Charging method of nonaqueous electrolyte secondary battery and charging system of nonaqueous electrolyte secondary battery

Abstract

The method for charging a non-aqueous electrolyte secondary battery comprises: a first charging step of charging a non-aqueous electrolyte secondary battery at a first constant current value I satisfying the following equation when the ratio of the capacity of the silicon compound to the rated capacity Q is set to x (0.1≤x≤0.5): 1st Charging; a high current charging step, after the first charging step is completed, the first constant current value I 1st Large constant current value I max Charging, formula: 82 / (81.8x+64)×(0.3 / 0.7)‑α≤I 1st / I max ≤82 / (81.8x+64)×(0.3 / 0.7)+α(α=0.3).

Description

Technical Field

[0001] The present disclosure relates to a charging method of a nonaqueous electrolyte secondary battery and a charging system of the nonaqueous electrolyte secondary battery. Background Art

[0002] Known to use SiO x Silicon compounds such as silicon oxide can absorb and store more lithium ions per unit volume than carbon materials such as graphite. For example, Patent Document 1 discloses a non-aqueous electrolyte secondary battery using graphite and silicon compounds as negative electrode active materials. In addition, Patent Document 2 discloses a charging method for a secondary battery for the purpose of reducing the initial irreversible capacity of a charge and discharge cycle.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2010-212228

[0006] Patent Document 2: Japanese Patent Application Publication No. 2000-106219 Summary of the invention

[0007] In addition, in a non-aqueous electrolyte secondary battery having a negative electrode containing a silicon compound, when the charging current is increased, for example, the silicon compound may be cracked, thereby aggravating the deterioration and making it difficult to ensure good cycle characteristics. On the other hand, when the charging current is suppressed to a low level, a long charging time is required. The present disclosure aims to provide a charging method as follows: in a non-aqueous electrolyte secondary battery having a negative electrode containing a carbon material and a silicon compound, efficient charging can be performed while ensuring good cycle characteristics.

[0008] A method for charging a nonaqueous electrolyte secondary battery as one embodiment of the present disclosure is a method for charging a nonaqueous electrolyte secondary battery having a negative electrode containing a carbon material and a silicon compound as negative electrode active materials, the method comprising: a first charging step of charging the nonaqueous electrolyte secondary battery at a first constant current value I satisfying the following formula when a ratio of a capacity of the silicon compound to a rated capacity Q is set to x (0.1≤x≤0.5) 1st and a high current charging step, after the first charging step is completed, with a current greater than the first constant current value I 1st Large constant current value I max to charge.

[0009] Formula: 82 / (81.8x+64)×(0.3 / 0.7)-α≤I 1st / I max≤82 / (81.8x+64)×(0.3 / 0.7)+α(α=0.3)

[0010] A charging system for a nonaqueous electrolyte secondary battery as one embodiment of the present disclosure is a charging system for charging a nonaqueous electrolyte secondary battery having a negative electrode containing a carbon material and a silicon compound as negative electrode active materials, and is characterized in that it has a charging control device that executes the above-mentioned charging method.

[0011] According to one embodiment of the present disclosure, a charging method can be provided as follows: in a non-aqueous electrolyte secondary battery having a negative electrode including a carbon material and a silicon compound, efficient charging can be performed while ensuring good cycle characteristics. In other words, according to the charging method involved in the present disclosure, it is possible to suppress the reduction of cycle characteristics while charging in a short time. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 1 is a block diagram showing a configuration of a charging system for a nonaqueous electrolyte secondary battery as an example of an embodiment.

[0013] Figure 2 It is a cross-sectional view of a nonaqueous electrolyte secondary battery as an example of an embodiment.

[0014] Figure 3 It is a diagram for explaining a charging method of a nonaqueous electrolyte secondary battery as an example of an embodiment.

[0015] Figure 4 This is a flowchart showing an example of a charging control process of a non-aqueous electrolyte secondary battery. DETAILED DESCRIPTION

[0016] In a non-aqueous electrolyte secondary battery having a negative electrode including a carbon material and a silicon compound, it is an important subject to provide a charging method that can efficiently charge in a short time and suppress the degradation of cycle characteristics. The inventors have identified a region where the capacity change from the silicon compound is large when the battery is charged, that is, a region where lithium ions are more easily absorbed and stored in the silicon compound than in the carbon material, and successfully and efficiently suppressed the degradation of the cycle characteristics by applying only the relaxed charging conditions based on the above formula to this region.

[0017] Below, an example of an embodiment of the present disclosure is described in detail. Below, a cylindrical battery obtained by accommodating a wound electrode body 14 in a cylindrical battery casing 15 is illustrated, but the battery casing is not limited to a cylindrical shape, for example, it may also be a square, or it may be a battery casing composed of a laminate including a metal layer and a resin layer. In addition, 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. In addition, the non-aqueous electrolyte secondary battery to which the charging method involved in the present disclosure can be applied as long as it is a battery having a negative electrode containing a carbon material and a silicon compound as a negative electrode active material.

[0018] Figure 1 1 is a block diagram showing a configuration of a non-aqueous electrolyte secondary battery charging system 1 as an example of an embodiment. Figure 1 As shown, the charging system 1 includes: a charging control device 2 for controlling the charging of the non-aqueous electrolyte secondary battery 10; and a battery monitoring unit 3 for monitoring the charging state of the battery. The non-aqueous electrolyte secondary battery 10 is connected to a load 101, and the stored power is supplied to the load 101. The charging system 1 may also include a battery group (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, in parallel, or in series and parallel.

[0019] The charging system 1 can be widely used in charging devices and charging equipment for non-aqueous electrolyte secondary batteries including carbon materials and silicon compounds as negative electrode active materials, for example, it can be applied to various devices and equipment such as electric vehicles, hybrid vehicles, vehicle charging equipment, power storage equipment, and chargers for electric tools. The charging control device 2 can be assembled in the battery module or can be configured as a part of the control device of the device or equipment such as the vehicle equipped with the charging system 1.

[0020] The charging control device 2 is a device that executes the 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 3. The charging control device 2 has: a first charging control component 4 that executes a first charging step; a second charging control component 5 that executes a second charging step; a large current charging control component 6 that executes a large current charging step; and a constant voltage charging control component 7 that executes a constant voltage charging step, which will be described in detail later. The charging control device 2 has, for example, a rectifier circuit that converts the AC power of the power supply 100 into a specified DC power and supplies it to the non-aqueous electrolyte secondary battery 10.

[0021] The charging control device 2 is composed of an integrated circuit such as an IC chip or an LSI chip, and includes a storage unit 8 and a CPU as a calculation processing unit. The CPU has a function of reading and executing a program stored in advance in the storage unit 8. The storage unit 8 has a function of temporarily storing the read program, processing data, etc., and a function of storing a control program, a threshold value, etc. The functions of the above-mentioned charging control components are realized by executing the control program stored in the storage unit 8, for example.

[0022] In addition, the charging control device 2 has a constant current circuit that controls the charging current so as to supply a DC power of a predetermined current value to the battery, and a constant voltage circuit that controls the charging voltage so as to supply a DC power of a predetermined voltage value to the battery, etc. In addition, the charging circuit such as the rectifier circuit, the constant current circuit, and the constant voltage circuit may be configured as a separate device from the charging control device 2. The charging control device 2 controls the charging circuit based on the battery charging state acquired from the battery monitoring unit 3, and performs charging of the non-aqueous electrolyte secondary battery 10.

[0023] The battery monitoring unit 3 detects, for example, the battery voltage and the charging current supplied to the non-aqueous electrolyte secondary battery 10. The charging control device 2 estimates the charging rate (SOC) based on the battery voltage obtained by the battery monitoring unit 3, and performs charging control based on the SOC. In addition, the SOC can also be estimated based on the charging and discharging current and the charging and discharging time. The method for estimating the SOC can apply a previously known method. Preferably, the charging control device 2 performs constant current charging (CC charging) including multiple steps until the battery voltage reaches a specified voltage, and then performs constant voltage charging (CV charging).

[0024] [Non-aqueous electrolyte secondary battery]

[0025] Figure 2 FIG. 1 is a cross-sectional view of a nonaqueous electrolyte secondary battery 10 as an example of an embodiment. Figure 2 As shown, the nonaqueous electrolyte secondary battery 10 includes an electrode body 14, a nonaqueous electrolyte (not shown), and a battery case 15 for accommodating the electrode body 14 and the nonaqueous electrolyte. The electrode body 14 has a winding structure in which the positive electrode 11 and the negative electrode 12 are wound via a separator 13. The battery case 15 includes a bottomed cylindrical packaging can 16 and a sealing body 17 for blocking the opening of the packaging can 16. In addition, the nonaqueous electrolyte secondary battery 10 includes a resin gasket 28 arranged between the packaging can 16 and the sealing body 17.

[0026] The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the non-aqueous solvent, for example, esters, ethers, nitriles, amide solvents, and mixed solvents of two or more of them can be used. The non-aqueous solvent may contain a halogen-substituted body in which at least a part of the hydrogen of these solvents is substituted with a halogen atom such as fluorine. In addition, the non-aqueous electrolyte is not limited to a liquid electrolyte and may also be a solid electrolyte using a gelled polymer or the like. As the electrolyte salt, for example, lithium salts such as LiPF 6 are used.

[0027] The electrode body 14 includes a strip-shaped positive electrode 11, a strip-shaped negative electrode 12, two strip-shaped 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 negative electrode 12 is formed with a size that is one lap larger than the positive electrode 11 to prevent lithium precipitation. 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 with a size that is at least one lap larger than the positive electrode 11 and are, for example, arranged to sandwich the positive electrode 11 therebetween.

[0028] Insulating plates 18 and 19 are respectively arranged above and below the electrode body 14. In Figure 2 the example shown, the positive electrode 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 electrode tab 21 attached to the negative electrode 12 extends toward the bottom side of the packaging can 16 through the outside of the insulating plate 19. The positive electrode 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 lid 27 which is the top plate of the sealing body 17 and is electrically connected to the filter 23 becomes the positive terminal. The negative electrode tab 21 is connected to the inner surface of the bottom of the packaging can 16 by welding or the like, and the packaging can 16 becomes the negative terminal.

[0029] The packaging can 16 is, for example, a metal container having a bottomed cylindrical shape. As described above, a gasket 28 is provided between the packaging can 16 and the sealing body 17, so that the internal space of the battery case 15 is sealed. The packaging can 16, for example, has a groove box portion (Japanese: 溝入れ部) 22 formed by pressing the side surface portion from the outside for supporting the sealing body 17. Preferably, the groove box portion 22 is formed in a ring shape along the circumferential direction of the packaging can 16, and the upper surface of the groove box portion 22 is used to support the sealing body 17. In addition, the upper end portion of the packaging can 16 is bent inward and is press-fitted to the peripheral portion of the sealing body 17.

[0030] 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 cover 27 are stacked in order from the electrode body 14 side. The components constituting the sealing body 17 have, for example, a disc shape or a ring shape, and the components except the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected to each other at their respective central portions, and an insulating member 25 is provided between their respective peripheral portions. When the internal pressure of the battery rises due to abnormal heat generation, the lower valve body 24 is deformed and broken in a manner that pushes the upper valve body 26 toward the cover 27 side, thereby cutting off the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure rises further, the upper valve body 26 breaks, and gas is discharged from the opening of the cover 27.

[0031] [positive electrode]

[0032] The positive electrode 11 has a positive electrode current collector and a positive electrode composite material layer formed on both surfaces of the positive electrode current collector. The positive electrode current collector can use a metal foil such as aluminum that is stable within the potential range of the positive electrode 11, a film that configures the metal on the surface, etc. The positive electrode composite material layer includes a positive electrode active material, a conductive material, and a binding material. The positive electrode 11 can be made, for example, by the following method: a positive electrode composite material slurry including a positive electrode active material, a conductive material, and a binding material is applied to the positive electrode current collector, and the positive electrode composite material layer is formed on both surfaces of the positive electrode current collector by compressing the coating after drying.

[0033] The positive electrode active material is mainly composed of lithium metal composite oxide. As the metal elements contained in the lithium metal composite oxide, Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, W, etc. can be listed. An example of a preferred lithium metal composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al. In addition, inorganic compound particles such as aluminum oxide and compounds containing lanthanide elements may also be attached to the surface of the lithium metal composite oxide particles.

[0034] As the conductive material included in the positive electrode composite material layer, carbon materials such as carbon black, acetylene black, Ketjen black, and graphite can be illustrated. As the binding material included in the positive electrode composite material layer, fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polypropylene (PAN), polyimide resins, acrylic resins, polyolefin resins, etc. can be illustrated. These resins can also be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or its salts, polyethylene oxide (PEO), etc.

[0035] [negative electrode]

[0036] 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. The negative electrode current collector can use a metal foil such as copper that is stable within the potential range of the negative electrode 12, a film with such a metal disposed on the surface layer, and the like. The negative electrode composite material layer contains a negative electrode active material and a binder material. The negative electrode 12 can be produced, for example, by the following method: coating a negative electrode composite material slurry containing a negative electrode active material, a binder material, etc. on the negative electrode current collector, and performing compression after drying the coating film to form the negative electrode composite material layer on both surfaces of the negative electrode current collector.

[0037] In the negative electrode composite material layer, a carbon material and a silicon compound that reversibly absorb, store, and release lithium ions are included as the negative electrode active material. Preferred carbon materials are natural graphites such as natural flake graphite, massive graphite, and earthy graphite, artificial graphites such as massive artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB), and the like. The content of the silicon compound in the negative electrode composite material layer is, for example, 1 to 15% by mass, preferably 5 to 10% by mass, relative to the total mass of the negative electrode active material. The mixing ratio of the silicon compound to graphite is, for example, a mass ratio of 1:99 to 15:85, preferably 5:95 to 10:90.

[0038] In addition, metals that alloy with lithium other than Si, alloys containing such metals, compounds containing such metals, etc. can also be used as the negative electrode active material. When using a material with low conductivity such as lithium titanate as the negative electrode active material, a conductive material such as carbon black can also be added to the negative electrode composite material layer.

[0039] As the silicon compound, silica represented by SiO x is exemplified. The silica represented by SiO x has, for example, a structure in which fine particles of Si are dispersed in an amorphous SiO 2 matrix. An example of a preferred silica is SiO x (0.5 ≤ x ≤ 1.6). The silicon compound can also be composite particles obtained by dispersing fine particles of Si in a lithium silicate (Li 2y SiO (2+y) (0 < y < 2)) phase.

[0040] Preferably, a conductive coating film made of a material with higher conductivity than that of the silica is formed on the surface of the particles of the silica represented by SiO x . As the material constituting the conductive coating film, at least one selected from carbon materials, metals, and metal compounds can be exemplified. Among them, carbon materials such as amorphous carbon are preferred. The carbon coating film can be formed, for example, by methods such as the CVD method using acetylene, methane, etc.; mixing coal tar pitch, petroleum pitch, phenolic resin, etc. with SiO xThe particles are mixed and heat treated. Alternatively, conductive fillers such as carbon black can be attached to SiO by using a binder. x The conductive coating is formed on the surface of the particles. For example, the conductive coating is x The mass of the particles is formed in a range of 0.5 to 10 mass %.

[0041] As in the case of positive electrode 11, the binding material included in the negative electrode composite material layer can use fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, etc. When using an aqueous solvent to prepare the composite material slurry, it is preferred to use CMC or its salt, a dispersant of styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salt, polyvinyl alcohol, etc.

[0042] [Diaphragm]

[0043] The separator 13 uses a porous sheet having ion permeability and insulation. Specific examples of the porous sheet include microporous films, woven fabrics, nonwoven fabrics, etc. As the material of the separator 13, olefin resins such as polyethylene and polypropylene, cellulose, etc. are preferred. The separator 13 can be any structure of a single-layer structure or a laminated structure. A heat-resistant layer, etc. can also be formed on the surface of the separator 13.

[0044] Below, refer to Figure 3 The method of charging the nonaqueous electrolyte secondary battery 10 will be described in detail. Figure 3 It shows the battery capacity, charging current and dQ Si Here, Q is the rated capacity of the battery, Q Si It refers to the capacity derived from the silicon compound. The rated capacity Q is, for example, 3000 mAh to 6000 mAh. In the non-aqueous electrolyte secondary battery 10, the negative electrode 12 is generally the capacity limiting electrode, so the negative electrode capacity is the battery capacity. This charging method is described later in I max It is particularly preferred to be 0.5C or more, or 0.7C or more.

[0045] The nonaqueous electrolyte secondary battery 10 is charged via at least two constant current charging steps, wherein the two constant current charging steps include: a first charging step in which the ratio of the capacity of the silicon compound to the rated capacity Q is set to x (0.1≤x≤0.5), and a first constant current value I is set to 1st For a battery capacity Q satisfying the following equation 1 1st and a high current charging step, after the first charging step, at a constant current value I 1st Large constant current value I max to charge.

[0046] Formula 1: 0.38x+0.063-α1≤Q1st / Q≤0.38x+0.063+α1

[0047] Here, α1 is preferably 0.1, more preferably 0.05.

[0048] like Figure 3 As shown, the battery capacity Q 1st In the charging region, the capacity Q derived from silicon compounds Si The change in the amount (dQ Si / dQ) is large, and lithium ions are more easily absorbed and stored in the silicon compound than in graphite. In this region, constant current charging with a low current value is performed, thereby suppressing the cracking of the silicon compound and maintaining good cycle characteristics. Formula 1 is the dQ of OCV obtained when the Si capacity ratio is changed. Si The capacity ratio x of the silicon compound relative to the rated capacity Q (negative electrode capacity) is obtained by detecting dV / dQ, which represents the voltage change dV relative to the capacity change dQ over a predetermined period of time.

[0049] For charging the nonaqueous electrolyte secondary battery 10, it is preferred that a second charging step is provided between the first charging step and the high current charging step, in which the battery is charged at a current higher than the first constant current value I 1st Larger than the current value I of the high current charging step max The second small constant current value I 2nd That is, when the battery capacity reaches Q 1st When the first charging step is completed, the second charging step is performed. In the second charging step, the second constant current value I 2nd For a battery capacity Q satisfying the following equation 2 2nd The charging is performed. Formula 2 is the same experimental formula as Formula 1.

[0050] Formula 2: 0.13x+0.173-α2≤Q 2nd / Q≤0.13x+0.173+α2

[0051] Here, α2 is preferably 0.1, more preferably 0.05.

[0052] like Figure 3 As shown, the battery capacity Q 2nd In the charging area, the capacity Q Si The change in the amount of silicon is large, and it is easier to absorb and store lithium ions in silicon compounds than in graphite. 2nd In the charging region, constant current charging with a low current value is performed, thereby suppressing the cracking of the silicon compound and maintaining good cycle characteristics.2nd In the charging area, with the charging capacity Q 1st Compared with the charging area, the capacity Q Si The change in is small, so it is preferably set to I 1st 2nd To improve the efficiency of charging. Figure 3 As shown in the example, in the initial stage of charging of the non-aqueous electrolyte secondary battery 10, there are two dQ Si / dQ peak value. Battery capacity Q 1st The range corresponds to the width of the first peak, the battery capacity Q 2nd The range corresponds to the second peak width.

[0053] In the first charging step, it is preferred to satisfy the first constant current value I of the following formula 3: 1st The charging is performed. Formula 3 is the same experimental formula as Formulas 1 and 2.

[0054] Formula 3: 82 / (81.8x+64)×(0.3 / 0.7)-α3≤I 1st / I max ≤82 / (81.8x+64)×(0.3 / 0.7)+α3

[0055] Here, α3 is preferably 0.3, more preferably 0.2.

[0056] In capacity Q Si The amount of change is large, and it is easier for silicon compounds to absorb and store lithium ions than graphite. In the initial stage of charging, the execution current value is suppressed to I 1st By charging with a constant current, the cracking of the silicon compound can be suppressed, thereby maintaining good cycle characteristics.

[0057] In addition, in the second charging step, it is preferred that the second constant current value I satisfying the following formula 4 2nd The charging is performed. Formula 4 is the same experimental formula as Formulas 1 to 3.

[0058] Formula: 36 / (122.4x+10.9)×(0.5 / 0.7)-α4≤I 2nd / I max ≤36 / (122.4x+10.9)×(0.5 / 0.7)+α4

[0059] Here, α4 is preferably 0.3, more preferably 0.2.

[0060] In capacity Q Si The amount of change is large, and it is easier for silicon compounds to absorb and store lithium ions than graphite. In the initial stage of charging, the execution current value is suppressed to I 2nd ​By charging with a constant current, the cracking of the silicon compound can be suppressed, thereby maintaining good cycle characteristics.

[0061] In this charging method, when the battery capacity reaches Q 1st When the battery capacity reaches Q 2nd When the constant current value I max The high current charging step is performed. max It is the maximum charging current among multiple charging steps. Si In the charging region where the change in current is small, the current is increased to max The charging process is performed so that the charging time can be shortened. The high current charging process ends when the battery voltage reaches a predetermined threshold value (e.g., 4.2 V). Thereafter, CV charging (constant voltage charging process) is performed at a predetermined battery voltage (e.g., 4.2 V) until the current reaches a predetermined threshold value.

[0062] Figure 4 1 is a flowchart showing an example of the control process in the above-mentioned charging method. Here, a specific example of the charging control will be described by taking the case where the remaining capacity of the nonaqueous electrolyte secondary battery 10 is less than the start level of CV charging as an example.

[0063] like Figure 4 As shown in the example, when charging the battery, the remaining capacity of the battery is first confirmed (S10, S11). For example, the charging control device 2 estimates the SOC (remaining capacity) of the battery based on the detection information such as the battery voltage obtained by the battery monitoring unit 3. And, when the remaining capacity of the battery is the above Q 1st In the following cases, the first constant current value I 1st Charge until the battery capacity reaches Q 1st The first charging step is performed by the function of the first charging control unit 4.

[0064] On the other hand, when the remaining capacity of the battery is above Q 1st Above and Q 2nd In the following cases, the second constant current value I 2nd Charge until the battery capacity reaches Q 2nd The second charging step is performed by the function of the second charging control unit 5. Then, when the remaining capacity of the battery reaches Q 2nd As a condition, the constant current value I maxThe high current charging step (S14, S15) is performed until the battery voltage reaches a predetermined threshold. The high current charging step is performed by the function of the high current charging control unit 6. That is, in this embodiment, three stages of CC charging are performed until the battery voltage reaches a predetermined threshold.

[0065] When the battery voltage reaches a predetermined threshold value, a constant voltage charging step (S16) is performed to perform CV charging until the current reaches a predetermined threshold value. The constant voltage charging step is performed by the function of the constant voltage charging control unit 7.

[0066] Example

[0067] The present disclosure will be further described below by way of examples, but the present disclosure is not limited to these examples.

[0068] <Example 1>

[0069] [Production of positive electrode]

[0070] Use LiNi 0.82 Co 0.15 Al 0.03 O 2 The composite oxide represented by is used as the positive electrode active material. 100 parts by mass of the positive electrode active material, 1 part by mass of acetylene black and 0.9 parts by mass of polyvinylidene fluoride are mixed, and N-methyl-2-pyrrolidone is added in an appropriate amount to prepare a positive electrode composite material slurry. Next, the positive electrode composite material slurry is applied to both surfaces of a long strip of positive electrode collector composed of aluminum foil, and the coating is dried. The dried coating is compressed and cut into a specified electrode size to produce a positive electrode having a positive electrode composite material layer formed on both surfaces of the positive electrode collector. An exposed portion is provided in the central portion of the long side direction of the positive electrode so that the surface of the current collector is exposed due to the absence of the composite material layer, and the aluminum positive electrode tab is welded to the exposed portion.

[0071] [Production of negative electrode]

[0072] 94 parts by mass of graphite powder and SiO (SiO x, x=1) as the negative electrode active material. 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 dispersant of styrene-butadiene rubber are mixed, and water is added in an appropriate amount to prepare a negative electrode composite material slurry. Next, the negative electrode composite material slurry is applied to both surfaces of a long strip of negative electrode collector composed of copper foil, and the coating is dried. The dried coating is compressed and cut into a specified electrode size to produce a negative electrode having a negative electrode composite material layer formed on both surfaces of the negative electrode collector. An exposed portion in which the composite material layer is not present and the surface of the current collector is exposed is provided at one end of the long side direction of the negative electrode (the end on the winding end side of the electrode body), and a negative electrode tab made of nickel is welded to the exposed portion.

[0073] [Preparation of non-aqueous electrolyte]

[0074] LiPF was dissolved in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) at a volume ratio of 25:75 (1 atm, 25°C). 6 The concentration was adjusted to 1 mol / L to prepare a non-aqueous electrolyte solution.

[0075] [Fabrication of non-aqueous electrolyte secondary battery]

[0076] After the positive electrode and the negative electrode are wound on a winding core via a diaphragm composed of a polyethylene microporous film, the winding core is removed to produce a wound electrode body. Next, the electrode body is inserted into an iron cylindrical packaging can, and the negative electrode tab is resistance welded to the bottom inner surface of the packaging can. After the non-aqueous electrolyte is injected into the packaging can, the positive electrode tab is welded to the sealing body, and the opening of the packaging can is sealed with the sealing body, thereby producing a cylindrical non-aqueous electrolyte secondary battery with a diameter of 18 mm, a height of 65 mm, and a rated capacity Q of 3350 mAh. SiO x The ratio x of the capacity to the rated capacity Q is 0.21.

[0077] [Battery initial charge and discharge]

[0078] Under room temperature, the battery was CC charged under the charging conditions shown in Table 1 until the battery voltage reached 4.2 V, and then CV charged at a constant voltage of 4.2 V until the current reached 168 mA. In Example 1, the first charging step and the high current charging step satisfying the conditions of the above formulas 1 and 3 were performed. After charging, the battery was discharged at a constant current of 0.5 C until the battery voltage reached 2.5 V. This charge and discharge cycle was repeated 100 times, and the value obtained by dividing the battery capacity of the 100th cycle by the initial battery capacity was calculated as the capacity retention rate.

[0079] <Examples 2 to 4>

[0080] CC-CV charging was performed in the same manner as in Example 1 except that the charging conditions were changed to those shown in Table 1. In Examples 2 to 4, a first charging step satisfying the conditions of equations 1 and 3, a second charging step satisfying the conditions of equations 2 and 4, and a high current charging step were performed.

[0081] <Comparative Examples 1 and 2>

[0082] Except that one stage of CC charging was performed under the charging conditions shown in Table 1, CC-CV charging was performed in the same manner as in Example 1.

[0083] [Table 1]

[0084]

[0085] As shown in Table 1, according to the charging profiles of Examples 1 and 2, the capacity retention rate is higher than that of Comparative Example 2, and good cycle characteristics can be maintained. In addition, in Examples 1 and 2, the same capacity retention rate as that of Comparative Example 1 in which the charging time is long can be achieved. That is, according to the charging profiles of Examples 1 and 2, it is possible to efficiently perform charging while ensuring good cycle characteristics.

[0086] Description of Reference Numerals

[0087] 1: Charging system; 2: Charging control device; 3: Battery monitoring unit; 4: First charging control component; 5: Second charging control component; 6: High current charging control component; 7: Constant voltage charging control component; 8: Storage unit; 10: Non-aqueous electrolyte secondary battery; 11: Positive electrode; 12: Negative electrode; 13: Diaphragm; 14: Electrode body; 15: Battery casing; 16: Packaging can; 17: Sealing body; 18, 19: Insulating plate; 20: Positive electrode tab; 21: Negative electrode tab; 22: Slot box; 23: Filter; 24: Lower valve body; 25: Insulating member; 26: Upper valve body; 27: Cover; 28: Gasket; 100: Power supply; 101: Load.

Claims

1. A method for charging a non-aqueous electrolyte secondary battery, the non-aqueous electrolyte secondary battery having a negative electrode containing a carbon material and a silicon compound as negative electrode active materials, the charging method comprising: In the first charging step, when the ratio of the capacity of the silicon compound to the rated capacity Q is set to x, a first constant current value I that satisfies the following formula is used. 1st Charging is performed, wherein 0.1≤x≤0.5; and A high current charging step, after the first charging step is completed, with a current higher than the first constant current value I 1st Large constant current value I max To charge, Formula: 82 / (81.8x + 64)×(0.3 / 0.7) - α ≤ I 1st / I max ≤ 82 / (81.8x + 64)×(0.3 / 0.7) + α, Where α = 0.3, There is also a second charging step between the first charging step and the high current charging step. In the second charging step, a second constant current value I 2nd To charge, Formula: 36 / (122.4x + 10.9)×(0.5 / 0.7) - α ≤ I 2nd / I max ≤ 36 / (122.4x + 10.9)×(0.5 / 0.7) + α。 2. A non-aqueous electrolyte secondary battery charging system for charging a non-aqueous electrolyte secondary battery having a negative electrode containing a carbon material and a silicon compound as a negative electrode active material, The nonaqueous electrolyte secondary battery charging system includes a charging control device that executes the nonaqueous electrolyte secondary battery charging method according to claim 1 .

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