Control method for non-aqueous electrolyte secondary battery

Abstract

To shorten a charging time while suppressing metal deposition in a non-aqueous electrolyte secondary battery.SOLUTION: A control method for a non-aqueous electrolyte secondary battery 1 includes temporarily increasing a charging current A1 at the start of charging when a charge-discharge history H1 immediately before the start of charging indicates a rest or discharge, as compared to when the charge-discharge history H1 immediately before the start of charging indicates a charge.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for controlling a non-aqueous electrolyte secondary battery. [Background technology]

[0002] For example, Japanese Patent Application Laid-Open Publication No. 2015-23684 discloses a charging system that can shorten the charging time for a secondary battery. This charging system supplies a constant charging current. Then, constant current charging is performed with the constant charging current until the closed circuit voltage of the secondary battery reaches a threshold voltage. After that, constant current charging is performed with the charging current reduced by a predetermined current reduction amount until the closed circuit voltage increases by a voltage increase amount. This process is repeated a predetermined number of times, and then the supply of charging current is stopped.

[0003] For example, Japanese Patent Application Laid-Open Publication No. 2023-46937 discloses a method for charging a lithium-ion secondary battery, in which the current value of the charging current is controlled so as to be proportional to the reciprocal of the square root of the charging time, thereby charging the lithium-ion secondary battery. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-23684 [Patent Document 2] Japanese Patent Application Publication No. 2023-46937 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, in the charging method disclosed in, for example, Japanese Patent Application Laid-Open No. 2023-46937, after a predetermined charging time has elapsed, the charging current is controlled to decrease as the charging time elapses. By decreasing the current in this manner, it is possible to suppress the occurrence of lithium precipitation. However, the charging time may be delayed as the charging current decreases. It is preferable to suppress lithium precipitation while keeping the charging time as short as possible. [Means for solving the problem]

[0006] In the control method for a nonaqueous electrolyte secondary battery disclosed herein, when the charge / discharge history immediately before the start of charging is pause or discharge, the charge current is temporarily increased at the start of charging compared to when the charge / discharge history immediately before the start of charging is charge.

[0007] According to the control method for a nonaqueous electrolyte secondary battery disclosed herein, if the charge / discharge history immediately before the start of charging is a rest or discharge, the battery is not in an overvoltage state, and metal precipitation is unlikely to occur in the nonaqueous electrolyte secondary battery even if the charge current is temporarily increased. Therefore, if the charge / discharge history immediately before the start of charging is a rest or discharge, by temporarily increasing the charge current at the start of charging, it is possible to reduce the charge time and suppress the occurrence of metal precipitation. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing a battery system. [Figure 2] FIG. 2 is a vertical cross-sectional view schematically showing the internal structure of a nonaqueous electrolyte secondary battery. [Figure 3] FIG. 3 is a perspective view schematically showing an electrode assembly of a nonaqueous electrolyte secondary battery. [Figure 4] FIG. 4 is a graph showing the first current information, which is a graph showing the magnitude of the charging current according to the magnitude of the current SOC. [Figure 5] FIG. 5 is a graph showing second current information, which is a graph showing the magnitude of the charging current according to the magnitude of the current SOC. [Figure 6]FIG. 6 is a flowchart showing a method for controlling a nonaqueous electrolyte secondary battery at the start of charging the nonaqueous electrolyte secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, one embodiment of the technology disclosed herein will be described with reference to the drawings. It should be noted that the embodiment described here is not intended to limit the present invention in any way. Each drawing is a schematic diagram and does not necessarily faithfully reflect an actual product. Furthermore, the same reference numerals are appropriately used for components and parts that perform the same function, and redundant explanations will be omitted where appropriate.

[0010] A method for controlling a nonaqueous electrolyte secondary battery according to this embodiment will be described below. FIG. 1 is a schematic diagram showing a battery system 100. Here, the method for controlling a nonaqueous electrolyte secondary battery is embodied, for example, by the battery system 100 shown in FIG. 1. As shown in FIG. 1, the battery system 100 includes a nonaqueous electrolyte secondary battery 1 and a control device 70. There may be multiple or a single nonaqueous electrolyte secondary battery 1. From the viewpoint of adjusting the battery capacity, operating voltage, and the like in accordance with an external load, it is preferable that the battery system 100 uses multiple nonaqueous electrolyte secondary batteries 1. The multiple nonaqueous electrolyte secondary batteries 1 may be connected in series, in parallel, or in a combination of series and parallel.

[0011] The nonaqueous electrolyte secondary battery 1 includes a positive electrode active material and a negative electrode active material. In this embodiment, a lithium ion secondary battery is used as the nonaqueous electrolyte secondary battery 1. However, the type of the nonaqueous electrolyte secondary battery 1 is not particularly limited, and for example, a sodium ion secondary battery may be used. An example of the nonaqueous electrolyte secondary battery 1 will be described below.

[0012] The nonaqueous electrolyte secondary battery 1 is connected to a load (not shown). The load is not particularly limited, but may be, for example, a drive device such as an electric motor of a vehicle, or an inverter. A smoothing capacitor may be connected to the load to reduce sudden changes in current. Here, the battery system 100 is mounted on a vehicle such as a hybrid vehicle, a plug-in hybrid vehicle, or an electric vehicle, and is used as a power source that supplies power to an electric motor that drives the vehicle. However, the battery system 100 is not limited to use in vehicles.

[0013] Fig. 2 is a vertical cross-sectional view schematically showing the internal structure of the nonaqueous electrolyte secondary battery 1. Fig. 3 is a perspective view schematically showing an electrode assembly 20 of the nonaqueous electrolyte secondary battery 1. As shown in Fig. 2, the nonaqueous electrolyte secondary battery 1 includes a case 10, an electrode assembly 20, and a nonaqueous electrolyte (not shown).

[0014] The case 10 is a box-shaped container. In this embodiment, a rectangular case 10 is used. An electrode assembly 20 and a non-aqueous electrolyte are housed inside the case 10. For example, a metal material (such as aluminum) having a certain strength is used for the case 10. 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 assembly 20 inside the case 10. Specifically, the positive electrode terminal 12 is connected to a positive electrode sheet 30 (see FIG. 3) of the electrode assembly 20. For example, aluminum or the like is used for the positive electrode terminal 12. On the other hand, the negative electrode terminal 14 is connected to a negative electrode sheet 40 (see FIG. 3) of the electrode assembly 20. For example, copper or the like is used for the negative electrode terminal 14.

[0015] The electrode assembly 20 is a power generating element of the nonaqueous electrolyte secondary battery 1. As shown in FIG. 3, the electrode assembly 20 includes a positive electrode sheet 30, a negative electrode sheet 40, and a separator 50. In this embodiment, the electrode assembly 20 is a wound electrode assembly. The wound electrode assembly is produced by stacking and winding the positive electrode sheet 30, the negative electrode sheet 40, and the separator 50. However, the structure of the electrode assembly 20 is not particularly limited, and may have another conventionally known structure (for example, a stacked electrode assembly).

[0016] As shown in FIG. 3, the positive electrode sheet 30 has a positive electrode core 32, which is a conductive metal foil, and a positive electrode active material layer 34 formed on the surface of the positive electrode core 32. The positive electrode core 32 is made of aluminum or the like. The positive electrode active material layer 34 contains a positive electrode active material, a conductive material, a binder, and the like. The positive electrode active material may be, for example, a lithium composite metal oxide having a layered structure or a spinel structure (for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNiO2, LiCoO2, LiFeO2, LiMn2O4, LiNi 0.5 Mn 1.5 Examples of the conductive material include carbon materials such as acetylene black and graphite. Examples of the binder include resin materials such as polyvinylidene fluoride (PVdF).

[0017] The negative electrode sheet 40 has a negative electrode core 42, which is a conductive metal foil, and a negative electrode active material layer 44 formed on the surface of the negative electrode core 42. The negative electrode core 42 is made of copper or the like. 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. The negative electrode active material may also include a silicon-containing material. 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). In this embodiment, the charge density of the negative electrode active material layer 44 is 1.4 g / cm 3 The weight of the negative electrode active material layer 44 is 20 mg / cm 2 That's all.

[0018] The separator 50 is an insulating sheet interposed between the positive electrode sheet 30 and the negative electrode sheet 40. Resin materials such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide can be used for the separator 50. A heat-resistant layer containing an inorganic filler may be formed on the surface of the separator 50. Examples of inorganic fillers that can be used 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 to fix the heat-resistant layer to the surface. Examples of binders that can be used include resin binders such as polyvinylidene fluoride (PVdF) and acrylic resins.

[0019] The nonaqueous electrolyte typically contains a nonaqueous solvent and an electrolyte salt (in other words, a supporting salt). As the nonaqueous solvent, various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones commonly used in electrolytes for lithium-ion secondary batteries can be used without any particular limitation. Of these, 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), and trifluorodimethyl carbonate (TFDMC). These nonaqueous solvents can be used alone or in appropriate combinations of two or more. Examples of the electrolyte salt include lithium salts such as LiPF, LiBF, and lithium bis(fluorosulfonyl)imide (LiFSI), and LiPF is particularly preferred. The non-aqueous electrolyte may contain various additives, such as an oxalate complex, a film-forming agent such as vinylene carbonate (VC), a gas generating agent such as biphenyl (BP) or cyclohexylbenzene (CHB), and a thickener.

[0020] Next, the control device 70 shown in Fig. 1 will be described. The control device 70 controls the charging and discharging of the nonaqueous electrolyte secondary battery 1. As shown in Fig. 1, the control device 70 controls the magnitude of the charging current passed through the nonaqueous electrolyte secondary battery 1 when charging the nonaqueous electrolyte secondary battery 1. 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 multiple computers.

[0021] The control device 70 is equipped with a sensor 71. The sensor 71 has a voltage sensor 71a, a current sensor 71b, and a temperature sensor 71c. The voltage sensor 71a detects the battery voltage of the nonaqueous electrolyte secondary battery 1. The current sensor 71b detects the battery current of the nonaqueous electrolyte secondary battery 1. The temperature sensor 71c detects the battery temperature of the nonaqueous electrolyte secondary battery 1. The types of the voltage sensor 71a, the current sensor 71b, and the temperature sensor 71c are not particularly limited as long as they can detect the battery voltage, battery current, and battery temperature, respectively, and conventionally known sensors can be used.

[0022] 1, the control device 70 includes a storage unit 81, an acquisition unit 83, a determination unit 85, a charging current determination unit 87, and a charging control unit 89. Each of the units 81 to 89 of the control device 70 may be realized by one or more processors or may be realized by a circuit. Specific features of each of the units 81 to 89 will be described later.

[0023] Incidentally, when charging the nonaqueous electrolyte secondary battery 1, metals (e.g., lithium) contained in the nonaqueous electrolyte may precipitate (hereinafter referred to as lithium precipitation). To prevent such lithium precipitation from occurring during charging, the magnitude of the charging current A1 (see FIG. 4) is changed according to the state of charge (in other words, the charging rate) of the nonaqueous electrolyte secondary battery 1. Here, the state of charge of the nonaqueous electrolyte secondary battery 1 is referred to as SOC (State Of Charge).

[0024] FIG. 4 is a graph showing first current information D11, illustrating the magnitude of charging current A1 according to the magnitude of the current SOC. In FIG. 4, the polygonal lines for each current SOC partially overlap. Each polygonal line for each current SOC overlaps with the polygonal line for a higher SOC. For example, the polygonal line for a current SOC of 20% overlaps with the polygonal line for a current SOC of 30% in the portion where the SOC is 30% or higher. For example, as shown in FIG. 4, when the current SOC of the nonaqueous electrolyte secondary battery 1 is low (here, SOC less than 50%), the charging current A1 is set to the maximum allowable value A11. Here, the maximum allowable value A11 refers to the maximum current value that can be flowed through the nonaqueous electrolyte secondary battery 1. On the other hand, as shown in FIG. 4, when the current SOC is medium-high (here, SOC greater than or equal to 50%), the charging current A1 is reduced as the SOC increases. In this way, lithium deposition during charging can be suppressed by controlling the charging current A1 of the nonaqueous electrolyte secondary battery 1. However, when the SOC is currently in the medium to high range, the charging current A1 becomes small, which increases the charging time, which is a problem.

[0025] Therefore, the present inventors have studied various methods for reducing the charging time while suppressing lithium deposition during charging of a nonaqueous electrolyte secondary battery 1. As a result of their studies, they have found that lithium deposition can be suppressed even when the charging current A1 is temporarily increased based on the charge / discharge history H1 (see FIG. 1) immediately before the start of charging, for example, when the charge / discharge history H1 immediately before the start of charging is in a rest or discharge state and the current SOC is in a medium-high SOC. In this way, by temporarily increasing the charging current A1, the charging time can be reduced.

[0026] In this embodiment, the charge / discharge history H1 shown in FIG. 1 records the history of charging and discharging the nonaqueous electrolyte secondary battery 1. Here, the charge / discharge history H1 records the charge / discharge state and the execution time in association with each other. The charge / discharge state includes charging, discharging, and resting of the nonaqueous electrolyte secondary battery 1. Here, charging and discharging refer to states in which the nonaqueous electrolyte secondary battery 1 is being charged or discharged, respectively. Resting refers to a state in which neither charging nor discharging is being performed on the nonaqueous electrolyte secondary battery 1. The execution time refers to the time during which the associated charge / discharge state (charging, discharging, resting) is performed. The charge / discharge history H1 may also include the start time and end time of each charge / discharge state. In this embodiment, the control device 70 can acquire the immediately preceding charge / discharge state (e.g., immediately before the start of charging) and the execution time of that charge / discharge state from the charge / discharge history H1 in association with each other.

[0027] Here, when charging of the nonaqueous electrolyte secondary battery 1 is started, the value of the charging current A1 at the start of charging of the nonaqueous electrolyte secondary battery 1 is determined based on the charge / discharge state of the charge / discharge history H1 immediately before the start of charging. In this embodiment, if the charge / discharge history H1 immediately before the start of charging is charging, the charging current A1 is determined based on the current SOC of the nonaqueous electrolyte secondary battery 1 at the start of charging and the first current information D11 shown in FIG. 4. As shown in FIG. 4, according to the first current information D11, when the current SOC is low (here, SOC is less than 50%), the charging current A1 is set to the maximum allowable value A11. When the current SOC is medium-high (here, SOC is 50% or more), the value of the charging current A1 is set so that the charging current A1 decreases as the current SOC increases. In this embodiment, the first current information D11 is stored in the storage unit 81 (see FIG. 1) in the form of a map or a list so that the current SOC and the charging current A1 are associated with each other.

[0028] FIG. 5 is a graph showing the second current information D12. FIG. 5 shows the relationship between the magnitude of the charging current A1 and the magnitude of the current SOC. In FIG. 5, as in FIG. 4, the polygonal lines for each current SOC partially overlap. Each polygonal line for each current SOC overlaps with the polygonal line for a higher SOC. For example, the polygonal line for a current SOC of 50% overlaps with the polygonal line for a current SOC of 60% in the portion where the SOC is 60% or higher. On the other hand, when the charging / discharging history H1 immediately before the start of charging is paused or discharging, the charging current A1 is temporarily increased at the start of charging compared to when the charging / discharging history H1 immediately before the start of charging is charging. Here, "when the charging / discharging history H1 is paused or discharging" refers to a continuous execution time (hereinafter referred to as continuous execution time) during which the charging / discharging state of the charging / discharging history H1 immediately before the start of charging is paused or discharging, being at least 5 minutes or more. When the charge / discharge state during this continuous execution time of "at least 5 minutes" is only paused, only discharged, or both paused and discharged, but not charged, it is referred to as "when the charge / discharge history H1 is paused or discharged." In other cases, it is referred to as "when the charge / discharge history H1 is charging." As described above, when the charge / discharge history H1 is paused or discharged, there is no overvoltage state, and lithium deposition is unlikely to occur even if the charging current A1 is temporarily increased. Therefore, when the charging / discharge history H1 immediately before the start of charging is paused or discharged, temporarily increasing the charging current A1 at the start of charging can reduce the charging time while suppressing lithium deposition.

[0029] Here, when the charge / discharge history H1 is in a rest or discharge state, the charging current A1 is determined based on the current SOC and the second current information D12 shown in FIG. 5. Like the first current information D11, the second current information D12 is mapped or listed so that the current SOC and the charging current A1 are associated with each other, and is stored in the storage unit 81 (see FIG. 1). In the second current information D12 shown in FIG. 5, when the current SOC is low (SOC less than 50%), the charging current A1 is set to the maximum allowable value A11, as in the first current information D11 (see FIG. 4). On the other hand, in the second current information D12, when the current SOC at the start of charging is medium-high SOC (SOC equal to or greater than 50%), the charging current A1 at the start of charging is temporarily set to a value (here, the maximum allowable value A11) higher than that of the first current information D11. Here, the SOC range (here, current SOC) of the nonaqueous electrolyte secondary battery 1 where charging is performed by increasing the charging current A1 is 50% to 80%. That is, when the current SOC is outside the range of 50% to 80%, the charging current A1 is set according to the first current information D11 shown in Fig. 4. In this way, by temporarily increasing the charging current A1 when the current SOC is between 50% and 80%, it is possible to efficiently shorten the charging time while suppressing the occurrence of lithium deposition.

[0030] In this embodiment, the "temporary" increase in the charging current A1 refers to a predetermined extension time T1 (see FIG. 5). As shown in FIG. 5, the extension time T1 is set according to the current SOC at the start of charging. For example, in terms of the battery characteristics of the nonaqueous electrolyte secondary battery 1, the higher the current SOC, the more likely lithium deposition occurs. Therefore, in this embodiment, the extension time T1 is set to be shorter as the current SOC increases. For example, when the current SOC at the start of charging is 70%, the extension time T1 is set to be shorter than when the current SOC is 60%. Note that when the time for temporarily increasing the charging current A1 (in other words, the time set to the allowable maximum value A11) exceeds the extension time T1, the charging current A1 is reduced in the same manner as with the first current information D11 (see FIG. 4). That is, the charging current A1 is reduced as the current SOC increases. The range of the extension time T1 is not particularly limited, but is, for example, 50 to 500 seconds, preferably 100 to 250 seconds. In this embodiment, a maximum allowable amount of lithium deposition in the nonaqueous electrolyte secondary battery 1 (for example, the amount of lithium deposition on the surface of the negative electrode) is set in advance. Here, the value of the charging current A1 when temporarily increased and the extension time T1 are set so that the amount of lithium deposition is equal to or less than the maximum allowable amount even if the current SOC becomes high.

[0031] In this embodiment, the increase in the charging current A1 is varied depending on the execution time of the pause or discharge in the charge / discharge history H1. The increase here refers to the increase in the charging current A1 relative to the first current information D11 (here, when the charge / discharge history H1 is charging) at the same current SOC. Here, if the continuous execution time when the charge / discharge history H1 immediately before the start of charging is paused or discharged is long, the increase in the charging current A1 is increased. That is, if the continuous execution time is long, the charging current A1 is relatively increased. Note that the specific range of the increase is not particularly limited. For example, if the continuous execution time when the charge / discharge history H1 immediately before the start of charging is paused or discharged is 5 to 30 minutes, the increase in the charging current A1 is set to 20 A to 100 A. In this way, if the continuous execution time when the charge / discharge history H1 is paused or discharged is long, an overvoltage state is unlikely to occur, so even if the increase in the charging current A1 is increased, lithium deposition is unlikely to occur.

[0032] In this embodiment, the increase in the charging current A1 may be increased or decreased depending on the battery temperature of the nonaqueous electrolyte secondary battery 1 during charging. The "battery temperature of the nonaqueous electrolyte secondary battery 1" refers to, for example, the highest temperature of the nonaqueous electrolyte secondary battery 1. Here, when the charging current A1 is small during charging, the amount of heat generated by the nonaqueous electrolyte secondary battery 1 is small, resulting in a small increase in the battery temperature. On the other hand, when the charging current A1 is large, the amount of heat generated by the nonaqueous electrolyte secondary battery 1 is large, resulting in a large increase in the battery temperature. As the battery temperature increases, resistance decreases, making it difficult for lithium to deposit if charging is started at a low battery temperature. Here, when the battery temperature of the nonaqueous electrolyte secondary battery 1 increases during charging, the increase in the charging current A1 is reduced. For example, the greater the increase in the battery temperature of the nonaqueous electrolyte secondary battery 1 during charging, the smaller the increase in the charging current A1 is. The increased temperature here refers to, for example, the increase in the battery temperature of the nonaqueous electrolyte secondary battery 1 relative to the battery temperature at the start of charging. In this embodiment, for example, when the battery temperature is high, the charging time is shortened due to the characteristics of the nonaqueous electrolyte secondary battery 1. Therefore, when the battery temperature of the nonaqueous electrolyte secondary battery 1 is equal to or higher than a predetermined reference temperature, the increase in charging current may be reduced. In this case, even if the increase in charging current is small, the charging time can be shortened because the battery temperature is high. Note that the relationship between the increase in battery temperature and the charging current A1 is not particularly limited. For example, when the battery temperature of the nonaqueous electrolyte secondary battery 1 during charging rises to 10°C or higher, the increase in charging current A1 is set to 0 A to 20 A.

[0033] Next, a method for controlling the nonaqueous electrolyte secondary battery 1 at the start of charging the nonaqueous electrolyte secondary battery 1 will be described with reference to the flowchart of Fig. 6. At the start of charging the nonaqueous electrolyte secondary battery 1, the memory unit 81 (see Fig. 1) stores the charge / discharge history H1 (see Fig. 1) up to the immediately preceding time.

[0034] First, in step S101 of FIG. 6, the acquisition unit 83 of FIG. 1 acquires the battery voltage, battery current, and battery temperature of the nonaqueous electrolyte secondary battery 1. Here, the voltage sensor 71a of FIG. 1 detects the battery voltage, and the acquisition unit 83 acquires the battery voltage detected by the voltage sensor 71a from the voltage sensor 71a. The current sensor 71b of FIG. 1 detects the battery current, and the acquisition unit 83 acquires the battery current detected by the current sensor 71b from the current sensor 71b. Furthermore, the temperature sensor 71c of FIG. 1 detects the battery temperature, and the acquisition unit 83 acquires the battery temperature detected by the temperature sensor 71c from the temperature sensor 71c. The battery voltage, battery current, and battery temperature of the nonaqueous electrolyte secondary battery 1 acquired by the acquisition unit 83 are stored in the memory unit 81 of FIG. 1.

[0035] Next, in step S103 of Fig. 6, the determination unit 85 of Fig. 1 determines whether the charge / discharge history H1 immediately before the start of charging is pause or discharge. Here, the determination unit 85 makes this determination based on the charge / discharge history H1 stored in the storage unit 81. Here, if the charge / discharge history H1 immediately before the start of charging is charge, the process proceeds to step S105 of Fig. 6.

[0036] On the other hand, if the determination unit 85 determines in step S103 of FIG. 6 that the charge / discharge history H1 immediately before the start of charging indicates a pause or discharge, the process proceeds to step S107 of FIG. 6. In step S107, the determination unit 85 determines whether the battery temperature of the nonaqueous electrolyte secondary battery 1 is equal to or lower than a threshold value Th1. The threshold value Th1 is a predetermined value and is pre-stored in the storage unit 81 of FIG. 1. For example, when the battery temperature of the nonaqueous electrolyte secondary battery 1 is near room temperature, if the charging current A1 becomes too large, heat generated by the charging current A1 may easily cause deterioration or failure of the nonaqueous electrolyte secondary battery 1. In this case, in order to reduce heat generation in the nonaqueous electrolyte secondary battery 1, it may be necessary to limit the charging current A1 or cool the nonaqueous electrolyte secondary battery 1, which may result in a longer charging time. Therefore, in the present embodiment, the threshold value Th1 is preferably set to a temperature at which the battery temperature of the nonaqueous electrolyte secondary battery 1 does not become too high and generate heat during charging (for example, room temperature or a temperature higher by a predetermined temperature than the room temperature). Here, if the battery temperature is higher than the threshold value Th1, it is preferable not to temporarily increase the charging current A1 at the start of charging in order to prevent the charging time from becoming longer. Therefore, if the battery temperature is higher than the threshold value Th1, proceed to step S105 in FIG.

[0037] In step S105, if the charge / discharge history H1 immediately before the start of charging is charging, or if the battery temperature is higher than threshold value Th1, the charge current determination unit 87 of FIG. 1 determines the charge current A1 at the start of charging of the nonaqueous electrolyte secondary battery 1. The charge current determination unit 87 determines the charge current A1 based on the first current information D11 shown in FIG. 4. Here, the charge current determination unit 87 first calculates the current SOC of the nonaqueous electrolyte secondary battery 1 based on the battery voltage, battery current, and battery temperature acquired in step S101 of FIG. 6. The current SOC can be calculated using a conventionally known method. Next, the charge current determination unit 87 determines the charge current A1 corresponding to the current SOC based on the first current information D11 shown in FIG. 4. Here, if the current SOC is low (SOC less than 50%), the charging current A1 is set to the maximum allowable value A11, and if the current SOC is medium to high (SOC 50% or higher), the charging current A1 is determined in accordance with the first current information D11 so that the charging current A1 decreases as the current SOC increases, and the flowchart of Figure 6 is terminated.

[0038] 6, if the determination unit 85 determines that the battery temperature of the nonaqueous electrolyte secondary battery 1 is equal to or lower than the threshold value Th1, the process proceeds to step S109. In step S109, if the charge / discharge history H1 immediately before the start of charging indicates rest or discharge and the battery temperature of the nonaqueous electrolyte secondary battery 1 is equal to or lower than the threshold value Th1, the charge current determination unit 87 determines the charge current A1 based on the second current information D12 shown in FIG. 5. Here, as in step S105, the charge current determination unit 87 calculates the current SOC of the nonaqueous electrolyte secondary battery 1 based on the battery voltage, battery current, and battery temperature detected by the voltage sensor 71a, current sensor 71b, and temperature sensor 71c. Thereafter, the charge current determination unit 87 determines the charge current A1 corresponding to the current SOC based on the second current information D12 shown in FIG. 5. Here, if the current SOC is low, the charge current A1 is set to the maximum allowable value A11. On the other hand, if the current SOC is medium-high, the charging current A1 is temporarily increased. Here, the charging current A1 is determined so that the charging current A1 is equal to the maximum allowable value A11 for the extended time T1. Note that, at this time, the charging current A1 may be adjusted so that it is increased if the continuous execution time of pauses or discharges in the charging / discharging history H1 is long, and decreased if the continuous execution time is short.

[0039] In this manner, the magnitude of the charging current A1 at the start of charging can be determined. In this embodiment, the charging control unit 89 in Fig. 1 starts charging the nonaqueous electrolyte secondary battery 1 at the determined charging current A1. At this time, if the charge / discharge history H1 immediately before the start of charging is charging, the charging control unit 89 calculates the current SOC at predetermined intervals and performs charging while appropriately changing the charging current A1 based on the first current information D11 shown in Fig. 4 so that the charging current A1 corresponds to the current SOC.

[0040] On the other hand, if the charge / discharge history H1 immediately before the start of charging indicates rest or discharge, charging is started by temporarily setting the charge current A1 to the maximum allowable value A11 (here, for the extended time T1). At this time, if the battery temperature rises, the charge current A1 may be adjusted to gradually decrease. Then, after the extended time T1 has elapsed since the start of charging, the charge current A1 is decreased. At this time, the charge control unit 89 calculates the current SOC at predetermined intervals and, just as when the charge / discharge history H1 indicates charging, performs charging while appropriately changing the charge current A1 to match the current SOC based on the second current information D12 (in other words, the first current information D11) in FIG. 5.

[0041] Examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in the examples.

[0042] First, a lithium-ion secondary battery was prepared as a nonaqueous electrolyte secondary battery as follows. Here, lithium nickel manganese cobalt composite oxide (NCM) as the positive electrode active material layer, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were mixed in a mass ratio of NCM:AB:PVdF = 97.5:1.5:1.0. The molar ratio of nickel, cobalt, and manganese in the lithium nickel manganese cobalt composite oxide was nickel:cobalt:manganese = 80:10:10. An appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to the resulting mixture to prepare a positive electrode composite slurry. The positive electrode composite slurry was applied by weight to both sides of a long piece of aluminum foil and dried. The coating was then roll-pressed using a rolling roller to produce a positive electrode sheet.

[0043] Graphite as the negative electrode active material layer, carboxymethyl cellulose (CMC) as a thickener, and styrene-butadiene rubber (SBR) as a binder were mixed in ion-exchange water in a mass ratio of graphite:CMC:SBR=98.3:0.7:1.0 to prepare a negative electrode composite slurry. The negative electrode composite slurry was applied to both sides of a long copper foil and dried. The coating was then roll-pressed with a rolling roller to produce a negative electrode sheet.

[0044] The separator was made of polyethylene (PE) with aluminum oxide on its surface via polyvinylidene fluoride (PVdF).

[0045] 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 nonaqueous electrolyte.

[0046] The positive electrode sheet and the negative electrode sheet were wound with a separator interposed therebetween to prepare a wound electrode assembly, which was then housed in a square battery case together with the prepared non-aqueous electrolyte and sealed airtight to obtain the lithium ion secondary batteries of Examples 1 to 22.

[0047] Next, charging was carried out on the lithium ion secondary batteries of Examples 1 to 22. The charging conditions for the lithium ion secondary batteries of Examples 1 to 22 are shown in Table 1 below.

[0048] [Table 1]

[0049] In the charging conditions in Table 1, battery temperature refers to the battery temperature at the start of charging for the lithium-ion secondary batteries in Examples 1 to 22. The maximum current refers to the charging current at the start of charging, and the extension time refers to the time during which the charging current is temporarily increased. Here, the lithium-ion secondary batteries in Examples 1 to 22 were charged until the SOC changed from the start SOC to the end SOC. For the lithium-ion secondary batteries in Examples 1 to 3, the charging current was set based on the first current information D11 shown in FIG. 4 without referring to the charging / discharging history, and charging was performed. Therefore, the immediately preceding charging / discharging history and the extension time of the maximum current are not shown in Examples 1 to 3. On the other hand, for the lithium-ion secondary batteries in Examples 4 to 22, the charging current at the start of charging and the extension time of the charging current were set according to the charging / discharging state of the immediately preceding charging / discharging history. For the lithium-ion secondary batteries in Examples 4 to 22, the charging current was set based on the second current information D12 shown in FIG. 5, and charging was performed by temporarily increasing the charging current at the start of charging. Here, the maximum current of 182 A indicates the maximum allowable value A11 (see FIG. 5). In Examples 18 to 20, the immediately preceding charge / discharge history was charging, but the charging current was set based on the second current information D12 shown in FIG. 5, and charging was performed by temporarily increasing the charging current.

[0050] In the previous charge / discharge history in Table 1, the number on the left (e.g., 1 / 3C) when the charge / discharge state is discharge indicates the C rate at the time of discharge. The execution time of the previous charge / discharge history is the time during which the corresponding charge / discharge state was performed continuously.

[0051] Here, Table 1 shows the charging times (seconds and minutes) required when charging the lithium ion secondary batteries for Examples 1 to 22 based on the charging conditions in Table 1. Then, after charging the lithium ion secondary batteries of Examples 1 to 22 under the charging conditions in Table 1, the presence or absence of lithium deposition was confirmed for each lithium ion secondary battery. Here, an operator visually confirmed the presence or absence of lithium deposition throughout the entire battery case of the lithium ion secondary battery. The presence or absence of lithium deposition for Examples 1 to 22 is shown in Table 1 above.

[0052] As shown in Table 1, in Examples 4 to 17, when the immediately preceding charge-discharge history (specifically, immediately before the start of charge) was a rest or discharge, temporarily increasing the charge current (here, setting the charge current to the maximum current for the extended time) resulted in a relatively shorter charge time compared to Examples 1 to 3, when the charge current was not temporarily increased. Furthermore, as in Examples 18 to 20, when the immediately preceding charge-discharge history was a charge, temporarily increasing the charge current made lithium deposition more likely to occur. This is thought to be because, if charging had been performed immediately before the start of charge, the lithium ion secondary battery was in an overvoltage state, and therefore the amount of lithium on the negative electrode surface was particularly large, or the negative electrode potential became a less noble potential, making lithium deposition more likely to occur. For example, in order to suppress the overvoltage state, the charge density of the negative electrode active material layer of the lithium ion secondary battery was increased (for example, to 1.4 g / cm 3 or more), while increasing the basis weight (for example, 20 mg / cm 2 On the other hand, as in Examples 4 to 9, when the immediately preceding charge / discharge history was rest or discharge, the amount of lithium on the negative electrode surface of the lithium ion secondary battery was smaller than when charging, or the negative electrode potential was a noble potential, making it difficult for lithium deposition to occur, and therefore it is believed that lithium deposition did not occur even when the charging current was temporarily increased.

[0053] As in Examples 4 to 17, the magnitude of the charging current when temporarily increasing the charging current to the maximum current varies depending on the battery specifications, battery temperature, and SOC of the lithium-ion secondary battery. However, as in Examples 1 to 3, the charging current is preferably approximately 1.2 to 2 times larger than the charging current at the same starting SOC when the immediately preceding charge / discharge history is not referenced. For example, comparing Examples 4 and 15 with Example 1, when the starting SOC is 50%, the magnitude of the charging current temporarily increased is preferably approximately 1.05 to 1.15 times larger. For example, comparing Examples 5 and 16 with Example 2, when the starting SOC is 60%, the magnitude of the charging current temporarily increased is preferably approximately 1.3 to 1.5 times larger. For example, comparing Examples 6 and 17 with Example 3, when the starting SOC is 70%, the magnitude of the charging current temporarily increased is preferably approximately 1.7 to 2 times larger.

[0054] As in Examples 4 to 17, the expansion time when temporarily increasing the charging current is preferably about 100 to 250 seconds. However, the higher the initial SOC at the start of charging, the shorter the expansion time is preferably.

[0055] As in Examples 4 to 17, when the charge / discharge state in the immediately preceding charge / discharge history was a rest or discharge and the execution time of that charge / discharge state was 5 minutes or longer, lithium deposition did not occur even when the charge current was temporarily increased. On the other hand, as in Examples 21 and 22, when the charge / discharge state in the immediately preceding charge / discharge history was a rest or discharge and the execution time of that charge / discharge state was less than 5 minutes (here, 1 minute), lithium deposition occurred when the charge current was temporarily increased to the maximum current. As such, when the execution time of the immediately preceding rest or discharge is short, the lithium ion secondary battery becomes overvoltage, the amount of lithium on the negative electrode surface becomes large, or the negative electrode potential becomes a less noble potential, which is thought to make lithium deposition more likely to occur. Therefore, in order to eliminate the overvoltage state, it is preferable that the execution time of the rest or discharge is 5 minutes or longer. Therefore, by temporarily increasing the charge current when the execution time of the rest or discharge in the immediately preceding charge / discharge history is 5 minutes or longer, it is possible to reduce the charge time while suppressing lithium deposition.

[0056] The invention disclosed herein has been described in various ways. Unless otherwise specified, the embodiments described herein do not limit the present invention. Furthermore, the embodiments of the invention disclosed herein can be modified in various ways, and each component and each process described herein can be omitted or combined as appropriate, unless a particular problem arises.

[0057] As described above, this specification includes the disclosures set forth in the following sections. Section 1: A method for controlling a non-aqueous electrolyte secondary battery, comprising: A control method for a non-aqueous electrolyte secondary battery, wherein when the charge / discharge history immediately before the start of charging is rest or discharge, the charge current is temporarily increased at the start of charging compared to when the charge / discharge history immediately before the start of charging is charge.

[0058] Section 2: Item 2. The method for controlling a non-aqueous electrolyte secondary battery according to item 1, wherein the increase in the charging current is changed depending on the time of rest or discharge in the charge / discharge history.

[0059] Section 3: 3. The method for controlling a non-aqueous electrolyte secondary battery according to item 1 or 2, wherein, when the battery temperature of the non-aqueous electrolyte secondary battery increases during charging, the increase in the charging current is reduced.

[0060] Section 4: 3. The method for controlling a non-aqueous electrolyte secondary battery according to item 1 or 2, wherein the SOC region of the non-aqueous electrolyte secondary battery charged with the increased charging current is within a range of 50% to 80%. [Explanation of symbols]

[0061] 1 Nonaqueous electrolyte secondary battery 70 Control device 100 Battery System A1 charging current H1 Charge / discharge history

Claims

1. A method for controlling a non-aqueous electrolyte secondary battery, comprising: A control method for a non-aqueous electrolyte secondary battery, wherein when the charge / discharge history immediately before the start of charging is rest or discharge, the charge current is temporarily increased at the start of charging compared to when the charge / discharge history immediately before the start of charging is charge.

2. 2. The method for controlling a non-aqueous electrolyte secondary battery according to claim 1, wherein the increase in the charging current is changed depending on the time of rest or discharge in the charge / discharge history.

3. 3. The method for controlling a non-aqueous electrolyte secondary battery according to claim 1, further comprising reducing an increase in the charging current when the battery temperature of the non-aqueous electrolyte secondary battery increases during charging.

4. 3. The method for controlling a non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is charged with an increased charging current in an SOC region within a range of 50% to 80%.

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