WO2016129528A1 - 蓄電装置 - Google Patents
蓄電装置 Download PDFInfo
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- WO2016129528A1 WO2016129528A1 PCT/JP2016/053537 JP2016053537W WO2016129528A1 WO 2016129528 A1 WO2016129528 A1 WO 2016129528A1 JP 2016053537 W JP2016053537 W JP 2016053537W WO 2016129528 A1 WO2016129528 A1 WO 2016129528A1
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- secondary battery
- positive electrode
- negative electrode
- active material
- charge
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- 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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
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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]
- G01R31/385—Arrangements for measuring battery or accumulator variables
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- 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
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- 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
- H01M10/44—Methods for charging or discharging
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- 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
- H01M10/46—Accumulators structurally combined with charging apparatus
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- 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
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- 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
- H01M10/44—Methods for charging or discharging
- H01M10/441—Methods for charging or discharging for several batteries or cells simultaneously or sequentially
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- 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
- H01M2004/021—Physical characteristics, e.g. porosity, surface area
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/0013—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries acting upon several batteries simultaneously or sequentially
- H02J7/0025—Sequential battery discharge in systems with a plurality of batteries
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/0029—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries with safety or protection devices or circuits
- H02J7/00302—Overcharge protection
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- 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
Definitions
- the present invention relates to a power storage device including a charging device and a secondary battery.
- This power storage device includes a secondary battery as a storage battery and a dedicated charging device. When storing electricity, this power storage device uses a dedicated charging device to charge the secondary battery, and when there is a power demand from an external load, the electricity charged in the secondary battery is transmitted to the external load. It is possible to do.
- the secondary battery has a charge end voltage that is the maximum value of the charge voltage at which it can be safely charged.When the voltage rises above this charge end voltage, the active material layer that forms the electrode is the so-called overcharge. It will fall into a state. It is known that when a secondary battery falls into an overcharged state, the constituent materials of the secondary battery are destroyed, the decomposition of the electrolyte on the surface of the material is accelerated, and the like, resulting in rapid deterioration. That is, in order to extend the life of the secondary battery, it is necessary to prevent falling into an overcharged state during charging, and to prevent material destruction and acceleration of electrolyte decomposition.
- a plurality of secondary batteries may be connected in series and used as an assembled battery. is there.
- control for preventing overcharge is usually performed in units of assembled batteries, and control in units of single cells is not performed. Therefore, in the control of each assembled battery, a specific secondary battery constituting the assembled battery may fall into an overcharged state depending on the degree of deterioration, individual differences, and the like, and the overcharged state of the specific secondary battery cannot be resolved. Therefore, when a plurality of secondary batteries are connected in series to form an assembled battery, it is essential to use a secondary battery with overcharge resistance for each secondary battery.
- Patent Document 1 in order to prevent such a specific secondary battery from falling into an overcharged state, a charge depth detection battery having an inflection region set in advance to an arbitrary charge depth, An assembled battery in which a battery for detecting a charging depth is connected in series has been proposed. According to the assembled battery described in Patent Document 1, when the voltage of the unit cell for detecting the charging depth becomes the charging depth detecting voltage, the charging depth of the entire assembled battery can be detected with high accuracy, and the voltage range is not overcharged. It is said that it can be used inside.
- an object of the present invention is to provide a power storage device that can prevent an overcharged state from occurring when charging without using a battery for detecting the depth of charge.
- a power storage device including a secondary battery and a charging device that charges the secondary battery
- the secondary battery includes a positive electrode, a negative electrode
- the secondary battery has a non-aqueous electrolyte sandwiched between the positive electrode and the negative electrode, the metal ion can move between the positive electrode and the negative electrode through the non-aqueous electrolyte,
- the positive electrode and the negative electrode can be charged / discharged by the insertion / desorption reaction of the metal ions between the non-aqueous electrolyte and the positive electrode and the negative electrode are both active with an average thickness of 0.3 mm or more.
- the charging device is electrically connected to the secondary battery, and charges the secondary battery with only a constant current during charging, up to a charge end voltage by the charging device.
- the amount said a positive electrode and the 80% or more 97% or less power storage device design capacity calculated from specific capacity per unit weight of the negative electrode.
- the “end-of-discharge voltage” here is a limit value of the voltage generated in the secondary battery, for example, a voltage limited by a limiter. That is, it is a rated value for safely discharging the secondary battery.
- the “end-of-charge voltage” here is a limit value of the voltage generated in the secondary battery, and is a voltage limited by a limiter, for example. That is, it is a rated value for safely charging the secondary battery.
- a secondary battery that performs charging / discharging by such insertion / desorption reaction mainly includes a contact resistance component between constituent materials and a metal ion from an electrode as a resistance component included in a resistance loss (IR drop). There is a diffusion resistance component generated when diffusing into the non-aqueous electrolyte.
- the contact resistance and the diffusion resistance are made as small as possible to bring the actual capacity closer to the designed capacity.
- metal ions are highly reactive with oxygen and moisture in the air. Therefore, safety may be impaired if an overcharged state occurs. For this reason, in order to prevent damage due to overcharging, it is generally performed that charging is performed at a constant current up to a certain capacity, and then charging is performed so as not to exceed the charging end voltage by changing to a constant voltage.
- the average thickness of the active material layer of the positive electrode and the negative electrode is increased to 0.3 mm or more, and 80% or more and 97% or less of the design capacity. It is suppressed. That is, in the secondary battery of this aspect, a state in which metal ions are difficult to diffuse is created, the diffusion resistance component is increased, and a diffusion rate-controlled state of metal ions is spontaneously formed.
- the secondary battery of this aspect is charged with a constant current up to the end-of-charge voltage by the charging device in a state where the capacity as designed does not come out.
- the secondary battery device of this aspect the internal active material layer itself is in an overcharged state as long as the voltage rises due to the diffusion resistance component even if it is overcharged above the end-of-charge voltage. It will not be. Therefore, it is difficult for the constituent materials of the secondary battery to be destroyed and the decomposition of the electrolyte to be accelerated.
- the charge end voltage is reached, the designed full charge capacity is not reached, so that overcharge of the secondary battery can be prevented without using a battery for detecting the charge depth. Therefore, it is possible to simplify the control and reduce the cost.
- a preferred aspect is that when 80 charge / discharge cycles are performed at a current value at which charging or discharging ends in 8 hours in the range from the discharge end voltage to the charge end voltage, the capacity relative to the capacity of the secondary battery before the charge / discharge cycle is increased. The decrease is 2% or less.
- the decrease in capacity relative to the capacity of the secondary battery before the charge / discharge cycle is 2% or less, and apparently there is almost no decrease in capacity due to deterioration of the secondary battery. However, it is hard to feel the capacity drop.
- the above-described aspect is that the capacity with respect to the capacity of the secondary battery before the charge / discharge cycle is obtained when the charge / discharge cycle is performed 100 times at a current value at which charging or discharging ends in 8 hours in the range from the discharge end voltage to the charge end voltage. Is more preferably 2% or less.
- a plurality of the secondary batteries have an assembled battery connected in series, and the charging device charges each secondary battery in the assembled battery unit.
- the secondary battery does not enter an overvoltage state within a certain voltage range even when the charge end voltage is exceeded. For this reason, even if there is a variation in capacity due to deterioration or individual differences of the secondary batteries constituting the assembled battery, a process for suppressing the variation in capacity of each secondary battery is not required. That is, when the assembled battery of this aspect is an assembled battery that is simply connected in series, the voltage of the assembled battery can be controlled as a whole, and the capacity variation suppressing process of each secondary battery is not required. For this reason, the charge / discharge currents flowing through all the secondary batteries are always the same, and the charge charges of all the secondary batteries are always the same.
- a more preferable aspect is to have a plurality of the assembled batteries, and the charging device performs voltage monitoring and control in units of the assembled batteries during charging.
- a preferable aspect is that the external power supply system can be interconnected and power can be transmitted to the external power supply system side.
- the “external power supply system” here includes not only a commercial power supply system but also an external load such as a household load.
- power can be transmitted to the external power supply system by being parallel to the external power supply system, and power transmission to the external power supply system can be blocked by disconnecting from the external power supply system. Therefore, for example, when the amount of electric power is insufficient, it can function as an auxiliary power source by being paralleled. In addition, when a failure or the like occurs in the power storage device, it can be safely repaired or exchanged by disconnecting.
- a preferred aspect is that the secondary battery can be discharged at a constant current or other than a constant current.
- each of the secondary batteries has a porosity of the active material layer of 15% or more.
- the porosity of each of the positive electrode active material layer and the negative electrode active material layer is 15% or more, ion diffusion is not limited so that good battery performance can be obtained.
- non-aqueous electrolyte is a non-aqueous electrolyte obtained by dissolving a solute with a solvent, and the solvent is a carbonate.
- solute is a compound containing lithium and halogen.
- the active material layer of the negative electrode includes at least one negative electrode active material selected from lithium titanium oxide and a material obtained by substituting a part of ions of the lithium titanium oxide with another metal ion. It is.
- the active material layer of the positive electrode contains at least one positive electrode active material selected from lithium manganese oxide and lithium manganese oxide in which a part of ions of the lithium manganese oxide is replaced with another metal ion. It is.
- the above-described aspect includes a positive electrode and a negative electrode having an active material layer capable of inserting / extracting metal ions, and movement of the metal ions sandwiched between them and responsible for electrical conduction therebetween. And at least one of the electrodes has an active material layer having an average thickness of 0.3 mm or more on the surface thereof, and only at a constant current (CC). It is good also as there being no fall of a capacity
- FIG. 2 is a perspective view schematically showing the secondary battery of FIG. 1. It is sectional drawing of the secondary battery of FIG.
- the power storage device 1 is a power storage device that is mainly attached to a building such as a building or a house.
- the power storage device 1 is a power storage device capable of temporarily storing electricity transmitted from a power generation system (not shown) such as a solar power generation system or a fuel cell system or an external power supply system 50 such as a commercial power supply system.
- the power storage device 1 is also a power supply device that supplies stored electricity to an external power supply system 50 such as an external load or a commercial power supply system.
- the power storage device 1 includes a power control device 2 (charging device) and a secondary battery system 3 as main components.
- the power storage device 1 of the present embodiment is such that the diffusion of metal ions is rate-limiting when the secondary battery 15 constituting the secondary battery system 3 is charged.
- One of the main features is that the battery 15 is charged.
- the power supply control device 2 is a power supply control device capable of controlling voltage and current, and can be interconnected with an external power supply system 50 such as an external load or a commercial power supply system. That is, the power supply control device 2 can be paralleled and disconnected from the external power supply system 50.
- the power supply control device 2 is a charging device that transmits power to the secondary battery system 3 to charge the secondary battery system 3, and transmits electricity charged in the secondary battery system 3 to the external power system 50 side. It is also a power transmission device.
- the power supply control device 2 can be charged and discharged independently with respect to each assembled battery 5 of the secondary battery system 3. That is, the power supply control device 2 is electrically connected to each assembled battery 5 via the wiring member 16, and can monitor and control the voltage for each assembled battery 5.
- the secondary battery system 3 has a plurality of assembled batteries 5 built in a housing 8, and each assembled battery 5 can store electricity. Each assembled battery 5 is electrically connected to the power supply control device 2 independently as shown in FIG.
- the secondary battery system 3 of the present embodiment incorporates three assembled batteries 5 as shown in FIGS.
- the assembled battery 5 includes a plurality of secondary batteries 15 and a wiring member 16, and each secondary battery 15 is electrically connected in series via the wiring member 16. Yes.
- five secondary batteries 15 are electrically connected in series.
- the secondary battery 15 is a secondary battery having metal ion conductivity, specifically, a lithium ion secondary battery having lithium ion conductivity.
- the secondary battery 15 includes a positive electrode member 10, a negative electrode member 11, and a nonaqueous electrolyte 23, and the secondary battery 15 is a metal between the positive electrode 20 of the positive electrode member 10 and the negative electrode 21 of the negative electrode member 11. Ions can move.
- the positive electrode 20 and the negative electrode 21 can be charged / discharged due to the insertion / desorption reaction of metal ions with the non-aqueous electrolyte 23. That is, the secondary battery 15 is charged / discharged by conducting lithium ions as metal ions between the positive electrode 20, the electrolyte 23, and the negative electrode 21 shown in FIG.
- the secondary battery 15 has terminal members 25, 26 straddling the inside and outside of the enclosure 27.
- each of the terminal members 25 and 26 is connected to the positive electrode member 10 and the negative electrode member 11 inside the enclosure 27 as shown in FIG. 4, and the other end is connected to the end of FIG. Thus, it is exposed to the outside of the enclosure 27 and can be connected to the wiring member 16.
- the secondary battery 15 may be appropriately provided with a mechanism for releasing the generated gas or the like on the exterior of the enclosure 27.
- the secondary battery 15 may be provided with a mechanism for appropriately injecting an additive for recovering the function of the deteriorated secondary battery 15 from the outside of the battery 15.
- the number of stacked secondary battery cells 17 as the stacked body can be appropriately set so as to express a desired battery capacity. Further, pressure may be applied in the stacking direction of the electrodes 20, 21, pressure may be applied inside the secondary battery 15, or pressure may be applied from the outside of the enclosure 27 that is an exterior.
- the secondary battery 15 of the present embodiment has a plurality of secondary battery cells 17 built in an enclosure 27.
- the secondary battery cell 17 is a laminated body in which the positive electrode 20, the negative electrode 21, and the separator 22 are laminated. That is, the secondary battery cell 17 is a portion in which the separator 22 including the electrolyte 23 is sandwiched between the positive electrode 20 and the negative electrode 21.
- the positive electrode member 10 is a plate-like or film-like electrode member, and the positive electrode 20 is formed on one side or both sides thereof.
- the positive electrode 20 includes an active material layer 31 capable of inserting and removing metal ions, and the positive electrode active material layer 31 is laminated on both surfaces or one surface of a plate-shaped or film-shaped current collector 30. It is. That is, the positive electrode 20 is a part of the positive electrode member 10 and is a part in which the positive electrode active material layer 31 is laminated on the current collector 30.
- the secondary battery 15 of the present embodiment includes two positive electrode members 10a and 10b (10), and includes a plurality of positive electrodes 20a to 20c.
- the positive electrode active material layer 31 is formed on one surface of the current collector 30, and the positive electrode 20a is formed.
- positive electrode active material layers 31 and 31 are formed on both surfaces of a current collector 30, and positive electrodes 20b and 20c are formed. That is, the positive electrode member 10a has electrodes on one side, and the positive electrode member 10b has electrodes on both sides.
- the positive electrode active material layer 31 includes a positive electrode active material as a main component, and includes a conductive additive and / or a binder as necessary.
- the positive electrode active material layer 31 of the present embodiment includes a positive electrode active material as a main component, and a conductive additive and a binder are added.
- main component refers to a component that determines performance.
- the “main component” here refers to a component occupying 50% or more of the whole.
- the main component of the positive electrode active material is at least one selected from the group consisting of lithium manganese oxide, an oxide obtained by substituting a part of manganese with a different element, lithium iron phosphate, and lithium manganese phosphate. preferable. By so doing, material deterioration can be reduced even when the voltage suddenly rises in the latter half of charging.
- the main component of the positive electrode active material is more preferably at least one selected from the group consisting of lithium manganese oxide and an oxide obtained by substituting part of the manganese with a different element.
- the main component of the positive electrode active material is a metal ion containing at least one selected from the group consisting of nickel, aluminum, magnesium, titanium, chromium, cobalt, and iron from the viewpoint of being extremely resistant to overcharge. It is particularly preferred.
- the average thickness of the positive electrode active material layer 31 formed on the surface of the current collector 30 is 0.3 mm or more.
- the average thickness of the positive electrode active material layer 31 formed on the surface of the current collector 30 is preferably 1.5 mm or less. If it is this range, even if it becomes diffusion-controlled, the capacity
- the porosity of the positive electrode active material layer 31 is preferably 15% or more and 60% or less, and more preferably 15% or more and 40% or less.
- the porosity of the positive electrode active material layer 31 is less than 15%, ion diffusion is too limited, and it is difficult to obtain good battery performance.
- the porosity of the positive electrode active material layer 31 is more than 60%, there may be poor contact between the active materials or between the active material and the conductive additive, and the battery performance may be deteriorated. Further, when the porosity is large, the volume energy density is lowered, and therefore it is preferably within the above range.
- the negative electrode member 11 is a plate-like or film-like electrode member, and the negative electrode 21 is formed on one side or both sides thereof.
- the negative electrode 21 includes an active material layer 41 capable of inserting and removing metal ions, and the negative electrode active material layer 41 is laminated on both sides or one side of a plate-like or film-like current collector 40. It is. That is, the negative electrode 21 is a part of the negative electrode member 11 where the negative electrode active material layer 41 is laminated on the current collector 40.
- the secondary battery 15 of this embodiment includes two negative electrode members 11a and 11b (10), and includes a plurality of negative electrodes 21a to 21c.
- negative electrode active material layers 41 and 41 are formed on both surfaces of the current collector 40 to form negative electrodes 21a and 21b.
- the negative electrode active material layer 41 is formed on one surface of the current collector 40 to form the negative electrode 21c. That is, the negative electrode member 11a has electrodes on both sides, and the negative electrode member 11b has electrodes on one side.
- the negative electrode 21a is a counter electrode of the positive electrode 20a of the positive electrode member 10a
- the negative electrode 21b is a counter electrode of the positive electrode 20b of the positive electrode member 10b.
- the negative electrode 21c is a counter electrode of the positive electrode 20c of the positive electrode member 10b.
- the negative electrode active material layer 41 includes a negative electrode active material as a main component, and includes a conductive additive and / or a binder as necessary.
- the negative electrode active material layer 41 of the present embodiment includes a negative electrode active material as a main component, and a conductive additive and a binder are added.
- the main component of the negative electrode active material is preferably an oxide containing titanium, molybdenum oxide, niobium oxide, or tungsten oxide.
- the main component of the negative electrode active material is more preferably at least one selected from the group consisting of lithium titanium oxide and a material obtained by substituting part of titanium of the lithium titanium oxide with another metal ion.
- the main component of the negative electrode active material is particularly preferably niobium as the other metal ion from the viewpoint of being extremely resistant to overcharging and effective in extending the life.
- the average thickness of the negative electrode active material layer 41 formed on the surface of the current collector 40 is 0.3 mm or more.
- the average thickness of the negative electrode active material layer 41 is 0.3 mm or more, the diffusion of metal ions tends to be rate-limiting in the charging reaction, and even when the secondary battery 15 reaches the end-of-charge voltage, it is added to the active material layer 41.
- the voltage can be kept below the end-of-charge voltage. For this reason, it is possible to suppress the material breakdown and the acceleration of the decomposition of the electrolyte 23 due to the overvoltage exceeding the charge end voltage being applied to the secondary battery 15.
- the average thickness of the negative electrode active material layer 41 formed on the surface of the current collector 40 is preferably 1.5 mm or less. If it is this range, the capacity
- the porosity of the negative electrode active material layer 41 is preferably 15% or more and 60% or less, and more preferably 15% or more and 40% or less.
- the porosity is less than 15%, the diffusion of lithium ions is too limited, so that good battery performance is difficult to obtain.
- the porosity exceeds 60% there may be a contact failure between the active materials or between the active material and the conductive additive, and the battery performance may be deteriorated. Further, when the porosity is large, the volume energy density is lowered, and therefore it is preferably within the above range.
- the current collectors 30 and 40 are conductive members formed of a conductive material and having conductivity.
- the conductive material constituting the current collectors 30 and 40 include copper, aluminum, nickel, titanium, an alloy containing at least one of these, or a conductive polymer.
- the shape of the current collectors 30 and 40 include a foil shape, a mesh shape, a punching shape, an expanding shape, and a foam structure.
- the conductive material used for such a current collector may be stable at the electrode operating potential. In the lithium ion secondary battery as in this embodiment, when the operating potential is 0.7 V or less with respect to the lithium metal, copper and its alloy are preferable, and when it is 0.7 V or more, aluminum and its alloy are preferable.
- the binder constituting the positive electrode active material layer 31 and the negative electrode active material layer 41 is not particularly limited as long as it has binding properties and can be dispersed in water or an organic solvent.
- the binder include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), styrene-butadiene copolymer (SBR), polyacrylic acid ester, polyvinyl At least one selected from the group consisting of alcohol (PVA), carboxymethyl cellulose (CMC), polyimide (PI) and derivatives thereof can be used. You may add a dispersing agent and a thickener to these.
- the conductive support material which comprises the positive electrode active material layer 31 and the negative electrode active material layer 41 is not specifically limited, A carbon material or / and a metal microparticle are preferable.
- the carbon material include natural graphite, artificial graphite, vapor-grown carbon fiber, carbon nanotube, acetylene black, ketjen black, carbon black, and furnace black.
- the metal fine particles include copper, aluminum, nickel, and an alloy containing at least one of these. Further, the fine particles of inorganic material may be plated. These carbon materials and metal fine particles may be used alone or in combination of two or more.
- the separator 22 is impregnated with the electrolyte 23, and examples thereof include a porous material or a nonwoven fabric.
- the material of the separator 22 is preferably a material that does not dissolve in the organic solvent constituting the electrolyte 23, and specifically, a polyolefin polymer such as polyethylene or polypropylene, a polyester polymer such as polyethylene terephthalate, cellulose, or glass. An inorganic material is mentioned.
- the thickness of the separator 22 is preferably 1 ⁇ m or more and 500 ⁇ m or less. If the thickness is less than 1 ⁇ m, the separator 22 tends to break due to insufficient mechanical strength, causing an internal short circuit. On the other hand, when the thickness is larger than 500 ⁇ m, the load resistance of the battery 15 tends to decrease due to the increase in the internal resistance of the battery 15 and the distance between the positive electrode 20 and the negative electrode 21. A more preferable thickness is 10 ⁇ m or more and 300 ⁇ m or less.
- the electrolyte 23 is an electrolyte that has metal ion conductivity and can insert and desorb metal ions between each positive electrode 20 and each negative electrode 21 along with electric conduction.
- the electrolyte 23 is a non-aqueous electrolyte that does not substantially contain water.
- the electrolyte 23 is not particularly limited, but is an electrolyte solution in which a solute is dissolved in a nonaqueous solvent, a gel electrolyte in which a polymer is impregnated with an electrolyte solution in which a solute is dissolved in a nonaqueous solvent, a solid electrolyte, an ionic liquid, and silica fine particles
- a solid electrolyte that is pseudo-solidified by mixing can be used.
- the electrolyte 23 of the present embodiment is a non-aqueous electrolyte in which a solute is dissolved in a non-aqueous solvent, and is a liquid electrolytic solution, and is filled in the enclosure 27.
- the non-aqueous solvent preferably includes a cyclic aprotic solvent and / or a chain aprotic solvent, and more preferably a carbonate.
- a cyclic aprotic solvent include cyclic carbonates, cyclic esters, cyclic sulfones, and cyclic ethers.
- examples of the chain aprotic solvent include a chain carbonate, a chain carboxylic acid ester, or a chain ether.
- a solvent generally used as a solvent for nonaqueous electrolytes such as acetonitrile may be used. More specifically, dimethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, ⁇ -butyrolactone, 1,2-dimethoxyethane, sulfolane, dioxolane, or propion For example, methyl acid can be used.
- These solvents may be used singly or in combination of two or more.
- a mixed solvent of two or more types is used. It is preferable to use it. Further, gel electrolytes, pseudo solid electrolytes, and sulfur-based solid electrolytes in which a polymer is impregnated with an electrolytic solution or an ionic liquid can also be used.
- the concentration of the solute contained in the electrolyte 23 is preferably 0.5 mol / L or more and 2.0 mol / L or less. If the concentration of the solute contained in the electrolyte 23 is less than 0.5 mol / L, desired ionic conductivity may not be exhibited.
- the solute contained in the electrolyte 23 may contain a trace amount of additives such as a flame retardant and a stabilizer.
- the amount of the electrolyte 23 is not particularly limited, but is preferably 0.1 mL or more per 1 Ah of battery capacity. When the amount of the electrolyte 23 is less than 0.1 mL, the conduction of ions accompanying the electrode reaction cannot catch up, and the desired battery performance may not be exhibited. In addition, when using a solid electrolyte as the electrolyte 23, it may be pressure-molded as it is, or it may be formed into a sheet using the binder used for the electrodes 20 and 21 described above.
- the positive electrode active material layer 31 of the positive electrode 20a faces the negative electrode active material layer 41 constituting the negative electrode 21a with the separator 22 including the electrolyte 23 interposed therebetween.
- the positive electrode active material layer 31 of the positive electrode 20b faces the negative electrode active material layer 41 constituting the negative electrode 21b with the separator 22 including the electrolyte 23 interposed therebetween.
- the positive electrode active material layer 31 of the positive electrode 20c faces the negative electrode active material layer 41 constituting the negative electrode 21c with the separator 22 including the electrolyte 23 interposed therebetween.
- the ends of the current collectors 30, 30 constituting the positive electrode members 10 a, 10 b are in contact with each other, and one of the positive electrode members 10 a, 10 b is connected to the terminal member 25.
- the end portions of the current collectors 40, 40 of the negative electrode members 11a, 11b are in contact with each other, and one of the negative electrode members 11a, 11b is connected to the terminal member 26.
- the electrolyte 23 is filled in the enclosure 27, and each separator 22 is impregnated with the electrolyte 23.
- charge / discharge control which is one of the features of the power storage device 1 of the present embodiment will be described.
- the external power supply system 50 is disconnected as necessary, and the power supply control device 2 determines the battery pack 5 of the secondary battery system 3 until the charge end voltage is reached. Charge with current only. That is, in the charge control of the present embodiment, the secondary battery 15 is charged by the power supply control device 2 until the end-of-charge voltage is reached in the assembled battery 5 unit.
- the charging rate at this time is preferably 1 / 16C (1 / 16C) or more, and more preferably 1 / 12C (1 / 12C) or more.
- the charging rate is preferably 1C or less, more preferably 1 / 2C (1 / 2C) or less, and further preferably 1 / 4C (1 / 4C) or less.
- the battery is charged at 1 / 8C (1 / 8C).
- 1C refers to a current value at which a cell having a known capacity is subjected to constant current discharge and discharge is completed in one hour.
- the capacity of the secondary battery 15 when charged to the end-of-charge voltage at 1/8 C is 80% or more and 97% or less of the design capacity, and preferably 90% or more of the design capacity.
- the “designed capacity” here refers to a capacity calculated from the specific capacity per unit weight of the positive electrode 20 and the negative electrode 21.
- the discharge control of the present embodiment electricity is transmitted from the power supply control device 2 to the external power supply system 50 side in parallel with the external power supply system 50 according to the power demand on the external power supply system 50 side. That is, in the discharge control of the present embodiment, unlike the charge control, not only a constant current but also a non-constant current is output from each assembled battery 5 according to the power demand on the external power supply system 50 side. As the discharge control of this embodiment, for example, an arbitrary assembled battery 5 is discharged by applying a load with a constant wattage or a constant resistance.
- the physical properties of the secondary battery 15 of this embodiment will be described. Specifically, in the power storage device 1 of the present embodiment, a case where the secondary battery 15 is subjected to a predetermined number of charge / discharge cycles between the discharge end voltage and the charge end voltage will be described.
- the rate of decrease in capacity after the charge / discharge cycle with respect to the capacity before the charge / discharge cycle when 80 charge / discharge cycles are performed at a charge / discharge rate of 1/8 C is 2% or less, 0% Preferably there is. That is, the assembled battery 5 does not appear to have a reduced capacity under the condition that 80 charge / discharge cycles are performed at a charge / discharge rate of 1 / 8C.
- each secondary battery 15 constituting the assembled battery 5 has a capacity reduction rate after the charge / discharge cycle with respect to the capacity before the charge / discharge cycle when 80 charge / discharge cycles are performed at a charge / discharge rate of 1 / 8C. Is 2% or less, preferably 1% or less, and more preferably 0%. That is, the secondary battery 15 apparently has no capacity reduction under the condition that 80 charge / discharge cycles are performed at a charge / discharge rate of 1 / 8C.
- the assembled battery 5 has a capacity decrease rate after the charge / discharge cycle of 100% charge / discharge cycle at a charge / discharge rate of 1/8 C, and the capacity decrease rate after the charge / discharge cycle is 2% or less, and 1% or less. It is preferable that That is, the assembled battery 5 does not appear to have a reduced capacity under the condition that 100 charge / discharge cycles are performed at a charge / discharge rate of 1 / 8C.
- the secondary battery 15 constituting the assembled battery 5 has a capacity reduction rate after the charge / discharge cycle with respect to the capacity before the charge / discharge cycle when the charge / discharge cycle is performed 100 times at a charge / discharge rate of 1 / 8C. 2% or less, preferably 1% or less, and more preferably 0% or less. That is, the secondary battery 15 apparently has no capacity reduction under the condition that 100 charge / discharge cycles are performed at a charge / discharge rate of 1 / 8C.
- each secondary battery 15 constituting the assembled battery 5 the average thickness of the electrode active material layers 31, 41 of the electrodes 20, 21 is as large as 0.3 mm or more, so that the charging reaction is performed between the electrodes 20, 21, the electrolyte 23, and the like. Lithium ion diffusion rate is between. That is, each secondary battery 15 has a large diffusion resistance due to diffusion of metal ions contributing to the battery reaction.
- the increase in the voltage in the late stage of charging of the secondary battery 15 includes an increase due to diffusion resistance caused by diffusion of metal ions contributing to the battery reaction and an increase due to contact resistance between materials inside the secondary battery. Yes.
- the average thickness of the electrode active material layers 31 and 41 is as large as 0.3 mm or more, the diffusion resistance due to the diffusion of metal ions contributing to the battery reaction is large, and the voltage in the late stage of charging. The rate of increase is large. Therefore, even if each secondary battery 15 is apparently overcharged at a charge end voltage or higher, a voltage lower than the charge end voltage is applied to the active material layers 31 and 41 inside the actual secondary battery 15. ing. Therefore, it is considered that the active material layers 31 and 41 inside the secondary battery 15 are suppressed in terms of material destruction due to overvoltage and acceleration of decomposition of the electrolyte 23, and apparently there is no decrease in capacity.
- the metal of the electrolyte 23 reaches the end of the negative electrode active material layer 41 even when the end-of-charge voltage is reached.
- the ions are not sufficiently diffused, and the rate limiting of the capacity occurs due to the diffusion of metal ions. Therefore, even if the capacity is reduced due to the deterioration of the secondary battery 15, if the capacity is reduced within a certain range, there is no apparent capacity reduction. That is, the voltage due to the diffusion resistance of the metal ions is added to the voltage due to the electromotive force and the internal resistance of the secondary battery. Therefore, the charging is completed at an earlier stage than reaching the design capacity of the secondary battery.
- the design capacity is 100, for example, 80 is charged as a full charge capacity due to a voltage increase due to the diffusion resistance of metal ions.
- the “full charge capacity” here is the rated capacity of the battery, and means that it is not recommended for use of the battery to store more electricity. For this reason, even if the actual full charge capacity is reduced from 100 to 90, for example, due to the deterioration of the secondary battery 15, the battery is only charged up to 80 in the first place, so that the full charge capacity reaches 90. . Therefore, it is considered that the deterioration of the secondary battery 15 is not reflected in the capacity apparently and the capacity is not apparently decreased.
- each secondary battery 15 is unlikely to be in an overvoltage state, and there is no need to control capacity variation for each secondary battery 15. Therefore, it is possible to charge and discharge in units of the assembled battery 5 without charging and discharging each secondary battery 15 individually. For the same reason, it is possible to monitor and control the voltage in units of 5 assembled batteries. That is, since it is not necessary to individually monitor the voltage of each secondary battery 15, the assembled battery 5 and the battery system 3 can be simplified and inexpensive. Further, according to the power storage device 1 of the present embodiment, even when there is a variation in the end-of-charge voltage between the secondary batteries 15 constituting the assembled battery 5, the specific secondary battery 15 does not become an overvoltage and is stable over a long period of time. Can be maintained. That is, according to the power storage device 1, each secondary battery 15 is excellent in overvoltage resistance and becomes a power storage device having a long life as a whole.
- the power supply control device 2 controls each assembled battery 5 independently, even if there is a power request from the external power supply system 50 side, it is optional according to the power request.
- the assembled battery 5 can be discharged for power transmission.
- the power supply control apparatus 2 controls each assembled battery 5 independently, it is also possible to charge only the assembled battery 5 whose capacity has been reduced by discharging.
- the power storage device 1 is connected to the external power supply system 50 and used for power transmission, but the present invention is not limited to this. However, in view of the long life and high safety features of the present invention, it is preferable that the external power supply system 50 including the commercial power supply is connected to the external power supply system 50 as described above.
- the negative electrode 21 of the secondary battery 15 includes an oxide containing titanium as a negative electrode active material.
- an oxide containing titanium is used as the negative electrode active material, an abnormally active site may be generated in the oxide containing titanium during charging and discharging. When this abnormally active site is generated, the solvent of the electrolyte 23 may be decomposed to generate gas. Therefore, it is preferable that the positive electrode 20 which makes the pair contains the positive electrode active material which has as a main component the lithium cobalt oxide which has the capability to absorb the gas generated in the fixed charge state.
- the positive electrode 20 contains a positive electrode active material mainly composed of this lithium cobalt oxide, it becomes vulnerable to overcharge.
- a positive electrode containing lithium cobalt oxide and a positive electrode coated with another type of active material are used as the secondary battery 15. Then, it is preferable to disconnect the positive electrode containing lithium cobalt oxide after charging these electrodes to a constant current while being electrically insulated.
- one or more positive electrode active materials selected from the group consisting of lithium manganese oxide and an oxide obtained by substituting a part of the manganese with a different element are mainly used as the first positive electrode as another type of positive electrode.
- a positive electrode as a component is used.
- a positive electrode containing lithium cobalt oxide is used as the second positive electrode.
- the first positive electrode has a normal charge / discharge function
- the second positive electrode has a function of absorbing gas.
- the second positive electrode is electrically separated from the first positive electrode, the first positive electrode and the second positive electrode are charged to a constant current at the same time, and then the second positive electrode is electrically disconnected.
- the charged second electrode is present in the battery, and the second electrode containing the positive electrode active material mainly composed of lithium cobalt oxide absorbs the gas generated in the secondary battery. Can be made.
- the secondary battery 15 is a stack of the secondary battery cells 17 including the positive electrode 20 / the separator 22 / the negative electrode 21, but the present invention is not limited to this.
- the secondary battery may be obtained by winding a secondary battery cell composed of a positive electrode / separator / negative electrode.
- the secondary battery cell 17 is laminated and then covered with the laminate film that is the enclosure 27, but the present invention is not limited to this.
- the secondary battery 15 may be covered with a laminate film that is an enclosure 27 after being wound. Further, after the secondary battery cell 17 is wound or laminated, it may be packaged with a rectangular, oval, cylindrical, coin, button, or sheet metal can.
- a liquid nonaqueous electrolyte is used as the electrolyte 23, and the positive electrode 20, the negative electrode 21, and the separator 22 are impregnated with the nonaqueous electrolyte responsible for lithium ion conduction.
- the present invention is limited to this. Is not to be done.
- the electrolyte 23 may be impregnated in the positive electrode 20 and the negative electrode 21, or may be in a state only between the positive electrode 20 and the negative electrode 21. Further, if the positive electrode 20 and the negative electrode 21 are not in direct contact with the gel electrolyte 23, the separator 22 may not be used.
- the positive electrode 20 and the negative electrode 21 of the secondary battery 15 are formed by laminating the positive electrode active material layer 31 or the negative electrode active material layer 41 on one side or both sides of the current collectors 30 and 40.
- the present invention is not limited to this.
- the electrode of the secondary battery 15 may have a form in which the positive electrode active material layer 31 is formed on one side of the current collector and the negative electrode active material layer 41 is formed on the other side. That is, the electrode of the secondary battery may be a bipolar electrode having the positive electrode 20 and the negative electrode 21 on both sides.
- an insulating material is preferably disposed between the positive electrode and the negative electrode in order to prevent a liquid junction between the positive electrode and the negative electrode through the current collector.
- a separator is disposed between the positive electrode and the negative electrode of the adjacent bipolar electrode, and in the layer where the positive electrode and the negative electrode face each other, in order to prevent liquid junction, It is preferable that an insulating material is disposed around the positive electrode and the negative electrode.
- the three assembled batteries 5 are connected in parallel to the power supply control device 2, but the present invention is not limited to this.
- the secondary battery system 3 may appropriately connect a desired number of assembled batteries 5 to the power supply control device 2 in series according to a desired size and voltage, or a desired number of assembled batteries 5 to the power supply control device 2. May be connected in parallel as appropriate.
- the secondary battery 15 is a lithium ion secondary battery.
- the present invention is not limited to this and is another secondary battery that is charged and discharged by metal ion conduction. May be.
- it may be a sodium ion secondary battery or the like, or a multivalent ion secondary battery such as a magnesium secondary battery or an aluminum air battery.
- the secondary battery 15 protrudes from the enclosure 27 in the direction in which the terminal members 25 and 26 are separated from each other, but the present invention is not limited to this.
- the terminal members 25 and 26 may protrude from the enclosure 27 in the same direction from the enclosure 27.
- the secondary batteries 15 constituting each assembled battery 5 are the same type of batteries, but the present invention is not limited to this.
- One assembled battery 5 may be composed of a lithium ion secondary battery, and the other assembled battery 5 may be composed of a sodium ion secondary battery. Further, the capacity of each assembled battery 5 may be varied.
- each assembled battery 5 is charged / discharged at a uniform charge / discharge rate, but the present invention is not limited to this.
- the charge / discharge rate may be changed for each assembled battery 5.
- the secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 4 were produced by the following method, and the performance was evaluated. Each evaluation condition is as described in Table 1.
- Li 1.1 Al 0.1 Mn 1.8 O 4 (hereinafter also referred to as LAMO), LiNi 0.5 Mn 1.5 O 4 (hereinafter also referred to as LiNiMO), or Li 4 Ti 5 O 12 as an electrode active material
- LAMO Li 1.1 Al 0.1 Mn 1.8 O 4
- LiNiMO LiNi 0.5 Mn 1.5 O 4
- Li 4 Ti 5 O 12 Li 4 Ti 5 O 12 as an electrode active material
- Each electrode is mixed with 6.8 parts by weight of a conductive additive (acetylene black) and 6.8 parts by weight of a binder in terms of solid content with respect to 100 parts by weight of each powder (hereinafter also referred to as LTO).
- An active material mixture corresponding to the active material was prepared. And the electrode was produced using this mixture, and also the secondary battery was produced combining these electrodes.
- Electrode active material powder Each electrode active material was manufactured by the following method.
- Li 1.1 Al 0.1 Mn 1.8 O 4 which is a positive electrode active material
- LAMO Li 1.1 Al 0.1 Mn 1.8 O 4
- an aqueous dispersion of manganese dioxide, lithium carbonate, aluminum hydroxide, and boric acid was prepared, and a mixed powder was obtained by a spray drying method.
- the amounts of manganese dioxide, lithium carbonate and aluminum hydroxide were adjusted so that the molar ratio of lithium, aluminum and manganese was 1.1: 0.1: 1.8.
- the mixed powder was heated at 900 ° C. for 12 hours in an air atmosphere, and then again heated at 650 ° C. for 24 hours. Finally, the powder was washed with 95 ° C. water and dried to obtain a positive electrode active material powder.
- the positive electrode active material LiNi 0.5 Mn 1.5 O 4 (LiNiMO) was produced by the method described in the literature (Journal of PowerSources, 81-82, 90 (1999)). That is, lithium hydroxide, manganese oxide hydroxide, and nickel hydroxide were first mixed so that the molar ratio of lithium, manganese, and nickel was 1: 1.5: 0.5. Next, the mixture was heated at 550 ° C. in an air atmosphere, and then heated again at 750 ° C. to obtain a positive electrode active material powder.
- the negative electrode active material Li 4 Ti 5 O 12 was produced by a method described in the literature (Journal of Electrochemical Society, 142, 1431 (1995)). That is, first, titanium dioxide and lithium hydroxide were mixed so that the molar ratio of titanium to lithium was 5: 4. Next, the mixture was heated at 800 ° C. for 12 hours under a nitrogen atmosphere to obtain a powder of a negative electrode active material.
- the average particle diameters of the active materials measured by a laser diffraction scattering method particle size distribution analyzer were LAMO: 16 ⁇ m, LiNiMO: 11 ⁇ m, and LTO: 7 ⁇ m.
- the electrode active material and the conductive aid were mixed using an automatic mortar.
- the obtained mixed powder was transferred to a stainless steel bowl, a binder dispersed in water was added, and premixed using an alumina pestle. Thereafter, water and a solvent other than water were added to adjust the solid concentration to 80%, and the mixture was mixed again to obtain an active material mixture.
- the above active material mixture was dispersed on an aluminum expanded metal (aperture 1 mm ⁇ 2 mm, thickness 0.1 mm) and molded by pressing from above. Then, the electrode was produced by vacuum-drying at 170 degreeC. The thickness of the electrode containing the aluminum expanded metal after drying was about 1.0 mm.
- LAMO or LiNiMO was used as the positive electrode and LTO was used as the negative electrode.
- the electrode obtained above was laminated in the order of positive electrode / separator / negative electrode to produce a laminate.
- separator two cellulose non-woven fabrics (thickness: 25 ⁇ m) were used.
- an aluminum tab serving as a lead electrode was vibration welded to the positive electrode and the negative electrode, and the laminated body with the tab was put into a bag-shaped aluminum laminate sheet.
- a lithium metal electrode was used as the negative electrode, and a nickel tab vibration-welded to an electrode prepared by pressing lithium metal onto a stainless steel sheet was used.
- a non-aqueous electrolyte secondary battery was produced.
- the number of cycles is 100, and the voltage of the secondary battery at both ends of the unit cell or the assembled battery is monitored, and the charge is terminated when the charge end voltage is reached, and the discharge end voltage. Control was performed to stop the discharge when it reached.
- Table 1 shows values of the end-of-charge voltage, end-of-discharge voltage, actual measurement / design capacity ratio, and capacity retention rate of the unit cell or the assembled battery.
- Examples 1 to 5 are secondary batteries using LAMO as the positive electrode and LTO as the negative electrode (hereinafter, also referred to as LTO / LAMO secondary battery), both of which have a positive electrode thickness and a negative electrode thickness of 0.3 mm or more. did.
- the porosity of the positive electrode and the negative electrode was 35%.
- the battery is used as a unit cell, and in Example 5, an assembled battery in which five unit cells are connected in series was used.
- the measured capacity was smaller than the designed capacity calculated from the specific capacity per unit weight.
- Examples 1 to 5 it is considered that the charging reaction is a lithium ion diffusion rate-determining, and the actually measured voltage value is increased by this diffusion resistance.
- the capacity retention rate under the above measurement conditions showed 100% even after 100 cycles. That is, in Examples 1 to 5, even if the voltage generated in the secondary battery appears to be an overcharged state equal to or higher than the end-of-charge voltage under conditions including concentration polarization in the electrolyte and internal battery resistance.
- the material of the active material layer is only applied with a voltage lower than the end-of-charge voltage. For this reason, it is considered that acceleration of material destruction and decomposition of the electrolytic solution was suppressed. Therefore, Examples 1 to 5 can be used as a long-life secondary battery.
- Example 5 an assembled battery in which five secondary batteries are connected in series was used. However, when the assembled battery is controlled to switch to discharging when it reaches the end-of-charge voltage, the capacity retention rate is the same. there were.
- the voltage of each secondary battery is expected to be different at the end of charging, but includes a voltage increase due to the concentration polarization of the electrolyte as in the case of the single battery. Therefore, it is considered that neither material destruction nor electrolyte decomposition reaction occurred, and no capacity reduction was observed.
- Examples 6 and 7 are secondary batteries using LiNiMO for the positive electrode and LTO for the negative electrode (hereinafter also referred to as LTO / LiNiMO secondary battery), both of which have a positive electrode thickness and a negative electrode thickness of 0.3 mm or more. did.
- the porosity of the positive electrode and the negative electrode was both 35%.
- LTO / LiNiMO secondary batteries of Examples 6 and 7 even when a charge / discharge cycle test was performed under conditions of constant current control and a charge end voltage of 3.5 V, due to the influence of lithium ion diffusion, A capacity of 100% was not developed, and the capacity retention rate was good.
- Comparative Examples 1 to 4 are LTO / LAMO secondary batteries using LAMO for the positive electrode and LTO for the negative electrode, both of which had a positive electrode thickness and a negative electrode thickness of 0.2 mm.
- the porosity of the positive electrode and the negative electrode was 35%.
- this LTO / LAMO secondary battery was used as a unit cell, and in Comparative Example 3, an assembled battery in which five unit cells were connected in series was used.
- the actual measurement / design capacity ratio was 100%, and the capacity could be taken out as the design capacity.
- Comparative Example 2 an LTO / LAMO secondary battery using LAMO as the positive electrode and LTO as the negative electrode was used, and the thickness of the positive electrode and the thickness of the negative electrode were both 0.3 mm. In Comparative Example 2, the porosity of the positive electrode and the negative electrode was both 35%. In Comparative Example 2, five unit cells are connected in series to form an assembled battery, and when charging the assembled battery, charging is performed at a constant current until reaching the end-of-charge voltage. The battery was charged at a constant voltage until the current value reached 1 / 40C at the end voltage (CCCV). In Comparative Example 2, the actual measurement / design capacity ratio was 100% when the charging was completed, and the capacity retention rate was reduced although the capacity could be taken out as designed. This is because the voltage increase of each secondary battery connected in series was uneven, the secondary battery that had been increased in voltage was loaded, and the capacity decreased due to degradation of the active material and decomposition of the electrolyte on the electrode surface. It is thought to be caused by.
- Comparative Example 4 an LTO / LAMO secondary battery using LAMO as the positive electrode and LTO as the negative electrode was used, and the thickness of the positive electrode and the thickness of the negative electrode were both 1.0 mm. In Comparative Example 4, the porosity of the positive electrode and the negative electrode was both 10%. In Comparative Example 4, when the charging was completed, the actual measurement / design capacity ratio was 72%, and the capacity maintenance rate was also reduced to 92%. This is because, in the LTO / LAMO secondary battery of Comparative Example 4, the diffusion rate of metal ions in the electrolytic solution is slowed by reducing the porosity of the electrodes. For this reason, it is considered that local reactions are likely to occur in addition to the difficulty in expressing the design capacity.
- the reaction rate of the active material layers of the positive electrode and the negative electrode can be controlled by diffusion of lithium ions. And by charging only with a constant current in this state, even if 80 charge / discharge cycles are performed at a current value at which charging or discharging ends in 8 hours, material deterioration hardly occurs in the active material layer, and the capacity is substantially reduced. It turned out that it becomes a secondary battery without a fall.
Abstract
Description
この蓄電装置は、蓄電池たる二次電池と、専用の充電装置を備えている。この蓄電装置は、蓄電する際には、専用の充電装置を使用して二次電池に充電し、外部負荷から電力要求があった場合には、二次電池に充電した電気を外部負荷に送電することが可能となっている。
このような場合には、通常、組電池単位で過充電を防止する制御を行っており、単電池単位での制御はなされていない。そのため、組電池単位の制御では、劣化度合や個体差等によって、組電池を構成する特定の二次電池が過充電状態に陥る場合があり、特定の二次電池の過充電状態を解消できない。それ故に、複数の二次電池を直列接続して組電池を構成する場合は、各二次電池に過充電耐性のある二次電池を使用することが必須となっていた。
ここでいう「充電終止電圧」とは、二次電池に発生する電圧の制限値であって、例えば、リミッターにて制限される電圧である。すなわち、二次電池を安全に充電するための定格値である。
ここで、このような挿入・脱離反応によって充放電を行う二次電池は、抵抗損失(IRドロップ)に含まれる抵抗成分として、主に構成材料間の接触抵抗成分と、金属イオンが電極から非水電解質に拡散する際に生じる拡散抵抗成分がある。
通常の二次電池では、設計容量通りの出力を得るために、接触抵抗や拡散抵抗をできる限り小さくして、実際の容量を設計した容量に近づけている。
また、リチウム二次電池等の二次電池では、金属イオンが空気中の酸素や水分との反応性が高いので、過充電状態に陥ると、安全が損なわれる可能性がある。そのため、過充電による破損を防止するために、一定容量まで定電流で充電した後、定電圧に変更して充電終止電圧を超えないように充電を行うことが一般的に行われている。
一方、本様相の二次電池によれば、これらの従来の常識に反して、正極及び負極の活物質層の平均厚みを0.3mm以上と厚くし、設計容量の80%以上97%以下に抑えている。すなわち、本様相の二次電池では、敢えて金属イオンが拡散しにくい状態を作って、拡散抵抗成分を大きくし、自発的に金属イオンの拡散律速の状態を形成している。
そして、本様相の二次電池は、設計容量通りの容量が出ない状態で充電装置によって充電終止電圧まで定電流で充電している。そのため、充電完了となる充電終止電圧となっても、実際に二次電池の構成部材に印加されている電圧は、拡散抵抗成分の増加による抵抗損失の分だけ低い。それ故に、本様相の二次電池装置によれば、仮に充電終止電圧以上に過充電してしまっても、拡散抵抗成分による電圧上昇の範囲であれば、内部の活物質層自体は過充電状態にはならない。そのため、二次電池の構成材料の破壊や電解質の分解の加速が発生しにくい。
このように、本様相によれば、充電終止電圧に達しても設計上の満充電容量に達しないので、充電深度検知用の電池を用いなくても、二次電池の過充電を防止できる。そのため、制御の簡略化及び低コスト化が可能である。
したがって、充放電の度に、劣化した二次電池に負荷が集中することを防止でき、組電池としての寿命が長くできる。
ここでいう「商用電源系統」とは、購入等によって電力会社等から供給される電源系統をいう。
蓄電装置1は、太陽光発電システムや燃料電池システムなどの発電システム(図示しない)や商用電源系統などの外部電源系統50から送電された電気を一時的に蓄電可能な蓄電装置である。また、蓄電装置1は、蓄電した電気を外部負荷や商用電源系統などの外部電源系統50に対して供給する電力供給装置でもある。
そして、本実施形態の蓄電装置1は、二次電池システム3を構成する二次電池15が充電時において金属イオンの拡散が律速となるものであり、電源制御装置2によって定電流でのみ二次電池15を充電する点を主な特徴の一つとしている。
また、電源制御装置2は、二次電池システム3に対して送電して二次電池システム3を充電する充電装置であり、二次電池システム3に充電された電気を外部電源系統50側に送電する送電装置でもある。
電源制御装置2は、二次電池システム3の各組電池5に対して独立して充放電可能である。すなわち、電源制御装置2は、各組電池5と配線部材16を介して電気的に接続されており、組電池5単位で電圧を監視及び制御可能となっている。
また、二次電池15は、封入体27の内外に端子部材25,26が跨って配されている。すなわち、各端子部材25,26の一方の端部は、図4のように、封入体27の内部でそれぞれ正極部材10及び負極部材11と接続されており、他方の端部は、図3のように封入体27の外部に露出して配線部材16と接続可能となっている。
二次電池セル17は、図4のように、正極20、負極21、及びセパレータ22が積層された積層体である。すなわち、二次電池セル17は、正極20及び負極21によって電解質23を含んだセパレータ22を挟持した部分である。
正極部材10は、板状又はフィルム状の電極部材であり、その片面又は両面に正極20が形成されたものである。
正極20は、金属イオンの挿入・脱離が可能な活物質層31を備えるものであり、板状又はフィルム状の集電体30の両面又は片面上に正極活物質層31が積層されたものである。すなわち、正極20は、正極部材10の一部であって、集電体30上に正極活物質層31が積層された部分である。
正極部材10aは、集電体30の片面に正極活物質層31が形成されて正極20aが形成されている。正極部材10bは、集電体30の両面に正極活物質層31,31が形成されて正極20b,20cが形成されている。
すなわち、正極部材10aは、片面が電極となっており、正極部材10bは、両面が電極となっている。
正極活物質層31は、正極活物質を主要成分とするものであり、必要に応じて導電助材及び/又はバインダーが含まれている。
本実施形態の正極活物質層31は、正極活物質を主成分とし、導電助材及びバインダーが添加されている。
ここでいう「主要成分」とは、性能を決定する成分をいう。
ここでいう「主成分」とは、全体の50%以上占める成分をいう。
正極活物質の主成分は、リチウムマンガン酸化物、及びそのマンガンの一部を異種元素で置換した酸化物からなる群から選ばれる1種以上であることがより好ましい。正極活物質の主成分は、過充電に対して非常に耐性がある観点から、前記異種元素がニッケル、アルミニウム、マグネシウム、チタン、クロム、コバルト、鉄から選ばれる少なくとも1種を含む金属イオンであることが特に好ましい。
正極活物質層31の平均厚みが0.3mm以上であることにより、充電反応において金属イオンの拡散が律速状態となりやすく、二次電池15が充電終止電圧に到達した場合でも活物質層31に加わる電圧を充電終止電圧以下に留めることができる。そのため、充電終止電圧以上の過電圧が二次電池15にかかることによる材料破壊や電解質23の分解の加速を抑制できる。
集電体30の表面に形成された正極活物質層31の平均厚みは、1.5mm以下であることが好ましい。
この範囲であれば、拡散律速となっても、充電終止電圧まで充電したときの容量が正極20の単位重量当たりの固有の容量から算出される設計容量に対して下がりすぎない。
正極活物質層31の空隙率が15%未満の場合、イオン拡散が制限されすぎるので、良好な電池性能が得られにくい。
正極活物質層31の空隙率が60%超過の場合、活物質同士もしくは活物質と導電助材の接触不良になることがあり、電池性能が低下する恐れがある。
また、空隙率が大きい場合には体積エネルギー密度が低下するため、前記範囲内であることが好ましい。
負極部材11は、板状又はフィルム状の電極部材であり、その片面又は両面に負極21が形成されたものである。
負極21は、金属イオンの挿入・脱離が可能な活物質層41を備えるものであり、板状又はフィルム状の集電体40の両面又は片面上に負極活物質層41が積層されたものである。すなわち、負極21は、負極部材11の一部であって、集電体40上に負極活物質層41が積層された部分である。
負極部材11aは、集電体40の両面に負極活物質層41,41が形成されて負極21a,21bが形成されている。負極部材11bは、集電体40の片面に負極活物質層41が形成されて負極21cが形成されている。すなわち、負極部材11aは、両面が電極となっており、負極部材11bは、片面が電極となっている。
負極21aは、正極部材10aの正極20aの対極となっており、負極21bは、正極部材10bの正極20bの対極となっている。また、負極21cは、正極部材10bの正極20cの対極となっている。
負極活物質層41は、負極活物質を主要成分とするものであり、必要に応じて導電助材及び/又はバインダーが含まれている。
本実施形態の負極活物質層41は、負極活物質を主成分とし、導電助材及びバインダーが添加されている。
負極活物質の主成分は、リチウムチタン酸化物、及びリチウムチタン酸化物のチタンの一部を他の金属イオンで置換したものからなる群から選ばれる1種以上であることがより好ましい。負極活物質の主成分は、過充電に対して非常に耐性があり、より長寿命化に効果がある観点から、前記他の金属イオンがニオブであることが特に好ましい。
負極活物質層41の平均厚みが0.3mm以上であることにより、充電反応において金属イオンの拡散が律速状態となりやすく、二次電池15が充電終止電圧に到達した場合でも活物質層41に加わる電圧を充電終止電圧以下に留めることができる。そのため、充電終止電圧以上の過電圧が二次電池15にかかることによる材料破壊や電解質23の分解の加速を抑制できる。
集電体40の表面に形成された負極活物質層41の平均厚みは、1.5mm以下であることが好ましい。
この範囲であれば、充電終止電圧まで充電したときの容量が負極21の単位重量当たりの固有の容量から算出される設計容量から下がりすぎない。
空隙率が15%未満の場合、リチウムイオンの拡散が制限されすぎるため、良好な電池性能が得られにくい。
空隙率が60%超過の場合、活物質同士もしくは活物質と導電助材の接触不良になることがあり、電池性能が低下する恐れがある。
また、空隙率が大きい場合には体積エネルギー密度が低下するため、前記範囲内であることが好ましい。
集電体30,40を構成する導電性材料としては、例えば、銅、アルミニウム、ニッケル、チタン、及びこれら少なくとも1種を含む合金又は導電性を有する高分子が挙げられる。
集電体30,40の形状としては、箔状、メッシュ状、パンチング状、エキスパンド状、又は発泡構造体が挙げられる。このような集電体に用いられる導電性材料は、電極作動電位で安定であればよい。本実施形態のようなリチウムイオン二次電池においては、作動電位がリチウム金属基準で0.7V以下では、銅およびその合金が好ましく、0.7V以上ではアルミニウムおよびその合金が好ましい。
正極活物質層31及び負極活物質層41を構成するバインダーは、結着性があり、水又は有機溶媒に分散可能なものであれば、特に限定されない。
バインダーは、例えば、ポリフッ化ビニリデン(PVdF)、ポリテトラフルオロエチレン(PTFE)、テトラフルオロエチレン-ヘキサフルオロプロピレン共重合体(FEP)、スチレン-ブタジエン共重合体(SBR)、ポリアクリル酸エステル、ポリビニルアルコール(PVA)、カルボキシメチルセルロース(CMC)、ポリイミド(PI)およびそれら誘導体からなる群から選ばれる少なくとも1種を用いることができる。これらに分散剤、増粘剤を加えても良い。
正極活物質層31及び負極活物質層41を構成する導電助材は、特に限定されないが、炭素材料又は/及び金属微粒子が好ましい。
炭素材料として、例えば、天然黒鉛、人造黒鉛、気相成長炭素繊維、カーボンナノチューブ、アセチレンブラック、ケッチェンブラック、カーボンブラック、またはファーネスブラックなどが挙げられる。
金属微粒子としては、例えば、銅、アルミニウム、ニッケルおよびこれら少なくとも1種を含む合金が挙げられる。
また、無機材料の微粒子にめっきを施したものでも良い。これら炭素材料および金属微粒子は1種類でも良いし、2種類以上用いても良い。
セパレータ22は、電解質23が含浸したものであり、多孔質材料又は不織布等が挙げられる。
セパレータ22の材質としては、電解質23を構成する有機溶媒に対して溶解しないものが好ましく、具体的にはポリエチレンもしくはポリプロピレンなどのポリオレフィン系ポリマー、ポリエチレンテレフタレートなどのポリエステル系ポリマー、セルロース、またはガラスなどの無機材料が挙げられる。
1μm未満であるとセパレータ22の機械的強度の不足により破断し、内部短絡する傾向がある。
一方、500μmより厚い場合、電池15の内部抵抗と、正極20及び負極21の電極間距離が増大することにより、電池15の負荷特性が低下する傾向がある。より好ましい厚みは、10μm以上300μm以下である。
電解質23は、金属イオン伝導性をもち、各正極20及び各負極21との間で電気伝導に伴って金属イオンの挿入・脱離が可能な電解質である。また電解質23は、水を実質的に含まない非水電解質である。
電解質23は、特に限定されないが、非水溶媒に溶質を溶解させた電解液、非水溶媒に溶質を溶解させた電解液を高分子に含浸させたゲル電解質、固体電解質、イオン液体とシリカ微粒子を混合し、疑似固体化した固体電解質などを用いることができる。
本実施形態の電解質23は、非水溶媒に溶質を溶解させた非水電解質であって、液体状の電解液であり、封入体27内に充填されている。
この環状の非プロトン性溶媒としては、環状カーボネート、環状エステル、環状スルホンまたは環状エーテルなどが例示される。
一方、鎖状の非プロトン性溶媒としては、鎖状カーボネート、鎖状カルボン酸エステルまたは鎖状エーテルなどが例示される。
より具体的には、ジメチルカーボネート、メチルエチルカーボネート、ジメチルカーボネート、ジプロピルカーボネート、メチルプロピルカーボネート、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、γ-ブチロラクトン、1,2-ジメトキシエタン、スルホラン、ジオキソラン、またはプロピオン酸メチルなどを用いることができる。これら溶媒は1種類で用いてもよいし、2種類以上混合して用いてもよいが、後述の溶質の溶解させやすさ、リチウムイオンの伝導性の高さから、2種類以上混合した溶媒を用いることが好ましい。
また、高分子に電解液またはイオン液体をしみこませたゲル状電解質、疑似固体電解質および硫黄系固体電解質も用いることができる。
電解質23に含まれる溶質の濃度は、0.5mol/L以上2.0mol/L以下であることが好ましい。
電解質23に含まれる溶質の濃度が0.5mol/L未満では所望のイオン伝導性が発現しない場合がある。
一方、電解質23に含まれる溶質の濃度が2.0mol/Lより高いと、溶質がそれ以上溶解しない場合がある。
なお、電解質23には、難燃剤、安定化剤などの添加剤が微量含まれてもよい。
電解質23の量が0.1mL未満の場合、電極反応に伴うイオンの伝導が追いつかず、所望の電池性能が発現しない場合がある。
なお、電解質23として固体電解質を用いる場合には、そのまま加圧成形しても良いし、前述の電極20,21に用いたバインダーを使用し、シート状に成形して使用しても良い。
正極20aの正極活物質層31は、電解質23を含んだセパレータ22を挟んで、負極21aを構成する負極活物質層41と対向している。正極20bの正極活物質層31は、電解質23を含んだセパレータ22を挟んで、負極21bを構成する負極活物質層41と対向している。正極20cの正極活物質層31は、電解質23を含んだセパレータ22を挟んで、負極21cを構成する負極活物質層41と対向している。
正極部材10a,10bを構成する集電体30,30の端部は、互いに接触しており、正極部材10a,10bのうち一方の正極部材10が端子部材25と接続されている。
同様に、負極部材11a,11bの集電体40,40の端部は、互いに接触しており、負極部材11a,11bのうち一方の負極部材11が端子部材26と接続されている。
電解質23は、封入体27の内部に充填されており、各セパレータ22は電解質23が含浸している。
このときの充電レートは、1/16C(16分の1C)以上であることが好ましく、1/12C(12分の1C)以上であることがより好ましい。
また充電レートは、1C以下であることが好ましく、1/2C(2分の1C)以下であることがより好ましく、1/4C(4分の1C)以下であることがさらに好ましい。
これらの範囲であれば、充電に時間がかかりすぎず、二次電池15の構成部材に負荷がかかりすぎない。
本実施形態では、1/8C(8分の1C)で充電している。
ここでいう「1C」とは、既知の容量を持つセルを定電流放電して,1時間で放電終了となる電流値をいう。
ここでいう「設計容量」とは、正極20及び負極21の単位重量当たりの固有の容量から算出される容量をいう。
同様に、組電池5を構成する各二次電池15は、1/8Cの充放電レートで充放電サイクルを80サイクル行った場合の充放電サイクル前の容量に対する充放電サイクル後の容量の低下率は、2%以下であり、1%以下であることが好ましく、0%であることがより好ましい。すなわち、二次電池15は、1/8Cの充放電レートで充放電サイクルを80サイクル行う条件では、見かけ上容量低下がない。
同様に組電池5を構成する二次電池15は、1/8Cの充放電レートで充放電サイクルを100サイクル行った場合の充放電サイクル前の容量に対する充放電サイクル後の容量の低下率は、2%以下であり、1%以下であることが好ましく、0%以下であることがより好ましい。すなわち、二次電池15は、1/8Cの充放電レートで充放電サイクルを100サイクル行う条件では、見かけ上容量低下がない。
ここで、二次電池15の充電後期の電圧の上昇は、電池反応に寄与する金属イオンの拡散に起因する拡散抵抗による上昇と、二次電池内部での材料間の接触抵抗による上昇を含んでいる。
本実施形態の二次電池15では、電極活物質層31,41の平均厚みが0.3mm以上と厚いため、電池反応に寄与する金属イオンの拡散に起因する拡散抵抗が大きく、充電後期における電圧上昇率が大きい。そのため、各二次電池15が見かけ上充電終止電圧以上の過充電状態になっても、実際の二次電池15の内部の活物質層31,41には、充電終止電圧以下の電圧が印加されている。そのため、二次電池15の内部の活物質層31,41は、過電圧に至ることによる材料破壊や電解質23の分解の加速が抑制され、見かけ上容量低下がなかったと考えられる。
ここでいう「満充電容量」とは、電池の定格容量であって、それ以上の電気を蓄えることは電池の使用上推奨されないという量のことである。
このことから、仮に二次電池15の劣化により、実際の満充電容量が例えば100から90に低下したとしても、そもそも80までしか充電しないから、満充電容量が90に至るまでに満充電となる。そのため、二次電池15の劣化が見かけ上容量に反映されず、見かけ上容量低下がなかったと考えられる。
また本実施形態の蓄電装置1によれば、組電池5を構成する二次電池15間で充電終止電圧にばらつきがある場合でも、特定の二次電池15が過電圧にならず、長期間において安定した状態を維持できる。すなわち、蓄電装置1によれば、各二次電池15が過電圧耐性に優れ、全体として長寿命な蓄電装置となる。
しかしながら、本発明の長寿命、高安全という特長に鑑みると、上記した実施形態のように商用電源を含む外部電源系統50に系統連系されて用いることが好ましい。
ここで、チタンを含む酸化物を負極活物質として使用する場合、充放電の際に、チタンを含む酸化物において、異常活性点が発生することがある。この異常活性点が発生すると、電解質23の溶媒が分解してガスが発生する場合がある。
そのため、その対をなす正極20は、一定の充電状態で発生したガスを吸収する能力があるリチウムコバルト酸化物を主成分とする正極活物質を含むことが好ましい。
しかし、正極20は、このリチウムコバルト酸化物を主成分とする正極活物質を含むと、過充電に対し脆弱となる。
そこで、本発明の効果を奏さしめつつ、このようなガス発生を抑制せしめる観点から、二次電池15として、リチウムコバルト酸化物を含んだ正極と、他の種類の活物質を塗布した正極を使用し、これらの電極を電気的に絶縁した状態で同時に一定電流まで充電した後に、リチウムコバルト酸化物を含んだ正極を切り離すことが好ましい。
具体的には、他の種類の正極たる第1の正極として、リチウムマンガン酸化物およびそのマンガンの一部を異種元素で置換した酸化物からなる群から選ばれる1種以上の正極活物質を主成分とする正極を使用する。第2の正極としてリチウムコバルト酸化物を含んだ正極を使用する。すなわち、第1の正極に通常の充放電の機能を担わせ、第2の正極にガスを吸収する機能を担わせる。そして、第2の正極を第1の正極と電気的に分離されておき、第1の正極と第2の正極を同時に一定電流まで充電した後に、第2の正極を電気的に切り離す。
こうすることによって、充電状態の第2の電極を電池内に存在させ、リチウムコバルト酸化物を主成分とする正極活物質を含んだ第2の電極によって、二次電池中に発生したガスを吸収させることができる。
二次電池は、正極/セパレータ/負極からなる二次電池セルを巻回したものであってもよい。
二次電池15が二次電池セル17を巻回したものである場合には、巻回した後に封入体27であるラミネートフィルムで外装してもよい。
また、二次電池セル17を巻回した後、又は積層した後に、角形、楕円形、円筒形、コイン形、ボタン形、シート形の金属缶で外装してもよい。
電解質23としてゲル状の非水電解質を使用する場合は、電解質23が正極20及び負極21に含浸していてもよいし、正極20・負極21間のみにある状態でもよい。また、ゲル状の電解質23により正極20・負極21間が直接接触していなければ、セパレータ22を使用しなくてもよい。
例えば、二次電池15の電極は、集電体の片面に正極活物質層31、もう片面に負極活物質層41を形成させた形態であってもよい。すなわち、二次電池の電極は、正極20及び負極21をそれぞれ両面にもつバイポーラ電極であってもよい。
二次電池の電極をバイポーラ型の電極とする場合には、集電体を介した正極と負極の液絡を防止するため、絶縁材料が正極と負極間に配置されることが好ましい。
また、二次電池の電極をバイポーラ電極とする場合は、隣り合うバイポーラ電極の正極と負極との間にセパレータを配置し、正極と負極とが対向した層内は、液絡を防止するため、正極および負極の周辺部に絶縁材料が配置されることが好ましい。
二次電池システム3は、所望の大きさや電圧によって、電源制御装置2に対して所望数の組電池5を適宜直列接続してもよいし、電源制御装置2に対して所望数の組電池5を適宜並列接続してもよい。
また、並列の個数には、特に制限がなく、使用する用途によって自由に設計することができる。
一の組電池5をリチウムイオン二次電池で構成し、他の組電池5をナトリウムイオン二次電池で構成してもよい。また、各組電池5の容量を異ならせてもよい。
電極活物質であるLi1.1Al0.1Mn1.8O4(以下、LAMOともいう)、LiNi0.5Mn1.5O4(以下、LiNiMOともいう)、又はLi4Ti5O12(以下、LTOともいう)の各々の粉末100重量部に対して、導電助材(アセチレンブラック)を6.8重量部、バインダーを固形分換算で6.8重量部混合して、各々の電極活物質に対応する活物質混合物を調製した。そして、この混合物を用いて電極を作製し、更にこれらの電極を組み合わせて二次電池を作製した。
各々の電極活物質は、以下の方法で製造した。
すなわち、二酸化マンガン、炭酸リチウム、水酸化アルミニウム、およびホウ酸の水分散液を調製し、スプレードライ法で混合粉末を得た。
このとき、二酸化マンガン、炭酸リチウムおよび水酸化アルミニウムの量は、リチウム、アルミニウム、及びマンガンのモル比が1.1:0.1:1.8となるように調製した。次に、この混合粉末を空気雰囲気下900℃で12時間加熱した後、再度650℃で24時間加熱した。最後に、この粉末を95℃の水で洗浄後、乾燥させることによって正極活物質の粉末を得た。
すなわち、まず水酸化リチウム、酸化水酸化マンガン、及び水酸化ニッケルをリチウム、マンガン、及びニッケルのモル比が1:1.5:0.5となるように混合した。次に、この混合物を空気雰囲気下550℃で加熱した後に、再度750℃で加熱することによって正極活物質の粉末を得た。
すなわち、まず二酸化チタンと水酸化リチウムを、チタンとリチウムとのモル比を5:4となるように混合した。次に、この混合物を窒素雰囲気下800℃で12時間加熱することによって負極活物質の粉末を得た。
活物質混合方法および電極作製方法を以下に示す。
その後に、170℃で真空乾燥することにより電極を作製した。乾燥後のアルミニウムエキスパンドメタルを含む電極の厚さはおよそ1.0mmであった。
LAMOまたはLiNiMOを正極として使用し、LTOを負極として使用した。
次に、正極及び負極に引き出し電極となるアルミニウムタブを振動溶接させた後に、このタブ付きの積層体を袋状のアルミラミネートシートに入れた。
正極及び負極の容量の測定には、負極としてリチウム金属電極を用い、ステンレス製シートにリチウム金属を圧着させることにより作製した電極に、ニッケルタブを振動溶接したものを使用した。
前記積層体入りの袋の中に、非水電解液(プロピレンカーボネート/エチルメチルカーボネート=3/7vol%、LiPF6 1mol/L)を入れた後に、袋の出口を引き出し電極ごと熱封止することによって非水電解質二次電池を作製した。
この二次電池を充放電することにより測定される、各電極が持つ単位重量当たりの固有の容量は、LAMOは100mAh/g、LiNiMOは130mAh/g、LTOは165mAh/gであった。
正極にLAMO又はLiNiMOを、負極にLTOを用いた二次電池を、単独で、又は同じ種類の二次電池同士を直列接続した組電池として、外装の外側から金属板で挟んだ状態で、8時間で充電又は放電が終わる電流値(1/8Cレート)で充放電サイクル試験を行った。すなわち、前記組電池は、前記直列接続の任意の点に流れる電流IC(CHARGE)であって、含まれる二次電池に共通に流れる電流ICを1/8Cとして、含まれる全ての二次電池を充放電した。
この単電池又は組電池の充電終止電圧、放電終止電圧、実測/設計容量比、容量維持率の値を表1に示す。
実施例1~5は、正極にLAMO、負極にLTOを用いた二次電池(以下、LTO/LAMO二次電池ともいう)であり、いずれも正極の厚み及び負極の厚みが0.3mm以上とした。実施例1~5では、正極及び負極の空隙率をいずれも35%とした。
実施例1~4では、単電池として使用しており、実施例5では、5つの単電池を直列に接続した組電池を使用した。
実施例1~5の二次電池では、2.8Vの充電終止電圧に到達した際に、実測の容量は、単位重量当たりの固有の容量から計算される設計容量よりも小さい値となった。
これは、電池反応に関わるリチウムイオンの拡散が追い付かず、電解液中のリチウムイオンの濃度分極により、実測される電圧値が大きくなったことによると考えられる。すなわち、実施例1~5は、充電反応がリチウムイオンの拡散律速となっており、この拡散抵抗の分、実測される電圧値が大きくなったことによると考えられる。
また、実施例1~5は、上記した測定条件での容量維持率が100サイクル後も100%を示した。
すなわち、実施例1~5は、電解液中の濃度分極と、電池内部抵抗を含む条件下では、二次電池に発生する電圧が、見かけ上、充電終止電圧以上の過充電状態になっても、実際には、活物質層の材料には充電終止電圧以下の電圧しかかかっていない。そのため、材料破壊や電解液の分解の加速は抑制されたと考えられる。それ故に、実施例1~5は、長寿命な二次電池として使用することができる。
二次電池を直列接続した場合、充電終止時にそれぞれの二次電池の電圧が異なると予想されるが、単電池の場合と同様に電解液の濃度分極による電圧上昇を含んでいる。そのため、材料破壊や電解液分解反応が起こらず、容量低下は見られなかったと考えられる。
実施例6,7は、正極にLiNiMO、負極にLTOを用いた二次電池(以下、LTO/LiNiMO二次電池ともいう)であり、いずれも正極の厚み及び負極の厚みが0.3mm以上とした。実施例6,7では、正極及び負極の空隙率をいずれも35%とした。
実施例6,7のLTO/LiNiMO二次電池は、定電流制御、充電終止電圧3.5Vの条件下で充放電サイクル試験を行った場合も、リチウムイオン拡散の影響により、設計容量に対して100%の容量は発現せず、容量維持率は良好であった。
比較例1,3は、正極にLAMO、負極にLTOを用いたLTO/LAMO二次電池であり、いずれも正極の厚み及び負極の厚みが0.2mmとした。比較例1,3では、正極及び負極の空隙率をいずれも35%とした。
比較例1では、このLTO/LAMO二次電池を単電池として使用しており、比較例3では、この単電池を5つ直列に接続した組電池を使用した。
比較例1,3では、実測/設計容量比が100%となり、容量を設計容量通りに取り出すことができた。これは、電極の厚みが薄いので、電解液の濃度分極が充電後期の電圧の立ち上がりに寄与する部分が小さく、大きな濃度分極が発生する前に活物質中の全てのリチウムイオンが脱離、又は挿入している。そのため、設計容量どおりの容量を取り出すことができたと考えられる。
また、比較例1のように単電池のみかつ定電流制御で充放電を行った場合には、容量維持率は良好であったが、比較例3に示すように当該二次電池を5個直列接続した場合には、容量維持率が低下した。このことは、直列した各二次電池の電圧上昇が均一ではないことに加え、電解液の濃度分極の影響が極めて小さい。このため、先に充電終止電圧に到達した二次電池の負荷が大きくなり、活物質の劣化や電解液分解反応が起こることで、容量維持率が低下したと考えられる。
比較例2では、正極及び負極の空隙率をいずれも35%とした。
また比較例2では、5つの単電池を直列に接続して組電池とし、この組電池を充電する際に、充電終止電圧に到達するまで定電流で充電し、充電終止電圧に到達すると、充電終止電圧で電流値が1/40Cとなるまで定電圧で充電した(CCCV)。
この比較例2では、充電完了時に実測/設計容量比が100%となり、容量を設計容量通り取り出せているものの、容量維持率は低下した。
これは、直列接続した各二次電池の電圧上昇にばらつきがあり、先に電圧が上がった二次電池に負荷がかかり、活物質の劣化や電極表面の電解液の分解により容量が減少したことに起因すると考えられる。
また、比較例4では、正極及び負極の空隙率をいずれも10%とした。
比較例4では、充電完了時に実測/設計容量比が72%となり、容量維持率も92%と低下した。これは、比較例4のLTO/LAMO二次電池では、電極の空隙率を小さくすることで電解液中の金属イオンの拡散速度が遅くなる。そのため、設計容量を発現させることが困難になることに加え、局部的な反応が起こりやすくなったためと考えられる。
2 電源制御装置
5 組電池
10 正極部材
11 負極部材
20 正極
21 負極
22 セパレータ
23 電解質
31 正極活物質
41 正極活物質
50 外部電源系統
Claims (11)
- 二次電池と、前記二次電池を充電する充電装置を備えた蓄電装置であって、
前記二次電池は、正極と、負極と、前記正極及び前記負極に挟まれる非水電解質を有し、
前記二次電池は、金属イオンが非水電解質を介して前記正極及び前記負極との間を金属イオンが移動可能であって、前記正極及び前記負極がそれぞれ前記非水電解質との間で前記金属イオンの挿入・脱離反応が起こって充放電可能であり、
前記正極及び前記負極は、いずれも平均厚みが0.3mm以上の活物質層を備えており、
前記充電装置は、前記二次電池に電気的に接続され、充電時に前記二次電池に対して定電流のみで充電するものであり、
前記充電装置によって充電終止電圧まで充電したときの前記二次電池の容量は、前記正極及び前記負極の単位重量当たりの固有の容量から算出される設計容量の80%以上97%以下であることを特徴とする蓄電装置。 - 放電終止電圧から充電終止電圧の範囲において、8時間で充電又は放電が終わる電流値で充放電サイクルを80サイクル行ったときに、充放電サイクル前の二次電池の容量に対する容量の低下が2%以下であることを特徴とする請求項1に記載の蓄電装置。
- 複数の前記二次電池が直列接続された組電池を有し、
前記充電装置は、前記組電池単位で各二次電池を充電することを特徴とする請求項1又は2に記載の蓄電装置。 - 前記組電池を複数有し、
前記充電装置は、充電時に前記組電池単位で電圧の監視及び制御を行うことを特徴とする請求項3に記載の蓄電装置。 - 外部電源系統に連系可能であり、
前記外部電源系統側に送電可能であることを特徴とする請求項1~4のいずれかに記載の蓄電装置。 - 前記二次電池は、定電流又は定電流以外で放電可能であることを特徴とする請求項1~5のいずれかに記載の蓄電装置。
- 前記二次電池は、前記活物質層の空隙率がそれぞれ15%以上であることを特徴とする請求項1~6のいずれかに記載の蓄電装置。
- 前記非水電解質は、溶質を溶媒で溶かした非水電解液であり、
前記溶媒は、炭酸塩であることを特徴とする請求項1~7のいずれかに記載の蓄電装置。 - 前記溶質は、リチウムとハロゲンを含む化合物であることを特徴とする請求項8に記載の蓄電装置。
- 前記負極の活物質層は、リチウムチタン酸化物、及びリチウムチタン酸化物のイオンの一部を別の金属イオンで置換したものから選ばれる少なくとも1種以上の負極活物質を含むことを特徴とする請求項1~9のいずれかに記載の蓄電装置。
- 前記正極の活物質層は、リチウムマンガン酸化物、及びリチウムマンガン酸化物のイオンの一部を別の金属イオンで置換したものから選ばれる少なくとも1種以上の正極活物質を含むことを特徴とする請求項1~10のいずれかに記載の蓄電装置。
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US10680449B2 (en) | 2020-06-09 |
JP6783149B2 (ja) | 2020-11-11 |
CN107004898A (zh) | 2017-08-01 |
US20180131202A1 (en) | 2018-05-10 |
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EP3258527A4 (en) | 2018-08-22 |
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