG. 10, the relationship between the number of cycles and the capacity retention rate for the lithium-ion secondary batteries of Example 2, Example 3, and Example 5 is shown.

[0064] For the lithium-ion secondary batteries of Examples 1 to 5, the post-endurance resistances after 250 cycles, 500 cycles, and 1000 cycles were measured by the same method as the measurement of the initial resistance. Using the initial resistance and the post-endurance resistance, the following formula (2): Resistance increase rate (%) = Post-endurance resistance / Initial resistance × 100 (2) was used to calculate the resistance increase rate (%) in the cycle test. The results of the evaluation of the resistance increase rate are shown in FIGS. 9 and 10.

[0065] From the comparison between Example 1 and Example 4 (see Fig. 7), and the comparison between Example 2 and Example 5 (see Fig. 8), it can be seen that when the charge-discharge conditions are controlled so as not to charge and discharge in the state of charge-discharge depth where phase change occurs after the damage amount D becomes equal to or more than the threshold Th, the capacity is more likely to be maintained as compared with the case where the charge-discharge conditions are not controlled. From the comparison between Example 1 and Example 4 (see Fig. 9), and the comparison between Example 2 and Example 5 (see Fig. 10), it can be seen that when the charge-discharge conditions are controlled so as not to charge and discharge in the state of charge-discharge depth where phase change occurs after the damage amount D becomes equal to or more than the threshold Th, the resistance is less likely to increase as compared with the case where the charge-discharge conditions are not controlled.

[0066] From the comparison between Example 3 and Example 4 (see Figs. 7 and 9), and the comparison between Example 3 and Example 5 (see Figs. 8 and 10), it can be seen that even when a high-Ni-containing lithium composite oxide is used as the positive electrode active material, by controlling the charge-discharge conditions as described above, the capacity retention rate and the resistance increase rate are the same as those of a lithium-ion secondary battery that does not use a high-Ni-containing lithium composite oxide.

[0067] Hereinafter, the damage coefficient α used for calculating the damage amount D will be described. Here, an example of a method for setting the damage coefficient α by testing will be described for the lithium-ion secondary batteries of Example 1 and Example 2. Note that the following description is not intended to limit the present invention to such a form.

[0068] <Setting of Damage Coefficient α> The damage coefficient α can be set based on the capacity retention rate during the cycle test. Here, the setting of the damage coefficient α will be described based on the results obtained in the evaluation of the capacity retention rate described above. Note that the method for setting the damage coefficient α is not limited to the following method, and may be appropriately set by prior tests or the like.

[0069] In FIGS. 7 and 8, the horizontal axis of the graph is the square root of the number of cycles, and the vertical axis is the capacity retention rate. The capacity retention rate is plotted for each number of cycles. According to the trials of the present inventors, when the positive electrode active material does not deteriorate abnormally, the capacity retention rate for each number of cycles is plotted substantially on a straight line. When the positive electrode active material deteriorates abnormally due to a phase change, the capacity retention rate drops significantly at that point, and the slope of the graph changes. In other words, an inflection point appears in the graph showing the relationship between the square root of the number of cycles and the capacity retention rate. Here, the amount of damage D at the inflection point on the graph was set to 100.

[0070] As shown in FIG. 7, in the lithium-ion secondary battery of Example 1, an inflection point appears after 250 cycles. The damage coefficient α may be calculated based on the inflection point and the number of cycles at which the inflection point appears. The damage coefficient α for the positive electrode active material of the lithium-ion secondary battery of Example 1 is, for example, 100 / (250 cycles) 1 / 2 = 6.33 can be calculated. As shown in FIG. 8, in the lithium-ion secondary battery of Example 2, an inflection point appears after 500 cycles. The damage coefficient α for the positive electrode active material of the lithium-ion secondary battery of Example 2 is similarly 100 / (500 cycles) 1 / 2 = 4.48 can be calculated. At this time, the amount of damage D is given by the following formula (3): Amount of damage D = damage coefficient α × (number of cycles) 1 / 2 (3) may be calculated based on. Also, the threshold Th can be set to 100. The method for calculating the damage coefficient α is not limited to the method described above.

[0071] By changing the conditions of parameters related to the damage given to the positive electrode active material, such as the charge-discharge current I, the battery temperature T, and the change in dV / dQ, and performing a cycle test, a map of the damage coefficient α may be prepared. Hereinafter, as an example, the preparation of a map of the damage coefficient α determined based on the charge-discharge current I, the battery temperature T, and the change in dV / dQ will be described.

[0072] The cycle tests were carried out at different charge-discharge currents I, and the damage coefficient α was calculated for each charge-discharge current I. Here, using the lithium-ion secondary battery of Example 1, when the charge-discharge current I was set to 50 A, 100 A, and 200 A, the cycle tests were carried out in the same manner as above for each case. Here, the battery temperature T was fixed at 60°C. FIG. 11 is a graph showing the relationship between the number of cycles and the capacity retention rate. As shown in FIG. 11, the smaller the charge-discharge current I, the greater the decrease in the capacity retention rate, and the larger the charge-discharge current I, the smaller the decrease in the capacity retention rate tended to be. According to the findings of the present inventor, the larger the charge-discharge current I, the faster the phase change region P is passed through, and thus the phase change can be suppressed.

[0073] Based on the graph obtained when the cycle tests were carried out at different charge-discharge currents I, the damage coefficient α was calculated. Here, in the same manner as the above-described method for calculating the damage coefficient α, the damage coefficient α was calculated based on the inflection point of the graph. Although the detailed calculation is omitted, the damage coefficient α when the charge-discharge current I was set to 50 A was 10.0. The damage coefficient α when the charge-discharge current I was set to 100 A was 6.3. The damage coefficient α when the charge-discharge current I was set to 50 A was 5.6.

[0074] Also, the cycle tests were carried out at different battery temperatures T, and the damage coefficient α was calculated for each battery temperature T. Here, using the lithium-ion secondary battery of Example 1, when the battery temperature T was set to 60°C, 25°C, and -10°C, the cycle tests were carried out in the same manner as above for each case. Here, the charge-discharge current I was fixed at 50 A. FIG. 12 is a graph showing the relationship between the number of cycles and the capacity retention rate. As shown in FIG. 12, the higher the battery temperature T, the greater the decrease in the capacity retention rate, and the lower the battery temperature T, the smaller the decrease in the capacity retention rate tended to be. According to the findings of the present inventor, the higher the battery temperature T, the more cracks and the like occur in the positive electrode active material, and the phase change can proceed.

[0075] Based on the graph obtained when the cycle test was carried out at different battery temperatures T, the damage coefficient α was calculated. Although the detailed calculation is omitted, the damage coefficient α when the battery temperature T was set to 60 °C was 10.0. The damage coefficient α when the battery temperature T was set to 25 °C was 4.2. The damage coefficient α when the battery temperature T was set to -10 °C was 0.

[0076] Also, the cycle test was carried out in different charge-discharge ranges, and the damage coefficient α was calculated for each charge-discharge range. The charge-discharge range was set based on the SOC. The lower limit SOC of the charge-discharge range was fixed at 0%. It was set by changing the upper limit SOC of the charge-discharge range. Here, using the lithium-ion secondary battery of Example 1, when the upper limit SOC of the charge-discharge range was set to 100%, 93%, and 87% respectively, the cycle test was carried out in the same manner as above. FIG. 13 is a graph showing the relationship between the number of cycles and the capacity retention rate. As shown in FIG. 13, when the upper limit SOC was set to 87%, the decrease in the capacity retention rate was smaller compared to the cases where the upper limit SOC was set to 93% and 100%. The decrease in the capacity retention rate was about the same between the cases where the upper limit SOC was set to 93% and 100%. According to the findings of the present inventors, the larger the change in dV / dQ in the phase change region P, the more cracks and the like occur in the positive electrode active material, and the phase change can proceed. In addition to the capacity retention rate, the resistance increase rate when the upper limit SOC was changed was evaluated in the same manner as above. Although the detailed description is omitted, similar to the capacity retention rate, when the upper limit SOC was set to 87%, the resistance increase rate was lower compared to the cases where the upper limit SOC was set to 93% and 100%.

[0077] Based on the graph obtained when the cycle test was carried out at different upper limit SOCs, the damage coefficient α was calculated. Although the detailed calculation is omitted, the damage coefficient α when the upper limit SOC was set to 100% and 93% was 6.3. The damage coefficient α when the upper limit SOC was set to 87% was 5.3.

[0078] In this way, by changing and testing parameters such as the charge and discharge current I, the battery temperature T, and the change in dV / dQ, and obtaining the relationship between each parameter and the damage coefficient α, a map for calculating the damage coefficient α may be prepared.

[0079] As described above, the technology disclosed herein has been variously described. Unless otherwise specified, the embodiments described herein do not limit the present invention. Further, the technology disclosed herein can be variously modified, and unless a particular problem occurs, each component and each process described herein can be appropriately omitted or appropriately combined. Further, this specification includes the disclosures described in the following sections.

[0080] Item 1: A control method for a battery system including a non-aqueous electrolyte secondary battery, wherein the non-aqueous electrolyte secondary battery includes a positive electrode active material and a negative electrode active material, the positive electrode active material undergoes a phase change during charge and discharge of the non-aqueous electrolyte secondary battery, after reaching a specific condition, charging and discharging are not performed, or are restricted, in the charge-discharge depth region where the phase change occurs. A control method for a battery system.

[0081] Item 2: The battery system includes a detection unit that detects the charge-discharge depth region where the phase change occurs based on the voltage change amount with respect to the charge-discharge capacity, a calculation unit that calculates the amount of damage caused by performing charge and discharge in the charge-discharge depth region where the phase change occurs, and a control unit that restricts the use of the charge-discharge depth region where the phase change occurs when the amount of damage exceeds a threshold value The control method for a battery system according to Item 1, comprising the above.

[0082] Item 3: The detection of the voltage change amount is performed at a constant current value or less, and SOC-dV / dSOC is used as a substitute at a current value greater than that. The control method for a battery system according to Item 2.

[0083] Item 4: The control method of the battery system according to Item 2 or 3, wherein the limit amount is gradually changed with respect to the integrated value of the damage amount.

[0084] Item 5: The control method of the battery system according to any one of Items 2 to 4, wherein when the damage amount exceeds the threshold value, the use is restricted only in the low voltage range.

Explanation of Signs

[0085] 1 Non-aqueous electrolyte secondary battery 10 Case 12 Positive electrode terminal 14 Negative electrode terminal 20 Electrode body 30 Positive electrode plate 32 Positive electrode core 34 Positive electrode active material layer 40 Negative electrode plate 42 Negative electrode core 44 Negative electrode active material layer 50 Separator 70 Control device 71 Sensor 71a Voltage sensor 71b Current sensor 71c Temperature sensor 72 Charge and discharge capacity detection unit 73 SOC detection unit 74 Detection unit 75 Judgment unit 76 Calculation unit 77 Memory unit 78 Comparison unit 79 Control unit 100 Battery system

Claims

1. A method for controlling a battery system including a non-aqueous electrolyte secondary battery, wherein the non-aqueous electrolyte secondary battery includes a positive electrode active material and a negative electrode active material, the positive electrode active material undergoes a phase change during charge and discharge of the non-aqueous electrolyte secondary battery, after reaching a specific condition, charge and discharge are not performed in the charge depth region where the phase change occurs, or charge and discharge are restricted, the battery system includes a detection unit that detects the charge depth region where the phase change occurs based on the amount of voltage change with respect to the charge and discharge capacity, a calculation unit that calculates the amount of damage caused by performing charge and discharge in the charge depth region where the phase change occurs, and a control unit that restricts the use of the charge depth region where the phase change occurs when the amount of damage exceeds a threshold value ; A method for controlling a battery system.

2. The detection of the amount of voltage change is performed at a constant current value or less, and substitution is made using SOC - dV / dSOC at a current value greater than that, according to the method for controlling a battery system according to Claim 1.

3. The limiting amount changes gradually with respect to the integrated value of the amount of damage, according to the method for controlling a battery system according to Claim 1 or 2.

4. When the amount of damage exceeds the threshold value, only the low voltage range is restricted in use, according to the method for controlling a battery system according to Claim 1 or 2.

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