JP2020005467A - Power storage element and power storage system - Google Patents

Abstract

To monitor the state of a power storage element with a simple configuration.SOLUTION: In a charge-discharge curve indicating the relationship between the remaining capacity and an output voltage, a power storage element has: a first stable area in which the output voltage falls within a predetermined error range from a first voltage with respect to a change in remaining capacity in a first range; a second stable area in which the output voltage falls within the predetermined error range from a second voltage being a higher voltage than the first voltage with respect to a change in remaining capacity in a second range; and a first inclined area in which the output voltage changes from the first voltage to the second voltage with respect to a change in remaining capacity within a range between the first range and the second range.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a power storage element and a power storage system.

  2. Description of the Related Art Electric storage elements are used as power sources for edge devices such as wearable devices, hybrid vehicles, electric vehicles, and the like. Among them, non-aqueous electrolyte secondary batteries (lithium ion secondary batteries) having a high energy density are widely used as power storage elements.

  As such a power storage element, for example, there is a power storage device used as a battery in a battery pack provided in a hybrid vehicle. The power storage device is charged to a predetermined voltage by a current supplied from a charging unit, and the current charged in the battery is supplied to a motor (for example, see Patent Document 1).

  The power storage device has a positive electrode, a negative electrode, and a non-aqueous electrolyte, and the positive electrode or the negative electrode contains two or more active materials having different output characteristics with respect to battery voltage. Therefore, the charging rate vs. voltage curve indicating the relationship between the charging rate and the voltage of the power storage device includes a plurality of regions having different voltage change amounts, and includes a plurality of relatively flat regions and a plurality of relatively flat regions. And a relatively large slope region to be formed.

  Here, in the power storage device of Patent Literature 1, in a region where the charge rate versus voltage curve of the power storage device has a relatively large slope, the voltage changes in a slope in accordance with the charge rate. For this reason, conventionally, when charging and discharging a power storage device, it is necessary to obtain the output voltage and the remaining capacity in accordance with the shape of the charging rate versus voltage curve, and a system for monitoring the state of the power storage device is complicated. It becomes.

  An object of one embodiment of the present invention is to monitor a state of a power storage element with a simple configuration.

  In the charge / discharge curve showing the relationship between the remaining capacity and the output voltage, the power storage element according to one embodiment of the present invention has a structure in which the output voltage changes by a predetermined error from the first voltage with respect to a change in the remaining capacity in a first range. A first stable region that falls within a range of; and a change in the remaining capacity within a second range, wherein the output voltage falls within a range of the predetermined error from a second voltage that is a voltage higher than the first voltage. A second stable region, and a first inclined region in which 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. And

  According to one embodiment of the present invention, the state of a power storage element can be monitored with a simple structure.

1 is a block diagram illustrating a configuration of a power storage system according to a first embodiment. FIG. 4 is a diagram showing an example of a charge / discharge curve showing a relationship between an output voltage and a remaining capacity. FIG. 4 is an explanatory diagram illustrating a relationship between a maximum current that can be supplied to a load unit and an output voltage. 4 is a flowchart illustrating a method for controlling discharge of a storage element. FIG. 9 is a block diagram illustrating a configuration of a power storage system according to a second embodiment. It is a block diagram showing an example of other composition of a power storage system. FIG. 13 is a block diagram illustrating a configuration of a power storage system according to a third embodiment. It is a block diagram showing an example of other composition of a power storage system. FIG. 14 is a block diagram illustrating a configuration of a power storage system according to a fourth embodiment. FIG. 4 is an explanatory diagram illustrating a relationship between a maximum current that can be input from a DC power supply and an output voltage. 4 is a flowchart illustrating a method for controlling charging of a storage element.

  Hereinafter, embodiments of the present invention will be described in detail.

[First Embodiment]
(Power storage system)
A power storage system including a power storage element according to one embodiment will be described with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of the power storage system according to the first embodiment. As shown in FIG. 1, the power storage system 100A includes a power storage element 110, a monitoring unit 120, and switch units 130A and 130B. Power storage system 100 </ b> A supplies power charged in power storage element 110 to load unit 200.

  Each member constituting power storage system 100A will be described.

  The storage element 110 is a chargeable / dischargeable non-aqueous electrolyte secondary battery (lithium ion secondary battery), and has a positive electrode, a negative electrode, and an electrolyte.

  The charge and discharge characteristics of the storage element 110 will be described. FIG. 2 shows an example of a charge / discharge curve showing the relationship between the remaining voltage and the output voltage as the charge / discharge characteristics of the storage element 110. As shown in FIG. 2, the charge / discharge curve showing the relationship between the remaining capacity and the output voltage of the storage element 110 is such that the remaining capacity of the storage element 110 is 0.2 C at 25 ° C. ± 5 ° C. It is a charge / discharge curve when performing constant current charge / discharge in the output voltage range from 0% to 100%. The output voltage when the remaining capacity of the storage element 110 is 0% is the output voltage at the time of complete discharge (discharge end voltage), and the output voltage when the remaining capacity is 100% is the output voltage at the time of full charge. (Charging end voltage). The charge / discharge curve of power storage element 110 shown in FIG. 2 is a typical charge / discharge curve of power storage element 110, and may vary depending on the type of power storage element 110, use environment, current value, or the like.

  As shown in FIG. 2, the charge / discharge curve of power storage element 110 has stable region A and inclined region B connecting between stable regions A. The storage element 110 is repeatedly charged and discharged 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 decreases to a predetermined value (for example, 20%) at the time of discharging, and is higher than the output voltage at the time of complete discharging (for example, 2.5 V). (For example, 2.7 V).

  The upper limit voltage VH is an output voltage when the remaining capacity of the storage element 110 increases to a predetermined value (for example, 80%) during charging, and is lower than the voltage (for example, 4.2 V) at the time of full charge (for example, 4.2 V). For example, 3.7V).

  The stable region A is a region where the change in the output voltage is small with respect to the change in the remaining capacity of the power storage element 110, and is a region where the slope 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, preferably 3% or less. Is more preferable and 1% or less is further preferable.

  The stable area A has a first stable area A1, a second stable area A2, and a third stable area A3. The remaining capacities of the first stable area A1, the second stable area A2, and the third stable area A3 increase in the order of the first stable area A1, the second stable area A2, and the third stable area A3. The output voltages of the first stable region A1, the second stable region A2, and the third stable region A3 increase in the order of the first stable region A1, the second stable region A2, and the third stable region A3.

  The first stable region A1 is a region where the change in the remaining capacity is in a first range, and is a region where the error of the output voltage in the region is within a predetermined range with respect to the first voltage V1 lower than the lower limit voltage VL. is there.

  The second stable region A2 is a region in which the change in the remaining capacity is in the second range. The second stable region A2 has a predetermined output voltage error in the region that is higher than the lower limit voltage VL and lower than the upper limit voltage VH. This is an area within the range.

  The third stable region A3 is a region in which the change in the remaining capacity is in a third range, and in which the error of the output voltage in the region is within a predetermined range with respect to the third voltage V3 higher than the upper limit voltage VH. is there.

  The slope region B is a region where the change in the output voltage is large with respect to the change in the remaining capacity of the power storage element 110, and is a region where the slope of the charge and 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 that in the stable region A.

  The inclined region B has a first inclined region B1 and a second inclined region B2.

  The first inclined area B1 is an area formed between the first stable area A1 and the second stable area A2. In the first inclined region B1, the range of the change in the remaining capacity is a range between the first range and the second range. The range of the change in 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 stable region A2 and the third stable region A3. In the second inclined region B2, the range of the change in the remaining capacity is a range between the second range and the third range. The range of change in the remaining capacity in the second inclined region B2 is narrower than the second range and the third range.

  Note that neither the region where the remaining capacity is higher than the first stable region A1 nor the region where the remaining capacity is lower than the third stable region A3 is not included in the inclined region B. This is a region where the remaining voltage is higher than the first stable region A1 is a region where the output voltage drops to the discharge termination voltage, and a region where the remaining voltage is lower than the third stable region A3 is where the output voltage is lower than the charge termination voltage. This is because these regions are not regions that connect regions where the output voltage is stable.

  In the charge / discharge curve of the storage element 110, when the storage element 110 discharges the maximum current that can be supplied to the load unit 200, the output voltage of the storage element 110 drops from the second voltage V2 by a voltage drop ΔV1, and V2 '.

  FIG. 3 is an explanatory diagram illustrating a change in the output voltage when the maximum current that can be supplied to the load unit 200 is discharged from the storage element 110. As shown in FIG. 3, when the storage element 110 discharges the maximum current Imax that can be supplied to the load section 200 when the voltage of the storage element 110 is the second voltage V2, the voltage of the storage element 110 is changed from the second voltage V2 to the voltage The voltage drops by the amount of the drop ΔV1 to become the maximum falling voltage V2 ′.

  As shown in FIG. 2, the maximum falling voltage V2 'is higher than the lower limit voltage VL, and the lower limit voltage VL 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 larger than the voltage drop ΔV1 of the second voltage V2.

  Note that the charge and discharge curve of power storage element 110 shown in FIG. 2 includes two inclined regions B between first stable region A1 and third stable region A3, but may include three or more.

  In the charge / discharge curve of power storage element 110 shown in FIG. 2, when the power storage element 110 is charged with the maximum current (maximum charging current) when charging, the voltage of power storage element 110 increases from second voltage V2 by a voltage increase ΔV2 Rises to the maximum rising voltage V2 ″. The voltage rise ΔV2 and the maximum rise voltage V2 ″ are to be considered when charging the electric storage element 110, and thus will be described in detail later.

  In order for the storage element 110 to exhibit charge / discharge characteristics such as the charge / discharge curve in FIG. 2, control can be performed by adjusting the electrode active material forming the positive electrode or the negative electrode of the storage element 110.

  The positive electrode, the negative electrode, and the electrolyte included in the storage element 110 will be described.

  The positive electrode will be described. The positive electrode can be formed including one or more positive electrode active materials. 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 output voltage.

  The positive electrode active material is capable of inserting and removing lithium (Li) ions with respect to the same negative electrode and non-electrolyte (operable), and is capable of inserting and removing Li ions depending on the type of material forming the positive electrode active material. The resulting voltage range (operating voltage range) of the storage element 110 is different.

  When the positive electrode is formed of a plurality of positive electrode active materials having different output characteristics, as the positive electrode active material, a plurality of positive electrode active materials having different Li-containing compositions coexist in the primary particles while inserting and removing Li ions. A material in which a separation reaction proceeds can be used. In the process in which the Li ion insertion / desorption reaction proceeds, the free energy of the positive electrode active material is kept constant. Therefore, the potential of the Li ion insertion / desorption reaction remains constant, so that the output voltage of the storage element 110 can maintain a stable value within a certain range.

  Further, when the positive electrode is formed of a plurality of electrode active materials having different output characteristics, the different positive electrode active materials do not react with each other even if the positive electrode contains different positive electrode active materials. Therefore, insertion / removal of lithium ions at the voltage during charge / discharge appears in charge / discharge characteristics depending on the respective positive electrode active materials.

  Examples of the positive electrode active material include a composite oxide of a transition metal and lithium, an inorganic compound such as a transition metal oxide or a transition metal sulfide, and an organic compound.

As the composite oxide, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMnO ₂ or LiMn ₂ O ₄ ), lithium iron pyrophosphate (Li ₂ FeP ₂ O ₇ ), nickel manganese Lithium oxide (LiNi _0.5 Mn _1.5 O ₄ ), lithium vanadium nickelate (LiNiVO ₄ ); lithium iron phosphate (LiFePO ₄ ), lithium cobalt phosphate (LiCoPO ₄ ), lithium manganese phosphate (LiMnPO ₄ ) having an olivine structure ) Or lithium nickel phosphate (LiNiPO ₄ ); lithium vanadium phosphate having a NASICON structure (Li ₃ V ₂ (PO ₄ ) ₃ ).

Examples of the transition metal oxide include MnO ₂ , MnO, and V ₂ O ₅ .

  Examples of the transition metal sulfide include FeS and TiS.

Note that, as the above-mentioned inorganic compound, a compound in which a transition metal is replaced with a different element may be used as the positive electrode active material. For example, Li ₃ V ₂ (PO ₄ ) ₃ may modify part of the structure of vanadium phosphate.

  Examples of the organic compound include a quinone compound, a disulfide compound, a diazine compound, a radialene compound, a rubeanic acid compound, and an organic radical compound.

As the positive electrode active material, among the above-mentioned inorganic compounds and organic compounds, it is preferable to use Li ₃ V ₂ (PO ₄ ) ₃ .

  One of these positive electrode active materials may be used alone, or two or more thereof may be used.

  The positive electrode active material is formed into particles using the above-described inorganic compound or organic compound, and the particles of the positive electrode active material are formed into a plurality of fine particles (primary particles) by agglomeration. Consists of particles.

When the positive electrode is formed of a single positive electrode active material, it is preferable to use Li ₃ V ₂ (PO ₄ ) ₃ as the positive electrode active material. Li ₃ V ₂ (PO ₄ ) ₃ may be a compound obtained by partially modifying the structure of vanadium phosphate.

When the positive electrode active material is Li ₃ V ₂ (PO ₄ ) ₃ , the average particle diameter of the particles of Li ₃ V ₂ (PO ₄ ) ₃ is preferably 3 μm or less. By setting the average particle diameter of the Li ₃ V ₂ (PO ₄ ) ₃ particles to 3 μm or less, diffusion of Li ions in the Li ₃ V ₂ (PO ₄ ) ₃ particles can be promoted.

  The average particle diameter refers to a volume average particle diameter based on an effective diameter, and the average particle diameter is measured by, for example, a laser diffraction / scattering method or a dynamic light scattering method.

When the positive electrode active material is Li ₃ V ₂ (PO ₄ ) ₃ , part or all of the surface of the primary particles of Li ₃ V ₂ (PO ₄ ) ₃ may be coated with carbon. In this case, the coating amount of carbon is preferably 2 wt% or more based on the weight of Li ₃ V ₂ (PO ₄ ) ₃ . By coating the surface of the primary particles of Li ₃ V ₂ (PO ₄ ) ₃ with a certain amount or more of carbon, the electron conductivity of the particles of Li ₃ V ₂ (PO ₄ ) ₃ can be improved.

When the positive electrode active material is Li ₃ V ₂ (PO ₄ ) ₃ , the average particle diameter of the particles of Li ₃ V ₂ (PO ₄ ) ₃ is 3 μm or less, and the particles of Li ₃ V ₂ (PO ₄ ) ₃ are Is more preferably coated with a certain amount or more of carbon. Thereby, the diffusion of Li ions in the particles of Li ₃ V ₂ (PO ₄ ) ₃ can be promoted, and the electron conductivity of the particles of Li ₃ V ₂ (PO ₄ ) ₃ can be improved. The promotion of the diffusion of Li ions in the particles of Li ₃ V ₂ (PO ₄ ) ₃ and the improvement of the electron conductivity can reduce the voltage drop at the time of output to the load unit 200 and reduce the voltage drop ΔV1. Thereby, the setting range of the lower limit voltage VL is expanded, so that the setting of the lower limit voltage VL can be relaxed.

  It is assumed that the positive electrode is formed of a plurality of positive electrode active materials having different output characteristics with respect to the output voltage. In this case, the positive electrode includes at least one positive electrode active material having a stable region A at a potential noble than 4.0 V with respect to the oxidation-reduction potential of Li, and a positive electrode having a stability region A higher than 4.0 V with respect to the redox potential of Li. It is preferable to have at least one type of positive electrode active material having a stable region A at a low potential.

As the positive electrode active material, Li ₃ V ₂ (PO ₄ ) ₃ can be used as the positive electrode active material having the stable region A at a potential nobler than 4.0 V with respect to the oxidation-reduction potential of Li.

LiFePO ₄ can be used as the positive electrode active material having the stable region A at a potential lower than 4.0 V with respect to the oxidation-reduction potential of Li.

Therefore, when the positive electrode is formed of a plurality of positive electrode active materials having different output characteristics with respect to the output voltage, the positive electrode active material includes Li ₃ V ₂ (PO ₄ ) ₃ and LiFePO ₄ or LiNi _0.5 Mn _1.5 O ₄ . It is preferred to include. Thereby, the charge / discharge curve of power storage element 110 can have a plurality of stable regions A as shown in FIG.

  The negative electrode will be described. The negative electrode can be formed including one or more negative electrode active materials. The negative electrode may be formed of a single negative electrode active material, or may be formed of a plurality of negative electrode active materials having different output characteristics with respect to output voltage.

  Like the positive electrode active material, the negative electrode active material is capable of inserting and removing (operating) Li ions with and from the same positive electrode and non-electrolyte, and inserts Li ions according to the type of material forming the negative electrode active material. The voltage range (operating voltage range) of the power storage element 110 generated due to the detachment is different.

  When the negative electrode is formed of a plurality of negative electrode active materials having different output characteristics, as in the case of the positive electrode active material, the negative electrode active material takes a form in which a plurality of negative electrode active materials having different Li-containing compositions coexist in the primary particles. However, a material in which the Li ion insertion / desorption reaction proceeds can be used. In the process of the Li ion insertion / desorption reaction proceeding, the free energy of the negative electrode active material is kept constant. Therefore, the potential of the Li ion insertion / desorption reaction remains constant, so that the output voltage of the storage element 110 can maintain 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, the different negative electrode active materials do not react with each other even if the negative electrode includes different negative electrode active materials. Therefore, the insertion / removal of Li ions at the voltage during charging / discharging appears in the charging / discharging 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 inserting and extracting Li ions can be used. Examples of such a material include composite oxides of transition metals and Li, metal oxides, alloy materials, inorganic compounds such as transition metal sulfides, carbon materials, organic compounds, and Li metals.

Examples of the composite oxide include LiMnO ₂ , LiMn ₂ O ₄ , lithium titanate (Li ₄ Ti ₅ O ₁₂ , Li ₂ Ti ₃ O ₇ ), lithium manganese titanate (LiMg _1/2 Ti _3/2 O ₄ ), lithium cobalt titanate _{(LiCo 1/2 Ti 3/2 O 4)} , lithium zinc titanate _{(LiZn 1/2 Ti 3/2 O 4)} , lithium iron titanate (LiFeTiO _4), lithium chromate titanate (LiCrTiO ₄ ), Lithium strontium titanate (Li ₂ SrTi ₆ O ₁₄ ), lithium barium titanate (Li ₂ BaTi ₆ O ₁₄ ), and the like.

Examples of the metal oxide include TiO ₂ , WO ₃ , MoO ₂ , MnO ₂ , V ₂ O ₅ , SiO ₂ , SiO, and SnO ₂ .

  Examples of alloy-based materials include Al, Si, Sn, Ge, Pb, As, and Sb.

  Examples of the transition metal sulfide include FeS and TiS.

  Examples of the carbon material include graphite, non-graphitizable carbon, graphitizable carbon, and the like.

  As the inorganic compound, a compound in which the transition metal of the above composite oxide is replaced with a different element may be used.

  Examples of the organic compound include a quinone compound, a disulfide compound, a diazine compound, a radialene compound, a rubeanic acid compound, and an organic radical compound.

  Among the above, it is preferable to use lithium titanate or graphite as the negative electrode active material.

  One of these negative electrode active materials may be used alone, or two or more thereof may be used.

  The negative electrode active material is formed into a particle shape using the above-described material capable of inserting and extracting Li ions, 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 negative electrode active material particles is preferably 3 μm or less. Similarly to the above-described positive electrode active material, by reducing the average particle diameter of the particles of the negative electrode active material, diffusion of Li ions in the particles can be promoted.

  By promoting the diffusion of Li ions, the voltage drop at the time of output to the load unit 200 can be reduced, and the voltage drop ΔV1 can be reduced. Thereby, the setting range of the lower limit voltage VL is expanded, and the setting of the lower limit voltage VL can be relaxed.

  The electrolyte will be described. As the electrolyte, a solid electrolyte or a non-aqueous electrolyte can be used. The non-aqueous electrolyte is a solution in which an electrolyte salt is dissolved in a non-aqueous solvent, and may be a liquid (electrolyte solution) or a gel electrolyte using a non-aqueous electrolyte as a substrate.

  The non-aqueous electrolyte is obtained by dissolving a Li salt as a supporting salt in an organic solvent.

  Examples of the organic solvent include 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; tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxycarbonate. Ether compounds such as ethane; sulfur compounds such as ethyl methyl sulfone and butane sultone; and phosphorus compounds such as triethyl phosphate and trioctyl phosphate can be used. Among these, the organic solvent can be used alone or in combination of two or more.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO _3, and a composite salt thereof can be used.

  Note that the non-aqueous electrolyte may include a radical scavenger, a surfactant, a flame retardant, or the like for improving the characteristics of the power storage element 110.

  The storage element 110 may include a separator between the positive electrode and the negative electrode. The separator is interposed between the electrodes, and has a function of separating the positive electrode and the negative electrode and holding the electrolyte. The separator may have any of the above functions, and for example, a thin film or a nonwoven fabric formed of polyethylene, polypropylene, or the like having many fine holes can be used.

  As shown in FIG. 1, monitoring section 120 is connected to power storage element 110. The monitoring unit 120 has a voltage detection unit 121 and a control unit 122.

  Voltage detection section 121 is connected to power storage element 110 and detects the voltage of power storage element 110.

  The control unit 122 is connected to the voltage detection unit 121, the switch units 130A and 130B, and the load unit 200. Control unit 122 calculates the remaining capacity of power storage element 110 corresponding to the voltage detected by 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 a range between lower limit voltage VL and upper limit voltage VH.

  The control unit 122 has a storage unit that stores a control program and various types of storage information, and a calculation unit that operates based on the control program. The storage means includes a RAM, a ROM, a storage, and the like. The calculation means includes a CPU and the like. The control unit 122 is realized by the arithmetic unit reading and executing a control program or the like stored in the storage unit. Further, information indicating the charge / discharge characteristics shown in FIG. 2 may be stored in the storage means of the control unit 122.

  Control unit 122 sets lower limit voltage VL of power storage element 110 as a threshold when power storage element 110 is discharged. When the output voltage of power storage element 110 detected by voltage detection section 121 is lower than lower limit voltage VL, control section 122 notifies load section 200 of an alarm signal indicating an overdischarge state.

  The output side of power storage element 110 is connected to load section 200 via power supply line L12. Power is supplied from the electric storage element 110 to the load unit 200.

  As shown in FIG. 1, switch unit 130A is provided on power supply line L11 on the input side of power storage element 110. Switch unit 130A connects or disconnects between power storage element 110 and power supply line L11.

  Switch unit 130B is provided on power supply line L12 on the output side of power storage element 110. Switch unit 130B connects or disconnects between power storage element 110 and power supply line L12.

  The load unit 200 operates by receiving power supply from the power storage system 100A. Examples of the load unit 200 include an edge device such as a wearable device, an electronic device, a generator and a motor of a hybrid vehicle, an electric vehicle, a ship or an aircraft, and the like.

  The load unit 200 starts operating when the voltage supplied from the power storage system 100A is equal to or higher than a predetermined value (for example, 4.2 V), and when the voltage supplied from the power storage system 100A is higher than a predetermined value (for example, 2.V). 5 V) or less, the operation is stopped. The voltage when the operation of the load unit 200 starts and when the operation of the load unit 200 stops is appropriately designed to a voltage value according to the type of the power storage element 110, the use of the power storage system 100A, and the like.

  The operation of power storage system 100A will be described. An external DC current is supplied to power storage element 110 via power supply line L11, whereby power storage element 110 is charged. At this time, switch unit 130A connects power storage element 110 to power supply line L11 (ON), and switch unit 130B disconnects power storage element 110 from power supply line L12 (OFF). When the storage element 110 is discharged, a DC current flows from the storage element 110 to the load unit 200 via the power supply line L12, and power is supplied from the 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 charges and discharges power storage element 110 according to the remaining capacity of power storage element 110, the operation state of load unit 200, and the like.

(Discharge control method)
Next, a method for controlling discharge of power storage element 110 using power storage system 100A will be described with reference to FIG. Note that in FIG. 4, it is assumed that power is charged to power storage element 110 to a remaining capacity corresponding to upper limit voltage VH.

FIG. 4 is a flowchart illustrating a method for controlling discharge of power storage element 110. As shown in FIG. 4, in power storage element 110, voltage detector 121 detects voltage V ₀ of power storage element 110 while supplying power charged in power storage element 110 to load section 200 (step S11). When the storage element 110 is discharging, the voltage of the storage element 110 gradually decreases from the upper limit voltage VH to the lower limit voltage VL.

Note that the voltage detection unit 121 continuously detects the voltage V ₀ of the power storage element 110, but can detect the voltage V ₀ at an arbitrary timing and may detect the voltage V ₀ at predetermined intervals. Voltage detecting section 121 may detect voltage V ₀ of power storage element 110 when power storage element 110 is discharged and power is not supplied to load section 200.

Subsequently, control unit 122 determines whether voltage V ₀ of power storage element 110 detected by voltage detection unit 121 is lower than lower limit voltage VL (step S12).

In step S12, it is assumed that the voltage V ₀ is lower than the lower limit voltage VL. In this case, control unit 122 determines that the remaining capacity of power storage element 110 is less than a predetermined value (for example, 20%), that power storage element 110 is in an overdischarged state, and sends a warning signal to load unit 200. Notify (step S13). Thereby, the load unit 200 can stop the operation after performing processing necessary for safely stopping the power storage system 100A, such as storage of data accumulated in the load unit 200.

On the other hand, in step S12, when voltage V ₀ of power storage element 110 is equal to or higher than lower limit voltage VL, control unit 122 determines that the remaining capacity of power storage element 110 is equal to or higher than the predetermined value (for example, 20%), and It is determined that discharge from 110 is possible, and the process returns to step S11.

  Subsequently, following step S13, control unit 122 stops the operation of power storage system 100A (step S14).

  Thereby, after safely stopping the operation of the load unit 200, the operation of the power storage system 100A can be stopped.

  The power storage system 100A configured as described above includes the power storage element 110 and the monitoring unit 120. The storage element 110 has such a characteristic that its charge and discharge curve has a stable area A and an inclined area B, as shown in FIG.

  For this reason, in the present embodiment, it is only necessary to monitor which of the stable region A (A1, A2, A3) and the inclined region B (B1, B2) the output voltage of the storage element 110 corresponds to. , The range of the remaining capacity of the storage element 110 can be determined. Therefore, according to the present embodiment, the state of power storage element 110 can be monitored with a simple configuration.

  Note that the state of power storage element 110 mainly includes the remaining capacity of power storage element 110 and the output voltage. Further, the state of power storage element 110 may include a state such as whether it is in an overdischarge state or whether it is in an overcharge state. Furthermore, the state of power storage element 110 may include the degree of deterioration of power storage element 110 and the like.

  In the present embodiment, the lower limit voltage VL is set as a threshold for detecting overdischarge of the storage element 110 between the first voltage V1 and the second voltage V2 of the charge / discharge curve shown in FIG.

  Therefore, the monitoring unit 120 of the present embodiment may compare the output voltage with the lower limit voltage VL only when the output voltage of the storage element 110 is between the first voltage V1 and the second voltage V2. With a simple configuration, it can be detected whether or not power storage element 110 is in an overdischarged state.

  Power storage system 100A prohibits discharge when the output voltage of power storage element 110 becomes lower than lower limit voltage VL. Therefore, when the storage element 110 is discharged to a predetermined value (for example, 20%) before the remaining capacity of the storage element 110 decreases excessively (or before the remaining capacity becomes 0%), the discharge of the storage element 110 is performed. Can be stopped. Thereby, power storage system 100A suppresses power storage element 110 from being over-discharged.

  In addition, power storage system 100A notifies load unit 200 of an alarm signal indicating that an overdischarge state has occurred, so that load unit 200 suddenly loses power supplied from power storage element 110, and operation is suddenly stopped. Troubles such as shutting down can be avoided.

  Further, since the power storage element 110 is a lithium ion secondary battery, it tends to be deteriorated when excessive discharge is repeated. According to the present embodiment, since the load on the power storage element 110 can be reduced, deterioration of the power storage element 110 can be suppressed. Power storage system 100A can extend the 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 larger than the voltage drop ΔV1 of the second voltage V2, and the lower limit voltage VL It is set between the voltage V1 and the maximum falling voltage V2 '. Thereby, the output voltage of power storage element 110 does not fall below lower limit voltage VL even if the voltage drop temporarily increases according to the output to load section 200. Therefore, even when the voltage drop temporarily increases, control unit 122 can prevent erroneous recognition that remaining capacity of power storage element 110 is low and a state in which a warning signal is notified. Thus, erroneous detection of the state of charge of power storage element 110 can be suppressed.

  As described above, since the power storage system 100A can monitor the state of the power storage element 110 with a simple configuration, it is suitably used as a power source for an edge device such as a wearable device, an electronic device, a hybrid vehicle, an electric vehicle, a ship, an aircraft, or the like. be able to.

  Note that, in the present embodiment, the lower limit voltage VL is set as a threshold value for stopping overdischarge of the storage element 110. However, the lower limit voltage VL may be set between the first voltage V1 and the second voltage V2, that is, within the first slope region B1. Any voltage value may be set as the threshold.

  In the present embodiment, a lithium ion secondary battery is used as the power storage element 110, but any battery that can be charged and discharged, such as an alkaline storage battery or a lead storage battery, can be used.

[Second embodiment]
A power storage system including a power storage element according to one embodiment will be described with reference to the drawings. Note that members having the same functions as those in the above embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. In the power storage system according to the present embodiment, a power generation element, a standby power storage element, and a power conversion unit are provided in the power storage system 100A according to the first embodiment shown in FIG.

  FIG. 5 is a block diagram illustrating a configuration of a 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 serving as a standby power storage element, power conversion unit 160, second power storage element 170, and monitoring unit 120. Note that, as second power storage element 170, power storage element 110 of power storage system 100A according to the above-described first embodiment is used.

  The power generating element 140A generates a direct current. As the power generation element 140A, a power generation element that collects energy such as light or heat and converts the energy into DC power can be used. As the power generation element 140A, for example, a solar cell (photovoltaic power generation element), a thermoelectric conversion element, or the like can be used.

  The power generating element 140A is configured to obtain a predetermined output voltage. For example, when the power generation element 140A is a solar cell, the solar cell is configured such that a plurality of solar cells are arranged on the light receiving surface side and connected in series, and a predetermined output voltage is obtained. When the power generation 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 side of power generating element 140A is connected to the input side of first power storage element 150 via power supply line L21. Power generating element 140 </ b> A supplies power to first power storage element 150.

  First power storage element 150 is charged with power output from power generation element 140A and supplies power to power conversion section 160. As the first storage element 150, for example, an electric double layer capacitor can be used. The capacity of the first power storage element 150 can be appropriately selected based on the power generation amount of the power generation element 140A, the power consumption of the load unit 200, the operation time of the load unit 200, and the like.

  The output side of first power storage element 150 is connected to the input side of power conversion section 160 via power supply line L22.

  Power conversion section 160 is a power conversion circuit that steps up or down the power supplied from first power storage element 150. The output side of power conversion section 160 is connected to the input side of second power storage element 170 via power supply line L23.

  As power converter 160, a DC / DC converter (DC voltage-DC voltage converter) or the like can be used. Power conversion section 160 converts a voltage input from first power storage element 150 into a voltage corresponding to charging of second power storage element 170. For example, when the output voltage of first power storage element 150 is lower than the voltage required by load section 200, power conversion section 160 boosts the power. When the output voltage of first power storage element 150 is high, power conversion section 160 controls the output voltage so that the voltage during charging of second power storage element 170 does not exceed a predetermined upper limit voltage.

  The second 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 described above, and thus the description of the second power storage element 170 is omitted.

  The capacity of the second power storage element 170 can be appropriately selected based on the power generation amount of the power generation element 140A, the power consumption of the load unit 200, the operation time of the load unit 200, and the like.

  It is preferable that the capacity of second power storage element 170 be larger than the capacity of first power storage element 150. The first power storage element 150 only needs to be able to temporarily store the power generated by the power generation element 140A, and the second power storage element 170 directly supplies power to the load unit 200. For this reason, it is preferable that the capacity of the second power storage element 170 be larger than the capacity of the first power storage element 150 so that the second power storage element 170 can easily cope with a change in the power consumption and the operation time of the load unit 200. In addition, it is preferable that the second power storage element 170 can store 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 secondary battery, so that first power storage element 150 tends to have a larger leak current than second power storage element 170. There is a tendency. Therefore, even if the capacity of the second storage element 170 is increased, the second storage element 170 can suppress the leak current as compared with the first storage element 150 including an electric double layer capacitor or the like.

  The output side of second power storage element 170 is connected to the input side of load section 200 via power supply line L24.

  The operation of the power storage system 100B will be described. The power generation element 140A converts external energy into DC power. DC power generated by power generating element 140A is supplied from power generating element 140A to first power storage element 150 via power supply line L21, and first power storage element 150 is charged. The power stored in first power storage element 150 is supplied to power conversion section 160 via power supply line L22, and is boosted or stepped down.

  Thereafter, the power stepped up or stepped down by power conversion section 160 is supplied to second power storage element 170 via power supply line L23, and is stored in second power storage element 170. At this time, the switch unit 130A turns on, and the switch unit 130B turns off. When the second power storage element 170 discharges, current flows from the second power storage element 170 to the load unit 200 via the power supply line L24, and power is supplied. At this time, the switch unit 130A turns off and the switch unit 130B turns on. The power storage system 100B charges and discharges the second power storage element 170 according to the remaining capacity of the second power storage element 170 or the operation state of the load unit 200.

  Since the power storage system 100B includes the power conversion unit 160, the power supplied from the first power storage element 150 is stepped up or down to the upper limit voltage VH, which is a constant voltage, by the power conversion unit 160. Thus, the second storage element 170 can be charged.

  In the present embodiment, as shown in FIG. 6, a power conversion unit 160 may be further connected to the load unit 200 via the power supply line L25 in addition to the second power storage element 170. In this case, a switch unit 130C is provided on the power supply line L25. The control unit 122 turns off the switch units 130A and 130B and turns on the switch unit 130C. Thereby, power storage system 100B can also supply the power generated by power generation element 140A directly to load section 200 without storing it in second power storage element 170, and use it in load section 200.

[Third Embodiment]
A power storage system including a power storage element according to one embodiment will be described with reference to the drawings. Note that members having the same functions as those in the above embodiments are given the same reference numerals, and detailed description thereof will be omitted. The power storage system according to the present embodiment is obtained by providing a converter in the power storage system 100B of the second embodiment shown in FIG.

  FIG. 7 is a block diagram illustrating a configuration of a power storage system according to the third embodiment. As shown in FIG. 7, power storage system 100C includes power generation element 140B, converter 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 collects energy such as vibration and converts the energy into AC power can be used. As the power generation element 140B, for example, a vibration power generation element or the like can be used.

  The output side of the power generating element 140B is connected to the input side of the converter 180 via the power supply line L31.

  Converter 180 converts AC power supplied from power generating element 140B to DC. As the converter 180, an AC-DC converter can be used.

  The output side of converter 180 is connected to the input side of first power storage element 150 via 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.

  The operation of power storage system 100C will be described. The power generation element 140B converts external energy into AC power. The AC power generated by the power generating element 140B is supplied from the power generating element 140B to the converter 180 via the power supply line L31. After converting the current from AC to DC by converter 180, the DC current is sent from converter 180 to first power storage element 150 via power supply line L32, and first power storage element 150 is charged. The power stored in first power storage element 150 is supplied to power conversion section 160 via power supply line L33, and is boosted or stepped down. Thereafter, the power stepped up or stepped down by power conversion section 160 is transmitted to second power storage element 170 via power supply line L34, and is stored in second power storage element 170. At this time, the switch unit 130A turns on and the switch unit 130B turns off. When the second power storage element 170 discharges, a current flows from the second power storage element 170 to the load unit 200 via the power supply line L35, and power is supplied. At this time, the switch unit 130A turns off and the switch unit 130B turns on. The power storage system 100C charges and discharges the second power storage element 170 according to the remaining capacity of the second power storage element 170 or the operation state of the load unit 200.

  In the present embodiment, as shown in FIG. 8, in addition to the second power storage element 170, the power conversion unit 160 may be further connected to the load unit 200 via the power supply line L36. In this case, a switch unit 130C is provided on the power supply line L36. The control unit 122 turns off the switch units 130A and 130B and turns on the switch unit 130C. Accordingly, the power storage system 100C can also directly supply the power generated by the power generation element 140B to the load unit 200 without storing the power in the second power storage element 170, and use the power in the load unit 200.

[Fourth embodiment]
A power storage system including a power storage element according to one embodiment will be described with reference to the drawings. Note that members having the same functions as those in the above embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. The power storage system according to the fourth embodiment controls overcharging of the power storage element 110 when the power storage element 110 is charged in the power storage system 100A of the first embodiment shown in FIG.

  FIG. 9 is a block diagram illustrating a configuration of a power storage system according to the 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. The components of 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.

  The power storage system 100D according to the present embodiment is configured such that when the power storage element 110 is charged, the charge / discharge curve of the power storage element 110 shown in FIG. The upper limit voltage VH is detected as a threshold for detecting overcharging.

  In the charge / discharge curve of the storage element 110 shown in FIG. 2, when the storage element 110 is charged with the maximum current that can be input from the DC power supply, the voltage of the storage element 110 rises from the second voltage V2 by a voltage increase ΔV2, It reaches the maximum rising voltage V2 ''.

  FIG. 10 is an explanatory diagram illustrating a relationship between output voltages when the storage element 110 is charged with the maximum current that can be input from the DC power supply. As shown in FIG. 10, when the voltage of storage element 110 is charged at the maximum current Imax that can be input from the DC power supply when the voltage of storage element 110 is the second voltage V2, the voltage of storage element 110 increases from second voltage V2. The voltage rises by the amount ΔV2 to reach the maximum voltage rise V2 ″.

  As shown in FIG. 2, the maximum rising voltage V2 ″ is lower than the upper limit voltage VH, and the upper limit voltage VH is 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 larger than the voltage increase ΔV2 of the second voltage V2.

  Control unit 122 shown in FIG. 9 sets upper limit voltage VH of power storage element 110 as a threshold when power storage element 110 is charged. Control unit 122 stops charging of power storage element 110 or stops operation of power storage system 100C when the voltage of power storage element 110 detected by voltage detection unit 121 exceeds upper limit voltage VH.

(Charging control method)
Next, a method for controlling charging of power storage element 110 using power storage system 100D will be described with reference to FIG. In FIG. 11, it is assumed that the storage element 110 has been discharged to a remaining capacity corresponding to the lower limit voltage VL.

FIG. 11 is a flowchart illustrating a method for controlling charging of power storage element 110. As illustrated in FIG. 11, the voltage detection unit 121 detects the voltage V ₀ of the power storage element 110 while supplying and charging the power storage element 110 (Step S21). While the storage element 110 is being charged, the voltage of the storage element 110 gradually increases.

Note that the voltage detection unit 121 continuously detects the voltage V ₀ of the power storage element 110, but can detect the voltage V ₀ at an arbitrary timing and may detect the voltage V ₀ at predetermined intervals. Further, voltage detecting section 121 may detect voltage V ₀ of power storage element 110 even when power storage element 110 is not charged.

Subsequently, control unit 122 determines whether or not voltage V ₀ of power storage element 110 detected by voltage detection unit 121 is higher than upper limit voltage VH (step S22).

In step S22, when voltage V ₀ is greater than upper limit voltage VH, control unit 122 determines that the remaining capacity of power storage element 110 has exceeded a predetermined value (for example, 80%) and that power storage element 110 is overcharged. It is determined that there is. In this case, control unit 122 turns off switch unit 130A and stops charging of power storage element 110 (step S23). Thus, charging of power storage element 110 is stopped.

On the other hand, in step S22, when voltage V ₀ of power storage element 110 is equal to or lower than upper limit voltage VH, control unit 122 determines that power storage element 110 has not reached the overcharged state, and returns to step S21.

  As described above, in power storage system 100D, it is only necessary to determine whether there is overcharging only when the output voltage of power storage element 110 is in second slope region B2. Therefore, in the present embodiment, it is not necessary to precisely detect the state of charge, and it is possible to suppress overcharging of the storage element 110 with a simple configuration.

  In the present embodiment, the upper limit voltage VH is set as a threshold value for stopping overcharging of the storage element 110. However, the upper limit voltage VH may be set between the second voltage V2 and the third voltage V3, that is, within the second inclined region B2. Any voltage value may be set as the threshold.

  In the present embodiment, charging and discharging may be performed in combination with the control method for discharging the power storage element 110 of the power storage system 100A according to the first embodiment shown in FIG.

  In the present embodiment, when charging the second storage element 170 of the power storage system 100B of the second embodiment shown in FIG. 5 and the power storage system 100C of the third embodiment shown in FIG. May be.

  As described above, the embodiment has been described. However, the above embodiment is presented as an example, and the present invention is not limited to the above embodiment. The above embodiment can be implemented in other various forms, and various combinations, omissions, replacements, changes, and the like can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and its equivalents.

100A to 100D power storage system 110 power storage element 120 monitoring unit 140A, 140B power generation element 150 first power storage element (standby power storage element)
160 power conversion unit 170 second power storage element 180 converter 200 load unit A stable area A1 first stable area A2 second stable area A3 third stable area B inclined area B1 first inclined area B2 second inclined area B3 third inclined area

JP-A-2006-125882

Claims (13)

In the charge and discharge curve showing the relationship between the remaining capacity and the output voltage,
A first stable region in which the output voltage is within a predetermined error range from the first voltage with respect to a change in the remaining capacity in a first range;
A second stable region in which the output voltage falls within a range of the predetermined error from a second voltage that is higher than the first voltage with respect to a change in the remaining capacity in a second range;
A power storage element comprising: a first slope region in which 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 difference between the first voltage and the second voltage is larger than the voltage drop when the maximum current is discharged to the load,
The power storage device according to claim 1, wherein a threshold value for detecting overdischarge is set in the first inclined region.   The power storage device according to claim 1, wherein the first voltage is lower than a lower limit voltage at which discharge is prohibited.   The power storage device according to claim 3, wherein a range between the first range and the second range is a range narrower than the first range and the second range. A third stable region in which the output voltage is within a range of the predetermined error from a third voltage that is higher than the second voltage with respect to a change in the remaining capacity in a third range;
The second slope region in which the output voltage changes from the second voltage to the third voltage with respect to a change in the remaining capacity in a range between the second range and the third range. The power storage device according to any one of claims 1 to 4. The difference between the second voltage and the third voltage is larger than the voltage rise when charging at the maximum current,
The power storage device according to claim 5, wherein a threshold value for detecting overcharge is set in the second inclined region.   The power storage device according to claim 5, wherein the third voltage is a voltage higher than an upper limit voltage at which charging is prohibited. Having a positive electrode and a negative electrode,
The power storage device according to claim 1, wherein one or both of the positive electrode and the negative electrode include one or more types of electrode active materials. A power storage element according to any one of claims 3 to 8,
When the output voltage is less than the lower limit voltage, a monitoring unit that detects overdischarge,
Power storage system including. The monitoring unit is
A voltage detection unit that detects the output voltage of the power storage element,
When the overdischarge is detected, a control unit that notifies an alarm signal to a load unit to which power is supplied from the power storage element,
The power storage system according to claim 9, comprising: A power generating element,
A reserve storage element that performs charging of the power generated by the power generation element and discharging of the charged power,
In addition,
The power storage system according to claim 9, wherein the power storage element is supplied with power from the standby power storage element.   The power storage system according to claim 11, further comprising: a power converter connected to the standby power storage element and boosting or stepping down power supplied from the standby power storage element and supplying the boosted or lowered power to the power storage element. When the current generated in the power generating element is an alternating current,
The power storage system according to claim 11, further comprising a converter connected to the power generation element, for converting power generated by the power generation element from AC to DC, and supplying the converted power to the standby power storage element.

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