JP6914637B2 - Lithium ion secondary battery - Google Patents

Description

One aspect of the present invention relates to a power storage device. Alternatively, one aspect of the present invention relates to a power storage system. Alternatively, one aspect of the present invention relates to a method for recovering the capacity of a power storage device.

One aspect of the present invention is not limited to the above technical fields. The technical field of one aspect of the invention disclosed in the present specification and the like relates to a product, a method, or a manufacturing method. Alternatively, one aspect of the invention relates to a process, machine, manufacture, or composition of matter. Therefore, as a technical field of one aspect of the present invention disclosed more specifically in the present specification, as an example, a semiconductor device, a display device, a power storage device, a storage device, a driving method thereof, or a manufacturing method thereof. Can be mentioned.

In addition, in this specification and the like, a power storage system means one or more devices including a power storage device. Further, the semiconductor device refers to all devices that can function by utilizing the semiconductor characteristics. A semiconductor device such as a transistor, a semiconductor circuit, an arithmetic unit, and a storage device are one aspect of the semiconductor device.

In recent years, portable electronic devices such as mobile phones, smartphones, electronic books (electronic books), and portable game machines have become widespread. For this reason, power storage devices represented by lithium ion secondary batteries, which are these drive power sources, are being actively researched and developed. In addition, the importance of power storage devices is increasing in various applications, such as hybrid vehicles and electric vehicles attracting attention due to growing interest in global environmental issues and petroleum resource issues.

Lithium-ion secondary batteries, which are widely used because of their high energy density, are positive electrodes containing active materials such as _{lithium cobalt oxide (LiCoO 2} ) and lithium iron phosphate (LiFePO _{4), and lithium ions.} It is composed of a negative electrode made of a carbon material such as graphite that can be stored and released, and an electrolytic solution in which an electrolyte made of a lithium salt such as _{LiBF 4} or LiPF _{6 is dissolved in an organic solvent such as ethylene carbonate or diethyl carbonate.} NS. Charging and discharging of a lithium ion secondary battery is performed by moving lithium ions in the lithium ion secondary battery between the positive electrode and the negative electrode via an electrolytic solution, and inserting and removing lithium ions into the positive electrode active material and the negative electrode active material. Will be done.

By repeating charging and discharging as described above, the lithium ion secondary battery undergoes reductive decomposition of the electrolytic solution (organic solvent) at the negative electrode. The electrons generated by the desorption of lithium ions at the positive electrode are consumed in the reduction decomposition, so that lithium in the positive electrode active material is deficient. That is, the capacity of the lithium ion secondary battery decreases due to repeated charging and discharging. In order to recover the reduced capacity, it is necessary to supplement the lithium ions deficient in the positive electrode active material.

In order to solve the above problem, the capacity of a lithium ion battery provided with a third electrode having an active material capable of releasing lithium ions in the battery and replenishing the deficient lithium ions by energizing the positive electrode and the third electrode. A recovery method is known (Patent Document 1).

Published in the United States US2014 / 0028264

A secondary battery such as a lithium-ion battery is a battery that can be charged and discharged, but its capacity gradually decreases due to repeated charging and discharging. If the capacity decreases, conditions such as operating limits deviate from the initial device design, causing inconvenience in use in devices equipped with secondary batteries.

Since the voltage range used in the conventional lithium-ion battery exceeds the potential window of the electrolytic solution, decomposition of the electrolytic solution is unavoidable. In particular, since the negative electrode has a potential far exceeding the potential window, the amount of decomposition of the electrolytic solution is large, which reduces the battery capacity.

An object of the present invention is to reduce a decrease in the capacity of a lithium ion battery and maintain the capacity during a period of use.

It also provides a new configuration of a power storage device for that purpose.

One of the factors that reduce the capacity of lithium-ion batteries is the reductive decomposition of the electrolytic solution at the negative electrode. At the time of charging, the positive electrode releases Li, and when the negative electrode undergoes reductive decomposition of the electrolytic solution, the amount of Li that reacts decreases, so that the capacity of the battery decreases.

On the other hand, oxidative decomposition of the electrolytic solution occurs on the positive electrode side. When the electrolytic solution is oxidatively decomposed on the positive electrode side during charging, Li is inserted or the electrolytic solution is reduced and decomposed on the negative electrode side. At this time, the capacity of the battery does not increase or change.

Therefore, in parallel with the positive electrode, activated carbon having a specific surface area sufficiently higher than that of the positive electrode active material is used to provide a sacrificial electrode that causes oxidative decomposition of the electrolytic solution in contact with the activated carbon. As a result, it is possible to suppress the decrease in capacity while minimizing the decomposition of the electrolytic solution in contact with the positive electrode.

Alternatively, by mixing a certain amount of activated carbon with the active material of the positive electrode electrode, such as the positive electrode active material of a lithium ion battery (LFP or LCO), oxidative decomposition is caused on the surface of the activated carbon.

The configuration of the invention disclosed herein includes a positive electrode, a negative electrode, a sacrificial electrode, a separator, and an electrolytic solution, the positive electrode has a positive electrode layer on a positive electrode current collector, and the negative electrode has a negative electrode layer. Is on the negative electrode current collector, the positive electrode layer and the negative electrode layer face each other via a separator, the sacrificial electrode is directly and electrically connected to the positive electrode, and the sacrificial electrode is the positive electrode layer and the negative electrode layer. It is a power storage device that is arranged at positions that do not face each other.

In the above configuration, the positive electrode layer has positive electrode active material particles, the sacrificial electrode has a sacrificial electrode layer, and the sacrificial electrode layer has activated carbon particles. In the above configuration, the total surface area (product of specific surface area and weight) of the activated carbon particles is 10 times or more the total surface area of the positive electrode active material particles. Activated carbon is used because the total surface area of activated carbon is higher than the total surface area of the active material under the assumption that electrolyte decomposition occurs in proportion to the surface area, the amount of decomposition on activated carbon is larger. This is because there will be more. Since decomposition on the active material also proceeds at the same time, the smaller the ratio between the total surface area of the active material and the total surface area of the activated carbon (the higher the weight ratio of the activated carbon), the more effective it is. However, if the ratio of activated carbon is high, the battery capacity may decrease.

Further, in the above configuration, the total weight of the activated carbon particles is 1/10 or less of the total weight of the positive electrode active material, which is a power storage device.

In addition, another configuration has a positive electrode, a negative electrode, a separator, and an electrolytic solution, the positive electrode has a positive electrode layer on the positive electrode current collector, and the negative electrode has a negative electrode layer on the negative electrode current collector. The positive electrode layer and the negative electrode layer face each other via a separator, the positive electrode has active material particles and activated carbon particles, and the surface area of the active carbon particles is higher than the surface area of the active material particles.

In each of the above configurations, the electrolytic solution has a first solvent and a second solvent, and the second solvent has a lower reduction potential and oxidation potential than the first solvent.

Further, in each of the above configurations, the electrolytic solution has a first solvent and a second solvent, and the second solvent is also characterized in that the oxidation potential is lower than the oxidation reaction potential of the positive electrode active material.

Further, in each of the above configurations, the second solvent has ether, which is a solvent having high reduction resistance, or at least one ether bond. The second solvent contains one of tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran.

Further, in each of the above configurations, the second solvent has a carbon chain having a length of 3 or more bonded to oxygen. By setting the length of the carbon chain bonded to oxygen to 3 or more, it can be said that the molecular weight around the CO bond is large, and it is possible to avoid the generation of gas during decomposition.

Further, in each of the above configurations, it is preferable that the second solvent is a cyclic ether because of its low viscosity. Alternatively, the second solvent is sulfide. Sulfide is one of the preferable sulfur-containing solvents because gas is unlikely to be generated during decomposition.

Further, in each of the above configurations, one of the features is that the sacrificial electrode is covered with a gel containing a second solvent to protect it. By covering at least a part of the sacrificial electrode with a gel containing the second solvent, the decomposition of the second solvent in the sacrificial electrode can be performed without the decomposition of the first solvent. For protection, it is preferable to cover the surface of the sacrificial electrode with a gel containing a second solvent.

According to the present invention, it is possible to reduce the decrease in the capacity of the lithium ion battery and maintain the capacity during the period of use.

In addition, a new configuration of the power storage device will be realized.

It is sectional drawing which shows one aspect of this invention. It is sectional drawing which shows one aspect of this invention. The figure for demonstrating the example of the power storage device. This is an example of an electronic device showing one aspect of the present invention. It is a figure which shows the cross section of an experimental sample. It is a figure which shows the experimental result. It is a figure which shows the experimental result. It is a figure which shows the experimental result. It is a figure which shows the experimental result. It is a figure which shows the equivalent circuit of the secondary battery at the time of CC charging, the relationship between the secondary battery voltage and time, and the relationship between the charging current and time of the secondary battery. It is a figure which shows the equivalent circuit of the secondary battery at the time of CCCV charging, the relationship between the secondary battery voltage and time, and the relationship between the charging current and time of the secondary battery. It is a figure which shows the relationship between the secondary battery voltage and time of a secondary battery at the time of CC discharge, and the relationship between the charge current and time of a secondary battery.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it is easily understood by those skilled in the art that the form and details thereof can be changed in various ways. Further, the present invention is not construed as being limited to the description contents of the embodiments shown below.

(Embodiment 1)
FIG. 1A is a schematic cross-sectional view showing an example of the power storage device of the present embodiment.

In FIG. 1A, the inside surrounded by the flat plate 10 and the sealing material 11 is filled with the electrolytic solution 17, and the sacrificial electrode layers 18a and 18b are provided on the electrodes electrically connected to the positive electrode 12. A positive electrode active material layer 13, a separator 14, a negative electrode active material layer 15, and a negative electrode 16 are laminated on the positive electrode 12. Further, an insulating sheet 19 is provided between the sacrificial electrode layer 18a and the other electrodes in order to prevent a short circuit between the sacrificial electrode layer 18a and the other electrodes. Further, the insulating sheet 19 may use the same material as the separator 14.

Activated carbon is provided as sacrificial electrode layers 18a and 18b on the electrodes electrically connected in contact with the positive electrode 12, and the capacity is restored by causing a reaction with the electrolytic solution 17. By taking the initiative in decomposing the electrolytic solution 17, the electrolytic solution 17 is decomposed while reducing damage to the positive electrode 12. With the configuration shown in FIG. 1A, it is possible to suppress a decrease in capacity while minimizing decomposition of the electrolytic solution in contact with the positive electrode.

The reason why activated carbon is used as the sacrificial electrode layers 18a and 18b is that the activated carbon is higher than the total surface area (product of specific surface area and weight) of the active material on the assumption that the decomposition of the electrolytic solution 17 occurs in proportion to the surface area. This is because the amount of decomposition on activated carbon is larger if the total surface area of the above is reached. Since decomposition on the active material also proceeds at the same time, the smaller the ratio between the total surface area of the active material and the total surface area of the activated carbon (the higher the weight ratio of the activated carbon), the more effective it is. However, if the ratio of activated carbon is high, the battery capacity will decrease.

Since the reaction occurs between the electrolytic solution 17 and the electrode, the sacrificial electrode layer can be arranged at a position not facing the positive electrode 12 and the negative electrode 16 as shown in FIG. 1 (A).

If the solvent added to the electrolytic solution 17 is a solvent having an oxidation reaction potential higher than the oxidation reaction potential of the positive electrode active material layer 13, a power storage device is used to some extent, and when the capacity decreases, the charging voltage is oxidized. Capacity can be added by charging at a voltage higher than the potential.

In the case of a solvent having an oxidation reaction potential lower than the oxidation reaction potential of the positive electrode active material layer 13, predoping to the negative electrode (lithium having a positive electrode capacity or more is inserted into the negative electrode) is automatically performed at the time of initial charging.

Additives may be added to decompose the electrolytic solution 17. Further, as an additive for the electrolytic solution, it is not preferable to generate gas, so it is preferable that gas is not easily generated and the carbon chain that binds to oxygen is long, and a solvent containing sulfur that the decomposition product is hard to gasify. Is also preferable. Specifically, as an additive for the electrolytic solution, an ether type such as THF, a cyclic ether, a thioether (sulfide) type or the like may be used.

Further, FIG. 1B shows another example in which the installation positions of the sacrificial electrode layers 18a and 18b are different from those in FIG. 1A. An example is shown in which the sacrificial electrode layer 18a is provided on the other surface of the positive electrode 12 which is not the surface on which the positive electrode active material layer is formed. Further, in FIG. 1B, the sacrificial electrode layer 18a is provided on the other surface, which is not the surface on which the positive electrode active material layer 13 in contact with the positive electrode 12 is formed. Further, the power storage device shown in FIG. 1B has a configuration of being wrapped with a sealing material 11.

Also in the power storage device shown in FIG. 1B, it is possible to suppress a decrease in capacity while minimizing decomposition of the electrolytic solution in contact with the positive electrode.

(Embodiment 2)
FIG. 2 shows a schematic cross-sectional view of the power storage device which is partially different from that of FIG. In this embodiment, an example in which the sacrificial electrode layer 18a is covered with gel is shown.

In FIG. 2, the inside surrounded by the flat plate 10 and the sealing material 11 is filled with the electrolytic solution 17, and the sacrificial electrode layer 18b is provided on the electrode electrically connected to the positive electrode 12. A positive electrode active material layer 13, a separator 14, a negative electrode active material layer 15, and a negative electrode 16 are laminated on the positive electrode 12.

In the present embodiment, as shown in FIG. 2, a sacrificial electrode 19 in contact with the positive electrode 12 is formed on the positive electrode 12, and a sacrificial electrode layer 18b covered with 18 g of gel is formed on the sacrificial electrode 19. The gel 18 g includes a polymer material to be gelled, and includes, for example, a silicone gel, an acrylic gel, an acrylonitrile gel, a polyethylene oxide gel, a polypropylene oxide gel, a fluorine polymer gel, and the like.

Further, the gel 18g contains a second solvent to prevent the sacrificial electrode layer 18b from coming into contact with the electrolytic solution 17 and decomposing. The second solvent has a lower reduction potential and oxidation potential than the solvent 17. Another feature of the second solvent is that the oxidation potential is lower than the oxidation reaction potential of the positive electrode active material.

The second solvent contained in 18 g of the gel has ether, which is a solvent having high reduction resistance, or at least one ether bond. The second solvent contained in 18 g of the gel contains one of tetrahydrofuran, 2-methyltetrahydrofuran and tetrahydropyran. Further, the second solvent contained in 18 g of the gel may have a carbon chain having a length of 3 or more bonded to oxygen. By setting the length of the carbon chain bonded to oxygen to 3 or more, it can be said that the molecular weight around the CO bond is large, and it is possible to avoid the generation of gas during decomposition. Further, it is preferable that the second solvent contained in 18 g of the gel is a cyclic ether because of its low viscosity. Alternatively, sulfide may be used as the second solvent contained in 18 g of the gel. Sulfide is one of the preferable sulfur-containing solvents because gas is unlikely to be generated during decomposition.

The power storage device shown in FIG. 2 is a laminated type, and although an example of a thin battery is shown, it may be a wound type. FIG. 3 shows an example of a winding type power storage device. The wound body 993 shown in FIG. 3A has a negative electrode 994, a positive electrode 995, and a separator 996.

The wound body 993 is formed by laminating a negative electrode 994 and a positive electrode 995 on top of each other with a separator 996 interposed therebetween, and winding the laminated sheet. A square storage battery is manufactured by covering the winding body 993 with a square sealing container or the like.

The number of layers of the negative electrode 994, the positive electrode 995, and the separator 996 may be appropriately designed according to the required capacity and the element volume. The negative electrode 994 is connected to the negative electrode current collector (not shown) via one of the lead electrode 997 and the lead electrode 998, and the positive electrode 995 is connected to the positive electrode current collector (not shown) via the other of the lead electrode 997 and the lead electrode 998. Is connected to.

The storage battery 990 shown in FIGS. 3B and 3C contains the above-mentioned winding body 993 inside the exterior body 991. A sacrificial electrode layer 999 is provided on the outside of the positive electrode 995. The sacrificial electrode layer 999 is preferably covered with a gel containing a second solvent. By providing the sacrificial electrode layer 999, it is possible to reduce the decrease in the capacity of the lithium ion battery and maintain the capacity during the period of use.

The wound body 993 has a lead electrode 997 and a lead electrode 998, and is impregnated with an electrolytic solution inside the exterior bodies 991 and 992. For the exterior bodies 991 and 992, a metal material such as aluminum or a resin material can be used. If a resin material is used as the material of the exterior bodies 991 and 992, the exterior bodies 991 and 992 can be deformed when an external force is applied, and a thin storage battery having flexibility can be produced.

It should be noted that this embodiment can be appropriately combined with other embodiments.

(Embodiment 3)
A new power storage device can be realized by using the sacrificial electrode layer obtained in the above embodiment.

New energy storage devices are, for example, for driving mobile information terminals such as mobile phones, hearing aids, imaging devices, vacuum cleaners, electric tools, electric shavers, lighting devices, toys, medical devices, robots, electric vehicles (hybrid vehicles), etc. It can be installed and used as a power source or a power source for power storage of buildings including houses.

In addition to supplying power to various parts, new power storage devices can be charged, so power can be stored from other power sources, and can also be used as a power storage device in power generation equipment such as solar cells. Can be used. Therefore, it leads to energy saving and CO _{2 reduction.}

FIG. 4A shows an example of a mobile phone. The mobile phone 7400 includes an operation button 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like, in addition to the display unit 7402 incorporated in the housing 7401. The mobile phone 7400 has a power storage device 7407.

FIG. 4B is a projection drawing illustrating an example of the appearance of the information processing apparatus 200. The information processing device 200 described in this embodiment includes an arithmetic unit 210, an input / output device 220, a display unit 230, and a power storage device 250.

The information processing device 200 has a communication unit, and the communication unit has a function of supplying information to the network and acquiring information from the network. Further, the communication unit 290 may be used to receive information delivered to a specific space, and image information may be generated based on the received information. For example, it is possible to receive and display teaching materials distributed in a classroom such as a school or a university and use them in a textbook. Alternatively, it is possible to receive and display materials distributed in a conference room of a company or the like.

Further, by providing the sacrificial electrode layer according to one aspect of the present invention on the current collector of the storage battery mounted on the wearable device as shown in FIG. 4C, the capacity decrease of the lithium ion battery can be reduced. The capacity can be maintained during the period of use.

For example, it can be mounted on a spectacle-type device 400 as shown in FIG. 4 (C). The spectacle-type device 400 has a frame 400a and a display unit 400b. By mounting the power storage device on the temple portion of the curved frame 400a, it is possible to obtain a spectacle-type device 400 having a good weight balance and a long continuous use time.

Further, it can be mounted on the headset type device 401. The headset-type device 401 has at least a microphone unit 401a, a flexible pipe 401b, and an earphone unit 401c. A power storage device can be provided in the flexible pipe 401b or in the earphone portion 401c.

In addition, it can be mounted on a device 402 that can be directly attached to the body. The power storage device 402b can be provided in the thin housing 402a of the device 402.

It can also be mounted on a device 403 that can be attached to clothing. The power storage device 403b can be provided in the thin housing 403a of the device 403.

Further, it can be mounted on the wristwatch type device 405. The wristwatch-type device 405 has a display unit 405a and a belt unit 405b, and a power storage device can be provided on the display unit 405a or the belt unit 405b.

On the display unit 405a, not only the time but also various information such as an incoming mail or a telephone call can be displayed.

Further, since the wristwatch type device 405 is a wearable device of a type that is directly wrapped around the wrist, a sensor for measuring the pulse, blood pressure, etc. of the user may be mounted. It is possible to accumulate data on the amount of exercise and health of the user and use it to maintain health.

It can also be mounted on the belt-type device 406. The belt-type device 406 has a belt portion 406a and a wireless power supply receiving portion 406b, and a power storage device can be mounted inside the belt portion 406a.

When the power storage device is mounted on a vehicle, a next-generation clean energy vehicle such as a hybrid electric vehicle (HEV), an electric vehicle (EV), or a plug-in hybrid vehicle (PHEV) can be realized.

It should be noted that this embodiment can be appropriately combined with other embodiments.

In order to improve the cycle characteristics, the following capacity increase experiments were conducted.

FIG. 5 shows a schematic cross-sectional view of the experimental sample.

In this embodiment, a sacrificial electrode 19 in contact with the positive electrode 12 and a sacrificial electrode layer 18b formed on the sacrificial electrode 19 are formed on the positive electrode 12.

Activated carbon is used as the sacrificial electrode layer 18b. The capacity is proportional to the voltage and becomes 26.7 mAh / g / V. Since the amount of the positive electrode supported corresponds to the high-capacity negative electrode, the amount of the positive electrode supported is very high, ignoring the electrode strength. The sacrificial electrode capacity is 2.3% of the total at 4.0 V with respect to the positive electrode capacity, and hardly contributes to the capacity.

Further, as a comparative example, a sacrificial electrode 19 and a cell (electrode size positive electrode: 20.5 cm ² negative electrode: 23.8 ^{cm 2} ) formed on the sacrificial electrode 19 without the sacrificial electrode layer 18b were prepared. PP (polypropylene) is used as the separator 14, and the electrolytic solution: 1.0 M LiPF ₆ / EC · DEC = 3: 7.

For the charge / discharge test, the charge / discharge tester TOSCAT (TOYO No. 2) of Toyo System was used. The measurement environment temperature was 25 ° C.

The results are shown in FIGS. 6, 7, and 8, respectively. FIG. 6A is charge / discharge data, and FIG. 6B is a graph showing the relationship between the number of cycles and the capacity. FIG. 7 is a transition of the discharge voltage after charging, and FIG. 8 is a bar graph showing the charge holding voltage and the discharge capacity of the capacity confirmation cycle.

From the discharge graph after CV charging (FIG. 7), the cycle can be performed with the plateau position almost unchanged until the CV charging voltage is 4.4V. When the CV charging voltage is 4.6V, the voltage gradually decreases, and when the CV charging voltage is 4.8V, the voltage decreases so that charging / discharging cannot be continued from the middle. Regarding the increase in capacity, the total charging time was set to 4 hours with 0.5C charging, but it was confirmed that the capacity increased slightly.

In addition, an experiment in which the charge cycle of a storage battery provided with a sacrificial electrode is measured and the difference in CV charging voltage is compared is shown below. Table 2 shows the sample configuration.

The specifications of each sample of the storage battery are as ^{follows: Laminate cell (electrode size positive electrode: 20.5 cm 2} negative electrode: 23.8 ^{cm 2} ), separator: PP (polypropylene), electrolyte: 1M LiTFSA EC: DEC = 1: 1 + LiPF6 2 wt% It was set to + VC 1 wt%.

For the charge / discharge test, the charge / discharge tester TOSCAT (TOYO No. 2) of Toyo System was used. The measurement environment temperature was 60 ° C.

The charging cycle measurement conditions were a charge / discharge rate of 0.5C, and the charging termination conditions were the four conditions shown in Table 3 below. In addition, a comparative example (ref) of a storage battery not provided with a sacrificial electrode was also subjected to charge cycle measurement.

From the cycle measurement result (FIG. 9) at 60 ° C., the CV charging voltage is 4.2 V at 60 ° C., so that the capacity retention rate is almost unchanged and the cycle can be performed. At 4.0 V, the capacitance retention rate gradually decreased, which was lower than the condition without the sacrificial electrode. Further, at 4.4 V, under the condition of 60 ° C., the voltage drops so that charging / discharging cannot be continued from the middle. In the configuration of the present application, it was confirmed that the capacity decrease during cycle charging / discharging can be suppressed by appropriately setting the charging voltage.

Here, CC (constant current) charging, CCCV charging, and CC discharging will be described.

<< CC charging >> CC charging will be described. CC charging is a charging method in which a constant current is passed through a secondary battery during the entire charging period, and charging is stopped when a predetermined voltage is reached. It is assumed that the secondary battery is an equivalent circuit having an internal resistance R and a secondary battery capacity C as shown in FIG. 10 (A). In this case, the secondary battery voltage V _B is the sum of the voltage V _C applied to the voltage V _R and the secondary battery capacity C according to the internal resistance R.

During CC charging, as shown in FIG. 10A, the switch is turned on and a constant current I flows through the secondary battery. During this time, since a current I is constant, the Ohm's law V R _{= R} × I, a voltage V _R is also constant according to the internal resistance R. On the other hand, the voltage V _C applied to the secondary battery capacity C increases with time. Therefore, the secondary battery voltage V _B rises with the passage of time.

Then, when the secondary battery voltage V _B reaches a predetermined voltage, for example, 4.1 V, charging is stopped. When the CC charging is stopped, as shown in FIG. 10B, the switch is turned off and the current I = 0. Therefore, the voltage _{V R} applied to the internal resistance R becomes 0V. _{Therefore, the secondary battery voltage V B} drops by the amount of the voltage applied to the internal resistance R.

FIG. 10 (C) shows an example of the _{secondary battery voltage V B} and the charging current during CC charging and after CC charging is stopped. It is shown that the secondary battery voltage V _B , which had been rising during CC charging, decreased slightly after CC charging was stopped.

<< CCCV charging >> Next, CCCV charging will be described. CCCV charging is a charging method in which first charging is performed to a predetermined voltage by CC charging, and then charging is performed until the current flowing by CV (constant voltage) charging decreases, specifically, until the final current value is reached. ..

During CC charging, as shown in FIG. 11A, the constant current power supply switch is turned on, the constant voltage power supply switch is turned off, and a constant current I flows through the secondary battery. During this time, since a current I is constant, the Ohm's law V R _{= R} × I, a voltage V _R is also constant according to the internal resistance R. On the other hand, the voltage V _C applied to the secondary battery capacity C increases with time. Therefore, the secondary battery voltage V _B rises with the passage of time.

Then, when the secondary battery voltage V _B reaches a predetermined voltage, for example, 4.3 V, the CC charge is switched to the CV charge. During CV charging, as shown in FIG. 11B, the constant voltage power supply switch is turned on, the constant current power supply switch is turned off, and the secondary battery voltage V _B becomes constant. On the other hand, the voltage V _C of the battery capacity C increases with time. Because it is _{V B = V R + V C} , by Ohm's law _V R = R × I, by reducing the current I flowing through the secondary battery, the voltage _{V R} applied to the internal resistance R is, with the lapse of time It becomes smaller. _{As the voltage V R} applied to the internal resistance R becomes smaller, the secondary voltage V _B becomes constant.

Then, when the current I flowing through the secondary battery reaches a predetermined current, for example, a current equivalent to 0.01 C, charging is stopped. When the CCCV charging is stopped, as shown in FIG. 11C, all the switches are turned off and the current I = 0. Therefore, the voltage _{V R} applied to the internal resistance R becomes 0V. However, since the voltage V _R applied to the internal resistance R by CV charging is sufficiently small, even run out of the voltage used to take the internal resistance R, the secondary battery voltage V _B is hardly lowered.

FIG. 11 (D) shows an example of the _{secondary battery voltage V B} and the charging current during the CCCV charging and after the CCCV charging is stopped. It is shown that the _{secondary battery voltage V B} hardly drops even when the CCCV charging is stopped.

<< CC discharge >> Next, CC discharge will be described. CC discharge is a discharge method in which a constant current is passed from a secondary battery during the entire discharge period, and the discharge is stopped when the secondary battery voltage VB reaches a predetermined voltage, for example, 2.5 V.

FIG. 12 shows an example of the secondary battery voltage V _{B and the discharge current during CC discharge.} It is shown that the secondary battery voltage V _{B drops as the discharge progresses.}

Next, the discharge rate and the charge rate will be described. The discharge rate is a relative ratio of the current at the time of discharge to the battery capacity, and is expressed in the unit C. In a battery having a rated capacity of X (Ah), the current corresponding to 1C is X (A). When discharged with a current of 2X (A), it is said to be discharged at 2C, and when discharged with a current of X / 5 (A), it is said to be discharged at 0.2C. The charging rate is also the same. When charged with a current of 2X (A), it is said to be charged with 2C, and when charged with a current of X / 5 (A), it is charged with 0.2C. It is said that

10: Flat plate 11: Encapsulant 12: Positive electrode 13: Positive electrode active material layer 14: Separator 15: Negative electrode active material layer 16: Negative electrode 17: Electrolyte 18a, 18b: Sacrificial electrode layer 18 g: Gel 19: Sacrificial electrode

Claims (3)

A first laminate having a positive electrode and a positive electrode active material layer,
A second laminate having a negative electrode and a negative electrode active material layer,
A separator between the positive electrode active material layer and the negative electrode active material layer facing each other,
A sacrificial electrode which contacts the surface of the positive electrode opposite to the surface of the positive electrode active said material layer is provided a positive electrode,
Contact with the sacrificial electrode, a sacrificial electrode layer and having an activated carbon,
The gel covering the sacrificial electrode layer and
Have,
Before SL sacrificial electrode layer is in contact with the electrolyte, and reacts with the electrolyte, a lithium ion secondary battery. In claim 1,
The gel is a lithium ion secondary battery containing a gelled polymer material. In claim 1 or 2,
The gel is a lithium ion secondary battery containing a solvent having a lower oxidation potential than the solvent contained in the electrolytic solution.

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