CN110658456B - Electric storage element and electric storage system - Google Patents

Electric storage element and electric storage system Download PDF

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CN110658456B
CN110658456B CN201910555217.1A CN201910555217A CN110658456B CN 110658456 B CN110658456 B CN 110658456B CN 201910555217 A CN201910555217 A CN 201910555217A CN 110658456 B CN110658456 B CN 110658456B
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voltage
storage element
power storage
power
range
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CN110658456A (en
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栗山博道
高井正巳
铃木荣子
中岛聪
柳田英雄
竹内重雄
菅野佑介
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Ricoh Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
    • G01R31/392—Determining battery ageing or deterioration, e.g. state of health
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
    • G01R31/396—Acquisition or processing of data for testing or for monitoring individual cells or groups of cells within a battery
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/48—Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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  • General Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Manufacturing & Machinery (AREA)
  • General Physics & Mathematics (AREA)
  • Inorganic Chemistry (AREA)
  • Secondary Cells (AREA)
  • Materials Engineering (AREA)
  • Tests Of Electric Status Of Batteries (AREA)
  • Charge And Discharge Circuits For Batteries Or The Like (AREA)
  • Battery Mounting, Suspending (AREA)

Abstract

The invention relates to an electric storage element and an electric storage system, and aims to provide a simple structure for monitoring the state of the electric storage element. A charge/discharge curve indicating a relationship between a residual capacity and an output voltage of an electric storage element according to the present invention includes a first stable region in which the output voltage is within a range of a predetermined error from a first voltage with respect to a change in the residual capacity within a first range, a second stable region, and a first slope region; in the second stable region, the output voltage is within a range that differs by a prescribed error from the second voltage that is greater than the first voltage with respect to a change in the remaining capacity within a second range; in the first tilt region, the output voltage changes from the first voltage to the second voltage with respect to a change in the remaining capacity in a range between the first range and the second range.

Description

Electric storage element and electric storage system
Technical Field
The present invention relates to an electric storage device and an electric storage system.
Background
The electric storage element is used as a power source for an edge device such as a wearable device, a hybrid vehicle, an electric vehicle, or the like. Among them, a nonaqueous electrolyte charge-discharge battery (lithium ion charge-discharge battery) having a high energy density has been widely used as an electric storage element.
An example of a device using the above-described power storage element is a power storage device using the power storage element as a battery in a battery pack provided in a hybrid vehicle. The power storage device is charged with a current supplied from the charging unit, and when the current reaches a predetermined voltage, the current in the charged battery supplies power to the motor (see, for example, japanese patent document 1 (japanese patent laid-open No. 2016-125882)).
The power storage device includes a positive electrode, a negative electrode, and a nonaqueous electrolyte, and the positive electrode or the negative electrode contains two or more active materials having different output characteristics with respect to a battery voltage. Therefore, the charging rate-voltage curve representing the relationship between the charging rate and the voltage of the power storage device has a plurality of regions having different voltage variation amounts, a plurality of relatively flat regions, and a region having a large inclination between the relatively flat regions.
In the region of the power storage device disclosed in patent document 1 in which the slope of the state of charge-voltage curve is large, the voltage changes with the change in the state of charge. Therefore, conventionally, when the power storage device is charged and discharged, it is necessary to obtain the output voltage and the remaining capacity in accordance with the shape of the state of charge-voltage curve, and therefore, a system for monitoring the state of the power storage device is complicated.
Disclosure of Invention
The purpose of the present invention is to monitor the state of an electric storage element with a simple configuration.
In order to achieve the above object, the present invention provides an electric storage element whose charge-discharge curve indicating a relationship between a residual capacity and an output voltage includes a first stable region in which the output voltage is within a range different by a predetermined error from a first voltage with respect to a change in the residual capacity within a first range, a second stable region, and a first inclined region; in the second stable region, the output voltage is within a range that differs by a prescribed error from the second voltage that is greater than the first voltage with respect to a change in the remaining capacity within a second range; in the first tilt region, the output voltage changes from the first voltage to the second voltage with respect to a change in the remaining capacity in a range between the first range and the second range.
The present invention has an effect of monitoring the state of the storage element with a simple configuration.
Drawings
Fig. 1 is a block diagram of a power storage system according to a first embodiment.
Fig. 2 is a charge/discharge graph showing an example of a correspondence relationship between an output voltage and a residual capacity.
Fig. 3 is a graph showing a relationship between a maximum current that can be supplied to the load portion and an output voltage.
Fig. 4 is a flowchart of the storage element discharge control method.
Fig. 5 is a block diagram of the power storage system according to the second embodiment.
Fig. 6 is a block diagram showing another example of the power storage system.
Fig. 7 is a block diagram of a power storage system according to a third embodiment.
Fig. 8 is a block diagram showing another example of the power storage system.
Fig. 9 is a block diagram of a power storage system according to a fourth embodiment.
Fig. 10 is a schematic diagram of the relationship between the maximum current that can be obtained by the dc power input and the output voltage.
Fig. 11 is a flowchart of a power storage element charging control method.
Detailed Description
Hereinafter, embodiments of the present invention will be described in detail.
[ first embodiment ]
Electricity storage system
An electric storage system including an electric storage element according to an embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a block diagram of a power storage system according to a first embodiment. As shown in fig. 1, power storage system 100A includes power storage element 110, monitoring unit 120, and switch units 130A and 130B. The power storage system 100A supplies power for charging the power storage element 110 to the load unit 200.
First, each member constituting the power storage system 100A will be described.
The storage element 110 is a chargeable/dischargeable nonaqueous electrolyte charge/discharge battery (lithium ion charge/discharge battery) and has a positive electrode, a negative electrode, and an electrolyte.
Next, charge/discharge characteristics of the power storage element 110 will be described. Fig. 2 is a charge/discharge curve showing an example of the relationship between the output voltage and the remaining capacity as the charge/discharge characteristics of the power storage element 110. As shown in fig. 2, the charge/discharge curve showing the relationship between the residual capacity and the output voltage of the power storage element 110 is a charge/discharge curve when constant current charge/discharge is performed at a current value of 0.2C in an output voltage range where the residual capacity of the power storage element 110 is 0% to 100% in an atmosphere of 25 ℃ ± 5 ℃. The output voltage when the remaining capacity of the storage element 110 is 0% is the output voltage when the discharge is completed (discharge end voltage), and the output voltage when the remaining capacity is 100% is the output voltage when the charge is fully charged (charge end voltage). The charge/discharge curve of the power storage element 110 shown in fig. 2 is a typical charge/discharge curve of the power storage element 110, and may vary depending on the type of the power storage element 110, the use environment, the current value, and the like.
As shown in fig. 2, the charge/discharge curve of the storage element 110 has a stable region a and an inclined region B connecting the stable region a. The storage element 110 repeats charge and discharge between the lower limit voltage VL and the upper limit voltage VH.
The lower limit voltage VL is an output voltage when the remaining capacity of the storage element 110 during discharge has decreased to a predetermined value (for example, 20%), and is an output voltage (for example, 2.7V) higher than the output voltage (for example, 2.5V) during full discharge.
The upper limit voltage VH is an output voltage when the remaining capacity of the power storage element 110 increases to a predetermined value (e.g., 80%) during charging, and is an output voltage (e.g., 3.7V) lower than a voltage (e.g., 4.2V) during full charging.
The stable region a is a region in which the change in output voltage is small with respect to the change in the remaining capacity of the storage element 110, and the inclination of the charge/discharge curve is relatively flat. In the present embodiment, a small change in the output voltage means that the error of the output voltage in the region is within a predetermined range, and the range of the error is preferably 5% or less, more preferably 3% or less, and still more preferably 1% or less.
The stable region a includes a first stable region a1, a second stable region a2, and a third stable region A3. The remaining capacities of the first stable region a1, the second stable region a2, and the third stable region A3 become higher in the order of the first stable region a1, the second stable region a2, and the third stable region A3. The output voltages of the first, second, and third stable regions a1, a2, and A3 become higher in the order of the first, second, and third stable regions a1, a2, and A3.
The first stable region a1 is a region where the change in remaining capacity is within a first range, and the error of the output voltage in this region is within a predetermined range with respect to the first voltage V1 which is lower than the lower limit voltage VL.
The second stable region a2 is a region where the change in remaining capacity is within a second range, and the error of the output voltage in this region is within a predetermined range with respect to the second voltage V2 which is higher than the lower limit voltage VL and lower than the upper limit voltage VH.
The third stable region a3 is a region where the change in remaining capacity is within a third range, and the error of the output voltage in this region is within a predetermined range with respect to the third voltage V3 that is higher than the upper limit voltage VH.
The inclined region B is a region in which the output voltage changes greatly with respect to the change in the remaining capacity of the power storage element 110, and is referred to as a region in which the inclination of the charge/discharge curve is large. In the present embodiment, a large change in the output voltage means that the slope of the charge-discharge curve is larger than the stable region a.
The inclined region B has a first inclined region B1 and a second inclined region B2.
The first inclined region B1 is a region between the first stabilization region a1 and the second stabilization region a 2. In the first inclined region B1, the range of variation in remaining capacity is a range between the first range and the second range. The range of variation of the remaining capacity in the first inclined region B1 is narrower than the first range and the second range.
The second inclined region B2 is a region formed between the second stabilization region a2 and the third stabilization region A3. In the second inclined region B2, the range in which the remaining capacity varies is a range between the second range and the third range. The range of variation of the remaining capacity in the second inclined region B2 is narrower than the second range and the third range.
In addition, neither an area having a residual capacity smaller than the first stable area a1 nor an area having a residual capacity larger than the third stable area A3 is included in the inclined area B. This is because the region where the remaining capacity is smaller than the first stable region a1 is a region where the output voltage drops to the discharge end voltage, and the region where the remaining capacity is larger than the third stable region A3 is a region where the output voltage rises to the charge end voltage, which are not regions connecting the regions where the output voltage is stable.
In the charge/discharge curve of the power storage element 110, when the power storage element 110 is discharged at the maximum current that can be supplied to the load unit 200, the output voltage of the power storage element 110 decreases by the voltage drop Δ V1 from the second voltage V2 to become the maximum drop voltage V2'.
Fig. 3 is a schematic diagram showing changes in output voltage when the storage element 110 is discharged with the maximum current that can be supplied to the load unit 200. As shown in fig. 3, when the voltage of the storage element 110 is the second voltage V2, and the storage element 110 is discharged at the maximum current Imax that can be supplied to the load unit 200, the voltage of the storage element 110 decreases by the voltage drop amount Δ V1 from the second voltage V2 to become the maximum drop voltage V2'.
As shown in fig. 2, the maximum falling voltage V2 'is higher than the lower limit voltage VL, which is between the first voltage V1 and the maximum falling voltage V2'. Therefore, the voltage difference between the first voltage V1 and the second voltage V2 is greater than the voltage drop Δ V1 of the second voltage V2.
In the charge/discharge curve of the power storage element 110 shown in fig. 2, two inclined regions B are included between the first stable region a1 and the third stable region A3, but three or more inclined regions B may be included.
In the charge/discharge curve of the power storage element 110 shown in fig. 2, when the power storage element 110 is charged at the maximum current (maximum charge current) at the time of charging, the voltage of the power storage element 110 increases from the second voltage V2 by the voltage increase Δ V2 to become the maximum increased voltage V2 ″. The voltage rise amount Δ V2 and the maximum rise voltage V2 ″ are factors to be considered when charging the electric storage element 110, and will be described in detail later.
By adjusting the electrode active material constituting the positive electrode or the negative electrode of the energy storage element 110, the energy storage element 110 can be controlled to exhibit charge and discharge characteristics such as the charge and discharge curve shown in fig. 2.
Here, a positive electrode, a negative electrode, and an electrolyte constituting the power storage element 110 will be described.
The positive electrode is first explained. The positive electrode may be formed of a positive electrode active material containing one or more species. The positive electrode may be formed of a single positive electrode active material, or may be formed of a plurality of positive electrode active materials having different output characteristics with respect to the output voltage.
The positive electrode active material is capable of insertion and desorption (operable) of lithium (Li) ions into and from the same negative electrode or non-electrolyte, and the voltage range (operating voltage range) of the storage element 110 accompanying insertion and desorption of Li ions differs depending on the type of material forming the positive electrode active material.
When the positive electrode is formed of a plurality of types of positive electrode active materials having different output characteristics, a material that undergoes an insertion/desorption reaction of Li ions while maintaining a state in which the plurality of types of positive electrode active materials having different Li content components in the primary particles coexist can be used as the positive electrode active material. The free energy of the positive electrode active material is kept constant during the insertion and detachment reaction of Li ions. Therefore, since the potential of the Li ion insertion/desorption reaction changes in a constant state, the output voltage of the storage element 110 can be maintained at a stable value within a certain range.
In addition, when the positive electrode is formed of a plurality of kinds of electrode active materials having different output characteristics, even if different positive electrode active materials are contained in the positive electrode, the different positive electrode active materials do not react with each other. Therefore, the insertion and desorption of lithium ions at the voltage during charge and discharge are exhibited in charge and discharge characteristics depending on the respective positive electrode active materials.
Examples of the positive electrode active material include inorganic compounds and organic compounds such as a composite oxide of a transition metal and lithium, a transition metal oxide, and a transition metal sulfide.
Examples of the composite oxide include lithium cobaltate (LiCoO)2) Lithium nickelate (LiNiO)2) Lithium manganate (LiMnO)2Or LiMn2O4) Lithium iron pyrophosphate (Li)2FeP2O7) Lithium nickel manganese oxide (LiNi)0.5Mn1.5O4) Lithium nickel vanadium oxide (LiNiVO)4) Lithium iron phosphate (LiFePO) having an olivine structure4) Lithium cobalt phosphate (LiCoPO)4) Lithium manganese phosphate (LiMnPO)4) Or lithium nickel phosphate (LiNiPO)4) (ii) a And lithium vanadium phosphate (Li) having NASICON structure3V2(PO4)3)。
Examples of transition metal oxides include MnO2MnO or V2O5。
Examples of transition metal sulfides include FeS or TiS.
In addition, the inorganic compound may be a compound obtained by replacing a transition metal with a different element as a positive electrode active material. For example, Li3V2(PO4)3Part of the structure of the vanadium phosphate can be modified.
Examples of the organic compound include a quinone compound, a disulfide compound, a diazine compound, a irradiated heterocyclic compound, a bronsted acid compound, or an organic radical compound.
Among the above inorganic compounds and organic compounds, Li is preferably used3V2(PO4)3As a positive electrode active material.
One of these positive electrode active materials may be used alone, or two or more of them may be used.
The positive electrode active material is formed into a particle shape by the above inorganic compound or organic compound, and the particles of the positive electrode active material are composed of secondary particles formed by aggregating a plurality of fine particles (primary particles) into a substantially spherical shape.
When the positive electrode is formed using a single positive electrode active material, Li is preferably used as the positive electrode active material3V2(PO4)3。Li3V2(PO4)3Or a compound in which a part of the structure of vanadium phosphate is modified.
The positive electrode active material is Li3V2(PO4)3In the case of (2), Li3V2(PO4)3The average particle diameter of the particles is preferably 3 μm or less. By reacting Li3V2(PO4)3The particles have an average particle diameter of 3 μm or less and can promote Li3V2(PO4)3Diffusion of Li ions within the particles.
Here, the average particle diameter refers to a volume average particle diameter based on the effective diameter, and is measured by, for example, a repetitive diffraction scattering method, a dynamic light scattering method, or the like.
When the positive electrode active material is Li3V2(PO4)3While Li3V2(PO4)3A part or all of the surface of the primary particles may be covered with carbon. In this case, the preferable coverage amount of carbon is Li3V2(PO4)32 wt% or more of (A). By covering Li with more than a certain degree of carbon3V2(PO4)3Primary particle surface capable of increasing Li 3V2(PO4)3The electron conductivity of the particles.
When the positive electrode active material is Li3V2(PO4)3When preferred, Li is3V2(PO4)3The particles have an average particle diameter of 3 μm or less and Li is coated with a predetermined amount of carbon or more3V2(PO4)3The surface of the particles. This can promote Li3V2(PO4)3Diffusion of Li ions in the particles and enhancement of Li3V2(PO4)3The electronic conductivity of the particles. Promotion of Li3V2(PO4)3The Li ions in the particles of (a) diffuse and the electron conductivity is improved, and the voltage drop when the Li ions are output to the load portion 200 is reduced, so that the voltage drop amount Δ V1 can be reduced. This increases the setting range of the lower limit voltage VL, and thus can ease the setting of the lower limit voltage VL.
The positive electrode is formed using a plurality of positive electrode active materials having different output characteristics with respect to the output voltage. In this case, it is preferable that the positive electrode includes at least one positive electrode active material having a stable region a at a potential higher by 4.0V than the oxidation-reduction potential of Li, and at least one positive electrode active material having a stable region a at a potential lower by 4.0V than the oxidation-reduction potential of Li.
Can use Li3V2(PO4)3The positive electrode active material has a stable region A at a potential 4.0V higher than the redox potential of Li.
LiFePO can be used4The positive electrode active material has a stable region A at a potential 4.0V lower than the redox potential of Li.
Therefore, when the positive electrode is formed using a plurality of types of positive electrode active materials having different output characteristics with respect to the output voltage, the positive electrode active material preferably contains Li3V2(PO4)3、LiFePO4Or LiNi0.5Mn1.5O4. As described above, the charge/discharge curve of the storage element 110 can have a plurality of stable regions a as shown in fig. 2.
The negative electrode is explained below. The anode may be formed to include one or more anode active materials. The negative electrode may be formed of a single negative electrode active material alone, or may be formed of a plurality of negative electrode active materials having different output characteristics with respect to the output voltage.
The negative electrode active material can insert and detach (can operate) Li ions into and from the same positive electrode or non-electrolyte as the positive electrode active material, and the voltage range (operating voltage range) of the storage element 110 accompanying the insertion and detachment of Li ions differs depending on the type of material forming the negative electrode active material.
When the negative electrode is formed of a plurality of negative electrode active materials having different output characteristics, a material which is the same as the positive electrode active material and which undergoes an insertion/desorption reaction of Li ions while maintaining a coexistence state of the plurality of negative electrode active materials having different Li content components in the primary particles may be used as the negative electrode active material. The free energy of the anode active material is kept constant during the insertion and extraction reaction of Li ions. Therefore, since the potential of the Li ion insertion/desorption reaction changes in a constant state, the output voltage of the storage element 110 can be maintained at a stable value within a certain range.
When the negative electrode is formed of a plurality of negative electrode active materials having different output characteristics, even if different negative electrode active materials are contained in the negative electrode, no reaction occurs between the different negative electrode active materials. Therefore, the insertion and desorption of Li ions at the voltage during charge and discharge are exhibited in charge and discharge characteristics depending on the respective negative electrode active materials, similarly to the positive electrode active material.
As the negative electrode active material, a material capable of occluding and releasing lithium ions can be used. Examples of such a material include a composite oxide of a transition metal and Li, a metal oxide, an alloy material, an inorganic compound such as a transition metal sulfide, a carbon material, an organic compound, and Li metal.
Examples of the composite oxides include LiMnO2、LiMn2O4Lithium titanate (Li4 Ti)5O12、Li2Ti3O7) Lithium manganese titanate (LiMn)1/2Ti3/2O4) Lithium cobalt titanate (LiCo)1/2Ti3/2O4) Lithium zinc titanate (LiZn)1/2Ti3/2O4) Lithium iron titanate (LiFeTiO)4) Lithium chromium titanate (LiCrTiO)4) Lithium strontium titanate (Li)2SrTi6O14) Barium lithium titanate (Li)2BaTi6O14) And the like.
Examples of metal oxides include TiO2、WO3、MoO2、MnO2、V2O5、SiO2SiO and SnO2And the like.
Examples of the alloy-based material include Al, Si, Sn, Ge, Pb, As, Sb, and the like.
Examples of transition metal sulfides include FeS and TiS.
Examples of the carbon material include graphite, non-graphitizable carbon, and graphitizable carbon.
As the inorganic compound, a compound in which a transition metal in the above-described composite oxide is substituted with a different element may be used.
Examples of the organic compound include quinone compounds, disulfide compounds, diazine compounds, irradiated heterocyclic compounds, buflomeric acid compounds, and organic radical compounds.
Among the above, lithium titanate or graphite is preferably used as the negative electrode active material.
One of these negative electrode active materials may be used alone, or two or more of them may be used.
The negative electrode active material is formed in a particle shape by the material into which the Li ion can be inserted and removed, and the particles of the negative electrode active material are secondary particles in which a plurality of fine particles (primary particles) are aggregated.
The average particle diameter of the particles of the negative electrode active material is preferably 3 μm or less. Similarly to the positive electrode active material, the average particle diameter of the particles of the negative electrode active material is reduced, whereby diffusion of Li ions in the particles can be promoted.
By promoting diffusion of Li ions, the voltage drop at the time of output to load unit 200 can be reduced, and voltage drop amount Δ V1 can be reduced. Thus, the setting range of the lower limit voltage VL is increased, and the setting of the lower limit voltage VL can be eased.
The electrolyte is explained below. The electrolyte may use a solid electrolyte or a non-aqueous electrolyte. The nonaqueous electrolyte is formed by dissolving an electrolyte salt in a nonaqueous solvent, and may be a liquid (electrolytic solution) or a gel-like electrolyte using a nonaqueous electrolyte as a matrix.
The nonaqueous electrolyte is formed by dissolving Li salt as a supporting salt in an organic solvent.
Cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran and dimethoxyethane; sulfur compounds such as ethylmethylsulfone and butane sultone; and a phosphorus compound such as triethyl phosphate or trioctyl phosphate as an organic solvent. The organic solvent may be one of the above solvents alone, or two or more of the solvents may be mixed.
As supporting salt, LiPF can be used6、LiBF4、LiClO4、LiAsF6、LiN(CF3SO2)2、LiCF3SO3、LiC4F9SO3And complex salts thereof, and the like.
In addition, the nonaqueous electrolyte may further contain a radical scavenger, a surfactant, a flame retardant, or the like in order to improve the characteristics of the power storage element 110.
The separator may be provided between the positive electrode and the negative electrode in the storage element 110. The separator is provided so as to be sandwiched between the electrodes, and has a function of separating the positive electrode from the negative electrode and holding an electrolyte. The separator may have the above-described functions, and for example, a film or a nonwoven fabric having a plurality of micropores formed of polyvinyl alcohol, polypropylene, or the like may be used.
As shown in fig. 1, the monitoring unit 120 is connected to the power storage element 110, and includes a voltage detection unit 121 and a control unit 122.
The voltage detector 121 is connected to the power storage element 110, and detects the voltage of the power storage element 110.
Control unit 122 is connected to voltage detection unit 121, switch units 130A and 130B, and load unit 200. The control unit 122 calculates the remaining capacity of the power storage element 110 corresponding to the voltage detected by the voltage detection unit 121. Control unit 122 controls charging and discharging of power storage element 110 such that the voltage of power storage element 110 falls within the range between lower limit voltage VL and upper limit voltage VH.
The control unit 122 includes a storage unit for storing a control program and various kinds of storage information, and an arithmetic unit for performing an operation based on the control program. The storage section may include a RAM, a ROM, or a register. The arithmetic unit includes a CPU and the like. The control unit 122 is realized by the arithmetic unit reading out and executing a control program or the like stored in the storage unit. The storage unit included in the control unit 122 may store information indicating charge/discharge characteristics as shown in fig. 2.
When the power storage element 110 is discharged, the control unit 122 sets the lower limit voltage VL of the power storage element 110 to a threshold value. When the output voltage of the power storage element 110 detected by the voltage detection unit 121 is lower than the lower limit voltage VL, the control unit 122 notifies the load unit 200 of an alarm signal indicating an overdischarge state.
The output end of the storage element 110 is connected to the load unit 200 through a power supply line L12. Electric power is supplied from the power storage element 110 to the negative charge unit 200.
As shown in fig. 1, switch unit 130A is provided on power supply line L11 at the input end of power storage element 110. Switch unit 130A connects power storage element 110 to power supply line L11 or disconnects power storage element 110 from power supply line L11.
The switch unit 130B is provided on a power supply line L12 at the output terminal of the storage element 110. Switch unit 130B connects power storage element 110 to power supply line L11 or disconnects power storage element 110 from power supply line L12.
Load unit 200 is a member that operates upon receiving power supply from power storage system 100A. Examples of the load unit 200 include an edge device such as a wearable device, an electronic device, a generator or a motor of a hybrid vehicle, an electric vehicle, a ship, an aircraft, or the like.
Load unit 200 is configured to start operating when the voltage supplied from power storage system 100A reaches a predetermined value (e.g., 4.2V) or more, and to stop operating when the voltage supplied from power storage system 100A reaches a predetermined value (e.g., 2.5V) or less. The voltage at the time of starting and stopping the operation of load unit 200 may be designed as appropriate according to the voltage value of the type of power storage element 110, the application of power storage system 100A, and the like.
The operation of power storage system 100A will be described below. The power storage element 110 is charged by supplying a dc current from the outside through the power supply line L11. At this time, switch unit 130A connects (turns on) power storage element 110 to power supply line L11, and switch unit 130B disconnects (turns off) power storage element 110 from power supply line L12. When the electric storage element 110 is discharged, a direct current flows from the electric storage element 110 to the load unit 200 via the electric power supply line L12, and electric power is supplied from the electric storage element 110 to the load unit 200. At this time, switch unit 130A disconnects power storage element 110 from power supply line L11, and switch unit 130B connects power storage element 110 to power supply line L12. Power storage system 100A performs charging and discharging of power storage element 110 in accordance with the remaining capacity of power storage element 110, the operating state of load unit 200, and the like.
Discharge control method
A method of controlling the discharge of the power storage element 110 with the power storage system 100A is described below with reference to fig. 4. In fig. 4, it is set that the electric power is charged to the surplus capacity corresponding to the upper limit voltage VH in the electric storage element 110.
Fig. 4 is a flowchart of a control method of controlling the discharge of the storage element 110. As shown in fig. 4, the power storage element 110 supplies power for charging the power storage element 110 to the load unit 200, and the voltage detector 121 detects the voltage V of the power storage element 110 0(step S11). During the discharge of the storage element 110, the voltage of the storage element 110 gradually decreases from the upper limit voltage VH to the lower limit voltage VL.
Voltage detection unit 121 continuously detects voltage V of power storage element 1100The detection may be performed at any time point, or may be performed at predetermined intervals. The voltage detection unit 121 may detect the voltage V of the storage element 110 when the storage element 110 is not discharged and power is supplied to the load unit 2000。
Then, controlUnit 122 determines voltage V of power storage element 110 detected by voltage detection unit 1210Whether or not it is smaller than the lower limit voltage VL (step S12).
In step S12, voltage V is set0Less than the lower limit voltage VL. In this case, the control portion 122 determines that the remaining capacity of the electric storage element 110 is less than a predetermined value (for example, 20%), and the electric storage element 110 is in an overdischarged state, and notifies the load portion 200 of an alarm signal (step S13). Thus, the load unit 200 can stop the operation of the load unit 200 after performing processing necessary to safely stop the power storage system 100A, such as storage of data stored in the load unit 200.
On the other hand, in step S12, voltage V of power storage element 1100When the voltage is equal to or higher than the lower limit voltage VL, the control unit 122 determines that the remaining capacity of the power storage element 110 is equal to or higher than a predetermined value (for example, 20%), and allows the power storage element 110 to discharge power, and the process returns to step S11.
Next, after step S13, control unit 122 stops the operation of power storage system 100A (step S14).
This makes it possible to stop the operation of the power storage system 100A after the operation of the load unit 200 is safely stopped.
The power storage system 100A configured as described above includes the power storage element 110 and the monitoring unit 120. The charge/discharge curve of the storage element 110 includes characteristics of a stable region a and an inclined region B as shown in fig. 2.
Therefore, in the present embodiment, the range of the remaining capacity of the power storage element 110 can be determined by monitoring which of the stable region a (a1, a2, A3) and the inclined region B (B1, B2) corresponds to the output voltage of the power storage element 110. Therefore, the present embodiment can monitor the state of the power storage element 110 with a simple configuration.
The state of the power storage element 110 mainly includes the remaining capacity and the output voltage of the power storage element 110. The state of the power storage element 110 may include whether it is in an overdischarged state or an overcharged state. Further, the state of the power storage element 110 may include the degree of deterioration of the power storage element 110, and the like.
In the present embodiment, the lower limit voltage VL is set to a threshold value for detecting excessive discharge of the power storage element 110 between the first voltage V1 and the second voltage V2 in the charge/discharge curve shown in fig. 2.
Therefore, the monitoring unit 120 of the present embodiment can detect whether or not the power storage element 110 is in the overdischarged state with a simple configuration by comparing the output voltage with the lower limit voltage VL only when the output voltage of the power storage element 110 is between the first voltage V1 and the second voltage V2.
When the output voltage of the storage element 110 is lower than the lower limit voltage VL, the power storage system 100A prohibits discharging. Therefore, when the power storage element 110 is discharged, the discharge of the power storage element 110 can be stopped in a state of being reduced to a predetermined value (for example, 20%) before the remaining capacity of the power storage element 110 is excessively reduced (or before the remaining capacity becomes 0%). In this way, power storage system 100A can suppress power storage element 110 from being in an overdischarged state.
Since the power storage system 100A notifies the load unit 200 of an alarm signal indicating an overdischarge state, the load unit 200 can avoid a failure such as an abrupt stop of operation due to an abrupt loss of electric power supplied from the power storage element 110.
The storage element 110 is a lithium ion charge-discharge battery, and repeated overdischarging tends to be easily deteriorated. On the other hand, in the present embodiment, the load on the power storage element 110 can be reduced, and therefore, deterioration of the power storage element 110 can be suppressed. Further, power storage system 100A can extend the service life of power storage element 110 by reducing the load on power storage element 110.
The power storage system 100A sets the voltage difference between the first voltage V1 and the second voltage V2 in the charge-discharge curve of the power storage element 110 to be greater than the voltage drop amount Δ V1 of the second voltage V2, and sets the lower limit voltage VL between the first voltage V1 and the maximum drop voltage V2'. In this way, although the voltage drop increases with the output to the load unit 200, the output voltage of the storage element 110 does not fall below the lower limit voltage VL. Therefore, even if the voltage drop increases, the control unit 122 can prevent the state in which the power storage element 110 erroneously recognizes that the remaining capacity is too low and transmits the alarm signal. Thereby suppressing erroneous detection of the state of charge of the electric storage element 110.
In this way, the power storage system 100A can monitor the state of the power storage element 110 with a simple configuration, and is therefore suitable for use as a power source for edge devices such as wearable devices, electronic devices, hybrid vehicles, electric vehicles, ships, aircrafts, and the like.
Although the lower limit voltage VL is set to the threshold value for stopping the over-discharge of the power storage element 110 in the present embodiment, an arbitrary voltage value may be set as the threshold value if the voltage is between the first voltage V1 and the second voltage V2, that is, within the first inclined region B1.
In the present embodiment, the storage element 110 is a lithium ion charge/discharge battery, but any chargeable/dischargeable battery may be used, such as an alkaline battery or a lead battery.
[ second embodiment ]
An electric storage system including an electric storage device according to an embodiment will be described with reference to the drawings. Hereinafter, components having the same functions as those of the above embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. The power storage system of the present embodiment is provided with a power generation element, a pre-storage element, and a power conversion unit in addition to the power storage system 100A of the first embodiment shown in fig. 1.
Fig. 5 is a block diagram of the power storage system according to the second embodiment. As shown in fig. 5, power storage system 100B includes power generation element 140A, first power storage element 150 as a pre-power storage element, power conversion unit 160, second power storage element 170, and monitoring unit 120. The power storage element 110 of the power storage system 100A according to the first embodiment is used as the second power storage element 170.
The power generation element 140A generates a direct current. As the power generation element 140A, a power generation element that recovers energy such as light and heat and converts the energy into direct current can be used. For example, a solar cell (solar power generation element), a thermoelectric conversion element, or the like can be used as the power generation element 140A.
The power generating element 140A is configured to obtain a predetermined output voltage. For example, when the power generating element 140A is a solar cell, a plurality of solar cells are arranged on one light receiving surface of the solar cell and connected in series, respectively, so that a predetermined output voltage is obtained. On the other hand, when the power generating element 140A is a thermoelectric conversion element, a plurality of thermoelectric conversion elements are connected in series to obtain a predetermined output voltage.
The output end of power generation element 140A is connected to the input end of first power storage element 150 via a power feed line L21, and supplies electric power to first power storage element 150.
First power storage element 150 is charged with the electric power output from power generation element 140A, and supplies electric power to power conversion unit 160. As the first electric storage element 150, for example, an electric double layer capacitor may be used. The capacitance of the first power storage element 150 can be appropriately selected according to the amount of power generation of the power generation element 140A, the amount of power consumption of the load unit 200, the operating time of the load unit 200, and the like.
The output terminal of first power storage element 150 is connected to the input terminal of power conversion unit 160 via a power supply line L22.
Power conversion unit 160 is a power conversion circuit for boosting or reducing the voltage of the power supplied from first power storage element 150. The output end of the power conversion unit 160 is connected to the input end of the second power storage element 170 via a power supply line L23.
As the power conversion unit 160, a DC/DC converter (a DC voltage-DC voltage conversion device) or the like can be used. Power conversion unit 160 converts the voltage input from first power storage element 150 into a voltage charged in accordance with second power storage element 170. For example, when the output voltage of first power storage element 150 is smaller than the voltage required by load unit 200, power conversion unit 160 boosts the electric power. When the output voltage of first power storage device 150 is high, power conversion unit 160 controls the output voltage so that the voltage at the time of charging second power storage device 170 does not exceed a predetermined upper limit voltage.
The second power storage element 170 is connected to the monitoring unit 120. The second power storage element 170 is the same as the power storage element 110 of the power storage system 100A of the first embodiment shown in fig. 1, and therefore, the description of the second power storage element 170 is omitted.
The capacitance of the second power storage element 170 may be appropriately selected according to the amount of power generation of the power generation element 140A, the amount of power consumption of the load unit 200, the operating time of the load unit 200, and the like.
The capacitance of the second power storage element 170 is preferably larger than the capacitance of the first power storage element 150. First power storage element 150 may be configured to temporarily store electric power generated by power generation element 140A, and second power storage element 170 may directly supply electric power to load unit 200. Therefore, it is preferable to set the capacity of the second power storage element 170 to be larger than the capacity of the first power storage element 150, in order to cope with the change in the power consumption or the operation time of the load unit 200. In addition, the second power storage element 170 is preferably capable of storing the transferred charge for a long time. Further, when first power storage element 150 is an electric double layer capacitor, second power storage element 170 is a lithium ion charge-discharge battery, and therefore first power storage element 150 tends to leak current more than second power storage element 170. In this way, even if the capacitance of the second power storage element 170 is increased, the second power storage element 170 can suppress the leakage current relatively compared to the first power storage element 150 configured by an electric double layer capacitor or the like.
The output terminal of the second power storage element 170 is connected to the input terminal of the load unit 200 via a power supply line L24.
Next, the operation of power storage system 100B will be described. The power generation element 140A converts energy from the outside into dc power. The dc power generated by power generation element 140A is supplied from power generation element 140A to first power storage element 150 via power supply line L21, and first power storage element 150 is charged. The electric power stored in first power storage element 150 is supplied to electric power conversion unit 160 via electric power supply line L22 and is stepped up or down.
Then, the electric power boosted or stepped down by the electric power conversion unit 160 is supplied to the second electric storage element 170 via the electric power feed line L23, and is stored in the second electric storage element 170. At this time, switch 130A is turned on, and switch 130B is turned off. When the second power storage element 170 is discharged, electric power is supplied from the second power storage element 170 to the load unit 200 via the electric power supply line L24. At this time, switch 130A is turned off, and switch 130B is turned on. Power storage system 100B performs charging and discharging of second power storage element 170 in accordance with the remaining capacity of second power storage element 170 or the operating state of load unit 200.
Since power conversion unit 160 is provided in power storage system 100B, the electric power supplied from first power storage element 150 is boosted or reduced to a constant voltage, that is, upper limit voltage VH by power conversion unit 160, and second power storage element 170 can be charged at a constant voltage.
In the present embodiment, as shown in fig. 6, the power conversion unit 160 may be further connected to the load unit 200 via a power supply line L25 in addition to the second power storage element 170. In this case, switch unit 130C is provided in power supply line L25. The control unit 122 turns off the switching units 130A and 130B and turns on the switching unit 130C. In this way, the power storage system 100B is directly supplied to the load unit 200 without storing the electric power generated by the power generation element 140A in the second power storage element 170, and is used by the load unit 200.
[ third embodiment ]
An electric storage system including an electric storage element according to an embodiment will be described below with reference to the drawings. Hereinafter, the same reference numerals are given to members having the same functions as those of the above embodiments, and detailed description thereof is omitted. The power storage system according to the present embodiment is provided with a converter in the power storage system 100B according to the second embodiment shown in fig. 5.
Fig. 7 is a block diagram of the power storage system according to the third embodiment. As shown in fig. 7, power storage system 100C includes power generation element 140B, inverter 180, first power storage element 150, power conversion unit 160, second power storage element 170, and monitoring unit 120.
The power generation element 140B generates an alternating current. As the power generation element 140B, a power generation element that recovers energy such as vibration and converts the energy into ac power can be used, and for example, a vibration power generation element or the like can be used.
The output end of power generation element 140B is connected to the input end of inverter 180 via power supply line L311.
Inverter 180 converts the power of the ac power supplied from power generation element 140B into dc power. An ac-dc converter may be used as the inverter 180.
The output terminal of inverter 180 is connected to the input terminal of first power storage element 150 via a power supply line L32.
The power supply lines L33 to L35 are the same as the power supply lines L22 to L24 of the power storage system 100B shown in fig. 5.
Here, the operation of the power storage system 100C will be described. The power generation element 140B converts energy from the outside into ac power. The ac power generated by power generation element 140B is supplied from power generation element 140B to inverter 180 via power supply line L31. After converter 180 converts the current from ac to dc, the dc current is supplied from converter 180 to first power storage element 150 via power supply line L32, and first power storage element 150 is charged. The electric power stored in first power storage element 150 is supplied to electric power conversion unit 160 via electric power supply line L33, and is stepped up or down. Then, the electric power boosted or stepped down by the electric power conversion unit 160 is supplied to the second electric storage element 170 via the electric power supply line L34, and is stored in the second electric storage element 170. At this time, switch 130A is turned on, and switch 130B is turned off. When the second power storage element 170 is discharged, electric power is supplied from the second power storage element 170 to the load unit 200 via the electric power supply line L35. At this time, switch 130A is turned off, and switch 130B is turned on. Power storage system 100C performs charging and discharging of second power storage element 170 in accordance with the remaining capacity of second power storage element 170 or the operating state of load unit 200.
As shown in fig. 8, in the present embodiment, in addition to the second power storage element 170, the power conversion unit 160 may be further connected to the load unit 200 via a power supply line L36. In this case, the switch unit 130C is provided in the power supply line L36. Control unit 122 turns off switches 130A and 130B and turns on switch 130C. Accordingly, power storage system 100C can supply the electric power generated by power generation element 140B directly to load unit 200 and use it by load unit 200 without being stored in second power storage element 170.
[ fourth embodiment ]
An electric storage system including an electric storage element according to an embodiment will be described with reference to the drawings. Hereinafter, the same reference numerals are given to members having the same functions as those of the above-described embodiment, and detailed description thereof is omitted. The power storage system according to the fourth embodiment can be used to control overcharge of the power storage element 110 when the power storage element 110 is charged in the power storage system 100A according to the first embodiment shown in fig. 1.
Fig. 9 is a block diagram of a power storage system according to a fourth embodiment. As shown in fig. 9, the power storage system 100D has the same configuration as the power storage system 100A of the first embodiment shown in fig. 1. The components constituting the power storage system 100D according to the present embodiment are the same as those of the power storage system 100A according to the first embodiment shown in fig. 1, and therefore, the description thereof is omitted.
The power storage system 100D of the present embodiment detects the upper limit voltage VH during charging of the power storage element 110 as a threshold for detecting overcharge in the second inclined region B2 at a stage of transition from the second voltage V2 to the third voltage V3 in the charge-discharge curve of the power storage element 110 shown in fig. 2.
In the charge/discharge curve of the power storage element 110 shown in fig. 2, when the power storage element 110 is charged with the maximum current that can be obtained by the input of the dc power supply, the voltage of the power storage element 110 increases by the voltage increase Δ V2 from the second voltage V2 to become the maximum increased voltage V2 ″.
Fig. 10 is a schematic diagram showing a relationship between output voltages when the power storage element 110 is charged with the maximum current that can be obtained by input from the dc power supply. As shown in fig. 10, when the voltage of the power storage element 110 is the second voltage V2, if the power storage element 110 is charged with the maximum current Imax that can be obtained from the dc power supply input, the voltage of the power storage element 110 increases by the voltage increase Δ V2 from the second voltage V2, and becomes the maximum increased voltage V2 ″.
As shown in fig. 2, the maximum rising voltage V2 "is lower than the upper limit voltage VH, which is located between the maximum rising voltage V2" and the third voltage V3. Therefore, the voltage difference between the second voltage V2 and the third voltage V3 is greater than the voltage rise Δ V2 of the second voltage V2.
When charging the power storage element 110, the control unit 122 shown in fig. 9 sets the upper limit voltage V H of the power storage element 110 to the threshold value. When the voltage of power storage element 110 detected by voltage detection unit 121 exceeds upper limit voltage VH, control unit 122 stops charging of power storage element 110 or operation of power storage device 100C.
Charging control method
Next, a method of controlling charging of the power storage element 110 with the power storage system 100D will be described with reference to fig. 11. In fig. 11, it is set that the electric storage element 110 is discharged to a residual capacity corresponding to the residual capacity being the lower limit voltage VL.
Fig. 11 is a flowchart of a control method of controlling charging of the electric storage element 110. As shown in fig. 11, the voltage detector 121 detects the voltage V0 of the electric storage element 110 while supplying electric power to the electric storage element 110 for charging (step S21). During charging of the power storage element 110, the voltage of the power storage element 110 gradually increases.
The voltage detector 121 continuously detects the voltage V of the electric storage element 1100However, the detection may be performed at any time or at predetermined intervals. The voltage detection unit 121 may detect the voltage V of the power storage element 110 when the power storage element 110 is not charged0。
Next, the control unit 122 determines the voltage V of the electric storage element 110 detected by the voltage detection unit 121 0Whether or not it is larger than the upper limit voltage VH (step S22).
In step S22, when the voltage V is lower than the predetermined value0If the voltage is higher than the upper limit voltage VH, the control unit 122 determines that the remaining capacity of the power storage element 110 exceeds a predetermined value (for example, 80%), and the power storage element 110 is in an overcharged state. In this case, control unit 122 turns off switch unit 130A and stops charging of power storage element 110 (step S23). This stops charging of the power storage element 110.
In contrast, in step S22, if the voltage V of the electric storage element 110 is low0If it is not higher than upper limit voltage VH, control unit 122 determines that storage element 110 has not reached the overcharged state, and returns to step S21.
In this way, in the power storage system 100D, it is possible to determine whether or not to overcharge only when the output voltage of the power storage element 110 is in the second inclined region B2. Therefore, in the present embodiment, it is not necessary to precisely detect the state of charge, and overcharge of the power storage element 110 can be suppressed with a simple configuration.
Although the upper limit voltage VH is set to the threshold value at which the overcharge of the power storage element 110 is stopped in the present embodiment, an arbitrary voltage value may be set as the threshold value if it is between the second voltage V2 and the third voltage V3, that is, within the second inclined region B2.
This embodiment may be combined with the method of controlling the discharge of the power storage element 110 of the power storage system 100A according to the first embodiment shown in fig. 1 to perform charge and discharge.
The present embodiment can be controlled in the same manner when charging the second power storage element 170 of the power storage system 100B according to the second embodiment shown in fig. 5 and the power storage system 100C according to the third embodiment shown in fig. 7.
The embodiments described above are merely examples of the disclosure, and the present invention is not limited to these embodiments. The above embodiments may be implemented in other various forms, and various modifications such as combinations, omissions, substitutions, and changes may be made without departing from the spirit of the invention. These embodiments and modifications are included in the scope and gist of the present invention, and are also included in the invention described in the claims and the equivalent scope thereof.

Claims (12)

1. An electric storage element whose charge-discharge curve representing a relationship between a residual capacity and an output voltage includes a first stable region, a second stable region, and a first inclined region,
in the first stable region, the output voltage is within a range of a prescribed error from the first voltage with respect to a change in the remaining capacity within a first range;
in the second stable region, the output voltage is within a range that differs by a prescribed error from a second voltage that is greater than the first voltage with respect to a change in the remaining capacity within a second range;
In the first slope region, the output voltage changes from the first voltage to the second voltage with respect to a change in the remaining capacity in a range between the first range and the second range, wherein a difference between the first voltage and the second voltage is larger than a voltage drop amount when a load is discharged at a maximum current, and a threshold value for detecting an excessive discharge is set between the first voltage and a maximum drop voltage by which the output voltage drops from the second voltage to the maximum drop voltage.
2. The power storage element according to claim 1, wherein the first voltage is less than a lower limit voltage at which discharge is prohibited.
3. The power storage element according to claim 2, wherein a range between the first range and the second range is narrower than the first range and the second range.
4. The power storage element according to claim 1, further comprising a third stable region and a second inclined region,
in the third stable region, the output voltage is within a range that is different by the prescribed error from a third voltage that is larger than the second voltage with respect to a change in the remaining capacity in a third range;
In the second tilt region, the output voltage is changed from the second voltage to the third voltage with respect to a change in remaining capacity in a range between the second range and the third range.
5. The power storage element according to claim 4,
a difference between the second voltage and the third voltage is larger than a voltage rise amount at the time of charging at a maximum current,
setting a threshold value for detecting overcharge in the second inclination area.
6. The power storage element according to claim 4 or 5, wherein the third voltage is larger than an upper limit voltage at which charging is prohibited.
7. The power storage element according to claim 1, wherein the element has a positive electrode and a negative electrode, and one or both of the positive electrode and the negative electrode has one or more electrode active materials.
8. An electricity storage system comprising the electricity storage element according to claim 2 or 3 and a monitoring portion for detecting charge and discharge when the output voltage is less than the lower limit voltage.
9. The power storage system according to claim 8, wherein the monitoring section has,
a voltage detection unit for detecting the output voltage of the electric storage element; and the number of the first and second groups,
a control section for notifying an alarm signal to a load section supplied with electric power by the electric storage element when the excessive discharge is detected.
10. The power storage system according to claim 8,
further comprising the steps of (a) further comprising,
a power generating element; and the number of the first and second groups,
a preliminary electric storage element for charging with the electric power generated by the power generation element and discharging the charged electric power,
the preliminary electric storage element supplies electric power to the electric storage element.
11. The power storage system according to claim 10, further comprising a power conversion unit connected to the preliminary power storage element, for supplying the electric power supplied from the preliminary power storage element to the power storage element after being boosted or reduced in voltage.
12. The electrical storage system according to claim 10, further comprising an inverter connected to the power generation element and configured to supply the electric power generated by the power generation element to the auxiliary electrical storage element after changing the electric power from ac to dc when the electric current generated by the power generation element is ac.
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