All-solid lithium-ion battery control system

Abstract

Provided is a control system for an all-solid-state lithium-ion battery that improves safety. An all-solid-state lithium-ion battery control system provided in a vehicle includes: an all-solid-state lithium-ion battery connected to a drive motor of the vehicle; and a control unit that controls input and output of current to the all-solid-state lithium-ion battery in such a manner that a first prescribed SOC of the all-solid-state lithium-ion battery is not exceeded during normal operation, the all-solid-state lithium-ion battery including lithium titanate in a negative electrode, the control unit accumulating the number of seconds or the current value for which the charge amount of the all-solid-state lithium-ion battery exceeds 100% of the SOC due to overcurrent, calculating a limit SOC reduction amount based on the accumulated value, calculating a second prescribed SOC based on the limit SOC reduction amount, and controlling the all-solid-state lithium-ion battery based on the second prescribed SOC.

Description

Technical Field

[0001] This application relates to an all-solid-state lithium-ion battery control system. Background Technology

[0002] Patent Document 1 discloses a control device for lithium-ion batteries that prevents battery degradation caused by lithium accumulation on the negative electrode surface due to wheel slippage or rapid acceleration / deceleration of the vehicle.

[0003] Specifically, Patent Document 1 discloses a lithium-ion battery control device for driving a drive motor and controlling a lithium-ion battery equipped with a heater. The lithium-ion battery control device is characterized by having: a counting unit for counting the number of times current flows through the drive motor; and a heating unit for heating the lithium-ion battery by means of the heater when the count value of the counting unit exceeds a predetermined number.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2010-212019 Summary of the Invention

[0007] Typically, secondary batteries installed in vehicles are controlled within a defined State of Charge (SOC) to prevent overcharging. However, as mentioned above, there are instances where overcharging can occur suddenly or instantaneously due to slippage during regeneration control. The inventors realized that in such cases, if an all-solid-state lithium-ion battery containing lithium titanate in the negative electrode is used, the battery capacity in the overcharge region decreases once the overcharge zone is reached. Furthermore, it was realized that if overcharging is achieved again in this state, the defined SOC decreases, potentially leading to resistance heating.

[0008] Therefore, the purpose of this disclosure is to provide an all-solid-state lithium-ion battery control system that can improve safety, in view of the above facts.

[0009] In this disclosure, as a means to solve the above-mentioned problems, a control system for an all-solid-state lithium-ion battery installed in a vehicle is provided, comprising: an all-solid-state lithium-ion battery connected to a drive motor of the vehicle; and a control unit that, during normal operation, controls the input and output of current to the all-solid-state lithium-ion battery in a manner not exceeding a first predetermined SOC of the all-solid-state lithium-ion battery, wherein the all-solid-state lithium-ion battery contains lithium titanate in the negative electrode, the control unit accumulates the number of seconds or the current value in which the charge of the all-solid-state lithium-ion battery exceeds 100% of the SOC due to overcurrent, calculates a limit SOC reduction amount based on the accumulated value, calculates a second predetermined SOC based on the limit SOC reduction amount, and controls the all-solid-state lithium-ion battery based on the second predetermined SOC.

[0010] The all-solid-state lithium-ion battery control system disclosed herein, in the event of a sudden entry into the overcharge region, monitors the decrease in the limit SOC of the all-solid-state lithium-ion battery and controls the all-solid-state lithium-ion battery based on a newly calculated second specified SOC. Therefore, even if it subsequently enters the overcharge region again, the battery can be controlled within the limit SOC, and battery heating can be suppressed. Thus, the all-solid-state lithium-ion battery control system improves safety. Attached Figure Description

[0011] Figure 1 This describes the relationship between voltage / temperature and SOC when an all-solid-state lithium-ion battery using LTO has undergone two overcharge cycles.

[0012] Figure 2 yes Figure 1 A comparison of the curves of the negative electrode (LTO) and positive electrode (NMC) in the experiment.

[0013] Figure 3 This is an example of the control flow in the first implementation.

[0014] Figure 4 This is an example of the control flow in the second implementation method. Detailed Implementation

[0015] [First Implementation]

[0016] The first embodiment provides an all-solid-state lithium-ion battery control system installed in a vehicle, the all-solid-state lithium-ion battery control system comprising an all-solid-state lithium-ion battery and a control unit.

[0017] All-solid-state lithium-ion batteries

[0018] The all-solid-state lithium-ion battery used in the first embodiment can be connected to a vehicle's drive motor to supply current to the drive motor or be charged through the motor's regenerative operation. Furthermore, if the all-solid-state lithium-ion battery includes lithium titanate in its negative electrode, other structures are not particularly limited. For example, the following structure may also be used.

[0019] An all-solid-state lithium-ion battery sequentially comprises a positive electrode layer, a solid electrolyte layer, and a negative electrode layer. These electrode elements can be a single unit or multiple units stacked together. Additionally, besides these electrode elements, it may also include a positive current collector and a negative current collector. Furthermore, an all-solid-state lithium-ion battery can also have an outer casing to encapsulate these elements. The outer casing refers to, for example, laminated packaging.

[0020] The positive electrode layer includes at least a positive electrode composite layer. As for the positive electrode active material, there are no particular limitations as long as it is a positive electrode active material that can be used in lithium-ion all-solid-state batteries. Examples include lithium cobalt oxide, lithium nickel oxide (NCA-based active material), lithium manganese oxide, and lithium nickel cobalt manganese oxide (NCM). Furthermore, the positive electrode layer can arbitrarily include a solid electrolyte, a conductive additive, or a binder. Examples of solid electrolytes include oxide solid electrolytes and sulfide solid electrolytes. Li7La3Zr2O is an example of an oxide solid electrolyte. 12 Li 7-x La3Zr 1-x Nb x O 12 Examples of sulfide solid electrolytes include Li3PS4 and Li2S-P2S5. Examples of conductive agents include acetylene black, Ketjen black, and fumed carbon fiber (VGCF). Examples of binders include butadiene rubber (BR), butene rubber (IIR), and polyvinylidene fluoride (PVdF). The content of these materials in the positive electrode layer and the thickness of the positive electrode layer can remain the same as before.

[0021] The solid electrolyte layer contains at least a solid electrolyte. There are no particular limitations on the type of solid electrolyte, as long as it is usable in a lithium-ion all-solid-state battery. For example, the same type of electrolyte used in the positive electrode layer can be used. Furthermore, the electrolyte layer may arbitrarily include a binder. Regarding the type of binder, the same type of binder used in the positive electrode layer can be used. The content of these binders in the electrolyte layer and the thickness of the electrolyte layer can remain the same as before.

[0022] The negative electrode layer contains lithium titanate (LTO) as the negative electrode active material. Other negative electrode active materials may also be included. Examples of other negative electrode active materials include metallic active materials such as Li and Si, and carbon active materials such as graphite. Furthermore, the negative electrode layer may arbitrarily contain a solid electrolyte, a conductive additive, or a binder. The types of solid electrolyte, conductive additive, and binder can be the same as those used in the positive electrode layer. The amounts of these materials in the negative electrode layer and the thickness of the negative electrode layer can remain the same as before.

[0023] Known metal foils can be used as both positive and negative current collectors. Examples include metal foils made of Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel.

[0024] There are no particular limitations on the manufacturing methods for the positive electrode layer, electrolyte layer, and negative electrode layer; they can be manufactured using known methods. For example, in the case of manufacturing the positive electrode layer, the material constituting the positive electrode layer is mixed with a solvent to form a slurry, which is then applied to a substrate or a positive current collector and dried to manufacture the positive electrode layer. The electrolyte layer and negative electrode layer can be manufactured using the same methods. Then, a laminate can be fabricated by sequentially stacking the positive current collector, positive electrode layer, electrolyte layer, negative electrode layer, and negative current collector.

[0025] <Control Department>

[0026] In the first embodiment, the control unit controls the input and output of current to the all-solid-state lithium-ion battery during normal operation, without exceeding a first specified state of charge (SOC) of the all-solid-state lithium-ion battery. The control unit is typically composed of a computing device such as a computer.

[0027] "Normal operation" refers to operation where the charge level of the all-solid-state lithium-ion battery is below 100% of its State of Charge (SOC). Furthermore, "First-defined SOC" refers to a threshold value calculated based on the limit SOC of the all-solid-state lithium-ion battery and set in a manner that prevents the charge level of the all-solid-state lithium-ion battery from reaching the limit SOC. "Limit SOC" refers to the charge level at which abnormal heating beyond the normal operating range does not occur.

[0028] As described above, the control unit controls the all-solid-state lithium-ion battery to maintain a state of charge not exceeding the first specified SOC. However, in cases where overcurrent occurs due to slippage or rapid acceleration / deceleration, the charge level of the all-solid-state lithium-ion battery may exceed 100% of the SOC. The inventors realized that in such cases, if an all-solid-state lithium-ion battery containing lithium titanate (LTO) in the negative electrode is used, the battery capacity in the overcharge region (the region where the SOC exceeds 100%) decreases once the battery enters the overcharge region. Furthermore, it was realized that if overcharging is achieved again in this state, the SOC threshold decreases, potentially leading to resistor heating.

[0029] use Figure 1 , Figure 2 Let me explain further. First, let me explain... Figure 1 . Figure 1 This describes the voltage / temperature versus SOC relationship of an all-solid-state lithium-ion battery using LTO after two overcharge cycles. Figure 1 As shown, the curves change during the first and second instances of overcharging. Specifically, the voltage shift is almost unchanged during the SOC period of 10% to 100%, but the voltage tends to rise after SOC reaches 100%. That is, once the battery enters the overcharge region, it is considered to be degraded.

[0030] Next, an explanation Figure 2 . Figure 2 yes Figure 1 A comparison of the curves for the negative electrode (LTO) and the positive electrode (NMC: lithium nickel manganese cobalt oxide) in the experiment. For example... Figure 2 As shown, there is no change in the curve for the positive electrode, but only the curve for the negative electrode changes. Furthermore, the negative electrode experiences damage due to overcharging, making it prone to becoming a dangerous mode. Therefore, according to... Figure 2 It is believed that the negative electrode (LTO) deteriorates due to overcharging.

[0031] Thus, when a vehicle is equipped with an all-solid-state lithium-ion battery that uses LTO in the negative electrode, the battery safety is reduced due to overcharging, so corresponding changes to the control are required.

[0032] Therefore, in the first embodiment, the control unit accumulates the number of seconds and the current value when the charge of the all-solid-state lithium-ion battery exceeds 100% of the SOC due to overcurrent, calculates the limit SOC reduction amount based on the accumulated number of seconds or the current value, calculates the second specified SOC based on the limit SOC reduction amount, and controls the all-solid-state lithium-ion battery based on the second specified SOC.

[0033] "SOC 100%" refers to the 100% charge level of an all-solid-state lithium-ion battery set according to the limit SOC, and is a value lower than the first specified SOC. "Limit SOC reduction" refers to the difference between the limit SOC before and after the reduction due to overcharging. This limit SOC reduction can be obtained by obtaining the relationship between the cumulative number of seconds or current values ​​exceeding 100% SOC and the limit SOC reduction through prior experiments or simulations. "Second specified SOC" is a threshold calculated based on the new limit SOC calculated according to the limit SOC reduction, and is a threshold set to prevent the charge level of the all-solid-state lithium-ion battery from reaching the reduced limit SOC. "Control of the all-solid-state lithium-ion battery according to the second specified SOC" means that the control unit controls the current input and output to the all-solid-state lithium-ion battery during normal operation to ensure that it does not exceed the second specified SOC.

[0034] In addition, when the control unit calculates the reduction amount of the limit SOC, it can control the vehicle to stop driving or stop regenerative charging if the current SOC is above the reduced limit SOC.

[0035] Next, Figure 3 An example of the control process used to implement the first embodiment is shown. Figure 3As shown, the control unit first accumulates the number of seconds and current value exceeding 100% SOC due to overcharging. Next, based on the accumulated value, it calculates the threshold SOC reduction amount. Then, it determines whether the current charge level is above or below the threshold SOC calculated based on the threshold SOC reduction amount. If the current charge level is above the threshold SOC, vehicle operation is stopped, or vehicle operation is stopped after recharge is stopped. If the current charge level is below the threshold SOC, control of the all-solid-state lithium-ion battery is performed according to the second predetermined SOC calculated based on the threshold SOC reduction amount, and vehicle operation continues.

[0036] [Second Implementation]

[0037] In the second embodiment, the control unit calculates the voltage slope after the charge level of the all-solid-state lithium-ion battery exceeds 100% of its SOC due to overcurrent, and controls the all-solid-state lithium-ion battery based on the voltage slope. Therefore, the rest of the structure is the same as in the first embodiment.

[0038] like Figure 1 As shown, the slope of the voltage changes after overcharging to exceed 100% SOC. Therefore, in the second embodiment, the safety of the battery is determined based on the slope of this voltage. If the slope of the voltage is above a predetermined value, it is considered a reduction in the threshold SOC, and control of the all-solid-state lithium-ion battery is implemented. In performing such control, it is necessary to obtain the relationship between the slope of the voltage exceeding 100% SOC and the threshold SOC beforehand through experiments or simulations.

[0039] Figure 4 An example of the control process used to implement the second embodiment is shown. Figure 4 As shown, firstly, the control unit calculates the voltage slope after the SOC exceeds 100% due to overcharging. Next, it determines whether the voltage slope is above or below a predetermined value. If the voltage slope is above the predetermined value, vehicle operation is stopped, or vehicle operation is stopped after recharge is stopped. If the voltage slope is below the predetermined value, the safety of the all-solid-state battery is considered to be ensured, all-solid-state lithium-ion battery control is implemented, and vehicle operation continues.

[0040] Industrial availability

[0041] The above describes the all-solid-state lithium-ion battery control system of this disclosure. According to the all-solid-state lithium-ion battery control system of this disclosure, the safety of all-solid-state lithium-ion batteries can be improved, and therefore it can be considered one of the important technologies in the field of secondary batteries used in vehicles.

Claims

1. A control system for an all-solid-state lithium-ion battery provided in a vehicle, the control system comprising: an all-solid-state lithium-ion battery connected to a drive motor of the vehicle; and a control unit configured to control input and output of electric current to the all-solid-state lithium-ion battery in such a manner that a state of charge (SOC) of the all-solid-state lithium-ion battery does not exceed a first predetermined SOC during normal operation, wherein the all-solid-state lithium-ion battery includes lithium titanate in a negative electrode, the control unit is configured to accumulate a number of seconds or a current value during which the SOC of the all-solid-state lithium-ion battery exceeds 100% due to overcurrent, calculate a limit SOC decrease amount based on the accumulated value, calculate a second predetermined SOC based on the limit SOC decrease amount, and control the all-solid-state lithium-ion battery based on the second predetermined SOC. ​ ​ ​

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