JP7091962B2 - Lithium-ion battery system and method for adjusting charge / discharge characteristics of lithium-ion batteries - Google Patents

Description

The present invention relates to a lithium ion battery system and a method for adjusting charge / discharge characteristics of a lithium ion battery.

Regarding the lithium ion battery, Patent Document 1 describes that the concentration of the electrolyte in the electrolytic solution is changed according to the concentration of the redox shuttle compound for suppressing overcharging in the electrolytic solution. Since the concentration of the redox shuttle compound depends on the concentration of the electrolyte, when the concentration of the redox shuttle compound is low, the concentration of the electrolyte is lowered to efficiently cause the redox shuttle phenomenon and suppress overcharging. be.

Further, in Patent Document 2, LiPF ₆ and LiPO ₂ F ₂ are used in combination as an electrolyte salt of an electrolytic solution of a lithium ion battery, and the concentration of the total electrolyte salt is set to 0.5 M or more and 2.0 M or less, and LiPO ₂ F. It is described that the concentration of ₂ is 0.01 M or more and 0.4 M or less.

Japanese Unexamined Patent Publication No. 2014-229512 Japanese Unexamined Patent Publication No. 2017-63043

By the way, it is known that when the operating temperature of a lithium ion battery is lowered, the charge / discharge resistance when the battery is charged / discharged (charged or discharged) increases. When the charging resistance becomes large, it becomes disadvantageous for quick charging, and when the discharging resistance becomes large, the voltage drop becomes large and it becomes difficult to output.

The present invention addresses the problem that the charge / discharge characteristics of a lithium ion battery deteriorate when the operating temperature of the lithium ion battery changes, as described above.

The present inventor has conducted experiments and research on the charge / discharge characteristics of a lithium-ion battery, and when a plurality of different types of lithium salts are used as the electrolyte of the electrolytic solution, the temperature characteristics of the charge / discharge resistance differ depending on the mixing ratio of the electrolyte. I found. For example, at a certain mixing ratio, the charge / discharge resistance decreases when the temperature is high, and at a different mixing ratio, the charge / discharge resistance decreases when the temperature is low.

Therefore, the present invention addresses the above-mentioned problems by utilizing the fact that the temperature-dependent relationship of the charge / discharge characteristics of the lithium-ion battery differs depending on the mixing ratio of the above-mentioned electrolytes.

The lithium-ion battery system disclosed here is
A lithium-ion battery having a positive electrode and a negative electrode, and using an electrolytic solution in which two or more kinds of electrolytes are dissolved in a solvent as a supporting electrolyte.
A temperature sensor that detects the operating temperature of the lithium-ion battery,
It is characterized by comprising a mixing ratio changing means for changing the mixing ratio of the two or more kinds of electrolytes in the electrolytic solution according to the operating temperature of the lithium ion battery detected by the temperature sensor.

According to this, it is possible to suppress that the charge / discharge characteristics of the lithium ion battery decrease with the change of the operating temperature by changing the mixing ratio of the electrolyte in the electrolytic solution according to the operating temperature of the lithium ion battery. Become.

Here, the "operating temperature of the lithium ion battery" is a temperature estimated from the temperature of the lithium ion battery itself, the temperature around the battery (hereinafter referred to as "environmental temperature"), or the charge / discharge characteristics of the lithium ion battery. You may.

In one embodiment of the lithium-ion battery system described above,
The lithium ion battery includes a main electrolyte and a sub-electrolyte as the supporting electrolytes.
The mixing ratio changing means sets the mixing ratio of the main electrolyte and the sub-electrolyte according to the operating temperature of the lithium-ion battery detected by the temperature sensor, and the charge / discharge resistance when the lithium-ion battery is charged / discharged. Is changed so that the mixing ratio is small.

According to this, when the operating temperature of the lithium ion battery changes, the mixing ratio of the electrolyte is changed so as to have a small charge / discharge resistance. Therefore, it is possible to improve the quick charge characteristics and suppress the decrease in output over a wide temperature range.

In one embodiment of the lithium-ion battery system described above,
The lithium ion battery includes a main electrolyte and a sub-electrolyte as the supporting electrolytes.
The above-mentioned mixing ratio changing means is
A main electrolyte supply device that supplies a main electrolyte containing a predetermined concentration of the main electrolyte to the lithium ion battery, and a main electrolyte supply device.
A sub-electrolyte supply device that supplies a sub-electrolyte containing a predetermined concentration of the sub-electrolyte to the lithium-ion battery, and a sub-electrolyte supply device.
An electrolyte discharge device that discharges the electrolyte from the lithium-ion battery,
Discharge of the electrolytic solution by the electrolytic solution discharging device so that the mixing ratio of the main electrolyte and the sub-electrolyte of the electrolytic solution of the lithium ion battery becomes a predetermined mixing ratio according to the operating temperature of the lithium ion battery. A controller for controlling the supply of the main electrolyte and the sub-electrolyte by each of the main electrolyte supply device and the sub-electrolyte supply device is provided.

According to this, the electrolyte is discharged from the lithium ion battery by the electrolyte discharge device, and the main electrolyte and the sub-electrolyte are supplied to the lithium ion battery by each of the main electrolyte supply device and the sub-electrolyte supply device. The mixing ratio of the main electrolyte and the sub-electrolyte in the electrolytic solution of the lithium ion battery can be set to the optimum mixing ratio in order to reduce the charge / discharge resistance.

In one embodiment of the lithium-ion battery system described above,
The main electrolyte supply device includes a main electrolyte tank for storing the main electrolyte containing a predetermined concentration of the main electrolyte.
The sub-electrolyte supply device includes a sub-electrolyte tank for storing the sub-electrolyte containing a predetermined concentration of the sub-electrolyte.
The electrolyte discharge device includes an electrolyte separation device that separates the electrolyte discharged from the lithium ion battery into an electrolyte containing the main electrolyte and an electrolyte containing the sub-electrolyte, and the separated main electrolyte. It is provided with a main electrolyte recovery line for recovering the contained electrolyte solution in the main electrolyte solution tank and a sub-electrolyte recovery line for recovering the separated electrolyte solution containing the sub-electrolyte in the sub-electrolyte solution tank.
The main electrolyte recovery line includes a main electrolyte concentration adjusting device that adjusts the main electrolyte concentration of the electrolyte to be recovered to the predetermined concentration of the main electrolyte stored in the main electrolyte tank.
The sub-electrolyte recovery line is provided with a sub-electrolyte concentration adjusting device that adjusts the sub-electrolyte concentration of the electrolytic solution to be recovered to the predetermined concentration of the sub-electrolyte stored in the sub-electrolyte tank.

According to this, the electrolytic solution discharged from the lithium ion battery due to the change of the mixing ratio of the sub-electrolyte of the main electrolyte can be reused in the lithium ion battery.

In one embodiment of the lithium-ion battery system described above,
The main electrolyte is LiPF ₆ (lithium hexafluorophosphate), and the sub-electrolyte is LiPO ₂ F ₂ (lithium difluorophosphate).

Since the main electrolyte is LiPF ₆ , the advantages of widening the potential window and increasing the electrical conductivity can be obtained. Since the sub-electrolyte is LiPO ₂ F ₂ , a high-quality film is formed at the interface between the positive electrode and the negative electrode, which is advantageous in suppressing the decomposition of the electrolytic solution.

Then, in the combination of the main electrolyte LiPF ₆ and the sub-electrolyte LiPO ₂ F ₂ , the temperature characteristics of the charge / discharge resistance of the lithium ion battery change depending on the mixing ratio of both. Therefore, by changing the mixing ratio according to the temperature, the charge / discharge resistance of the lithium ion battery can be kept low over a wide temperature range.

In one embodiment of the lithium-ion battery system described above,
The mixing ratio changing means increases the ratio of LiPO ₂ F ₂ to the total amount of LiPF ₆ and LiPO ₂ F ₂ as the operating temperature of the lithium ion battery becomes lower. For example, the ratio of LiPO ₂ F ₂ to the total amount of LiPF ₆ and LiPO ₂ F ₂ is set to 1% or more and 4% or less when the operating temperature of the lithium ion battery is 25 ° C., and the operating temperature of the lithium ion battery is -30. When the temperature is 5% or more and 15% or less, the charge / discharge resistance of the lithium ion battery can be kept low over a wide temperature range.

The method for adjusting the charge / discharge characteristics of the lithium ion battery disclosed here is as follows.
The lithium ion battery is provided with a positive electrode and a negative electrode, and uses an electrolytic solution obtained by dissolving LiPF ₆ and LiPO ₂ F ₂ in a solvent as supporting electrolytes.
It is characterized in that the mixing ratio of LiPF ₆ and LiPO ₂ F ₂ in the electrolytic solution is changed according to the operating temperature of the lithium ion battery.

According to this, the charge / discharge characteristics of the lithium ion battery deteriorate with the change of the operating temperature due to the change of the mixing ratio of the electrolyte in the electrolytic solution of the lithium ion battery according to the operating temperature of the lithium ion battery. It becomes possible to suppress.

In one embodiment of the charge / discharge characteristic adjustment method,
As the operating temperature of the lithium ion battery becomes lower, the ratio of LiPO ₂ F ₂ to the total amount of LiPF ₆ and LiPO ₂ F ₂ increases. For example, the ratio of LiPO ₂ F ₂ to the total amount of LiPF ₆ and LiPO ₂ F ₂ is set to 1% or more and 4% or less when the operating temperature of the lithium ion battery is 25 ° C., and the operating temperature of the lithium ion battery is -30. When the temperature is 5% or more and 15% or less, the charge / discharge resistance of the lithium ion battery can be suppressed low over a wide temperature range, the quick charging characteristics can be improved, and the output decrease can be suppressed.

According to the present invention, since the mixing ratio of the electrolyte in the electrolytic solution of the lithium ion battery is changed according to the operating temperature of the lithium ion battery, the charge / discharge characteristics of the lithium ion battery decrease with the change of the operating temperature. It becomes possible to suppress this.

Configuration diagram of the lithium-ion battery system. Block diagram of the control system of the system. Control flow diagram of the system. The graph which shows the relationship between the electrolyte mixture ratio and the discharge resistance of a lithium ion battery at an operating temperature of 25 ° C. The graph which shows the relationship between the electrolyte mixture ratio and the discharge resistance of a lithium ion battery at an operating temperature of −10 ° C. The graph which shows the relationship between the electrolyte mixture ratio and the discharge resistance of a lithium ion battery at an operating temperature of −20 ° C. The graph which shows the relationship between the electrolyte mixture ratio and the discharge resistance of a lithium ion battery at an operating temperature of −30 ° C.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The following description of preferred embodiments is merely exemplary and is not intended to limit the invention, its applications or its uses.

In the lithium ion battery system shown in FIG. 1, the lithium ion battery 1 includes a positive electrode, a negative electrode, and a separator that insulates the positive electrode and the negative electrode, and the main electrolyte and the sub-electrolyte are dissolved in a non-aqueous solvent as supporting electrolytes. Use a water electrolyte.

<Lithium-ion battery>
[Positive electrode]
The positive electrode is formed by mixing a positive electrode active material and an auxiliary agent (binding agent and conductive auxiliary agent) and applying them to a current collector. Aluminum foil is mentioned as a preferable current collector.

Preferred positive electrode active materials include composite metal oxides with lithium containing one or more selected from the group consisting of cobalt, manganese and nickel, phosphoric acid-based lithium compounds, and silicic acid-based lithium compounds. In particular, it is preferable to use lithium phosphate. These positive electrode active materials can be used alone or in combination of two or more.

Preferred phosphoric acid-based lithium compounds include, for example, LiMPO ₄ (M = transition metal Fe, Co, Ni, Mn, etc.) and Li ₂ MPO ₄ F (M = transition metal Fe, Co, Ni, Mn) having an olivine crystal structure. Etc.). Of these, lithium iron phosphate LiFePO ₄ is preferable. Examples of the silicic acid-based lithium compound include Li ₂ MSiO ₄ (M = transition metal Fe, Co, Ni, Mn, etc.).

As the binder, polyvinylidene fluoride (PVdF) can be preferably adopted. As the conductive auxiliary agent, carbon black, acetylene black, carbon nanofiber (CNF) and the like can be adopted.

[Negative electrode]
The negative electrode is formed by mixing a negative electrode active material and an auxiliary agent (binding agent and conductive auxiliary agent) and applying the negative electrode to a current collector. A copper foil is mentioned as a preferable current collector.

As the negative electrode active material, it is preferable to use a graphite-based carbon material, that is, artificial graphite or natural graphite. The graphite-based carbon material preferably has a low degree of graphitization from the viewpoint of improving the storage and release capacity of Li ions. Artificial graphite and hard carbon, which have a low degree of graphitization, are preferable as the negative electrode active material. Since natural graphite with high crystallinity deteriorates quickly, it is preferable to use it in combination with surface-treated natural graphite or artificial graphite.

As the binder, styrene-butadiene rubber (SBR), styrene-butadiene rubber in combination with carboxymethyl cellulose as a thickener (SBR-CMC), PVdF, an imide-based binder and the like can be preferably adopted. .. As the conductive auxiliary agent, carbon black, acetylene black, carbon nanofiber CNF and the like can be preferably adopted.

[Separator]
The separator is not particularly limited, but a monolayer or laminated microporous film of polyolefin such as polypropylene or polyethylene, a woven fabric, a non-woven fabric or the like can be adopted.

[Non-water electrolyte]
The non-aqueous electrolyte solution is obtained by dissolving a lithium salt (supporting electrolyte) in a non-aqueous solvent, and an additive is added as needed.

The type of non-aqueous solvent is not particularly limited, and is limited to cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), and dimethyl. Examples thereof include chain carbonate esters such as carbonate (DMC) and cyclic carboxylic acid esters such as γ-butyrolactone (GBL) and γ-valerolactone (GVL). As the non-aqueous solvent, one type may be used alone, or two or more types may be used in combination.

Additives for the non-aqueous solvent include a wettability improving solvent and a SEI forming solvent for improving the wettability of the electrolytic solution with respect to the separator.

Examples of the wettability improving solvent include dibutyl carbonate (DBC), methylbutyl carbonate (MBC), ethylbutyl carbonate (EBC) and the like. The amount of the wettability improving solvent added is preferably about 3% by mass or more and 10% by mass or less of the non-aqueous solvent.

Examples of the SEI-forming solvent include vinylene carbonate (VC), methylvinylene carbonate (MVC), ethylvinylene carbonate (EVC), fluorovinylene carbonate (FVC), vinylethylene carbonate (VEC), ethynylethylene carbonate (EEC), and ethylenesulfite. (ES), fluoroethylene carbonate (FEC) and the like. These SEI-forming solvents can be used alone or in combination of two or more. The amount of the SEI-forming solvent added is preferably about 0.5% by mass or more and 5% by mass or less of the non-aqueous solvent.

Preferred lithium salts include LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , LiN (SO ₂ F) ₂ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , and the like. The lithium salt may be used alone or in combination of two or more.

The concentration of the lithium salt in the non-aqueous electrolytic solution may be, for example, 0.5 M or more and 2.0 M or less.

In this embodiment, LiPF ₆ is adopted as the main electrolyte, LiPO ₂ F ₂ is adopted as the sub-electrolyte, and a mixed solvent of propylene carbonate (PC) and γ-butyrolactone (GBL) is adopted as the solvent (PC: GBL = 80: 20 (volume ratio)) is adopted.

<Structure of lithium-ion battery system>
The lithium-ion battery system is based on the temperature sensor 2 that detects the operating temperature of the lithium-ion battery 1 (environmental temperature in this example) and the operating temperature of the lithium-ion battery 1 detected by the temperature sensor 2. It is provided with a mixing ratio changing means 3 for changing the mixing ratio of the main electrolyte (LiPF ₆ ) and the sub-electrolyte (LiPO ₂ F ₂ ) in the non-aqueous electrolyte solution. The mixing ratio changing means 3 includes a main electrolytic solution supply device 4, an auxiliary electrolytic solution supply device 5, an electrolytic solution discharge device 6, and a controller 7 using a microcomputer.

The lithium ion battery 1 is provided with an electrolyte concentration sensor 8 that detects the concentration of the main electrolyte and the concentration of the sub-electrolyte in the electrolytic solution.

The main electrolyte supply device 4 includes a main electrolyte tank 11, a main electrolyte supply line 12 extending from the tank 11 to the lithium ion battery 1, a pump 13, a first flow meter 14, and a valve provided in the line 12. It is equipped with 15. The main electrolyte tank 11 stores the main electrolyte containing a predetermined concentration of the main electrolyte. By the operation of the pump 13, the main electrolytic solution stored in the main electrolytic solution tank 11 is supplied to the lithium ion battery 1 by the main electrolytic solution supply line 12.

The sub-electrolyte solution supply device 5 includes a sub-electrolyte solution tank 16, a sub-electrolyte solution supply line 17 extending from the tank 16 to the lithium ion battery 1, a pump 18, a second flow meter 19, and a valve provided in the line 17. It is equipped with 15. The sub-electrolyte tank 16 stores the sub-electrolyte containing the sub-electrolyte having a predetermined concentration. By the operation of the pump 18, the sub-electrolyte solution stored in the sub-electrolyte solution tank 16 is supplied to the lithium ion battery 1 by the sub-electrolyte solution supply line 17.

The valve 15 switches the connection between the main electrolyte supply line 12 and the sub-electrolyte solution supply line 17 to the lithium ion battery 1.

When the main electrolyte is supplied to the lithium ion battery 1 by the main electrolyte supply device 4, the mixing ratio of the main electrolyte and the sub-electrolyte in the electrolyte of the lithium ion battery 1 changes in the direction of decreasing the ratio of the sub-electrolyte. do. When the sub-electrolyte is supplied to the lithium ion battery 1 by the sub-electrolyte supply device 5, the mixing ratio of the lithium ion battery 1 changes in the direction of increasing the proportion of the sub-electrolyte.

The electrolyte discharge device 6 includes an electrolyte discharge line 21 extending from the lithium ion battery 1, a main electrolyte recovery line 22 and a sub-electrolyte recovery line 23 branched from the discharge line 21. A valve 24 for switching the connection of the electrolyte recovery lines 22 and 23 to the electrolyte discharge line 21 is provided at the branch portion of the lines 22 and 23.

The electrolyte discharge line 21 is provided with a pump 25 and an electrolyte separator 26. A solvent supply line 29 for supplying the solvent of the solvent tank 28 is connected to the upstream side of the electrolyte separation device 26 of the electrolyte discharge line 21. The connection portion is provided with a valve 31 for switching between a state in which both the lithium ion battery 1 and the solvent tank 28 are connected to the electrolyte separation device 26 and a state in which the solvent tank 28 is disconnected. The electrolyte separator 26 includes an anion exchange membrane having a difference between the permeability of the anion PF _6-1 of the main electrolyte and the permeability of the anion ^PO ₂ F _2-1 of the sub ^- electrolyte.

The sub-electrolyte recovery line 23 is connected to the electrolyte discharge line 21 by a valve 24, both the lithium ion battery 1 and the solvent tank 28 are connected to the electrolyte separation device 26 by a valve 31 to operate the pump 25. As a result, the electrolytic solution of the lithium ion battery 1 is supplied to the electrolyte separation device 26 together with the solvent of the solvent tank 28, and the anion PO ₂ F _2-1 of the sub ^- electrolyte in the electrolytic solution forms the anion exchange film of the electrolyte separation device 26. It permeates and flows to the sub-electrolyte recovery line 23.

After a lapse of a predetermined time, the valve 24 is operated to connect the main electrolyte recovery line 22 to the electrolyte discharge line 21. As a result, the anion PF _6-1 of the main electrolyte in the electrolytic solution ^permeates the anion exchange membrane of the electrolyte separation device 26 and flows to the main electrolyte recovery line 22.

The main electrolyte recovery line 22 is connected to the main electrolyte tank 11. The main electrolyte recovery line 22 is provided with a main electrolyte concentration sensor 32 for detecting the concentration of the main electrolyte in the electrolytic solution separated and sent by the electrolyte separation device 26, and a main electrolyte concentration adjusting device 33. The main electrolyte concentration adjusting device 33 supplies the main electrolyte or a solvent based on the concentration of the main electrolyte detected by the main electrolyte concentration sensor 32, so that the main electrolyte is stored in the main electrolyte tank 11. Adjust so that the concentration of the main electrolyte is the same as that of the liquid. The electrolytic solution having an adjusted main electrolyte concentration is supplied to the main electrolytic solution tank 11.

The sub-electrolyte recovery line 23 is connected to the sub-electrolyte tank 16. The sub-electrolyte recovery line 23 is provided with a sub-electrolyte concentration sensor 34 for detecting the concentration of the sub-electrolyte in the electrolytic solution separated and sent by the electrolyte separation device 26, and a sub-electrolyte concentration adjusting device 35. The sub-electrolyte concentration adjusting device 35 supplies the sub-electrolyte or the solvent based on the concentration of the sub-electrolyte detected by the sub-electrolyte concentration sensor 34, so that the sub-electrolyte is stored in the sub-electrolyte tank 16. Adjust so that the concentration of sub-electrolyte is the same as that of the liquid. The electrolytic solution having an adjusted sub-electrolyte concentration is supplied to the sub-electrolyte tank 16.

As shown in FIG. 2, the detection signals of the temperature sensor 2, the electrolyte concentration sensor 8, the flow meters 14, 19, the main electrolyte concentration sensor 32, and the sub-electrolyte concentration sensor 34 are given to the controller 7. The controller 7 has data on the optimum mixing ratio of the main electrolyte and the sub-electrolyte according to the operating temperature of the lithium ion battery 1, data on the main electrolyte concentration of the main electrolyte stored in the main electrolyte tank 11, and the sub-electrolyte. It contains data on the sub-electrolyte concentration of the sub-electrolyte stored in the tank 16. The operation of the pumps 13, 18, 25, valves 15, 24, 31 and the electrolyte concentration adjusting devices 33, 35 is controlled by the controller 7 based on the detection signals and various data.

<Control of change of electrolyte mixing ratio>
As shown in FIG. 3, in step S1 after the start, the controller 7 acquires the operating temperature of the lithium ion battery 1 detected by the temperature sensor 2 and the electrolyte concentration sensor 8 and the mixing ratio of the main electrolyte and the sub-electrolyte. In the following step S2, it is determined whether or not the current electrolyte mixing ratio is appropriate for the operating temperature based on the data on the operating temperature and the optimum mixing ratio. If it is appropriate, the control ends.

When it is determined in step S2 that the current electrolyte mixing ratio is not appropriate for the operating temperature, the process proceeds to step S3, and the optimum mixing ratio at the operating temperature is obtained from the above-mentioned data on the operating temperature and the optimum mixing ratio. Is obtained. In the following step S4, the main electrolyte or the sub-electrolyte to the lithium-ion battery 1 is charged so that the mixing ratio of the main electrolyte and the sub-electrolyte of the electrolyte of the lithium-ion battery 1 becomes the optimum mixing ratio according to the operating temperature. Supply and discharge of the electrolytic solution from the lithium ion battery 1 (recovery of the electrolyte) are performed.

First, when the mixing ratio of the lithium ion battery 1 is in a state where the ratio of the sub-electrolyte is large in view of the optimum mixing ratio, the amount of the main electrolyte required to make the mixing ratio the optimum mixing ratio is obtained. In calculating the required amount of the main electrolyte, the decrease in each of the main electrolyte and the sub-electrolyte caused by discharging a part of the electrolyte from the lithium ion battery 1 in the change of the mixing ratio is taken into consideration.

Then, the main electrolytic solution supply line 12 is connected to the lithium ion battery 1 by the first valve 15. The electrolyte discharge line 21 is connected to the sub-electrolyte recovery line 23 by the second valve 24, and the solvent tank 28 is connected to the electrolyte discharge line 21 by the third valve 31.

By the operation of the pumps 13 and 25, the required amount of the main electrolytic solution is supplied to the lithium ion battery 1, while the required amount of the electrolytic solution is discharged from the lithium ion battery 1. The anion PO ₂ F _2-1 of the sub ^- electrolyte is separated from the discharged electrolyte solution by the anion exchange membrane of the electrolyte separator 26, and the electrolyte solution containing this PO ₂ F _2-1 is sent to the sub ^- electrolyte recovery line 23. .. The electrolytic solution containing PO ₂ F _2-1 is sent to the sub ^- electrolyte tank 16 after the concentration of the sub-electrolyte is adjusted by the sub-electrolyte concentration adjusting device 35.

After a lapse of a predetermined time, the second valve 24 is switched so that the electrolyte discharge line 21 is connected to the main electrolyte recovery line 22. As a result, the electrolytic solution containing the anion ^PF _6-1 of the main electrolyte separated by the anion exchange membrane of the electrolyte separation device 26 is sent to the main electrolyte recovery line 22. The electrolytic solution containing the ^PF _6-1 is sent to the main electrolytic solution tank 11 after the concentration of the main electrolyte is adjusted by the main electrolyte concentration adjusting device 33.

When the mixing ratio of the lithium ion battery 1 is in a state where the ratio of the sub-electrolyte is small with respect to the optimum mixing ratio, the amount of the sub-electrolyte required to make the mixing ratio the optimum mixing ratio can be obtained. In calculating the required amount of the sub-electrolyte, the reduction amounts of the main electrolyte and the sub-electrolyte caused by the discharge of the electrolyte from the lithium ion battery 1 are taken into consideration as in the case of the supply of the main electrolyte. ..

Then, the sub-electrolyte supply line 17 is connected to the lithium ion battery 1 by the first valve 15, the electrolyte discharge line 21 is connected to the main electrolyte recovery line 22 by the second valve 24, and the solvent tank 28 is the third. It is connected to the electrolyte discharge line 21 by the valve 31.

By the operation of the pumps 18 and 25, the required amount of the auxiliary electrolytic solution is supplied to the lithium ion battery 1, while the required amount of the electrolytic solution is discharged from the lithium ion battery 1. As in the case of supplying the main electrolyte, the discharged electrolyte is separated into an electrolyte containing a main electrolyte and an electrolyte containing a sub-electrolyte by the anion exchange film of the electrolyte separation device 26, and the main electrolyte recovery line 22 is used. And is recovered in each of the main electrolyte tank 11 and the sub-electrolyte tank 16 by the sub-electrolyte recovery line 23.

<Effect of electrolyte mixing ratio on charging resistance of lithium-ion batteries>
A plurality of lithium ion batteries having different ratios of the sub-electrolyte LiPO ₂ F ₂ to the total amount of the main electrolyte LiPF ₆ and the sub-electrolyte LiPO ₂ F ₂ were prepared. Each lithium-ion battery is charged with a capacity of 50%, and at each operating temperature (environmental temperature) of 25 ° C, -10 ° C, -20 ° C, and -30 ° C, for a predetermined time (0.1 seconds, 1 second, 3). Constant current discharge was performed for seconds and 10 seconds), and the discharge resistance was calculated from the relationship between the voltage drop and the current value after each time. The results are shown in FIGS. 4 to 7.

As shown in FIG. 4, at an operating temperature of 25 ° C., the discharge resistance is the smallest when the concentration of the sub-electrolyte LiPO ₂ F ₂ is 2%, and the discharge resistance tends to increase as the concentration increases. There is. Even in the case where the operating temperature is −10 ° C. (FIG. 5), the discharge resistance tends to be the same as the operating temperature of 25 ° C. shown in FIG.

On the other hand, when the operating temperature reaches −20 ° C. (FIG. 6), the discharge resistance becomes the smallest when the concentration of the sub-electrolyte LiPO ₂ F ₂ is 5%. Further, when the operating temperature reaches −30 ° C. (FIG. 7), the discharge resistance becomes smaller when the concentration of the sub-electrolyte LiPO ₂ F ₂ is 10% than when it is 5%.

From the above, it can be seen that by changing the mixing ratio of the electrolyte according to the operating temperature of the lithium ion battery, it is possible to suppress the decrease in the discharge characteristics of the lithium ion battery depending on the operating temperature. That is, in order to keep the discharge resistance of the lithium ion battery low, it can be seen that it is preferable to increase the ratio of LiPO ₂ F ₂ to the total amount of LiPF ₆ and LiPO ₂ F ₂ as the operating temperature of the lithium ion battery becomes lower. .. In particular, the ratio of LiPO ₂ F ₂ to the total amount of LiPF ₆ and LiPO ₂ F ₂ is set to 1% or more and 4% or less when the operating temperature of the lithium ion battery is 25 ° C., and the operating temperature of the lithium ion battery is-. It can be seen that when the temperature is 30 ° C., it is preferably 5% or more and 15% or less.

The above embodiment shows an example in carrying out the present invention, and the electrolyte of the lithium ion battery is not limited to the above-mentioned two-kind mixture of LiPF ₆ and LiPO ₂ F ₂ , and other electrolytes. The present invention can be applied even in the case where three or more kinds of electrolytes are mixed and used.

1 Lithium ion battery 2 Temperature sensor 3 Mixing ratio changing means 4 Main electrolyte supply device 5 Sub-electrolyte supply device 6 Electrolyte discharge device 7 Controller 8 Electrolyte concentration sensor 11 Main electrolyte tank 14 1st flow meter 16 Sub-electrolyte tank 19 2nd flow meter 22 Main electrolyte recovery line 23 Sub-electrolyte recovery line 32 Main electrolyte concentration sensor 33 Main electrolyte concentration adjuster 34 Sub-electrolyte concentration sensor 35 Sub-electrolyte concentration adjuster

Claims (10)

A lithium ion battery having a positive electrode and a negative electrode, and using an electrolytic solution in which two or more kinds of lithium salts are dissolved in a solvent as a supporting electrolyte.
A temperature sensor that detects the operating temperature of the lithium-ion battery,
The lithium ion is provided with a mixing ratio changing means for changing the mixing ratio of the two or more kinds of electrolytes in the electrolytic solution according to the operating temperature of the lithium ion battery detected by the temperature sensor. Battery system. In claim 1,
The lithium ion battery includes a main electrolyte and a sub-electrolyte as the supporting electrolytes.
The mixing ratio changing means sets the mixing ratio of the main electrolyte and the sub-electrolyte according to the operating temperature of the lithium-ion battery detected by the temperature sensor, and the charge / discharge resistance when the lithium-ion battery is charged / discharged. A lithium-ion battery system characterized by changing to a smaller mixing ratio. In claim 2,
The above-mentioned mixing ratio changing means is
A main electrolyte supply device that supplies a main electrolyte containing a predetermined concentration of the main electrolyte to the lithium ion battery, and a main electrolyte supply device.
A sub-electrolyte supply device that supplies a sub-electrolyte containing a predetermined concentration of the sub-electrolyte to the lithium-ion battery, and a sub-electrolyte supply device.
An electrolyte discharge device that discharges the electrolyte from the lithium-ion battery,
Discharge of the electrolyte by the electrolyte discharge device so that the mixing ratio of the main electrolyte and the sub-electrolyte of the electrolyte of the lithium-ion battery becomes a predetermined mixing ratio according to the operating temperature of the lithium-ion battery. The lithium ion battery system comprises a controller for controlling the supply of the main electrolyte and the sub-electrolyte by each of the main electrolyte supply device and the sub-electrolyte supply device. In claim 3,
The main electrolyte supply device includes a main electrolyte tank for storing the main electrolyte containing a predetermined concentration of the main electrolyte.
The sub-electrolyte supply device includes a sub-electrolyte tank for storing the sub-electrolyte containing a predetermined concentration of the sub-electrolyte.
The electrolyte discharge device includes an electrolyte separation device that separates the electrolyte discharged from the lithium ion battery into an electrolyte containing the main electrolyte and an electrolyte containing the sub-electrolyte, and the separated main electrolyte. It is provided with a main electrolyte recovery line for recovering the contained electrolyte solution in the main electrolyte solution tank and a sub-electrolyte recovery line for recovering the separated electrolyte solution containing the sub-electrolyte in the sub-electrolyte solution tank.
The main electrolyte recovery line includes a main electrolyte concentration adjusting device that adjusts the main electrolyte concentration of the electrolyte to be recovered to the predetermined concentration of the main electrolyte stored in the main electrolyte tank.
The sub-electrolyte recovery line is provided with a sub-electrolyte concentration adjusting device that adjusts the sub-electrolyte concentration of the electrolyte to be recovered to the above-mentioned predetermined concentration of the sub-electrolyte stored in the sub-electrolyte tank. A lithium-ion battery system featuring. In claims 2 to 4,
A lithium ion battery system characterized in that the main electrolyte is LiPF ₆ and the sub-electrolyte is LiPO ₂ F ₂ . In claim 5,
The lithium ion battery system is characterized in that, as the operating temperature of the lithium ion battery becomes lower, the mixing ratio changing means increases the ratio of LiPO ₂ F ₂ to the total amount of LiPF ₆ and LiPO ₂ F ₂ . In claim 6,
The mixing ratio changing means sets the ratio of LiPO ₂ F ₂ to the total amount of LiPF ₆ and LiPO ₂ F ₂ to 1% or more and 4% or less when the operating temperature of the lithium ion battery is 25 ° C., and the lithium ion. A lithium ion battery system characterized in that it is 5% or more and 15% or less when the operating temperature of the battery is −30 ° C. A method for adjusting the charge / discharge characteristics of a lithium ion battery, which comprises a positive electrode and a negative electrode and uses an electrolytic solution in which LiPF ₆ and LiPO ₂ F ₂ are dissolved in a solvent as supporting electrolytes.
A method for adjusting charge / discharge characteristics of a lithium ion battery, which comprises changing the mixing ratio of LiPF ₆ and LiPO ₂ F ₂ in the electrolytic solution according to the operating temperature of the lithium ion battery. In claim 8,
A method for adjusting the charge / discharge characteristics of a lithium ion battery, which comprises lowering the ratio of LiPO ₂ F ₂ to the total amount of LiPF ₆ and LiPO ₂ F ₂ as the operating temperature of the lithium ion battery becomes lower. In claim 9.
The ratio of LiPO ₂ F ₂ to the total amount of LiPF ₆ and LiPO ₂ F ₂ is set to 1% or more and 4% or less when the operating temperature of the lithium ion battery is 25 ° C., and the operating temperature of the lithium ion battery is -30. A method for adjusting charge / discharge characteristics of a lithium ion battery, characterized in that the temperature is 5% or more and 15% or less when the temperature is high.

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