Charging method of non-aqueous electrolyte secondary battery, charge and discharge method, and charging system of non-aqueous electrolyte secondary battery

Abstract

Provided is a charging method with which charging with good efficiency can be possible while ensuring good cycle characteristics in a non-aqueous electrolyte secondary battery comprising a negative electrode that contains a carbon material. A charging method for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure comprises a switching step for switching the control temperature of a non-aqueous electrolyte secondary battery from high temperature to low temperature, wherein the non-aqueous electrolyte secondary battery includes a positive electrode and a negative electrode which reversibly perform intercalation and deintercalation of lithium ions, and the negative electrode contains, as a negative electrode active material, a carbon material and a silicon compound. The timing of the switching step is determined by detecting that dQGr / dQ, that is, the ratio of the amount of change in a capacity QGr of the carbon material to the amount of change in a battery capacity Q, becomes larger than dQSi / dQ, that is, the ratio of the amount of change in a capacity QSi of the silicon compound to the amount of change in the battery capacity Q.

Description

Technical Field

[0001] The present disclosure relates to a charging method, a charge-discharge method, and a charging system for a non-aqueous electrolyte secondary battery.

Background Art

[0002] Non-aqueous electrolyte secondary batteries are used as power sources for a wide range of devices including electric vehicles, and rapid charging is required from the perspective of improving the convenience of the devices. However, when charging at a rapid rate, the deterioration of the negative electrode active material, particularly silicon compounds, tends to progress rapidly at the initial stage of charging. The deterioration of the negative electrode active material causes a decrease in battery capacity. Patent Document 1 discloses a charging method for a secondary battery that reduces the initial irreversible capacity of the charge-discharge cycle by step charging.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, step charging has a problem in that the charging efficiency decreases because the current value is reduced to suppress the deterioration of the negative electrode active material.

[0005] Therefore, an object of the present disclosure is to provide a charging method that enables efficient charging while ensuring good cycle characteristics in a non-aqueous electrolyte secondary battery including a negative electrode containing a carbon material.

Means for Solving the Problems

[0006] A charging method for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes a positive electrode and a negative electrode that reversibly occlude and release lithium ions, and the negative electrode contains a carbon material and a silicon compound as a negative electrode active material. The charging method of the non-aqueous electrolyte secondary battery includes a switching step of switching the control temperature of the non-aqueous electrolyte secondary battery from a high temperature to a low temperature. The timing of the switching step is the ratio dQ of the change amount of the carbon material to the change amount of the battery capacity Q Gr of the change amount of Gr is detected and determined to be larger than the ratio dQ Si of the change amount of the silicon compound to the change amount of the battery capacity Q Si .

[0007] A charge-discharge method for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is characterized in that after charging the non-aqueous electrolyte secondary battery by the above charging method, it is discharged.

[0008] A charging system for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is a charging system for charging a non-aqueous electrolyte secondary battery including a negative electrode containing a carbon material and a silicon compound as a negative electrode active material, and is characterized by including a charging control device that executes the above charging method.

Advantages of the Invention

[0009] According to one aspect of the present disclosure, in a non-aqueous electrolyte secondary battery including a negative electrode containing a carbon material, it is possible to provide a charging method that enables efficient charging while ensuring good cycle characteristics. That is, according to the charging method according to the present disclosure, charging can be performed in a short time while suppressing a decrease in cycle characteristics.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0011] In a non-aqueous electrolyte secondary battery including a negative electrode containing a carbon material, it is an important issue to provide a charging method that can be efficiently charged in a short time and can suppress deterioration of cycle characteristics. The inventors of the present invention have succeeded in efficiently suppressing deterioration of cycle characteristics by switching the control temperature of the non-aqueous electrolyte secondary battery from a high temperature to a low temperature during charging of the battery.

[0012] Hereinafter, an example of an embodiment of the present disclosure will be described in detail. Hereinafter, a cylindrical battery in which a wound electrode body 14 is housed in a cylindrical battery case 15 will be exemplified, but the battery case is not limited to a cylindrical shape, and may be, for example, a rectangular shape, or a battery case composed of a laminate sheet including a metal layer and a resin layer. Further, the electrode body may be a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are alternately stacked via a separator. Note that the non-aqueous electrolyte secondary battery to which the charging method according to the present disclosure can be applied may be any battery including a negative electrode containing a carbon material and a silicon compound as a negative electrode active material.

[0013] FIG. 1 is a block diagram showing the configuration of a charging system 1 for a non-aqueous electrolyte secondary battery, which is an example of an embodiment. As illustrated in FIG. 1, the charging system 1 includes a charging control device 2 that controls the charging of the non-aqueous electrolyte secondary battery 10, and a battery monitoring unit 30 that monitors the charging state of the battery. The non-aqueous electrolyte secondary battery 10 is connected to a load 101 and supplies the stored power to the load 101. The charging system 1 may include a battery pack (also referred to as a battery pack or a battery module) in which a plurality of non-aqueous electrolyte secondary batteries 10 are connected in series, parallel, or series-parallel.

[0014] The charging system 1 can be widely applied to charging devices and charging facilities for non-aqueous electrolyte secondary batteries containing a carbon material as a negative electrode active material, such as vehicles such as electric vehicles and hybrid vehicles, vehicle charging facilities, power storage facilities, chargers for electric tools, and various other devices and facilities. The charging control device 2 may be incorporated into a battery module or may be configured as a part of a control device of a device or facility such as a vehicle on which the charging system 1 is mounted.

[0015] The charging control device 2 is a device that executes a charging method described later. When charging the battery, the charging control device 2 determines the charging conditions of the battery based on the charging state of the battery acquired from the battery monitoring unit 30. Although details will be described later, the charging control device 2 Constant current has a constant current charging control means 4 that executes a charging step and a constant voltage charging control means 6 that executes a constant voltage charging step. The charging control device 2 also has a switching means 8 that executes a switching step. The charging control device 2 has, for example, a rectifier circuit that converts the AC power of the power supply 100 into a predetermined DC power and supplies it to the non-aqueous electrolyte secondary battery 10.

[0016] The charging control device 2 is composed of an integrated circuit such as an IC chip or an LSI chip, and has a CPU which is an arithmetic processing unit and a storage unit 9. The CPU has a function of reading and executing a program etc. stored in advance in the storage unit 9. The storage unit 9 has a function of temporarily storing the read program, processing data etc. and a function of storing a control program, threshold value etc. The functions of the above-mentioned respective charging control means are realized, for example, by executing a control program stored in the storage unit 9.

[0017] Further, the charging control device 2 has a constant current circuit for controlling the charging current so that DC power of a predetermined current value is supplied to the battery, a constant voltage circuit for controlling the charging voltage so that DC power of a predetermined voltage value is supplied to the battery, etc. Note that the charging circuits such as a rectifying circuit, a constant current circuit, and a constant voltage circuit may be configured as devices separate from the charging control device 2. The charging control device 2 controls the charging circuit based on the charging state of the battery acquired from the battery monitoring unit 30 and executes the charging of the non-aqueous electrolyte secondary battery 10.

[0018] The battery monitoring unit 30 detects, for example, the charging current supplied to the non-aqueous electrolyte secondary battery 10 and the battery voltage. The charging control device 2 estimates the state of charge (SOC) from the battery voltage acquired by the battery monitoring unit 30 and executes charging control based on the SOC. The SOC indicates the ratio of the charged amount of electricity to the charging capacity from the fully discharged state to the fully charged state of the non-aqueous electrolyte secondary battery 10 in each charge-discharge cycle. Note that the SOC can also be estimated from the charge-discharge current and the charge-discharge time. Conventionally known methods can be applied to the method of estimating the SOC. The charging control device 2 performs constant current charging (CC charging) until the battery voltage reaches a predetermined voltage, and then performs constant voltage charging (CV charging).

[0019] [Non-aqueous electrolyte secondary battery] FIG. 2 is a cross-sectional view of a non-aqueous electrolyte secondary battery 10 which is an example of an embodiment. As illustrated in FIG. 2, the non-aqueous electrolyte secondary battery 10 includes an electrode body 14, a non-aqueous electrolyte (not shown), and a battery case 15 that houses the electrode body 14 and the non-aqueous electrolyte. The electrode body 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound with a separator 13 interposed therebetween. The battery case 15 is composed of a bottomed cylindrical outer can 16 and a sealing body 17 that closes the opening of the outer can 16. Further, the non-aqueous electrolyte secondary battery 10 includes a resin gasket 28 disposed between the outer can 16 and the sealing body 17.

[0020] The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the non-aqueous solvent, for example, esters, ethers, nitriles, amides, and a mixed solvent of two or more of these may be used. The non-aqueous solvent may contain a halogen-substituted product in which at least a part of the hydrogen of these solvents is substituted with a halogen atom such as fluorine. Note that the non-aqueous electrolyte is not limited to a liquid electrolyte, and may be a solid electrolyte using a gel polymer or the like. As the electrolyte salt, for example, a lithium salt such as LiPF6 is used.

[0021] The electrode body 14 is composed of a long positive electrode 11, a long negative electrode 12, two long separators 13, a positive electrode tab 20 joined to the positive electrode 11, and a negative electrode tab 21 joined to the negative electrode 12. The positive electrode 11 and the negative electrode 12 reversibly occlude and release lithium ions. The negative electrode 12 is formed to be slightly larger in size than the positive electrode 11 in order to prevent the precipitation of lithium. That is, the negative electrode 12 is formed longer than the positive electrode 11 in the longitudinal direction and the width direction (short side direction). The two separators 13 are formed to be at least slightly larger in size than the positive electrode 11 and are disposed, for example, so as to sandwich the positive electrode 11.

[0022] Insulating plates 18 and 19 are respectively arranged above and below the electrode body 14. In the example shown in FIG. 2, the positive tab 20 attached to the positive electrode 11 extends toward the sealing body 17 through the through-hole of the insulating plate 18, and the negative tab 21 attached to the negative electrode 12 extends toward the bottom side of the outer can 16 through the outside of the insulating plate 19. The positive tab 20 is connected to the lower surface of the filter 23 which is the bottom plate of the sealing body 17 by welding or the like, and the cap 27 which is the top plate of the sealing body 17 electrically connected to the filter 23 serves as the positive electrode terminal. The negative tab 21 is connected to the inner surface of the bottom of the outer can 16 by welding or the like, and the outer can 16 serves as the negative electrode terminal.

[0023] The outer can 16 is, for example, a metal container having a bottomed cylindrical shape. As described above, a gasket 28 is provided between the outer can 16 and the sealing body 17, and the internal space of the battery case 15 is sealed. The outer can 16 has, for example, a groove portion 22 formed by pressing the side surface portion from the outside to support the sealing body 17. The groove portion 22 is preferably formed in an annular shape along the circumferential direction of the outer can 16, and supports the sealing body 17 on its upper surface. Further, the upper end portion of the outer can 16 is bent inward and clamped to the peripheral edge portion of the sealing body 17.

[0024] The sealing body 17 has a structure in which a filter 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are laminated in this order from the electrode body 14 side. Each member constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each member except the insulating member 25 is electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected to each other at their central portions, and an insulating member 25 is interposed between the peripheral edge portions of each. When the internal pressure of the battery rises due to abnormal heat generation, the lower valve body 24 is deformed and broken so as to push up the upper valve body 26 toward the cap 27 side, thereby cutting off the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further rises, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0025] [Positive Electrode] The positive electrode 11 has a positive electrode current collector and positive electrode composite material layers formed on both sides of the positive electrode current collector. As the positive electrode current collector, a foil of a metal stable within the potential range of the positive electrode 11 such as aluminum, or a film with such a metal disposed on the surface layer can be used. The positive electrode composite material layer contains a positive electrode active material, a conductive material, and a binder. The positive electrode 11 can be manufactured, for example, by applying a positive electrode composite material slurry containing a positive electrode active material, a conductive material, a binder, etc. onto the positive electrode current collector, drying the coating film, and then compressing it to form the positive electrode composite material layer on both sides of the positive electrode current collector.

[0026] The positive electrode active material is mainly composed of a lithium metal composite oxide. Examples of the metal elements contained in the lithium metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, W, etc. An example of a preferred lithium metal composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al. Note that inorganic compound particles such as aluminum oxide and lanthanoid-containing compounds may be adhered to the particle surface of the lithium metal composite oxide.

[0027] Examples of the conductive material contained in the positive electrode composite material layer include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. Examples of the binder contained in the positive electrode composite material layer include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resin, acrylic resin, and polyolefin resin. These resins may be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or its salts, polyethylene oxide (PEO), etc.

[0028] [Negative electrode] The negative electrode 12 has a negative electrode current collector and negative electrode composite material layers formed on both surfaces of the negative electrode current collector. As the negative electrode current collector, a foil of a metal stable within the potential range of the negative electrode 12 such as copper, or a film having such a metal disposed on the surface layer can be used. The negative electrode composite material layer contains a negative electrode active material and a binder. The negative electrode 12 can be manufactured, for example, by applying a negative electrode composite material slurry containing a negative electrode active material, a binder, etc. onto the negative electrode current collector, drying the coating film, and then compressing it to form the negative electrode composite material layer on both surfaces of the negative electrode current collector.

[0029] The negative electrode composite material layer contains, as the negative electrode active material, a carbon material and a silicon compound that reversibly intercalate and release lithium ions. Suitable carbon materials are graphite such as natural graphite including flake graphite, massive graphite, and amorphous graphite, artificial graphite such as massive artificial graphite (MAG), and graphitized mesophase carbon microbeads (MCMB).

[0030] The silicon compound can intercalate more lithium ions per unit volume than a carbon material such as graphite, but is more likely to crack and deteriorate than the carbon material during charging. According to the charging method of the non-aqueous electrolyte secondary battery 10 according to the present disclosure described later, the current balance between graphite and the silicon compound changes, and the current concentration on the silicon compound at the initial stage of charging is alleviated, thereby suppressing the deterioration of the negative electrode active material containing the silicon compound. The content of the silicon compound in the negative electrode composite material layer is, for example, 1 to 25% by mass, preferably 5 to 10% by mass, based on the total mass of the negative electrode active material. The mixing ratio of the silicon compound and graphite is, for example, 1:99 to 25:75 by mass ratio, preferably 5:95 to 10:90.

[0031] In addition, as the negative electrode active material, a metal that alloys with lithium other than Si, an alloy containing such a metal, a compound containing such a metal, etc. may be used. When a material with low conductivity such as lithium titanate is used as the negative electrode active material, a conductive material such as carbon black may be added to the negative electrode composite material layer.

[0032] Examples of the silicon compound include a first silicon material (SiO) containing a silicon oxide phase and Si dispersed in the silicon oxide phase, a second silicon material (LSX) containing a lithium silicate phase and Si dispersed in the lithium silicate phase, a third silicon material (Si-C) containing a carbon phase and Si dispersed in the carbon phase, and the like. Among them, SiO, LSX, or Si-C is preferable.

[0033] It is preferable that a conductive film made of a material having higher conductivity than the silicon compound is formed on the particle surface of the silicon compound. Examples of the constituent material of the conductive film include at least one selected from carbon materials, metals, and metal compounds. Among them, carbon materials such as amorphous carbon are preferable. The carbon film can be formed, for example, by a CVD method using acetylene, methane, etc., or a method of mixing coal pitch, petroleum pitch, phenol resin, etc. with silicon compound particles and performing heat treatment. Alternatively, a conductive film may be formed by fixing a conductive filler such as carbon black to the particle surface of the silicon compound using a binder. The conductive film is formed, for example, at 0.5 to 10% by mass based on the mass of the silicon compound particles.

[0034] As the binder contained in the negative electrode composite material layer, fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, etc. may be used in the same manner as in the case of the positive electrode 11, but preferably styrene-butadiene rubber (SBR) or a modified product thereof is used. In the negative electrode composite material layer, for example, in addition to SBR, CMC or its salt, polyacrylic acid (PAA) or its salt, polyvinyl alcohol, etc. may be contained.

[0035] [Separator] For the separator 13, a porous sheet having ion permeability and insulation is used. Specific examples of the porous sheet include microporous thin films, woven fabrics, non-woven fabrics, etc. As the material of the separator 13, olefin resins such as polyethylene and polypropylene, cellulose, etc. are suitable. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator 13.

[0036] Generally, in the non-aqueous electrolyte secondary battery 10, since the negative electrode 12 serves as the capacity-limiting electrode, the negative electrode capacity becomes the battery capacity. The battery capacity of the non-aqueous electrolyte secondary battery 10 is, for example, 3000 mAh to 6000 mAh.

[0037] Hereinafter, with appropriate reference to FIGS. 3 to 4, the charging method of the non-aqueous electrolyte secondary battery 10 will be described in detail.

[0038] FIG. 3 is a graph showing changes in battery voltage and control temperature with respect to battery capacity when a charging method according to an example of an embodiment is performed on the non-aqueous electrolyte secondary battery 10 before the first charging. The charging method of the non-aqueous electrolyte secondary battery 10 has the following steps. (1) A constant-current charging step of charging at a constant current value I th until a predetermined voltage value V con is reached from the start of charging. (2) After the constant-current charging step, a constant-voltage charging step of charging at a constant voltage value V th until a predetermined current value I th is reached. (3) A switching step of switching the control temperature from a high temperature to a low temperature at a timing determined by detecting that the ratio dQ Gr / dQ of the change amount of the carbon material capacity Q Gr to the change amount of the battery capacity Q is larger than the ratio dQ Si / dQ of the change amount of the silicon compound capacity Q Si to the change amount of the battery capacity Q.

[0039] In the present embodiment, the switching step is performed at a predetermined timing during the constant-current charging step. That is, constant-current charging (CC charging) at a high temperature is performed from the start of charging until a predetermined timing, and then constant-current charging at a low temperature is performed until a predetermined voltage value V th is reached, and thereafter, constant-voltage charging (CV charging) at a low temperature is performed until a predetermined current value I thThis is carried out until a predetermined timing. In the initial charging region until the predetermined timing is reached, by setting the control temperature to a high temperature, the ion diffusion rate in the electrolyte increases, and the reaction in the negative electrode proceeds more uniformly. As a result, the current concentration on the negative electrode side in contact with the separator is alleviated, and the deterioration of the negative electrode active material is suppressed. In the terminal charging region after the predetermined timing is reached, by setting the control temperature to a low temperature, excessive lithium ion desorption from the positive electrode active material is suppressed, and the deterioration of the positive electrode active material is suppressed. As described above, efficient charging can be performed while ensuring good cycle characteristics. In this embodiment, the case where the switching step is performed during the constant current charging step is illustrated, but the switching step may also be performed during the constant voltage charging step.

[0040] The high temperature of the control temperature is, for example, 35°C or higher and 60°C or lower. Within this range, the deterioration of the negative electrode active material can be suppressed. The control temperature is the temperature for controlling the non-aqueous electrolyte secondary battery 10, and is, for example, the temperature of the environment (atmosphere) including the non-aqueous electrolyte secondary battery 10. The means for raising the control temperature is not particularly limited. For example, the environmental temperature may be raised by installing a heater around the non-aqueous electrolyte secondary battery 10.

[0041] The low temperature of the control temperature is, for example, 0°C or higher and less than 35°C. Within this range, the deterioration of the positive electrode active material can be suppressed. The low temperature may be room temperature. For example, the control temperature may be switched from high to low by reducing the output of the heater installed around the non-aqueous electrolyte secondary battery 10 or setting the output of the heater to zero.

[0042] The switching step may be performed when the state of charge (SOC) of the non-aqueous electrolyte secondary battery 10 is in the range of 30% to 60%. dQ Gr / dQ>dQ SiIt becomes / dQ at about 60% of the SOC of the non-aqueous electrolyte secondary battery 10, and it is preferable that the predetermined timing at which the switching step is executed does not exceed this from the viewpoint of suppressing the deterioration of the positive electrode active material. Further, the predetermined timing at which the switching step is executed is preferably 30% or more from the viewpoint of suppressing the deterioration of the negative electrode active material, particularly the silicon compound.

[0043] CC charging preferably includes a charging step of applying a current of 0.5C or more, more preferably includes a charging step of applying a current of 1.0C or more, and particularly preferably includes a charging step of applying a current of 1.5C or more. For example, the charging time from SOC15% to SOC85% may be 0.5 hours to 1 hour. Thus, according to the charge and discharge method of the present disclosure, charging can be performed very efficiently.

[0044] After charging the non-aqueous electrolyte secondary battery 10 by the above charging method, it can be discharged. Further, the above charging method and discharging may be repeated for the non-aqueous electrolyte secondary battery 10 after discharging. When charging is performed for the second time and later, it is preferable to determine in advance the SOC (remaining capacity) of the non-aqueous electrolyte secondary battery 10 at which CC charging starts.

[0045] Next, with reference to FIG. 4, the ratio dQ of the change amount of the capacity Q of the silicon compound to the change amount of the battery capacity Q Si and the ratio dQ of the change amount of the capacity Q of the carbon material to the change amount of the battery capacity Q Si will be described. FIG. 4 is a graph showing the changes in dQ Gr / dQ and dQ Gr / dQ with respect to the battery capacity when the charging method according to an example of the embodiment is performed on the non-aqueous electrolyte secondary battery 10 before the first charging. Si / dQ and dQ Gr / dQ.

[0046] In the initial region of charging, dQ Si / dQ is larger than dQ Gr / dQ, and lithium ions are more easily occluded in the silicon compound than in the carbon material. On the other hand, in the terminal region of charging, dQGr / dQ is dQ Si larger than / dQ, Silicon compound more Carbon material lithium ions are more likely to be occluded. Since the silicon compound has a larger expansion ratio and is more likely to crack due to charging compared to the carbon material, in the initial region of charging, the control temperature is set high to suppress the deterioration of the silicon compound, while in the terminal region of charging, the control temperature is set low to suppress the deterioration of the positive electrode active material, thereby ensuring good cycle characteristics and performing efficient charging.

[0047] dQ Gr / dQ and dQ Si / dQ are, for example, Battery the ratio dV / dQ of the change amount of the open circuit voltage OCV with respect to the capacity Q Change amount of is calculated from. More specifically, dQ Gr / dQ and dQ Si / dQ are, for example, calculated by minimizing the residual between the charge curve or discharge curve of the non-aqueous electrolyte secondary battery and the combined charge curve or discharge curve of the silicon compound, carbon material, and positive electrode contained in the negative electrode, using the charge curve or discharge curve of the non-aqueous electrolyte secondary battery, the charge curve or discharge curve of the silicon compound contained in the negative electrode, the charge curve or discharge curve of the carbon material contained in the negative electrode, or the charge curve or discharge curve of the positive electrode.

[0048] ΔQ when the OCV changes by ΔV is calculated by minimizing the residual between the charge curve or discharge curve of the non-aqueous electrolyte secondary battery and the combined charge curve or discharge curve of the silicon compound, carbon material, and positive electrode Si and ΔQ Gr (dQ Si / dV and dQ Gr / dV) can be calculated. During charging or discharging of the battery, since dV / dQ can be calculated by measuring the OCV, dQ Gr / dQ and dQ Si / dQ are each calculated using dV / dQ as (dQ Gr / dV) / (dV / dQ)=dQ Gr / dQ, (dQ Si / dV) / (dV / dQ)=dQ SiIt can be calculated as / dQ.

[0049] FIG. 5 is a charge curve showing the relationship between the OCV and the capacity of the battery. The charge curve illustrated in FIG. 5 has a plurality of inflection points. The inflection point of the charge curve indicates a change in the charge state at the negative electrode, particularly a change in the charge state of the Si-containing compound. And, a peak corresponding to the inflection point appears in the dV / dQ curve obtained from the charge curve. Also, a peak similar to the dV / dQ curve appears in the dQ Si / dQ curve obtained from the analysis of dV / dQ. Note that an inflection point indicating a change in the charge state of the Si-containing compound also appears in the discharge curve of the battery.

[0050] FIG. 6 is a flowchart showing an example of a control procedure in the above charging method. Here, a specific example of charge control will be described by taking the case where the remaining capacity of the non-aqueous electrolyte secondary battery 10 is less than the start level of CC charging as an example.

[0051] As illustrated in FIG. 6, when charging the battery, first, the remaining capacity of the battery is confirmed (S10). For example, the charge control device 2 estimates the SOC (remaining capacity) of the battery from the detection information such as the battery voltage acquired by the battery monitoring unit 30.

[0052] When the remaining capacity of the battery is equal to or less than a predetermined CC charging start level, dQ Gr / dQ>dQ Si / dQ is detected and CC charging is performed at a constant current value I con at a high control temperature until the SOC determined (hereinafter sometimes referred to as the switching SOC) is reached (S11, S12). The CC charging is executed by the function of the constant current charge control means 4.

[0053] After reaching the switching SOC, the control temperature is switched to a low temperature, and CC charging is performed at a constant current value I th until a predetermined voltage value V con is reached (S13, S14). The switching of the control temperature is executed by the function of the switching means 8.

[0054] The predetermined voltage value V thAfter reaching a predetermined current value I th until reaching a certain voltage value V th perform CV charging (S15, 16). CV charging is executed by the function of the constant voltage charging control means 6.

Example

[0055] Hereinafter, the present disclosure will be further described by way of examples, but the present disclosure is not limited to these examples.

[0056] <Example 1> [Fabrication of positive electrode] As the positive electrode active material, a composite oxide represented by LiNi 0.82 Co 0.15 Al 0.03 O2 was used. 100 parts by mass of the positive electrode active material, 1 part by mass of acetylene black, and 0.9 part by mass of polyvinylidene fluoride were mixed, and an appropriate amount of N-methyl-2-pyrrolidone was added to prepare a positive electrode composite material slurry. Next, the positive electrode composite material slurry was applied to both sides of a long positive electrode current collector made of aluminum foil, and the coating film was dried. After compressing the dried coating film, it was cut into a predetermined electrode size to fabricate a positive electrode having a positive electrode composite material layer formed on both sides of the positive electrode current collector. An exposed portion where the composite material layer was absent and the surface of the current collector was exposed was provided at the central portion in the longitudinal direction of the positive electrode, and an aluminum positive electrode tab was welded to the exposed portion.

[0057] [Fabrication of negative electrode] As the negative electrode active material, 94 parts by mass of graphite powder and SiO (SiO with a carbon coating formed on the particle surface x, 6 parts by mass of silicon oxide represented by (x = 1) was used. 100 parts by mass of the negative electrode active material, 1.5 parts by mass of sodium carboxymethyl cellulose, and 1 part by mass of a dispersion of styrene-butadiene rubber were mixed, and an appropriate amount of water was added to prepare a negative electrode composite material slurry. Next, the negative electrode composite material slurry was applied to both sides of a long negative electrode current collector made of copper foil, and the coating film was dried. After compressing the dried coating film, it was cut into a predetermined electrode size to produce a negative electrode having a negative electrode composite material layer formed on both sides of the negative electrode current collector. An exposed portion where the composite material layer was absent and the surface of the current collector was exposed was provided at one end in the longitudinal direction of the negative electrode (the end located on the winding end side of the electrode body), and a negative electrode tab made of nickel was welded to the exposed portion.

[0058] [Preparation of non-aqueous electrolyte solution] LiPF6 was dissolved in a mixed solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 25:75 (1 atm, 25 °C) so that the concentration became 1 mol / L to prepare a non-aqueous electrolyte solution.

[0059] [Fabrication of non-aqueous electrolyte secondary battery] After winding the above positive electrode and the above negative electrode around a winding core via a separator made of a microporous polyethylene film, the winding core was removed to fabricate a wound electrode body. Next, the electrode body was inserted into an iron cylindrical outer can, and the negative electrode tab was resistance welded to the inner surface of the bottom of the outer can. After injecting the above non-aqueous electrolyte solution into the outer can, the positive electrode tab was welded to the sealing body, and the opening of the outer can was sealed with the sealing body to fabricate a cylindrical non-aqueous electrolyte secondary battery having a diameter of 21 mm, a height of 70 mm, and a rated capacity Q of 4950 mAh. Regarding this non-aqueous electrolyte secondary battery, charge and discharge were performed, and it was found that dQ Gr / dQ > dQ Si / dQ at SOC of 60% or more.

[0060] [Evaluation of capacity retention rate] The above battery was CC charged at a constant current of 1.5C until the battery voltage reached 4.2V, and then CV charged at a constant voltage of 4.2V until the current reached 102mA. During the CC charging, before the SOC reached 60%, the heater was operated to set the control temperature to 40°C, and after the SOC reached 60%, the operation of the heater was stopped and the control temperature was set to room temperature (25°C). After charging, the battery was discharged at a constant current of 0.5C until the battery voltage reached 2.5V. This charge-discharge cycle was repeated 15 times, and the value obtained by dividing the battery capacity at the 15th cycle by the initial battery capacity was determined as the capacity retention rate.

[0061] [Evaluation of the increase rate of DC resistance] For each of the battery that had undergone the charge-discharge cycle once and the battery that had undergone the charge-discharge cycle 15 times, at room temperature, constant current charging was performed at a constant current of 0.3C until 4.2V was reached, and after reaching 4.2V, constant voltage charging was performed until the current value reached 0.02C. Then, constant current discharge was performed at a constant current of 1C for 10 seconds. The value obtained by dividing the difference between the open circuit voltage (OCV) and the closed circuit voltage (CCV) 10 seconds after discharge by the discharge current 10 seconds after discharge was defined as the DC resistance (DCIR), and the increase rate of the DCIR after 15 cycles with respect to the DCIR after the first cycle was calculated.

[0062] <Examples 2 to 3, Comparative Examples 1 to 3> CC-CV charging was performed in the same manner as in Example 1, except that the charging conditions (switching SOC, control temperature (high temperature, low temperature), charging rate) were changed to the conditions shown in Table 1. In Comparative Examples 1 and 2, without switching the control temperature, CC charging was performed at 25°C and 40°C, respectively.

[0063]

Table 1

[0064] As shown in Table 1, according to the charging profile of the examples, the capacity retention rate is higher and good cycle characteristics can be maintained compared to the comparative examples. That is, according to the charging profile of the examples, efficient charging can be achieved while ensuring good cycle characteristics. Also, it can be seen from Comparative Examples 1 and 2 that when the control temperature during CC charging is increased, the battery material deteriorates and the resistance increases. However, in Example 1, by combining low and high control temperatures during CC charging, the increase rate of the DC resistance can be suppressed while increasing the capacity retention rate.

Explanation of Symbols

[0065] 1 Charging system, 2 Charging control device, 4 Constant current charging control means, 6 constant electricity Voltage charging control hand steps, 8 Switching means, 9 Storage unit, 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Battery case, 16 Exterior can, 17 Sealing body, 18, 19 Insulating plates, 20 Positive electrode tab, 21 Negative electrode tab, 22 Grooved portion, 23 Filter, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Battery monitoring unit, 100 Power supply, 101 Load

Claims

1. A method for charging a non-aqueous electrolyte secondary battery, comprising a positive electrode and a negative electrode that reversibly occlude and release lithium ions, wherein the negative electrode contains a carbon material and a silicon compound as a negative electrode active material, including a switching step of switching the control temperature of the non-aqueous electrolyte secondary battery from a high temperature to a low temperature, The timing of the switching step is determined by detecting that the ratio dQ Ｇｒ / dQ of the change amount of the carbon material to the change amount of the battery capacity Q Ｇｒ is larger than the ratio dQ Ｓｉ / dQ of the change amount of the silicon compound to the change amount of the battery capacity Q Ｓｉ ​ A method for charging a non-aqueous electrolyte secondary battery.

2. dQ Ｇｒ / dQ and dQ Ｓｉ / dQ is the charging method of the non-aqueous electrolyte secondary battery according to claim 1, which is calculated from the ratio dV / dQ of the change in the open-circuit voltage to the change in the battery capacity Q.

3. dQ Ｇｒ / dQ and dQ Ｓｉ / dQ is calculated by a calculation that minimizes the residual between the charge curve or discharge curve of the non-aqueous electrolyte secondary battery and the combined charge curve or discharge curve of the silicon compound, the carbon material, and the positive electrode, using the charge curve or discharge curve of the non-aqueous electrolyte secondary battery, the charge curve or discharge curve of the silicon compound contained in the negative electrode, the charge curve or discharge curve of the carbon material contained in the negative electrode, or the charge curve or discharge curve of the positive electrode. The charging method of the non-aqueous electrolyte secondary battery according to claim 2.

4. The method for charging a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the high temperature is 35°C or higher and 60°C or lower.

5. The method for charging a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the low temperature is 0°C or higher and lower than 35°C.

6. The method for charging a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the switching step is performed in a range where the state of charge (SOC) of the non-aqueous electrolyte secondary battery is 30% to 60%.

7. A charge-discharge method for a non-aqueous electrolyte secondary battery, wherein the non-aqueous electrolyte secondary battery is charged by the charging method according to any one of claims 1 to 6 and then discharged.

8. A charging system for charging a non-aqueous electrolyte secondary battery including a negative electrode containing a carbon material as a negative electrode active material, A charging system for a non-aqueous electrolyte secondary battery, comprising a charging control device that executes the charging method according to any one of claims 1 to 6.

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