Control method for lithium secondary battery

Abstract

To provide a control method for a lithium secondary battery that can more safely eliminate dendrite precipitation.SOLUTION: A control method of a lithium secondary battery includes a dendrite detection step of detecting the presence or absence of dendrite precipitation on a negative electrode of a lithium secondary battery, a high-rate discharge step of performing high-rate discharge using a discharge control device that controls the discharge amount of the lithium secondary battery when dendrite precipitation is detected in the dendrite detection step, and a confinement pressure increase step of increasing the confinement pressure of the lithium secondary battery using a confinement pressure control device that controls the confinement pressure of the lithium secondary battery, which is executed after the high-rate discharge step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for controlling a lithium secondary battery. [Background technology]

[0002] In recent years, research and development into secondary batteries that contribute to energy efficiency has been conducted to ensure that more people have access to affordable, reliable, sustainable and advanced energy.

[0003] Lithium-ion secondary batteries, which have high voltage, capacity, and energy density, are widely used as secondary batteries. Recently, lithium metal batteries, which use lithium metal or its alloys as the negative electrode, have become known as lithium secondary batteries with even higher theoretical capacity. A problem with these lithium secondary batteries is the deposition of dendritic lithium metal on the negative electrode during charge-discharge cycles. The deposited lithium metal is also called dendrites, and if the dendrites grow and come into contact with the positive electrode, a short circuit may occur.

[0004] Patent Document 1 discloses a technology for controlling a lithium ion secondary battery, which, when it is determined that lithium has precipitated, estimates the recovery time required to recover the precipitated lithium, and when the recovery time is reached, limits the magnitude of the charging current flowing through the secondary battery to a reference value or less, and increases the restraining pressure of the secondary battery, thereby destroying inactive sites and suppressing a decrease in the battery capacity of the secondary battery. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-034264 Summary of the Invention [Problem to be solved by the invention]

[0006] The technology disclosed in Patent Document 1 increases the confining pressure of the secondary battery after a recovery time has elapsed since it was determined that lithium precipitation had occurred. Therefore, if the confining pressure of the secondary battery is increased when dendrite precipitation has progressed, there is a risk that the dendrites will break through the separator, causing a short circuit.

[0007] The present invention has been made in view of the above-mentioned problems, and has an object to provide a method for controlling a lithium secondary battery that can more safely eliminate the dendrite precipitation state. [Means for solving the problem]

[0008] (1) The present invention relates to a control method for a lithium secondary battery, the control method comprising: a dendrite detection step of detecting the presence or absence of dendrite precipitation in a negative electrode of the lithium secondary battery; a high-rate discharge step of performing high-rate discharge using a discharge control device that controls the discharge amount of the lithium secondary battery when dendrite precipitation is detected in the dendrite detection step; and a baffling pressure increase step, which is executed after the high-rate discharge step, of increasing the baffling pressure of the lithium secondary battery using a baffling pressure control device that controls the baffling pressure of the lithium secondary battery.

[0009] According to the invention (1), a method for controlling a lithium secondary battery can be provided that can more safely eliminate the precipitation state of dendrites.

[0010] (2) The method for controlling a lithium secondary battery according to (1), wherein the discharge rate in the high-rate discharge step is 1.0 C or higher.

[0011] According to the invention (2), safety during the confining pressure increasing step can be further improved.

[0012] (3) The method for controlling a lithium secondary battery according to (1) or (2), wherein the confining pressure of the lithium secondary battery after the increase in the confining pressure increasing step is 1.3 MPa or more.

[0013] According to the invention (3), the precipitation of dendrites can be reliably eliminated.

[0014] (4) The method for controlling a lithium secondary battery according to any one of (1) to (3), wherein the negative electrode of the lithium secondary battery includes a lithium metal layer.

[0015] According to the invention (4), it is possible to safely eliminate the dendrite precipitation state in a lithium secondary battery including a lithium metal layer where dendrites are more likely to precipitate. [Brief explanation of the drawings]

[0016] [Figure 1] 3 is a flowchart showing a control method for a lithium secondary battery according to the present embodiment. [Figure 2] 1 is a conceptual cross-sectional view showing the configuration of a lithium secondary battery cell according to an embodiment of the present invention. [Figure 3] 1 is a conceptual cross-sectional view showing the configuration of a secondary battery module formed of a plurality of lithium secondary battery cells according to an embodiment of the present invention. [Figure 4] 1 is a graph schematically showing the relationship between the restraining pressure on a secondary battery and the deposition thickness and porosity. DETAILED DESCRIPTION OF THE INVENTION

[0017] <Outline of Lithium Secondary Battery Control Method> The control method for a lithium secondary battery according to this embodiment is a method for safely eliminating the dendrite precipitation state when the occurrence of dendrites in the negative electrode of the lithium secondary battery is detected. The control method for a lithium secondary battery according to this embodiment includes a dendrite detection step S1, a high-rate discharge step S2, and a confining pressure increase step S3, as shown in FIG.

[0018] The method for controlling a lithium secondary battery according to the present embodiment may be applied to a lithium ion secondary battery or a lithium metal battery including a metallic lithium layer in the negative electrode. The method for controlling a lithium secondary battery according to the present embodiment is preferably applied to a lithium metal battery in which dendrite deposition is likely to occur in the negative electrode.

[0019] <Lithium secondary battery> Fig. 2 is a cross-sectional view showing an outline of a lithium secondary battery that is the subject of the control method for a lithium secondary battery according to this embodiment. As shown in Fig. 2, a battery cell 1 of the lithium secondary battery has an anode 2 including an anode active material layer 21 and an anode current collector 22, a cathode 3 including a cathode active material layer 31 and a cathode current collector 32, an electrolyte layer 4 laminated between the anode 2 and the cathode 3, and exterior bodies 51 and 52 that house the anode 2, the electrolyte layer 4, and the cathode 3.

[0020] (Negative electrode) The negative electrode 2 includes, for example, a negative electrode current collector 22 and a negative electrode active material layer 21 stacked adjacent to the negative electrode current collector 22. In addition to the above, the negative electrode 2 may also include a binder, a conductive additive, an electrolyte, etc. The binder, conductive additive, electrolyte, etc. are not particularly limited, and substances known as electrode materials for secondary batteries can be used.

[0021] When the lithium secondary battery is a lithium metal battery, the negative electrode active material layer 21 essentially contains a lithium metal layer. The lithium metal layer may be a layer of simple lithium metal or a layer of a lithium metal alloy. Materials constituting the lithium alloy are not particularly limited, but examples include tin, bismuth, antimony, zinc, copper, etc., and two or more of these may be used in combination.

[0022] When the lithium secondary battery is a lithium ion secondary battery, the negative electrode active material layer 21 contains a negative electrode active material.

[0023] The negative electrode active material is not particularly limited as long as it can occlude and release lithium ions. Examples thereof include metallic lithium, lithium alloys, metal oxides, metal sulfides, metal nitrides, Si, SiO, carbon materials, etc. Examples of the carbon materials include artificial graphite, natural graphite, hard carbon, soft carbon, etc.

[0024] The negative electrode current collector 22 is not particularly limited, and examples thereof include metals such as copper, stainless steel, and aluminum. The above metals are formed, for example, in the form of foils.

[0025] (Positive electrode) The positive electrode 3 includes, for example, a positive electrode current collector 32 and a positive electrode active material layer 31 laminated adjacent to the positive electrode current collector 32. In addition to the above, the positive electrode 3 may contain a binder, a conductive assistant, an electrolyte, etc. The binder, the conductive assistant, the electrolyte, etc. are not particularly limited, and substances known as electrode materials for secondary batteries can be applied.

[0026] The positive electrode active material contained in the positive electrode active material layer 31 is not particularly limited, and substances known as positive electrode active materials for lithium secondary batteries can be used. Examples of the positive electrode active material include ternary positive electrode materials such as LiCoO2, LiNiO2, NCM (Li(NixCoyMnz)O2, (0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1)), layered positive electrode active material particles such as LiVO2, LiCrO2, spinel type positive electrode active materials such as LiMn2O4, Li(Ni 0.25 Mn 0.75 )2O4, LiCoMnO4, Li2NiMn3O8, olivine type positive electrode active materials such as LiCoPO4, LiMnPO4, LiFePO4, etc. can be used.

[0027] The positive electrode current collector 32 is not particularly limited, and examples thereof include metals such as aluminum. The above metals are formed, for example, in the form of foils.

[0028] (Electrolyte layer) The electrolyte layer 4 is a layer containing an electrolytic solution in which an electrolyte is dissolved in a solvent. The electrolyte layer 4 may include a separator that prevents short-circuiting between the positive electrode 3 and the negative electrode 2, and preferably includes a separator, particularly when the lithium secondary battery is a lithium ion secondary battery. The electrolytic solution may be impregnated into the separator. As the separator, a material known as a separator for lithium secondary batteries, such as a nonwoven fabric or a microporous film, can be used.

[0029] The electrolyte may be gelled using a gelling agent, which is not particularly limited, and examples thereof include PEO (polyethylene oxide)-based gelling agents, PPO (polypropylene oxide)-based gelling agents, PAN (polyacrylonitrile)-based gelling agents, PVC (polyvinyl chloride) PVdF (polyvinylidene fluoride)-based gelling agents, PMMA (polymethyl methacrylate)-based gelling agents, PVdF-HEP (vinylidene fluoride-hexafluoropropylene copolymer)-based gelling agents, PDMS (polydimethylsiloxane)-based gelling agents, and low-molecular-weight gelling agents that utilize π-π stacking.

[0030] The electrolyte is not particularly limited, but examples thereof include lithium bis(fluorosulfonyl)imide (LiFSI), lithium hexafluorophosphate, lithium hexafluoroborate, and lithium bis(trifluoromethanesulfonyl)imide, and two or more of these may be used in combination.

[0031] The solvent is not particularly limited, but examples thereof include ethylene carbonate, propylene carbonate, dimethyl ether, fluoroethylene carbonate, dimethyl carbonate, hydrofluoroether, ethyl methyl carbonate, diethyl carbonate, and the like, and two or more of these may be used in combination.

[0032] (exterior body) The exterior bodies 51 and 52 house the laminated negative electrode 2, electrolyte layer 4, and positive electrode 3. As shown in Fig. 2, for example, a pair of laminate films can be used for the exterior bodies 51 and 52. The configuration of the exterior bodies is not particularly limited to the above, and any known exterior body applicable to secondary batteries can be used.

[0033] In addition to the above, the battery cell 1 has an electrode tab 6 shown in FIG. 3. The electrode tab 6 is electrically connected to the negative electrode 2 and / or the positive electrode 3. The electrode tab 6 is electrically connected to a discharge target (not shown). The battery cell 1 is subjected to high-rate discharge, which will be described later, via a discharge control device.

[0034] <Lithium secondary battery module> The control method for a lithium secondary battery according to this embodiment may be applied to a lithium secondary battery module 100 configured to include a plurality of the above-described battery cells 1. As shown in Fig. 3, the lithium secondary battery module 100 includes a plurality of battery cells 1, separators 101 disposed between adjacent battery cells 1, end plates 102 disposed on both ends of the plurality of stacked battery cells 1 and separators 101, bind bars 103, and lower plates 104.

[0035] The separators 101 ensure insulation between adjacent battery cells 1 and apply uniform surface pressure to the battery cells 1. The end plates 102 apply a binding pressure to the multiple battery cells 1. For example, a binding pressure increasing step S3 (described below) is performed by a binding pressure control device that controls the binding pressure applied to the multiple battery cells 1 by the end plates 102. The bind bars 103 improve the binding strength of the multiple stacked battery cells 1 and separators 101. The lower plates 104 secure the multiple stacked battery cells 1 and separators 101 in place.

[0036] In addition to the above, the lithium secondary battery module 100 may include a current sensor or the like capable of detecting current values ​​during charging and discharging. The above is one example of the configuration of a lithium secondary battery module, and the configuration of the lithium secondary battery module is not particularly limited to the above. The target of the control method for a lithium secondary battery according to this embodiment may be any configuration that is capable of controlling the restraining pressure and discharge current of the battery cell 1, and is not particularly limited to the above configuration.

[0037] <Method for controlling lithium secondary batteries> The control method for a lithium secondary battery according to this embodiment essentially comprises a dendrite detection step S1, a high-rate discharge step S2, and a bundling pressure increase step S3 shown in FIG.

[0038] (Dendrite detection process S1) The dendrite detection step S1 is a step of detecting whether or not dendrites are precipitated in the negative electrode 2. The presence or absence of dendrites is determined, for example, based on the current value and current flow time during charging of the battery cell 1. The current value is acquired, for example, by a current sensor provided in the battery cell 1 or the battery module 100. If dendrite precipitation is detected in the dendrite detection step S1, the process proceeds to the high-rate discharge step S2. If dendrite precipitation is not detected in the dendrite detection step S1, the dendrite detection step S1 is repeated until dendrite precipitation is detected.

[0039] (High-rate discharge process S2) The high-rate discharge step S2 is a step of performing high-rate discharge on the battery cell 1 if dendrite deposition is detected in the dendrite detection step S1. By performing high-rate discharge on the battery cell 1 on which dendrites have been deposited, lithium metal dissolves preferentially from the tips of the dendritic dendrites (lithium metal). This reduces the risk of the dendrite tips breaking through the separator or the like and causing a short circuit in the subsequent confining pressure increase step S3, thereby safely eliminating the dendrites. The discharge rate in the high-rate discharge step S2 is preferably 1.0 C or higher. A discharge rate of 1.0 C or higher creates a large concentration gradient on the lithium surface, thereby increasing the current density at the tips of the dendritic dendrites (lithium metal). As a result, the tips of the dendrites (lithium metal) are preferentially dissolved. This enables the removal of non-uniform lithium deposits and results in a uniform surface after discharge. The high-rate discharge is performed, for example, by a discharge control device that controls the amount of discharge from the battery cell 1.

[0040] (Confining pressure increase process S3) The confining pressure increasing step S3 is carried out after the high-rate discharge step S2. In the confining pressure increasing step S3, the confining pressure applied to the lithium secondary battery is increased to crush the dendritic, porous dendrites and improve the density. FIG. 4 is a graph schematically showing the relationship between the confining pressure (F) applied to the lithium secondary battery and the dendrite precipitation thickness (T) and porosity (P). As shown in FIG. 4, it is believed that the dendrite precipitation thickness (T) and porosity (P) decrease as the confining pressure increases. From the above perspective, it is preferable that the confining pressure of the lithium secondary battery before the increase in the confining pressure increasing step S3 is 0.5 to 1.2 MPa, while the confining pressure of the lithium secondary battery after the increase is 1.3 MPa or more.

[0041] The confining pressure increasing step S3 is performed by a confining pressure control device that controls the confining pressure of the lithium secondary battery. Specific configurations of the confining pressure control device include a pressure sensor that can detect the confining pressure of the battery cell 1, connecting members (e.g., bolts and nuts) that connect a pair of end plates 102 in the battery module 100, and a control unit that can control the confining pressure of the battery cell 1 applied by the connecting members. The confining pressure control device controls the confining pressure of the battery cell 1 by, for example, controlling the amount of fastening of the battery cell 1 by the connecting members.

[0042] The control method for a lithium secondary battery according to this embodiment includes a judgment step S4 in which it is determined whether or not to continue executing this control after the confining pressure increasing step S3. If it is determined in judgment step S4 that this control should be continued (S4: YES), the process returns to S1. If it is determined in judgment step S4 that this control should be terminated (S4: NO), this control is terminated. The above judgment in judgment step S4 may be made, for example, by input from the user executing the control method for a lithium secondary battery, or if no input from the user is made, it may be automatically determined that this control should be continued.

[0043] The control method for a lithium secondary battery according to this embodiment is executed by, for example, a control device, which is configured with, for example, a processor such as a CPU, storage devices such as a ROM (read-only memory) and a RAM (random-access memory), a communication interface capable of communicating with the discharge control device and the restraint pressure control device, and a bus connecting these components.

[0044] The specific configuration of the control unit of the discharge control device or the restraining pressure control device is not particularly limited, but may be realized, for example, by a PLC (Programmable Logic Controller) consisting of an input unit that receives information from sensors, etc., a processor such as a CPU, a power supply, and an output unit that transmits information to relays, etc.

[0045] The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments, and includes modifications and improvements within the scope of achieving the object of the present invention. [Explanation of symbols]

[0046] 1 Battery cell (lithium secondary battery) 2 negative electrode 21 Negative electrode active material layer (lithium metal layer, lithium metal alloy layer) S1 Dendrite detection process S2 High-rate discharge process S3 Confining pressure increase process

Claims

1. A method for controlling a lithium secondary battery, comprising: a dendrite detection step of detecting whether or not dendrites are precipitated in the negative electrode of the lithium secondary battery; a high-rate discharge step of performing high-rate discharge at a discharge rate of 1.0 C or more by a discharge control device that controls a discharge amount of the lithium secondary battery when precipitation of dendrites is detected in the dendrite detection step; a confining pressure increasing step, which is executed after the high-rate discharge step, of increasing the confining pressure of the lithium secondary battery by a confining pressure control device that controls the confining pressure of the lithium secondary battery, thereby crushing dendrites and improving the density of the negative electrode.

2. 2. The method for controlling a lithium secondary battery according to claim 1, wherein the confining pressure of the lithium secondary battery after the increase in the confining pressure increasing step is 1.3 MPa or more.

3. The method for controlling a lithium secondary battery according to claim 1 or 2, wherein the negative electrode of the lithium secondary battery includes a lithium metal layer.

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