JP2012016109A - Method and device of charging lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the decrease in capacity of lithium ion batteries by a simple method as well as to provide a charging method capable of preventing the shortening of life.SOLUTION: The method of charging a lithium ion battery includes a step to decide a recommendation period for start charging based on a change ratio ΔV/Δt per hour of an open circuit voltage of the lithium ion battery which is not being used. A period when the change ratio ΔV/Δt is smaller than a predetermined value is decided as the recommendation period for start charging. The predetermined value can be decided by at least one of the temperature of the lithium ion battery or the depth of discharge of the lithium ion battery.

Description

  The present invention relates to a method for charging a lithium ion battery and a charging device. Specifically, the present invention relates to control of the charging start timing of the lithium ion battery.

  A lithium ion battery has a high operating voltage and a high energy density, and can supply power for a relatively long time. Therefore, in recent years, use as a power source for driving motors of a hybrid electric vehicle (HEV), plug-in hybrid electric vehicle (PHEV), electric vehicle (EV), etc., a power source for a household power storage device, and the like has been studied.

  Above all, PHEV is equipped with a battery for driving a motor that can be charged at home, and is designed not to use a gasoline engine for short-distance movement, but to run only by rotating the motor. Therefore, it has been attracting attention in recent years from the viewpoint of further reducing greenhouse gas emissions.

  In general, PHEVs and EVs are usually left in a state in which a motor driving battery is charged to some extent in preparation for its use. For this reason, batteries that have been used are usually immediately connected to a charger and charging is often started. Here, the deterioration of the battery depends on the charging method of the battery. For example, when charging / discharging at a high rate is repeated, decomposition of the nonaqueous electrolyte and concentration distribution may occur, and the internal resistance may increase. Therefore, stable charging is not performed, and the output of the battery may be reduced.

  Therefore, in order to improve the capacity and output of the battery, Patent Document 1 discusses supplying two currents of different sizes to the battery while alternately switching them multiple times. Further, Patent Document 2 discloses performing recovery charge / discharge for recovering output deterioration when output deterioration of the secondary battery is detected.

JP 2010-45962 A JP 2010-49882 A

  However, Patent Documents 1 and 2 both improve the current supply method during charging, and in order to realize this, a highly functional and complicated charging circuit is required, which is disadvantageous in terms of cost.

  Further, the open circuit voltage of the battery in the resting state is macroscopically stabilized within a few minutes to several tens of minutes and becomes a steady state. However, microscopically, it has become clear that it takes a longer time to make the electronic state in the electrode uniform or to make the distribution of lithium ions in the nonaqueous electrolyte uniform. That is, the inside of the lithium ion battery is not stabilized for several hours after the discharge is stopped. If charging is started in this state, the stability of charging may be impaired and the battery life may be shortened.

SUMMARY OF THE INVENTION An object of the present invention is to provide a charging method and a charging apparatus that can suppress a decrease in capacity of a lithium ion battery and prevent a shortened life by a simple method.
One aspect of the present invention includes a step of determining a recommended charge start time based on a change rate ΔV / Δt per hour of an open circuit voltage of a paused lithium ion battery, and the change rate ΔV / Δt is: The present invention relates to a method for charging a lithium ion battery, wherein a time smaller than a predetermined value is determined as the recommended charging start time.

  According to another aspect of the present invention, a current supply circuit that supplies a current from an external or built-in DC power source to a lithium ion battery, and the use of the lithium ion battery is detected and the use is stopped. A unit for measuring the elapsed time, a voltage detection unit for measuring an open circuit voltage of the lithium ion battery during a pause, and an open circuit voltage of the lithium ion battery based on the open circuit voltage measured by the voltage detection unit Is a control unit that measures a rate of change ΔV / Δt per hour, determines a time when the rate of change ΔV / Δt is smaller than a predetermined value as a recommended charge start time, and controls the current supply circuit based on the determination And a charging device for a lithium ion battery.

  According to the present invention, in a lithium ion battery, the distribution of the lithium ion concentration in the nonaqueous electrolyte can be made as uniform as possible, and can be stably charged in a state in which the polarization in the electrode is eliminated. In addition, according to the present invention, since charging is not normally started until the recommended time, the period during which the battery is stored in a charged state is shortened. For this reason, it is possible to suppress the reduction in the capacity of the lithium ion battery and to effectively prevent the battery life from being shortened easily and at low cost.

It is a graph which shows the relationship between the resting time t when the use of a lithium ion battery is stopped, and the open circuit voltage V during resting. 2 is a graph showing a relationship between a change rate ΔV / Δt and a rest time t for the lithium ion battery of FIG. 1. It is a graph which shows the relationship between the resting time t and the open circuit voltage V during resting when discharging is stopped after discharging a lithium ion battery to different depths of discharge. It is a graph which shows the relationship between the rest time t and the open circuit voltage V during rest when discharge is stopped after discharging lithium ion batteries of different battery temperatures. 4 is a flowchart for explaining a method of charging a lithium ion battery according to an embodiment of the present invention. It is a circuit diagram of the charging device which implements the charging method of the lithium ion battery which concerns on one Embodiment of this invention. 4 is a flowchart for explaining a method of charging a lithium ion battery according to an embodiment of the present invention. 4 is a flowchart for explaining a method of charging a lithium ion battery according to an embodiment of the present invention. In the cycle characteristic test of Examples 1-3, it is a graph which shows the relationship between discharge capacity and cycle number.

In the present invention, the timing for starting the charging of the lithium ion battery is determined based on at least the rate of change per hour of the open circuit voltage of the lithium ion battery that is not operating. This is due to the following reason.
When the open circuit voltage V is plotted against the elapsed time (discharge stop time) t from the time when the use of the lithium ion battery is stopped, the voltage V rapidly recovers with the passage of time, and is several minutes to several tens of minutes Thus, the value is almost constant. On the other hand, the change rate ΔV / Δt (dV / dt) obtained by differentiating the plotting between the discharge pause time t and the open circuit voltage V shows a behavior different from the relationship between V and t.

  FIG. 1 shows that when a lithium ion battery having a battery temperature of 25 ° C. is discharged after the SOC is discharged to 0% (discharge depth is 100%) and the use is stopped, the pause time t and the open circuit voltage V during the pause are It is a graph which shows a relationship. FIG. 2 is a graph showing the relationship between t and V in FIG. 1 as a change rate ΔV / Δt (mV / min), and showing the relationship between the change rate and t.

  In FIG. 1, the open circuit voltage of the lithium ion battery rises rapidly after the discharge is stopped, and becomes a substantially constant value within a few minutes. That is, from FIG. 1, it appears as if the lithium ion battery is in a steady state within a few minutes and the distribution of lithium ions and charges in the battery is stabilized. However, in FIG. 2, it takes several hours for ΔV / Δt to reach a substantially constant value. When attention is paid to the microscopic change rate, it takes several hours for the open circuit voltage V to stabilize, and until that time, the charge distribution in the battery has not stabilized. It is shown that. If charging of the lithium ion battery is started in such an unstable state, the capacity and output of the battery are lowered, and the battery life is impaired.

  Therefore, in the present invention, focusing on the change rate ΔV / Δt, the recommended charging start time is determined based on this change rate. That is, the method for charging a lithium ion battery according to the present invention includes a step of determining a recommended charge start time based on the rate of change ΔV / Δt per hour of the open circuit voltage of the paused lithium ion battery.

  Specifically, a time when the change rate ΔV / Δt is smaller than a predetermined value is determined as a recommended charging start time. If a lithium ion battery is left in a charged storage state, the battery life will be shortened accordingly, so a time later than when the rate of change ΔV / Δt becomes smaller than a predetermined value is determined as a recommended charging start time. May be.

  Here, the predetermined value of the rate of change ΔV / Δt is determined corresponding to the time when the lithium ion and charge distribution in the battery is stabilized. This time is determined according to the type of battery, the nominal capacity, the type of equipment using the battery, and the like. For example, 1.2 mV / min, preferably 0.5 mV / min, more preferably 0.3 mV / min, or 0.2 mV / min, or 0.1 mV / min is suitable.

  In one aspect of the present invention, the step of determining the recommended charging start time includes (i) detecting a change rate ΔV / Δt before starting charging, (ii) comparing the change rate ΔV / Δt with a predetermined value, iii) Based on the comparison result, the recommended charging start time is determined. In this case, the operations (i) to (iii) are performed every time before the charging is started. The rate of change ΔV / Δt is measured continuously or intermittently from the discharge rest. Therefore, the battery can be charged based on the accurate change rate ΔV / Δt, which is advantageous for extending the life of the battery.

In another aspect of the present invention, the step of determining the recommended charging start time includes: (i) a relationship between an elapsed time t obtained by stopping use of a lithium ion battery obtained in advance and a rate of change ΔV / Δt. (Ii) Based on the function, a recommended discharge pause time t _App at which the change rate ΔV / Δt becomes a predetermined value is calculated, and (iii) the elapsed time t exceeds the recommended discharge pause time t _App The time is determined as the recommended charging start time. In this case, the function representing the relationship between the elapsed time t and the rate of change ΔV / Δt is measured in advance by the battery manufacturer or the manufacturer of the battery using device under one or more conditions. The obtained function is stored in, for example, a storage unit included in a control unit that controls the charging circuit, and is referred to before starting charging.

  FIG. 3 shows the relationship between the rate of change ΔV / Δt and the rest time t when a lithium ion battery with a battery temperature of 25 ° C. is discharged to a discharge depth of 60%, 80% or 100% and then stopped. It is a graph. FIG. 4 shows the relationship between the change rate ΔV / Δt and the rest time t when a lithium ion battery having a battery temperature of 0 ° C., 25 ° C. or 45 ° C. is discharged to a discharge depth of 100% and then stopped. It is a graph which shows.

  As apparent from FIGS. 3 and 4, when the temperature of the lithium ion battery increases or the depth of discharge increases, the elapsed time until the steady state tends to be delayed. This is because the diffusion rate of ions in the nonaqueous electrolyte and the reactivity of the active material differ depending on the battery temperature. The reactivity of the active material is also related to the depth of discharge.

  As described above, it is preferable that the function representing the relationship between the elapsed time t and the change rate ΔV / Δt is measured at various temperatures and various discharge depths and stored in a predetermined storage unit. And it is preferable to determine the predetermined value of the rate of change ΔV / Δt depending on at least one of the temperature of the lithium ion battery and the depth of discharge. Specifically, it is preferable to delay the recommended charging start time as the depth of discharge is deeper, and it is preferable to delay the recommended charging start time as the battery temperature is higher. In this case, the function to be referred to is a function representing the relationship between the elapsed time t, the rate of change ΔV / Δt, and at least one of the temperature of the lithium ion battery and the discharge depth of the lithium ion battery.

For example, a control device that controls a charging circuit substitutes at least one of temperature and discharge depth into a function as a variable, calls up the relationship between elapsed time t and change rate ΔV / Δt corresponding to the condition, and stabilizes the battery. The recommended discharge pause time t _App is calculated as a predetermined value serving as an index of. Then, a time exceeding the recommended discharge pause time _tApp is determined as a recommended charging start time.

If charging is to be started earlier than t _App , charging is performed based on an allowable charging start time t _alw separately calculated based on the rate of change ΔV / Δt (and other conditions if necessary). The start time can also be determined. In this case, based on the recommended discharge quiescent time t _App, it recommended to calculate the charging end time t _C, whether the charging end time t _DC desired than slow t _C, i.e., the t _C> t _DC The condition for determining the charging start time may be changed depending on whether or not the condition is satisfied.

For example, when t _C > t _DC , charging is started so that charging ends at a desired charging end time t _DC . At this time, it is preferable to calculate the allowable charging start time t _alw so that the rate of change ΔV / Δt is as small as possible, and perform charging based on t _alw . On the other hand, when t _C ≦ t _DC, the charging is started at the recommended charging start time obtained based on the function. By doing in this way, the user of the battery and the device using the battery can start charging at the recommended charging start time only when the time for resuming use is not limited and there is a time margin. Therefore, deterioration of the battery can be suppressed without difficulty.

Next, an example of a charging device for carrying out the above method will be described.
The charging apparatus includes a control unit that determines a time when the change rate ΔV / Δt is smaller than a predetermined value as a recommended charging start time. In addition to the control unit, such a charging device usually includes a current supply circuit (charging circuit) that supplies current to the lithium ion battery, a time measurement unit (such as a timer) that measures the discharge pause time of the lithium ion battery, A voltage detection unit for measuring an open circuit voltage of the lithium ion battery. The charging device may include a switch that switches presence / absence of electrical connection between the lithium ion battery and the current supply circuit. The current supply circuit supplies current from an external or built-in DC power source to the lithium ion battery.

The time measurement unit detects stoppage of use of the lithium ion battery and integrates the discharge pause time. The time measurement unit may be included in another unit constituting the charging device.
The charging device may further include a temperature detection unit that measures the temperature of the lithium ion battery. The temperature detection unit may be included in another unit that constitutes the charging device, such as a control unit.

The control unit has a predetermined function (a function of rate of change and conditions such as discharge pause time t, battery temperature and / or depth of discharge) and / or various other conditions (desired charge end time or desired charge start In addition to a storage unit for storing time etc., a calculation unit, a determination unit, a processing unit, and the like may be included.
Specifically, the control unit can include a CPU (Central Processing Unit), a microcomputer, an MPU (Micro Processing Unit), a wired logic circuit, a main storage device, an auxiliary storage device, and the like. .

In the arithmetic unit, for example, referring to the function stored in the storage unit, based on the voltage of the battery sent from the voltage detection unit, the discharge pause time sent from the time measurement unit, the condition stored in the storage unit, etc. Thus, the recommended discharge pause time _{tApp and the} like are calculated.

In the determination unit, for example, the recommended discharge time t _App calculated by the calculation unit is compared with the discharge pause time t, it is determined whether or not the condition of t> t _App is satisfied, and when the condition is not satisfied, The discharge rest state is continued. When the condition is not satisfied, a signal is sent to the calculation unit, and t _App is calculated again by the calculation unit after a predetermined time.
When the condition of t> t _App is satisfied, a signal is sent from the determination unit to the processing unit, the lithium ion battery and the current source are electrically connected according to an instruction from the processing unit, and charging of the lithium ion battery is started. .

When the user wants to finish charging at a time earlier than the recommended charging end time t _C calculated based on t _App and resume the use of the lithium ion battery, t _C and the input or storage unit The stored charging end time t _DC desired by the user is compared by the determination unit. When t _C > t _DC, the charging start time allowed by the calculation unit is calculated so that the charging ends at t _DC . The calculated charging start time and the discharge pause time t are compared by the determination unit, and when both become the same or immediately, the processing unit starts charging.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 5 is a flowchart for explaining a method of charging a lithium ion battery according to Embodiment 1 of the present invention. FIG. 6 is a circuit diagram of the charging device.
The charging device includes a charging circuit 14 that supplies a current from the external power supply 15, a switching circuit 16 having a changeover switch 16a, a control unit 12a that determines a recommended charging start time based on the change rate ΔV / Δt, and the like. Device 12. Control device 12 further includes a voltage detection unit 12b that measures the open circuit voltage of the lithium ion battery, and a time measurement unit 12c that measures the discharge pause time.

  In the charging device, a lithium ion battery (lithium ion battery equipped in PHEV or EV) 11 is set, and the lithium ion battery 11 is connected in parallel with the control unit 12a. The discharge pause time t measured by the time measurement unit is sent to the control unit 12a.

Based on the information stored in the storage unit, the control unit 12a stores a function indicating the relationship between the discharge pause times t and t and the rate of change ΔV / Δt, a predetermined value of ΔV / Δt, and the like. A calculation unit for calculating a recommended discharge pause time _tApp , a determination unit for comparing t and _tApp, and a processing unit for switching to the charging circuit 14 based on the determination result. The control device 12 may incorporate a charging circuit 14.
The starting point of the discharge pause time can be the time when the lithium ion battery is set in the charging device.

  The negative electrode of the lithium ion battery 11 and the negative electrode side terminal of the charging circuit 14 each have the same potential as the negative electrode terminal of the external power supply 15. The positive terminal of the lithium ion battery 11 and the positive terminal of the output circuit of the charging circuit 14 are connected to predetermined terminals 17 and 19 provided in the switching circuit 16, respectively.

  The changeover circuit 16 includes a changeover switch 16 a that controls connection between the positive electrode of the lithium ion battery 11 and the positive electrode side terminal of the output side circuit of the charging circuit 14. When the changeover switch 16a is turned on, the positive electrode of the lithium ion battery 11 and the positive electrode side terminal of the output side circuit of the charging circuit 14 are connected, and when the charging switch is turned off, the connection is cut.

The switching circuit 16 communicates with a control unit 12a having a determination unit that compares t and _tApp . The switching circuit 16 is controlled by the determination result in the determination unit.
When the switch 16a of the switching circuit 16 is turned on and the positive electrode of the lithium ion battery 11 is connected to the positive terminal of the output circuit of the charging circuit 14, the charging circuit 14 connects the lithium ion battery 11 to the control unit 12a. Charge according to the instructions. The open circuit voltage of the lithium ion battery 11 being charged may be monitored by the control unit 12a.

Next, taking the case of using the above charging device as an example, an example of the charging method of the present invention will be described with reference to the flowchart of FIG.
First, the lithium ion battery 11 is set in the charging device (S0). Then, the switching circuit 16 detects that the lithium ion battery has stopped discharging in a state where the changeover switch 16a is turned off (S1).

Simultaneously with the detection of the discharge pause, the time measurement unit 12c starts counting the discharge pause time t (S2). The counted t is always sent to the storage unit of the control unit 12a.
Next, the calculation unit of the control unit 12a calculates the discharge depth of the lithium ion battery based on the open circuit voltage sent from the voltage detection unit 12b and the information stored in the storage unit (S3). The control unit 12a substitutes the discharge depth as a variable for a predetermined function stored in the storage unit, and calls the relationship between the elapsed time t and the change rate ΔV / Δt corresponding to the condition. Then, the recommended discharge pause time _tApp is calculated so that ΔV / Δt becomes smaller than a predetermined value (for example, 0.5 mV / min) that is an index of battery stabilization (S4).

The determination unit of the control unit 12a compares the calculated t _App with the discharge pause time t (S5). When the comparison result is t ≦ t _App , the lithium ion battery is not sufficiently stabilized. In this case, the calculation unit of the control unit 12a calculates the discharge depth of the lithium ion battery again after a predetermined time (S3). In the case of t> t _App , the lithium ion battery is in a sufficiently stabilized state. In this case, the control unit 12a turns on the switch 16a of the switching circuit 16 by the processing unit to connect the lithium ion battery and the charging circuit 14 and starts charging the lithium ion battery (S6). .

Step S3~S5 is, t> t up _App of the conditions are satisfied, is repeatedly executed. When the discharge depth of the lithium ion battery is sequentially calculated based on the value of the open circuit voltage constantly sent from the voltage detection unit 12b, the determination accuracy of the discharge depth is improved, and the accurate charge start time and charge end time are calculated. can do.

  Charging can be performed by constant current charging and / or constant voltage charging. During the charging, the closed circuit voltage of the lithium ion battery is measured, and the charging is stopped when the measured value reaches a predetermined voltage.

FIG. 7 is a flowchart showing a modification of FIG.
The charging device further includes a temperature detection unit that measures the temperature of the lithium ion battery. In FIG. 7, the temperature of the lithium ion battery is measured by the temperature measurement unit after step S2 for starting the counting of the discharge pause time t (S10). The measured battery temperature is sent to the storage unit of the control unit 12a. Next, the calculation unit of the control unit 12a calculates the discharge depth of the lithium ion battery based on the open circuit voltage sent from the voltage detection unit 12b and the information stored in the storage unit (S3).

The control unit 12a substitutes the temperature and the discharge depth as variables into a predetermined function stored in the storage unit, and calls a function representing the relationship between the elapsed time t and the change rate ΔV / Δt corresponding to the condition. A recommended discharge pause time _tApp is calculated (S4).

FIG. 8 is a flowchart showing a modification of FIG. The charging device further includes a display unit (such as a liquid crystal monitor) that displays a recommended charging end time t _C.
8, in step S4, after calculating the t _App, the calculating section, based on the t _App, recommended calculating the charge end time t _C (S11). Note that t _C is normally calculated based on t _App , the depth of discharge, and the charging conditions.

The calculated t _C is displayed on the display unit. The control unit 12a compares the recommended charging end time t _C displayed on the display unit with the desired charging end time t _DC input by the user (S12). When t _C ≦ t _DC , the control unit 12a continues the pause for a while (S13), and then compares the t _App calculated in step S4 with the discharge pause time t (S5). When the comparison result is t ≦ t _App , the processing unit of the control unit 12a continues the discharge pause state (S13). In the case of t> t _App , the control unit 12a causes the processing unit to turn on the switch 16a of the switching circuit 16, thereby connecting the lithium ion battery and the charging circuit 14 and starting charging the lithium ion battery. (S6).

Steps S13 and S5 are repeatedly executed until the condition of t> t _App is satisfied.
If t _C > t _{DC in} step S12, the charging start time t _alw allowed by the calculation unit is calculated based on t _DC (S15). Thereafter, after the discharge is stopped for a while (S16), the determination unit compares t _alw calculated in step S15 with t (S17).

In step S17, when t ≧ t _alw , the processing unit _{turns on} the switch 16a of the switching circuit 16, connects the lithium ion battery and the charging circuit 14, and starts charging the lithium ion battery (S6). In the case of t <t _alw , the processing unit continues the discharge pause state (S16). Steps S16 and S17 are repeatedly executed until the condition t ≧ t _alw is satisfied.

The charging method and the charging device of the present invention can be applied to a known lithium ion battery. A lithium ion battery includes an electrode group having a positive electrode, a negative electrode, and a separator that separates them, and the electrode group is housed in a battery case together with a nonaqueous electrolyte.
Each of the positive electrode and the negative electrode includes a current collector and an active material layer disposed on the surface of the conductive substrate. Examples of the material for the positive electrode current collector include stainless steel, titanium, aluminum, and alloys thereof, and examples of the material for the negative electrode current collector include nickel, copper, and alloys thereof.

Examples of the positive electrode active material include a composite oxide containing lithium and cobalt, nickel, and / or manganese. Examples of the negative electrode active material include carbon-containing materials such as graphite, silicon oxide, and the like. The active material layer may contain an active material, a binder (such as a fluororesin and a rubber material), and, if necessary, a thickener and a conductive material.
Examples of the separator include a porous film made of polyolefin such as polyethylene and polypropylene.
The non-aqueous electrolyte includes a non-aqueous solvent such as carbonate ester and a lithium salt dissolved in the non-aqueous solvent. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , and LiN (CF ₃ SO ₂ ) ₂ .

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
(A) A lithium ion battery was produced as follows.
(1) Production of positive electrode 3 kg of lithium cobaltate, 12 kg of NMP (N-methyl-2-pyrrolidone) solution of polyvinylidene fluoride (trade name: PVDF # 1320, manufactured by Kureha Corporation), and 90 g of acetylene black Then, an appropriate amount of NMP was stirred with a double-arm kneader to prepare a positive electrode mixture slurry. This slurry was applied to both sides of an aluminum foil (positive electrode current collector) having a thickness of 15 μm, and the obtained coating film was dried and rolled to form a positive electrode active material layer, thereby producing a positive electrode having a total thickness of 160 μm. The positive electrode was cut to obtain a strip-shaped positive electrode having a width of 56 mm.

(2) Production of negative electrode 3 kg of artificial graphite, 75 g of a 40% by mass aqueous dispersion of a modified styrene butadiene rubber (trade name: BM-400B, manufactured by Nippon Zeon Co., Ltd.), 30 g of carboxymethyl cellulose, and an appropriate amount of water The mixture was stirred with a double arm kneader to prepare a negative electrode mixture slurry. This slurry was applied to both surfaces of a 10 μm thick copper foil (negative electrode current collector), and the obtained coating film was dried and rolled to form a negative electrode active material layer, thereby preparing a negative electrode having a total thickness of 180 μm. The negative electrode was cut to obtain a strip-shaped negative electrode having a width of 57 mm.

(3) Separator As the separator, a polyethylene porous film (trade name: A089, manufactured by Celgard Co., Ltd.) having a thickness of 20 μm was used.

(4) Preparation of non-aqueous electrolyte LiPF ₆ is dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1: 1: 1, and vinylene carbonate is added to prepare a non-aqueous electrolyte. did. The concentration of LiPF ₆ was 1 mol with respect to 1 liter of the mixed solvent. The amount of vinylene carbonate added was 3 parts by mass with respect to 100 parts by mass of the mixed solvent.

(5) Production of Lithium Ion Battery A separator was interposed between the strip-shaped positive electrode and the strip-shaped negative electrode, and these were wound to produce a cylindrical wound electrode group. The positive electrode current collector and the lower surface of the sealing plate having the safety valve were connected by an aluminum positive electrode lead. The negative electrode current collector was connected to the inner bottom surface of an iron-bottomed cylindrical battery case (inner diameter: 18 mm) with nickel plating on the surface by a nickel negative electrode lead. After the polypropylene insulating plates were attached to both ends in the longitudinal direction of the wound electrode group, the wound electrode group was accommodated in the battery case.
In a state where the inside of the battery case containing the electrode group was decompressed, 5.0 g of a nonaqueous electrolyte was injected and impregnated into the wound electrode group.

  Next, a sealing plate was disposed in the opening of the battery case via a polypropylene gasket, and the opening end of the battery case was crimped to the peripheral edge of the sealing plate. As a result, 30 cylindrical lithium ion batteries having an inner diameter of 18 mm, a height of 65 mm, and a design capacity of 2000 mAh were produced.

(B) Pre-treatment of battery Among the 30 lithium ion secondary batteries obtained in (A) above, 10 randomly extracted were subjected to charge / discharge treatment under the following conditions. This charge / discharge treatment was performed by placing the battery in a thermostat (25 ° C.) for charge / discharge testing.

  The lithium-ion battery was charged at a constant current of 0.7 C (1400 mA) up to 4.2 V, and then at a constant voltage of 4.2 V until the charging current reached 50 mA. The charged lithium-ion battery was left for 10 minutes and then discharged at a constant current of 1.0 C (2000 mA) until the depth of discharge reached 100%.

(C) Charging / discharging cycle characteristic test The lithium ion battery after the pretreatment was set in the charging device according to the circuit diagram of FIG. 6 and charged according to the flow of FIG. The battery temperature was 25 ° C. When calculated under the condition that the rate of change ΔV / Δt = 0.04, the recommended discharge pause time t _App was 2 hours and 58 minutes.
Charging was performed at a constant current of 0.3 C (600 mA) up to 4.2 V, and then at a constant voltage of 4.2 V until the charging current reached 50 mA.
The fully charged lithium ion battery was allowed to stand for 10 minutes after completion of charging, and then discharged at a constant current of 1.0 C (2000 mA) until the depth of discharge reached 100%.

  The above charge / discharge was repeated 1000 times, and the discharge capacity was determined every 100 cycles. The capacity ratio with respect to the first discharge capacity was calculated as a percentage. FIG. 9 is a graph showing the relationship between capacity (%) and the number of cycles. The capacity ratio was expressed as an average value of 10 lithium batteries.

Examples 2 and 3
Using the same lithium ion battery as in Example 1, based on t _App calculated under the conditions of change rate ΔV / Δt = 0.01 (Example 2) or ΔV / Δt = 0.1 (Example 3). The charge / discharge and cycle characteristic tests were performed in the same manner as in Example 1 except that the recommended charge start time was determined. The results are shown in FIG.

  As is apparent from FIG. 9, in Examples 1 to 3, the discharge capacities after repeating charge and discharge 1000 times are 73% (Example 1), 81% (Example 2), 65% (first time). Example 3), in which the decrease in discharge capacity is effectively suppressed. This is considered to be because charging can be started in a stable state of the lithium ion battery because the charging start time is determined based on the change rate ΔV / Δt.

Comparative Example 1
A cycle characteristic test was performed in the same manner as in Example 1 except that the same lithium ion battery as in Example 1 was used and charging was repeated 10 minutes after the end of discharge.
As a result, the discharge capacity after repeating charge and discharge 1000 times was 51% for the first time, which was significantly reduced.

  According to the charging method and the charging device of the present invention, the charging start timing of the used lithium ion battery is determined based on the rate of change ΔV / Δt per hour of the open circuit voltage of the paused lithium ion battery. Thereby, the fall of the capacity | capacitance of a lithium ion battery can be suppressed, and lifetime can be lengthened. In this invention, since such an effect is acquired by a simple method, it is suitable for charge of various lithium ion batteries, especially the lithium ion battery mounted in PHEV.

11 Lithium ion battery 12 Control device 12a Control unit 12b Voltage detection unit 12c Time measurement unit 14 Charging circuit 15 External power supply 16 Switching circuit 16a Changeover switch

Claims (10)

Determining the recommended charging start time based on the rate of change ΔV / Δt per hour of the open circuit voltage of the lithium-ion battery during suspension,
A method for charging a lithium ion battery, wherein a time when the change rate ΔV / Δt is smaller than a predetermined value is determined as the recommended charging start time.   The method for charging a lithium ion battery according to claim 1, wherein the predetermined value is determined depending on at least one of a temperature of the lithium ion battery and a discharge depth of the lithium ion battery.   The method for charging a lithium ion battery according to claim 1, wherein the predetermined value is 0.5 mV / min. Determining the recommended charging start time,
(I) Before the start of charging, the change rate ΔV / Δt is detected,
(Ii) comparing the rate of change ΔV / Δt with the predetermined value;
(Iii) The method for charging a lithium ion battery according to any one of claims 1 to 3, wherein the recommended charging start time is determined based on the comparison result. Determining the charging start time,
(I) Refer to a function representing the relationship between the elapsed time t after the use of the lithium ion battery determined in advance and the change rate ΔV / Δt,
(Ii) Based on the function, a recommended discharge pause time t _{App at} which the change rate ΔV / Δt is the predetermined value is calculated,
(Iii) The method for charging a lithium ion battery according to any one of claims 1 to 3, wherein a time exceeding the recommended discharge pause time _tApp is determined as the recommended charging start time.   The function is a function representing the relationship between the elapsed time t, the rate of change ΔV / Δt, and at least one of the temperature of the lithium ion battery and the discharge depth of the lithium ion battery, and the temperature and the discharge The method for charging a lithium ion battery according to claim 5, wherein the charging start time is determined depending on at least one of the depths.   The method for charging a lithium ion battery according to claim 2, wherein the charging start time is delayed as the depth of discharge increases.   The method for charging a lithium ion battery according to claim 2, wherein the charging start timing is delayed as the temperature increases. Furthermore,
(Iv) calculating a recommended charge end time t _C based on the recommended discharge pause time t _App ;
(V) comparing the recommended charging end time t _C with the charging end time t _DC desired by the user;
(Vi) When t _C > t _DC , charging is started so that charging ends at the end time t _DC , and when t _C ≦ t _DC , charging starts at the recommended charging start time. The method for charging a lithium ion battery according to claim 5, comprising steps. A current supply circuit for supplying current from an external or built-in DC power source to the lithium ion battery;
A unit for detecting the use stop of the lithium ion battery and measuring an elapsed time after the use is stopped;
A voltage detection unit for measuring an open circuit voltage of the lithium-ion battery during a pause;
A rate of change ΔV / Δt per hour of the open circuit voltage of the lithium ion battery is measured based on the open circuit voltage measured by the voltage detection unit, and the rate of change ΔV / Δt is smaller than a predetermined value And a control unit that controls the current supply circuit based on the determination, and a charging device for a lithium ion battery.

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