Secondary battery system

Abstract

An object of the present disclosure is to provide a secondary battery system capable of controlling charge and discharge so that a stop position of the charge and discharge becomes a peak top of a state of charge. One embodiment of the present disclosure relates to a secondary battery system including an electrical load (13) connected to a secondary battery (20), and a control device (40) that sets at least one peak top SOC range containing a peak top of a state of charge (SOC) in an SOC-dV / dQ curve, and ends charge or discharge of the secondary battery (20) in a case where the charge or discharge is stopped in the peak top SOC range, by avoiding the peak top SOC range due to discharge of the secondary battery (20) by the electrical load (13), wherein the SOC-dV / dQ curve is depicted by dV / dQ, which is a differential value of a change amount dV of a voltage V of the secondary battery (20) with respect to a change amount dQ of a capacity Q of the secondary battery (20), and a state of charge (SOC) expressed as a percentage of the capacity Q with respect to a capacity of a full charge state of the secondary battery (20).

Description

Technical Field

[0001] This disclosure relates to secondary battery systems. Background Technology

[0002] It is known that in secondary batteries, if charging and discharging are stopped at the peak of the Q-dV / dQ curve and the battery is left idle, degradation is accelerated. The Q-dV / dQ curve is a curve representing the relationship between the differential value of the change in voltage V relative to the change in capacity Q (dV / dQ) and the value of capacity Q. Patent Document 1 discloses a secondary battery system that pre-avoids peaks to set the state of charge (SOC) at the beginning and end of a charge-discharge cycle.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: JP 2013-196805 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] In the secondary battery system described in Patent Document 1, only the state of charge (SOC) at the beginning and end of the charge-discharge cycle is set. For example, if the user ends the charge-discharge cycle at the peak existing between the beginning and end, the degradation of the secondary battery is accelerated. Furthermore, if the charge-discharge cycle is set so that there is no peak between the beginning and end of the SOC, the battery capacity is significantly reduced.

[0008] The purpose of this disclosure is to provide a secondary battery system capable of controlling charging and discharging to avoid the end of charging and discharging being the peak of the state of charge (SOC).

[0009] Methods for solving problems

[0010] As one aspect of this disclosure, a secondary battery system comprises: a secondary battery having an electrode body and a non-aqueous electrolyte stacked together with a positive electrode and a negative electrode separated by a separator; an electrical load connected to the secondary battery; and a control device that sets at least one peak SOC range in the SOC-dV / dQ curve, including a peak SOC range, and terminates charging or discharging of the secondary battery by discharging the secondary battery through the electrical load to avoid the peak SOC range when charging or discharging stops within the peak SOC range. The SOC-dV / dQ curve is depicted by dV / dQ, which is the differential value of the change in voltage V of the secondary battery with respect to the change in capacity Q of the secondary battery, and the state of charge (SOC), which is expressed as a percentage of capacity Q with respect to the capacity of the secondary battery in its fully charged state.

[0011] As one aspect of this disclosure, a secondary battery system comprises: a secondary battery having an electrode body and a non-aqueous electrolyte stacked together with a positive electrode and a negative electrode separated by a separator; an auxiliary battery connected to the secondary battery; and a control device that sets at least one peak SOC range in the SOC-dV / dQ curve, including a peak SOC range, and terminates charging or discharging of the secondary battery by charging the secondary battery through the auxiliary battery to avoid the peak SOC range when charging or discharging stops within the peak SOC range. The SOC-dV / dQ curve is depicted by dV / dQ, which is the differential value of the change in voltage V of the secondary battery with respect to the change in capacity Q of the secondary battery, and the state of charge (SOC), which is expressed as a percentage of capacity Q with respect to the capacity of the secondary battery in its fully charged state.

[0012] Invention Effects

[0013] According to one aspect of this disclosure, charging and discharging can be controlled to prevent the end of charging and discharging from being the peak of the state of charge (SOC). Attached Figure Description

[0014] Figure 1 This is a block diagram illustrating one example of a secondary battery system.

[0015] Figure 2 This is a cross-sectional view of a secondary battery as an example of an implementation method.

[0016] Figure 3 A graph representing the SOC-dV / dQ curve.

[0017] Figure 4 A flowchart illustrating the charging control process.

[0018] Figure 5 This is a flowchart illustrating the discharge control process.

[0019] Figure 6 This is a block diagram illustrating another example of a secondary battery system.

[0020] Figure 7 A diagram illustrating the charging cycle of an embodiment. Detailed Implementation

[0021] The embodiments of this disclosure will now be described using the accompanying drawings. The shapes, materials, and quantities described below are illustrative and can be appropriately varied depending on the specifications of the secondary battery. Hereinafter, the same reference numerals will be used to describe the same elements throughout the drawings.

[0022] use Figure 1 An example of a secondary battery system according to this embodiment will be described. Figure 1 This is a block diagram representing the secondary battery system 10.

[0023] like Figure 1 As shown, the secondary battery system 10 is a system for controlling the charging and discharging of the secondary battery 20. The secondary battery system 10 includes: a secondary battery 20; a control device 40 for controlling the charging and discharging of the secondary battery 20; a voltage measuring device 11 for measuring the voltage of the secondary battery 20; a current measuring device 12 for measuring the charging current or discharging current of the secondary battery 20; an electrical load 13 connected to the secondary battery 20; and a switching switch 14 for connecting / disconnecting the secondary battery 20 and the electrical load 13.

[0024] The electrical load 13 discharges the secondary battery 20, preferably using a resistor. Furthermore, the resistor preferably has a resistance value capable of discharging the secondary battery 20 with a current value within its normally used range.

[0025] In the secondary battery system 10 of this embodiment, there is a structure with one secondary battery 20, but it is not limited to this. It may also have a structure with a battery pack obtained by combining multiple secondary batteries 20. In the secondary battery system 10 with the battery pack, the control device 40 controls the charging and discharging of the battery pack, and the electrical load 13 is connected to the battery pack.

[0026] use Figure 2 An example of a secondary battery 20 according to this embodiment will be described. Figure 2 This is a cross-sectional view showing the secondary battery 20.

[0027] like Figure 2 As shown, the secondary battery 20 is, for example, a cylindrical battery, having an electrode body 24, an electrolyte, an outer container 25 for housing the electrode body 24 and the electrolyte, and a sealing body 30 for blocking the opening of the outer container 25. The electrode body 24 includes a positive electrode plate 21, a negative electrode plate 22, and a separator 23, and has a structure in which the positive electrode plate 21 and the negative electrode plate 22 are wound into a spiral shape with the separator 23 in between.

[0028] The positive electrode plate 21 has a positive electrode core and a positive electrode binder layer formed on at least one side of the core. The positive electrode core can be made of aluminum, aluminum alloys, or a foil of a metal stable within the potential range of the positive electrode plate 21, or a film with the metal disposed on its surface. The positive electrode binder layer preferably comprises a positive electrode active material, a conductive agent such as acetylene black, and a binder such as polyvinylidene fluoride, and is formed on both sides of the positive electrode core. For example, a lithium transition metal composite oxide is used as the positive electrode active material. The positive electrode plate 21 can be manufactured by coating the positive electrode core with a positive electrode binder slurry comprising a positive electrode active material, a conductive agent, and a binder, drying the coating, and then compressing the coating to form a positive electrode binder layer on both sides of the core.

[0029] The negative electrode plate 22 has a negative electrode core and a negative electrode binder layer formed on at least one side of the core. The negative electrode core can be a foil of a metal stable within the potential range of the negative electrode plate 22, such as copper or a copper alloy, or a film with the metal disposed on its surface. The negative electrode binder layer preferably includes a negative electrode active material and a binder such as styrene-butadiene rubber (SBR), and is formed on both sides of the negative electrode core. The negative electrode active material can be, for example, graphite or a silicon-containing compound. The negative electrode plate 22 can be manufactured by coating the negative electrode core with a negative electrode binder slurry containing a negative electrode active material and a binder, drying the coating, and then compressing the coating to form a negative electrode binder layer on both sides of the core.

[0030] The electrolyte may be a non-aqueous electrolyte. A non-aqueous electrolyte comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous solvent may include esters, ethers, nitriles, amides, and mixtures of two or more of these solvents. The non-aqueous solvent may also contain halogen-substituted products obtained by substituting at least a portion of the hydrogen atoms of these solvents with halogen atoms such as fluorine. Furthermore, the non-aqueous electrolyte is not limited to a liquid electrolyte and may also be a solid electrolyte. The electrolyte salt may be a lithium salt such as LiPF6. The type of electrolyte is not particularly limited, and aqueous electrolytes may also be used.

[0031] The secondary battery 20 has insulating plates 26 and 27 respectively disposed above and below the electrode body 24. Figure 1 In the example shown, the positive lead 28, connected to the positive plate 21, extends through the through hole in the insulating plate 26 to the sealing body 30 side, and the negative lead 29, connected to the negative plate 22, extends through the outer side of the insulating plate 27 to the bottom surface 25A side of the outer can 25. The positive lead 28 is connected to the lower surface of the metal plate 31, which serves as the bottom plate of the sealing body 30, using welding or the like, and the cracked plate 32 of the sealing body 30, electrically connected to the metal plate 31, becomes the positive external terminal. The negative lead 29 is connected to the inner surface of the bottom surface 25A of the outer can 25 using welding or the like, and the outer can 25 becomes the negative external terminal.

[0032] The control device 40 is a device for performing charging control and discharging control, as detailed later. The charging control is to prevent the charging of the secondary battery 20 from ending within the peak charging rate range (described later). Similarly, the discharging control is to prevent the discharging of the secondary battery 20 from ending within the peak charging rate range. The control device 40 includes a CPU as an arithmetic processing unit for performing the above-described controls, and ROM, RAM, and a hard disk drive (HDD) as storage devices connected to the CPU.

[0033] like Figure 1As shown, the control device 40 includes a charge / discharge stop detection unit 41 for detecting the charging / discharging stop timing of the secondary battery 20, and a peak determination unit 42 for determining whether the charging state (hereinafter, SOC) at the charge / discharging stop timing is within the peak SOC range. Furthermore, the control device 40 is connected to a voltage meter 11, a current meter 12, and a switch 14.

[0034] The charge / discharge stop detection unit 41 has the function of detecting the timing of the charging stop of the secondary battery 20. The timing of the charging stop of the secondary battery 20 includes a timing when the secondary battery 20 is determined to be fully charged and charging stops, and a timing when charging stops after a predetermined time. In addition, the charge / discharge stop detection unit 41 can also detect the timing of the disconnection of the connection between the secondary battery 20 and the charger as the timing of the charging stop of the secondary battery 20.

[0035] Furthermore, the charge / discharge stop detection unit 41 has the function of detecting the timing of the discharge stop of the secondary battery 20. The timing of the discharge stop of the secondary battery 20 includes the timing when the discharge stops when the voltage of the secondary battery 20 drops to a predetermined value. In addition, the charge / discharge stop detection unit 41 can also detect the timing of the discharge stop of the secondary battery 20 as the timing when the connection between the secondary battery 20 and the battery load is disconnected.

[0036] The peak determination unit 42 has the function of determining whether the SOC of the secondary battery 20 at the charge / discharge stop timing detected by the charge / discharge stop detection unit 41 is within a set peak SOC range (hereinafter, peak range). The peak range is a defined range of SOC that includes the peak of the SOC-dV / dQ curve, which will be described in detail later.

[0037] use Figure 3 The peak and the SOC-dV / dQ curve are explained. Figure 3 A graph representing the SOC-dV / dQ curve.

[0038] Figure 3 The SOC-dV / dQ curve shown has SOC (%) on the horizontal axis and dV / dQ on the vertical axis. SOC is expressed as a percentage of the capacity Q of the secondary battery 20 relative to its capacity in a fully charged state. dV / dQ represents the differential value of the change in voltage V relative to the capacity Q of the secondary battery 20. dV / dQ can be calculated, for example, from the QV curve obtained by measuring the change in voltage V relative to capacity Q during charging or discharging.

[0039] The SOC-dV / dQ curve contains multiple peaks. A peak is a maximum point on the SOC-dV / dQ curve. The position and number of peaks in the SOC-dV / dQ curve are determined by the type of electrode materials, such as the active material, of the secondary battery 20. If charging or discharging of the secondary battery 20 is stopped and it is left idle at the SOC corresponding to a peak, self-discharge can easily occur, accelerating battery degradation. Figure 3 As shown, in the secondary battery 20, the peaks of dV / dQ are identified at SOCs of 10%, 25%, 45%, 60%, and 78% (P in the figure). In this embodiment, the range ±5% from the SOC corresponding to the peak is defined as the peak range. The peak range is preset in the RAM of the control device 40. The peak range can be arbitrarily set according to the type of electrode material, such as the active material of the secondary battery 20.

[0040] use Figure 4 The charging control is explained. Figure 4 A flowchart illustrating the charging control process.

[0041] The charging control, as described above, is designed to prevent the charging of the secondary battery 20 from ceasing during the peak charging period. According to the charging control, if charging of the secondary battery 20 stops during the peak charging period, the secondary battery 20 is discharged through the electrical load 13, thereby preventing the peak charging period from being reached and the charging process from ending.

[0042] In step S11, if the charge / discharge stop detection unit 41 detects a charging stop timing, the process proceeds to step S12. In step S12, if the peak determination unit 42 determines that the state of charge (SOC) of the secondary battery 20 at the charging stop timing is within a set peak range, the process proceeds to step S13. In step S13, the control device 40 turns on the switch 14 to connect the secondary battery 20 and the electrical load 13, and discharges the secondary battery 20. Steps S12 and S13 are repeated until the SOC of the secondary battery 20 at the charging stop timing leaves the peak range.

[0043] use Figure 5 The discharge control is explained. Figure 5 This is a flowchart illustrating the discharge control process.

[0044] The discharge control, as described above, is designed to prevent the secondary battery 20 from terminating its discharge during the peak period. According to the discharge control, if the secondary battery 20 stops discharging during the peak period, the discharge is stopped by the electrical load 13, thereby preventing the peak period from being reached and ending the discharge.

[0045] In step S21, if the charge / discharge stop detection unit 41 detects a discharge stop timing, the process proceeds to step S22. In step S22, if the peak determination unit 42 determines that the SOC of the secondary battery 20 at the discharge stop timing is within a set peak range, the process proceeds to step S23. In step S23, the control device 40 connects the secondary battery 20 and the electrical load 13 by turning on the switch 14, and discharges the secondary battery 20. Steps S22 and S23 are repeated until the SOC of the secondary battery 20 at the discharge stop timing leaves the peak range.

[0046] use Figure 6 Another example of the secondary battery system 110 of this embodiment will be described. Figure 6 This is a block diagram illustrating the secondary battery system 110.

[0047] like Figure 6 As shown, the secondary battery system 110 is a system for controlling the charging and discharging of the secondary battery 20. The secondary battery system 110 includes a secondary battery 20, a control device 40 for controlling the charging and discharging of the secondary battery 20, a voltage measuring device 11 for measuring the voltage of the secondary battery 20, a current measuring device 12 for measuring the charging current or discharging current of the secondary battery 20, an auxiliary battery 15 connected to the secondary battery 20, and a switching switch 14 for turning the connection between the secondary battery 20 and the auxiliary battery 15 on / off.

[0048] The auxiliary battery 15 charges the secondary battery 20, and preferably uses a secondary battery. The capacity of the secondary battery constituting the auxiliary battery 15 is smaller than that of the secondary battery 20, and preferably about 20% of the capacity of the secondary battery 20. Furthermore, in the secondary battery system 110, the auxiliary battery 15 can also be configured to discharge the secondary battery 20. However, from the perspective of controlling the auxiliary battery 15, it is preferable that the auxiliary battery 15 charges the secondary battery 20.

[0049] The control device 40 is a device that, when charging and discharging stops within the aforementioned peak range, terminates the charging and discharging of the secondary battery 20 by charging the secondary battery 20 with the auxiliary battery 15, thereby avoiding the peak range.

[0050] According to the charging control of the secondary battery system 110, when charging of the secondary battery 20 stops within the peak range, charging of the secondary battery 20 can be stopped by charging the secondary battery 20 through the auxiliary battery 15, thereby avoiding the peak range and ending the charging process. Furthermore, according to the discharging control of the secondary battery system 110, when discharging of the secondary battery 20 stops within the peak range, charging of the secondary battery 20 through the auxiliary battery 15 can be stopped by charging the secondary battery 20 through the peak range, thereby avoiding the peak range and ending the discharging process.

[0051] Furthermore, the present invention is not limited to the above-described embodiments and their variations, and various changes and improvements can be made within the scope of the claims of this application.

[0052] Example 1

[0053] [Example 1]

[0054] [Making the positive electrode plate]

[0055] Lithium aluminum nickel cobalt oxide (LiNi) was used as the positive electrode active material. 0.88 Co 0.09 Al 0.03 O2). 100 parts by weight of LiNi 0.88 Co 0.09 Al 0.03 O2 (positive electrode active material), 1.0 parts by weight of acetylene black, and 0.9 parts by weight of polyvinylidene fluoride (PVDF) (binder) were mixed in a solvent of N-methylpyrrolidone (NMP) to obtain a positive electrode slurry. This slurry was uniformly coated on both sides of an aluminum foil with a thickness of 15 μm. Next, after heat treatment at 100–150 °C in a heated dryer to remove NMP, the foil was compressed using pressure rollers. Then, the compressed positive electrode plate was heat-treated by contacting it with rollers heated to 200 °C for 5 seconds. The plate was then cut into pieces with a thickness of 0.144 mm, a width of 62.6 mm, and a length of 861 mm to produce the positive electrode plate.

[0056] [Making the negative electrode plate]

[0057] As the negative electrode active material, 95 parts by mass of graphite powder and 5 parts by mass of Si oxide were mixed. Then, 100 parts by mass of the negative electrode active material, 1 part by mass of CMC as a thickener, and 1 part by mass of styrene-butadiene rubber as a binder were dispersed in water to prepare a negative electrode slurry. This negative electrode slurry was coated on both sides of a copper foil negative electrode current collector with a thickness of 8 μm to form a negative electrode coating. Next, after drying, it was compressed using a pressure roller to a negative electrode thickness of 0.160 mm, and the thickness of the negative electrode binder layer was adjusted. The plate was then cut to a width of 64.2 mm and a length of 959 mm to produce the negative electrode plate.

[0058] [Preparation of non-aqueous electrolytes]

[0059] A non-aqueous electrolyte was prepared by dissolving 1.5 M LiPF6 in a mixed solvent obtained by mixing ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl acetate (MA) in a volume ratio of 20:75:5.

[0060] [Making a Cylindrical Battery]

[0061] First, an aluminum positive lead was attached to the positive current collector, and a nickel-copper-nickel negative lead was attached to the negative current collector. Next, an electrode body was fabricated by winding the positive and negative current collectors together with a polyethylene separator in between. Insulating plates were then placed above and below the electrode body. The negative lead was soldered to the battery casing, and the positive lead was soldered to a sealing plate with an internal pressure-operated safety valve, thus housing the battery inside an outer can. Subsequently, a non-aqueous electrolyte was injected into the outer can under pressure. Finally, the open end of the battery casing was riveted to the sealing plate through a gasket, thus creating a rechargeable battery. The battery capacity is 3400mAh.

[0062] [Definition of peak range]

[0063] In the SOC-dV / dQ curve of the battery, the range of ±5% from the SOC that becomes the peak is defined as the peak range.

[0064] [Evaluation of Degradation Rate]

[0065] like Figure 7 As shown, charge-discharge cycle tests were conducted at a rate of 20 hours each, covering a range from 15% to 90% SOC. The degradation rate was evaluated based on the slope of the capacity retention rate, obtained by plotting the total discharge capacity on the horizontal axis and the capacity retention rate on the vertical axis.

[0066] [Example 2]

[0067] like Figure 7 As shown, except that charge-discharge tests were conducted in the range of 15% to 65% SOC, the battery was manufactured in the same manner as in Example 1, and charge-discharge cycle tests were performed.

[0068] [Comparative Example]

[0069] like Figure 7 As shown, except that charge-discharge tests were conducted in the range of 15% to 78% SOC, the battery was manufactured in the same manner as in Example 1, and charge-discharge cycle tests were performed.

[0070] In Table 1, the degradation rates of Examples 1, 2 and the comparative examples are represented by a relative index with the degradation rate of Comparative Example 1 set to 1.

[0071] [Table 1]

[0072]

[0073] It can be seen that in Examples 1 and 2, where charging and discharging were not stopped within the peak range, the degradation rate was approximately one-third that of the Comparative Example where charging was stopped within the peak range. This is because, within the peak range, the voltage variation per unit capacity increases, and the Li insertion / deposition reaction becomes the dominant reaction. Therefore, it is believed that the state of stopping charging and discharging within the peak range becomes unstable, easily leading to self-discharge and promoting degradation.

[0074] Symbol Explanation

[0075] 10 Secondary battery system, 11 Voltage measuring device, 12 Current measuring device, 13 Electrical load, 14 Switch, 15 Auxiliary battery, 20 Secondary battery, 21 Positive plate, 22 Negative plate, 23 Separator, 24 Electrode body, 25 Outer can, 25A Bottom surface, 26 Insulating plate, 27 Insulating plate, 28 Positive lead, 29 Negative lead, 30 Sealing body, 31 Metal plate, 32 Crack plate, 40 Control device, 41 Charge / discharge stop detection unit, 42 Peak determination unit, 110 Secondary battery system.

Claims

1. A secondary battery system, comprising: A secondary battery has an electrode body consisting of positive and negative plates separated by a separator and a non-aqueous electrolyte. An electrical load, connected to the secondary battery; The charge / discharge stop detection unit detects the timing of the stoppage of charging or discharging of the secondary battery. The peak determination unit determines whether the state of charge (SOC) of the secondary battery at the time of the charge / discharge stop detected by the charge / discharge stop detection unit is within the set peak SOC range. as well as Control device, In the SOC-dV / dQ curve, multiple SOC ranges, each including a peak SOC, are defined. The SOC-dV / dQ curve is plotted by dV / dQ, which is the differential of the change in voltage V of the secondary battery with respect to the change in capacity Q of the secondary battery, and SOC expressed as a percentage of the capacity Q relative to the capacity of the secondary battery in its fully charged state. If the SOC of the secondary battery at the time when the peak determination unit determines that the charging or discharging stop time is within any of the multiple peak SOC ranges, the control device discharges the secondary battery through the electrical load to avoid each of the multiple peak SOC ranges, thereby ending the charging or discharging of the secondary battery.

2. A secondary battery system, comprising: A secondary battery has an electrode body consisting of positive and negative plates separated by a separator and a non-aqueous electrolyte. An auxiliary battery is connected to the secondary battery; The charge / discharge stop detection unit detects the timing of the stoppage of charging or discharging of the secondary battery. The peak determination unit determines whether the state of charge (SOC) of the secondary battery at the time of the charge / discharge stop detected by the charge / discharge stop detection unit is within the set peak SOC range. as well as Control device, In the SOC-dV / dQ curve, multiple SOC ranges, each including a peak SOC, are defined. The SOC-dV / dQ curve is plotted by dV / dQ, which is the differential of the change in voltage V of the secondary battery with respect to the change in capacity Q of the secondary battery, and SOC expressed as a percentage of the capacity Q relative to the capacity of the secondary battery in its fully charged state. If the SOC of the secondary battery at the time when the peak determination unit determines that the charging / discharging stop time is within any of the multiple peak SOC ranges, the control device charges the secondary battery through the auxiliary battery to avoid each of the multiple peak SOC ranges, thereby ending the charging or discharging of the secondary battery.

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