JP2021077570A - Determination device and determination method for determining precipitation of lithium contained in secondary battery - Google Patents

Abstract

To provide a determination device and a determination method, achieving increase in accuracy for determining precipitation of lithium.SOLUTION: A system 1 for determining precipitation of lithium that is contained in a lithium ion secondary battery includes a measuring instrument 7 for measuring AC impedance of the secondary battery and a controller 8 for determining presence or absence of the precipitation of the lithium. The measuring instrument calculates negative electrode reaction resistance of the secondary battery on the basis of characteristics in a specific frequency among characteristics of AC impedance of the secondary battery, and the controller determines that there is the precipitation of the lithium if the negative electrode reaction resistance drops by a predetermined value or more per unit time, during charge of the secondary battery.SELECTED DRAWING: Figure 1

Description

The present invention relates to a determination device and a determination method for determining the precipitation of lithium contained in a secondary battery.

Conventionally, a method for detecting the state of a lithium ion secondary battery provided with a non-aqueous electrolyte solution has been known (Patent Document 1). In the state detection method described in Patent Document 1, the phase difference is obtained as a specific frequency in the range of 0.1 Hz or more and less than 10 Hz (for example, 2 Hz) and the range of 10 Hz or more and 300 Hz or less (for example, 100 Hz), and the phase difference is determined. Based on this, the battery deterioration state and the lithium metal precipitation state at the negative electrode are discriminated.

JP-A-2009-244088

However, since the phase used for discrimination in the above-mentioned conventional method changes due to factors other than the precipitation of lithium metal, the above-mentioned conventional method has a problem that the determination accuracy of the lithium metal precipitation state is low. ..

An object to be solved by the present invention is to provide a determination device and a determination method with improved determination accuracy of lithium precipitation.

The present invention measures the AC impedance of a lithium-ion secondary battery, calculates the negative electrode reaction resistance of the secondary battery based on the characteristics of the AC impedance of the secondary battery at a specific frequency, and calculates the negative electrode reaction resistance of the secondary battery. The above problem is solved by determining that lithium is deposited when the negative electrode reaction resistance drops by a predetermined value or more per unit time during charging.

According to the present invention, the accuracy of determining the precipitation of lithium can be improved.

FIG. 1 is a block diagram showing a determination system for a secondary battery according to the present embodiment. FIG. 2 is a plan view of the secondary battery according to the present embodiment. FIG. 3 is a cross-sectional view of the secondary battery along the line III-III of FIG. FIG. 4 plots the real axis component value (Z') and the imaginary axis component value (-Z ") of the AC impedance measured by the impedance measuring device on the complex plane coordinates where the real axis and the imaginary axis are orthogonal to each other. It is a graph of the complex impedance plot (Nyquist plot; Cole Cole plot) including the arc locus obtained in the above. FIG. 5 is a circuit diagram showing an equivalent circuit of an electrolyte and a negative electrode contained in the secondary battery in the secondary battery according to the present embodiment. FIG. 6 is a graph showing the frequency characteristics of the overall reaction resistance, the positive electrode reaction resistance, and the negative electrode reaction resistance of the secondary battery in the secondary battery according to the present embodiment. FIG. 7 is a graph showing the temporal transition of the reaction resistance when lithium precipitation occurs in the secondary battery according to the present embodiment. FIG. 8 is a graph for explaining the temperature transition of the Nyquist plot of the imaginary part component Z ”that constitutes the AC impedance Z in the secondary battery according to the present embodiment. FIG. 9 is a graph showing the temporal transition of the reaction resistance in the secondary battery according to the present embodiment. FIG. 10 is a graph showing the frequency characteristics of the reaction resistance of the secondary battery in the secondary battery according to the present embodiment. FIG. 11 is a graph for explaining the relationship between the temperature of the secondary battery, the charging current, and the cell voltage at the precipitation point in the secondary battery according to the present embodiment. FIG. 12 is a flowchart showing the procedure of the determination process and the procedure of the charge process in the lithium precipitation determination system. FIG. 13 is a flowchart showing a subflow of the control process in step S12 shown in FIG.

FIG. 1 is a diagram showing a configuration of a determination system for determining the precipitation of lithium according to the present embodiment. The lithium precipitation determination system according to the present embodiment determines whether or not lithium is deposited in the lithium ion secondary battery. The lithium precipitation determination method, determination device, and determination system according to the present embodiment can be applied not only to an all-solid-state lithium ion secondary battery but also to a lithium ion battery containing an electrolytic solution. As shown in FIG. 1, the determination system 1 includes a secondary battery 2, a voltage sensor 3, a temperature sensor 4, a voltage / current adjusting unit 5, a current sensor 6, an impedance measuring instrument 7, a controller 8, and the like. It is equipped with an external power supply 9. The lithium precipitation determination system shown in FIG. 1 is a system for charging the secondary battery 2 with the electric power of the external power source 9, and at this time, the presence or absence of lithium precipitation in the secondary battery 2 is determined.

An all-solid-state lithium ion secondary battery will be described as an example of the secondary battery 2 in the present embodiment. The secondary battery 2 includes a positive electrode including a positive electrode active material layer containing a positive electrode active material capable of storing and releasing lithium ions, and a negative electrode including a negative electrode active material layer containing a negative electrode active material capable of storing and releasing lithium ions. It includes a power generation element having a solid electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer. The secondary battery 2 has an electrode tab, an electrode tab, and an exterior member accommodating the power generation element in addition to the power generation element. The detailed structure and material of the secondary battery will be described later.

The voltage sensor 3 is a sensor for detecting the input / output voltage of the secondary battery 2, and detects the cell voltage (voltage between terminals) between the positive electrode and the negative electrode of the secondary battery 2. The connection position of the voltage sensor 3 is not particularly limited as long as it can detect the cell voltage between the positive electrode and the negative electrode in the circuit connected to the secondary battery 2.

The temperature sensor 4 measures the outer surface temperature (environmental temperature) of the secondary battery 2. The temperature sensor 4 is attached to, for example, the surface of the case (exterior body, housing) of the secondary battery 2.

The voltage / current adjusting unit 5 is a circuit for adjusting the battery current and the cell voltage during charging and / or discharging of the secondary battery 2, and the current / current of the secondary battery 2 is based on a command from the controller 8. Adjust the voltage. The voltage / current adjusting unit 5 has a voltage conversion circuit or the like for converting the power output from the external power source into the charging voltage of the secondary battery.

The current sensor 6 is a sensor for detecting the input / output current of the secondary battery 2. The current sensor 6 detects the current supplied from the voltage / current adjusting unit 5 to the secondary battery 2 when charging the secondary battery 2, and detects the current supplied from the secondary battery 2 to the voltage / current adjusting unit 5 when discharging. To do.

The impedance measuring instrument 7 is connected to the secondary battery 2, and the AC perturbation current is passed through the secondary battery 2 as an input signal, and the response voltage corresponding to the AC signal (AC current) is acquired to acquire the response voltage of the secondary battery 2. Measure the AC impedance (complex impedance) of. The impedance measuring device 7 may be arbitrarily selected from those normally used as a general AC impedance measuring device. For example, the impedance measuring device 7 may measure the AC impedance of the secondary battery 2 by changing the frequency of the AC perturbing current with time by the AC impedance method. Further, a plurality of AC perturbation currents having different frequencies may be applied at the same time. The method for measuring AC impedance in the AC impedance method is not particularly limited. For example, an analog method such as the Lissajous method and the AC bridge method, and a digital method such as a digital Fourier integral method and a fast Fourier transform method by applying noise can be appropriately adopted. In the present embodiment, a plurality of AC perturbing currents having different frequencies are applied to the secondary battery 2 to measure the AC impedance. For a plurality of frequencies, for example, a graph in which the real part component Z'and the imaginary part component Z'that constitute the AC impedance Z measured by the impedance measuring instrument 7 are plotted on the complex plane coordinates (Nyquist plot; Cole Cole plot). Therefore, the reaction resistance component of the secondary battery 2 may be calculated as long as it can be calculated. The amplitude of the waveform (for example, sinusoidal wave) of the AC perturbation current applied to the battery is not particularly limited and can be set arbitrarily. The measurement result of the AC impedance measured by the impedance measuring device 7 is sent to the controller 8 as the output of the impedance measuring device 7.

The controller 8 has a CPU 81, a storage unit 82, and the like. The controller 8 is a control device that determines the presence or absence of precipitation of lithium contained in the secondary battery 2 based on the reaction resistance of the secondary battery 2 measured by the impedance measuring device 7. Further, the controller 8 charges the secondary battery 2 based on the cell voltage of the secondary battery 2 detected by the voltage sensor 3 and the charge / discharge current flowing through the secondary battery 2 detected by the current sensor 6. Control.

The external power source 9 is a power source for charging the secondary battery 2. As the power source, for example, a three-phase 200V AC power source is used. The external power supply 9 may be a single-phase 100V or single-phase 200V AC power supply. The external power supply 9 is not limited to alternating current, but may be a direct current power supply.

Next, the structure of the secondary battery (all-solid-state lithium ion secondary battery) 2 will be described with reference to FIGS. 2 and 3. FIG. 2 shows a plan view of the secondary battery 2 according to the present embodiment, and FIG. 3 shows a cross-sectional view of the secondary battery 2 along the lines III-III of FIG.

As shown in FIGS. 2 and 3, the secondary battery 2 is connected to a power generation element 101 having three positive electrode layers 102, seven electrolyte layers 103, and three negative electrode layers 104, and three positive electrode layers 102, respectively. The positive electrode tab 105, the negative electrode tab 106 connected to each of the three negative electrode layers 104, and the upper exterior member 107 and the lower exterior member 108 that house and seal the power generation element 101, the positive electrode tab 105, and the negative electrode tab 106, respectively. It is composed of and.

The number of the positive electrode layer 102, the electrolyte layer 103, and the negative electrode layer 104 is not particularly limited, and one positive electrode layer 102, three electrolyte layers 103, and one negative electrode layer 104 may form the power generation element 101. Further, the number of positive electrode layers 102, electrolyte layer 103, and negative electrode layer 104 may be appropriately selected, if necessary.

The positive electrode layer 102 constituting the power generation element 101 has a positive electrode side current collector 102a extending to the positive electrode tab 105 and a positive electrode active material layer formed on both main surfaces of a part of the positive electrode side current collector 102a. doing. The positive electrode side current collector 102a constituting the positive electrode layer 102 can be made of, for example, an electrochemically stable metal foil such as an aluminum foil, an aluminum alloy foil, a copper titanium foil, or a stainless steel foil. Nickel, iron, copper or the like may be used as the metal for the positive electrode side current collector 102a. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, and the like may be used.

A conductive resin may be used for the positive electrode side current collector 102a instead of the metal. The conductive resin can be composed of a non-conductive polymer material to which a conductive filler is added, if necessary. Examples of the non-conductive polymer material include polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE), etc.), polypropylene (PP), polyethylene terephthalate (PET), and the like, which have excellent potential resistance. Material is used. The conductive filler can be used without particular limitation as long as it is a conductive substance. For example, materials having excellent conductivity, potential resistance, or lithium ion blocking property include metals and conductive carbon. The metal is not particularly limited, and includes at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, and Sb, or at least one of these metals. Examples include alloys or metal oxides.

The positive electrode active material layer constituting the positive electrode layer 102 is not particularly limited, but is a layered rock salt type active material such as _{LiCoO 2} , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , Li (Ni-Mn-Co) O _{2 , LiMn 2} Examples include spinel-type active materials such as O ₄ , LiNi _0.5 Mn _1.5 O ₄ , olivine-type active materials such as _{LiFePO 4} and LiMnPO ₄ , and Si-containing active materials such as _{Li 2} FeSiO ₄ and Li _{2 MnSiO 4.} Be done. Examples of the oxide active material other than the above include Li ₄ Ti ₅ O ₁₂ . A composite oxide containing lithium and nickel is preferably used, and more preferably Li (Ni-Mn-Co) O ₂ and a part of these transition metals are substituted with other elements (hereinafter, simply ". Also referred to as "NMC composite oxide") is used. As described above, the NMC composite oxide also includes a composite oxide in which a part of the transition metal element is replaced with another metal element. Examples of other elements in that case include Ti, Zr, Nb, W, P and the like.

A sulfur-based positive electrode active material may be used for the positive electrode active material layer. Examples of the sulfur-based positive electrode active material include particles or thin films of an organic sulfur compound or an inorganic sulfur compound, which can be used to release lithium ions during charging and occlude lithium ions during discharging by utilizing the redox reaction of sulfur. Any substance that can be produced will do. Examples of the organic sulfur compound include a disulfide compound and a sulfur-modified polyacrylonitrile. Examples of the inorganic sulfur compound include sulfur (S), S-carbon composite, TiS ₂ , TiS ₃ , TiS ₄ , NiS, NiS ₂ , CuS, FeS ₂ , Li ₂ S, MoS ₂ , MoS _{3, and the} like.

A positive electrode active material other than the above may be used. Examples of the shape of the positive electrode active material include a particle shape (spherical shape, a fibrous shape), a thin film shape, and the like. The content of the positive electrode active material in the positive electrode active material layer is not particularly limited. The positive electrode active material layer may further contain at least one of a solid electrolyte, a conductive auxiliary agent, and a binder, if necessary. Examples of the shape of the positive electrode active material include a particle shape (spherical shape, a fibrous shape), a thin film shape, and the like. The content of the positive electrode active material in the positive electrode active material layer is not particularly limited. The positive electrode active material layer may further contain at least one of a solid electrolyte, a conductive auxiliary agent, and a binder, if necessary. Examples of the solid electrolyte include sulfide solid electrolytes and oxide solid electrolytes, and those exemplified as solid electrolytes capable of forming the electrolyte layer 103, which will be described later, can be used.

The conductive auxiliary agent is not particularly limited, but is preferably in the form of particles or fibers. When the conductive auxiliary agent is in the form of particles, the shape of the particles is not particularly limited, and may be any shape such as powder, sphere, rod, needle, plate, columnar, indefinite, flint, and spindle. It doesn't matter.

The average particle size (primary particle size) when the conductive auxiliary agent is in the form of particles is not particularly limited, but is preferably 0.01 to 10 μm from the viewpoint of the electrical characteristics of the battery.

Binders include polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are replaced by other halogen elements), polyethylene, polypropylene, polymethylpentene, polybutene, polyethernitrile, and poly. Tetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene / butadiene rubber (SBR), ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer and Thermoplastic polymers such as its hydrogenated products, styrene / isoprene / styrene block copolymers and their hydrogenated products; tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether co-weight Fluororesin such as coalescence (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF); Vinylidene Fluoride-Hexafluoropropylene Fluororesin (VDF-HFP Fluororesin), Vinylidene Fluoride-Hexafluoropropylene-Tetrafluoroethylene Fluororesin (VDF-HFP-TFE Fluororesin), Vinylidene Fluoride-Pentafluoro Propylene-based fluororubber (VDF-PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene Examples thereof include vinylidene fluoride-based fluororubbers such as vinylidene fluoride-chlorotrifluoroethylene-based fluororubbers (VDF-CTFE-based fluororubbers); epoxy resins; and the like. Of these, polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are more preferable.

Then, each positive electrode side current collector 102a constituting these three positive electrode layers 102 is joined to the positive electrode tab 105. As the positive electrode tab 105, an aluminum foil, an aluminum alloy foil, a copper foil, a nickel foil, or the like can be used.

The negative electrode layer 104 constituting the power generation element 101 includes a negative electrode side current collector 104a extending to the negative electrode tab 106 and a negative electrode active material layer formed on both main surfaces of a part of the negative electrode side current collector 104a. have.

The negative electrode side current collector 104a of the negative electrode layer 104 is an electrochemically stable metal foil such as a nickel foil, a copper foil, a stainless steel foil, or an iron foil.

The negative electrode layer 104 is formed of a layer containing a negative electrode active material. The type of the negative electrode active material is not particularly limited, and examples thereof include a carbon material, a metal oxide, and a metal active material. Examples of the carbon material include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, soft carbon and the like. Examples of the metal oxide include Nb ₂ O ₅ , Li ₄ Ti ₅ O ₁₂ , SiO and the like. Further, examples of the metal active material include simple metals such as In, Al, Si and Sn, and alloys such as _{TiSi, La 3} Ni ₂ Sn _7.

The negative electrode active material may be a Li-containing lithium alloy. The lithium alloy is selected from, for example, lithium and at least gold (Au), magnesium (Mg), aluminum (Al), calcium (Ca), zinc (Zn), tin (Sn), and bismuth (Bi). An alloy with one kind of metal can be mentioned. Further, the lithium alloy may be an alloy of lithium and two or more kinds of metals among the above-mentioned metals. Specific examples of the lithium alloy include, for example, lithium-gold alloy (Li-Au), lithium-magnesium alloy (Li-Mg), lithium-aluminum alloy (Li-Al), lithium-calcium alloy (Li-Ca), and the like. Examples thereof include a lithium-zinc alloy (Li-Zn), a lithium-tin alloy (Li-Sn), and a lithium-bismus alloy (Li-Bi).

The negative electrode active material layer may be any one containing a lithium alloy, and its composition is not particularly limited. For example, when a metal other than lithium constituting the lithium alloy is "Me", the following It can be any aspect of (1) to (3).
(1) A single layer made of only a lithium alloy (that is, a Li-Me layer)
(2) A layer provided with a layer made of lithium metal and a layer made of a lithium alloy (that is, a Li layer / Li-Me layer).
(3) A layer including a layer made of lithium metal, a layer made of a lithium alloy, and a layer made of a metal other than lithium (that is, Li layer / Li-Me layer / Me layer).
In the aspect of the above (2), it is desirable that the layer made of the lithium alloy (Li-Me layer) is the layer on the side of the electrolyte layer 103 (the layer forming the interface with the electrolyte layer 103), and the above (3). ), It is desirable that the layer made of a metal other than lithium (Me layer) is the layer on the side of the electrolyte layer 103 (the layer forming the interface with the electrolyte layer 103). In the case of a lithium metal layer containing a lithium metal and a layer containing a metal different from the lithium metal (intermediate layer), the intermediate layer is a layer between the lithium metal layer and the solid electrolyte, and is at least one of the lithium metals. It is desirable that a part and at least a part of the metal forming the intermediate layer are alloyed.

For example, the negative electrode includes the aspect (3) above, that is, a layer made of a lithium metal, a layer made of a lithium alloy, and a layer made of a metal other than lithium (that is, a Li layer / Li-Me layer / In the case of forming a Me layer), by laminating a lithium metal and a metal other than lithium, these interface portions are alloyed, whereby a layer made of a lithium alloy can be formed at these interfaces. .. The method of laminating the lithium metal and the metal other than lithium is not particularly limited, but is made of the lithium metal by depositing a metal other than lithium on the layer made of the lithium metal by vacuum vapor deposition or the like. A method of alloying these interfaces while forming a layer made of a metal other than lithium on the layer can be mentioned. Alternatively, a lithium metal is vapor-deposited on a layer made of a metal other than lithium by vacuum deposition or the like, and these interfaces are alloyed while forming a layer made of a lithium metal on a layer made of a metal other than lithium. The method etc. can be mentioned.

In the secondary battery 2 of the present embodiment, the three negative electrode layers 104 are configured such that each negative electrode side current collector 104a constituting the negative electrode layer 104 is joined to a single negative electrode tab 106. ing. That is, in the secondary battery 2 of the present embodiment, each negative electrode layer 104 is joined to a single common negative electrode tab 106.

The electrolyte layer 103 of the power generation element 101 prevents a short circuit between the positive electrode layer 102 and the negative electrode layer 104 described above, contains a solid electrolyte as a main component, and comprises the above-mentioned positive electrode active material layer and the negative electrode active material layer. It is a layer that intervenes between them. Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, polymer solid electrolytes, and the like, and sulfide solid electrolytes are preferable.

Examples of the sulfide solid electrolyte include LiI-Li ₂ S-SiS ₂ , LiI-Li ₂ S-P ₂ O ₅ , LiI-Li ₃ PO _4- P ₂ S ₅ , Li ₂ S-P ₂ S ₅ , LiI-Li ₃ PS ₄ , LiI-LiBr-Li ₃ PS ₄ , Li ₃ PS ₄ , Li ₂ S-P ₂ S ₅ , Li ₂ S-P ₂ S ₅ -Li I, Li ₂ S-P ₂ S _5- Li ₂ O, Li ₂ S-P ₂ S _{5 -Li 2} OLiI, Li ₂ S-SiS ₂ , Li ₂ S-SiS _2- LiI, Li ₂ S-SiS _2- LiBr, Li ₂ S-SiS _2- LiCl , Li ₂ S-SiS _2- B ₂ S _3- LiI, Li ₂ S-SiS _2- P ₂ S _5- LiI, Li _{2 SB 2} S ₃ , Li _{2 SP 2} S _5- ZmSn (However , M, n are positive numbers, Z is any of Ge, Zn, Ga), Li ₂ S-GeS ₂ , Li ₂ S-SiS _{2 -Li 3} PO ₄ , Li ₂ S-SiS _2- LixMOy (where x and y are positive numbers and M is any of P, Si, Ge, B, Al, Ga and In) and the like. The description of "Li ₂ SP ₂ S ₅ " means a sulfide solid electrolyte made by using a raw material composition containing _{Li 2} S and P ₂ S _{5, and the same applies to other descriptions.}

The sulfide solid electrolyte may have, for example, a Li ₃ PS ₄ skeleton, a Li ₄ P ₂ S ₇ skeleton, or a Li ₄ P ₂ S ₆ skeleton. .. Examples of the sulfide solid electrolyte having a Li ₃ PS _{4 skeleton include LiI-Li 3} PS ₄ , LiI-LiBr-Li ₃ PS ₄ , and Li ₃ PS ₄ . Examples of the sulfide solid electrolyte having a Li ₄ P ₂ S ₇ skeleton include a Li-PS solid electrolyte called LPS (for example, Li ₇ P ₃ S ₁₁ ). Further, as the sulfide solid electrolyte, for example, _{LGPS represented by Li (4-x)} Ge _(1-x) P _x S ₄ (x satisfies 0 <x <1) may be used. Among them, the sulfide solid electrolyte is preferably a sulfide solid electrolyte containing a P element, and the sulfide solid electrolyte is more preferably a material containing Li ₂ SP ₂ S ₅ as a main component. Further, the sulfide solid electrolyte may contain halogen (F, Cl, Br, I).

When the sulfide solid electrolyte is a Li ₂ SP ₂ S ₅ system, the ratio of Li ₂ S and P ₂ S ₅ is a molar ratio of Li ₂ S: P ₂ S ₅ = 50: 50 to 100. It is preferably in the range of: 0, and in particular, Li ₂ S: P ₂ S ₅ = 70:30 to 80:20. Further, the sulfide solid electrolyte may be sulfide glass, crystallized sulfide glass, or a crystalline material obtained by the solid phase method. The sulfide glass can be obtained, for example, by performing mechanical milling (ball mill or the like) on the raw material composition. Further, the crystallized sulfide glass can be obtained, for example, by heat-treating the sulfide glass at a temperature equal to or higher than the crystallization temperature. The ionic conductivity (for example, Li ion conductivity) of the sulfide solid electrolyte at room temperature (25 ° C.) ^{is preferably 1 × 10 -5} S / cm or more ^{, for example, 1 × 10 -4} S / cm. It is more preferably cm or more. The value of the ionic conductivity of the solid electrolyte can be measured by the AC impedance method.

Examples of the oxide solid electrolyte include compounds having a NASICON type structure and the like. As an example of a compound having a NASICON type structure, a compound _{(LAGP) represented by the general formula Li 1 + x} Al _x Ge _2-x (PO ₄ ) ₃ (0 ≦ x ≦ 2), a general formula Li _{1 + x} Al _x Ti ₂ Examples thereof include a compound (LATP) represented by _−x (PO ₄ ) _{3 (0 ≦ x ≦ 2).} In addition, as other examples of the oxide solid electrolyte, LiLaTIO (for example, Li _0.34 La _0.51 TiO ₃ ), LiPON (for example, Li _2.9 PO _3.3 N _0.46 ), LiLaZrO (for example, LiLaZrO). , Li ₇ La ₃ Zr ₂ O ₁₂ ) and the like.

The solid electrolyte layer 103 may further contain a binder in addition to the above-mentioned solid electrolyte. The binder is not particularly limited, but for example, the above-mentioned binder can be used.

The content of the solid electrolyte is, for example, preferably in the range of 10 to 100% by mass, more preferably in the range of 50 to 100% by mass, and preferably in the range of 90 to 100% by mass. More preferred.

Then, as shown in FIG. 3, the positive electrode layer 102 and the negative electrode layer 104 are alternately laminated via the electrolyte layer 103, and the electrolyte layer 103 is further laminated on the uppermost layer and the lowermost layer, respectively. As a result, the power generation element 101 is formed.

The power generation element 101 configured as described above is housed and sealed in the upper exterior member 107 and the lower exterior member 108 (sealing means). The upper exterior member 107 and the lower exterior member 108 for sealing the power generation element 101 are, for example, a resin obtained by laminating both sides of a resin film such as polyethylene or polypropylene or a metal foil such as aluminum with a resin such as polyethylene or polypropylene. -A state in which the positive electrode tab 105 and the negative electrode tab 106 are led out to the outside by heat-sealing the upper exterior member 107 and the lower exterior member 108, which are made of a flexible material such as a metal thin film laminate material. Then, the power generation element 101 is sealed.

The positive electrode tab 105 and the negative electrode tab 106 are provided with a seal film 109 at a portion that comes into contact with the upper exterior member 107 and the lower exterior member 108 in order to ensure adhesion to the upper exterior member 107 and the lower exterior member 108. It is provided. The seal film 109 is not particularly limited, but can be made of, for example, polyethylene, modified polyethylene, polypropylene, modified polypropylene, or a synthetic resin material having excellent electrolyte resistance and heat fusion properties such as ionomer.

Next, with reference to FIGS. 2 and 3, the structure and material when the secondary battery 2 is an electrolytic solution lithium ion secondary battery will be described. As for the common configuration between the above-mentioned all-solid-state lithium ion secondary battery and the electrolytic solution lithium ion secondary battery, the above description is appropriately incorporated. The structure and material of the battery described below are examples, and other well-known structures and / or materials may be used for the secondary battery 2.

The secondary battery (electrolytic solution lithium ion secondary battery) 2 has a positive electrode tab connected to three positive electrode layers 102, three negative electrode layers 104, and three positive electrode layers 102, respectively, as in the structure shown in FIG. From 105, a negative electrode tab 106 connected to each of the three negative electrode layers 104, and an upper exterior member 107 and a lower exterior member 108 that accommodate and seal the power generation element 101, the positive electrode tab 105, and the negative electrode tab 106, respectively. It is configured. The difference is that a separator is used instead of the electrolyte layer 103 shown in FIG. 3, and a non-aqueous electrolyte solution (not shown) is contained inside the battery.

The positive electrode active material layer constituting the positive electrode layer 102 is a mixture of a positive electrode active material, a conductive agent such as carbon black, and a binder such as polyvinylidene fluoride or an aqueous dispersion of polytetrafluoride ethylene. , Is formed by applying to a part of the main surface of the positive electrode side current collector 102a, drying and pressing.

（上記式（１）において、０．１≦ｘ≦０．５であり、式中のＭは、Ｎｉ_αＣｏ_βＭｎ_γＭ’_σ（ただし、０＜α≦０．５、０≦β≦０．３３、０＜γ≦０．５、０≦σ≦０．１、α＋β＋γ＋σ＝１、Ｍ’は金属元素である。）である。） The secondary battery 2 according to the present embodiment contains at least a positive electrode active material having a property that the resistance increases as the SOC increases as the positive electrode active material in the positive electrode active material layer constituting the positive electrode layer 102. The positive electrode active material having the property that the resistance increases as the SOC increases is not particularly limited, and examples thereof include a positive electrode material on the Li excess layer having _{LiMnO 3 as a mother structure.} Examples thereof include a compound represented by the general formula (1). In particular, since the compound represented by the following general formula (1) has a high potential and a high capacity, the secondary battery 10 has a high energy density by using such a compound as the positive electrode active material. can do. The compound represented by the following general formula (1) usually forms a solid solution.

(In the above formula (1), 0.1 ≦ x ≦ 0.5, and M in the formula is Ni _α Co _β Mn _{γ M'σ} (where 0 <α ≦ 0.5, 0 ≦ β ≦ 0.33, 0 <γ ≦ 0.5, 0 ≦ σ ≦ 0.1, α + β + γ + σ = 1, M'is a metal element.)

Further, in the compound represented by the above general formula (1), M'is not particularly limited as long as it is a metal element (metal element other than Li, Ni, Co, Mn), but Fe, V, Ti. , Al, Mg is preferable, and Ti is particularly preferable.

（上記式（２）において、０．１≦ｘ≦０．５、０＜α≦０．５、０≦β≦０．３３、０＜γ≦０．５、α＋β＋γ＝１である。） Further, in the above general formula (1), α, β, γ, σ are 0 <α ≦ 0.5, 0 ≦ β ≦ 0.33, 0 <γ ≦ 0.5, 0 ≦ σ ≦ 0.1. , Π + β + γ + σ = 1 is not particularly limited as long as it satisfies the range, but σ = 0 is preferable. That is, it is more preferable that the compound is represented by the following general formula (2).

(In the above formula (2), 0.1 ≦ x ≦ 0.5, 0 <α ≦ 0.5, 0 ≦ β ≦ 0.33, 0 <γ ≦ 0.5, α + β + γ = 1.)

The positive electrode active material layer includes positive electrode active materials other than the positive electrode active material having the property that resistance increases as the SOC increases, for example, lithium nickel oxide (LiNiO ₂ ) and lithium manganate (LiMn ₂ O). ₄ ), Lithium composite oxide such as lithium cobalt oxide (LiCoO _{2 ), LiFePO 4} or LiMnPO ₄ or the like may be contained.

Further, in the negative electrode active material layer constituting the negative electrode layer 104, a negative electrode active material, a conductive agent such as carbon black, a binder such as polyvinylidene fluoride, and a solvent such as N-methyl-2-pyrrolidone are added. It is formed by preparing a slurry, applying it to both main surfaces of a part of the negative electrode side current collector 104a, drying and pressing.

The negative electrode active material constituting the negative electrode active material layer is not particularly limited, and for example, one containing at least a negative electrode active material containing silicon or carbon as a main element can be used. Examples of the negative electrode active material containing silicon as a main element include silicon compounds such as silicon oxides in addition to silicon. Examples of the negative electrode active material containing carbon as a main element include non-graphitizable carbon, easily graphitized carbon, and graphite.

The separator prevents a short circuit between the positive electrode layer 102 and the negative electrode layer 104 described above, and may have a function of retaining an electrolyte. This separator is, for example, a microporous membrane composed of a polyolefin such as polyethylene (PE) or polypropylene (PP) having a thickness of about 25 μm, and when an overcurrent flows, the heat generated by the separator causes pores in the layer. It also has the function of being blocked and interrupting the current.

The electrolytic solution contained in the secondary battery 2 is a liquid in which a lithium salt such as lithium _{borofluoride (LiBF 4} ) or lithium hexafluorophosphate (LiPF _{6) is dissolved as a solute in an organic liquid solvent.} Examples of the organic liquid solvent constituting the electrolytic solution include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and the like. Ester-based solvents such as methyl formate (MF), methyl acetate (MA), and methyl propionate (MP) can be mentioned, and these can be mixed and used.

The secondary battery 2 according to the present embodiment is composed of the above-mentioned all-solid-state lithium ion secondary battery or the electrolytic solution lithium ion secondary battery.

Next, a determination method for determining the presence or absence of lithium precipitation and a charge control method for the secondary battery 2 in the present embodiment will be described. In the present embodiment, the method for determining the secondary battery 2 described below is executed by the impedance measuring device 7 and the controller 8. Further, the lithium precipitation determination control is executed during the charge control of the secondary battery 2. The charge control of the secondary battery 2 is executed by the voltage / current adjusting unit 5 and the controller 8. Although the graphs shown in the figures below FIG. 4 show the characteristics of the electrolytic solution lithium ion secondary battery, the method for determining lithium precipitation, the determination device, and the determination system according to the present embodiment are all-solid-state lithium. It can also be applied to ion secondary batteries.

First, the charge control of the secondary battery 2 will be described. In the present embodiment, the controller 8 gradually increases the current until the cell voltage of the secondary voltage 2 reaches a predetermined upper limit voltage, and when the charging current of the secondary battery 2 reaches the set current, the current value becomes constant. (So-called constant current control; CC charging). While charging the secondary battery 2, the controller 8 acquires detected values from the voltage sensor 3 and the current sensor 6 and manages the current flowing through the secondary battery 2 and the cell voltage applied to the secondary battery 2. There is. Further, the controller 8 manages the SOC of the secondary battery 2 based on the detection voltage of the voltage sensor 3. In the present embodiment, by charging the secondary battery 2 with the set current, the SOC of the secondary battery 2 increases, and the cell voltage of the secondary battery 2 gradually increases.

When the cell voltage of the secondary battery 2 reaches the upper limit voltage, the controller 8 performs constant voltage charging (CV charging) at the upper limit voltage. While the cell voltage of the secondary battery 2 is maintained at the upper limit voltage, the charging current is attenuated as the SOC of the secondary battery 2 increases. Then, in the present embodiment, when the charging current is attenuated and drops to the default end current value (cutoff current value), the charging of the secondary battery 20 is terminated. In the present embodiment, the charge of the secondary battery 20 is controlled in this way. The charging method is not limited to the so-called CC-CV charging as described above, and other charging methods may be used.

Next, the determination control of lithium precipitation in the secondary battery 2 will be described. In the present embodiment, in order to estimate the presence or absence of lithium precipitation in the secondary battery 2, the positive electrode reaction resistance and the negative electrode reaction resistance of the secondary battery 2 are first calculated. FIG. 4 shows the real axis component value (Z') and the imaginary axis component value (-Z ") of the AC impedance measured by the impedance measuring device 7 on the complex plane coordinates in which the real axis and the imaginary axis are orthogonal to each other. It is a graph of a complex impedance plot (Nyquist plot; Cole Cole plot) including an arc locus obtained by plotting. The AC impedance (Z) is represented by the definition formula of Z = Z'+ jZ ”. Under the definition formula, in the graph of FIG. 4, the vertical axis is −Z ”, the capacitive reactor is drawn as minus, and the inducible impedance is drawn as plus.

The impedance measuring instrument 7 applies AC signals of a large number of frequency values within a predetermined frequency band, and for each frequency value, the real axis component value (Z') and the imaginary axis component value (-Z ") of the AC impedance. The predetermined frequency band includes at least the frequency for measuring the reaction resistance. On the complex plane coordinates where the real axis and the imaginary axis are orthogonal to each other, the real axis component value is the real of the complex plane coordinates. When the imaginary axis component value is plotted as the imaginary axis component of the complex plane coordinates as the axis component, a complex impedance plot (Nyquist plot; Cole Cole plot) including an arc locus is obtained in a predetermined frequency band as shown in FIG. is. indicate sizes are. electrolytic resistance distance electrolyte resistance from the origin of the complex plane coordinates to H point indicating the minimum value of the high-frequency side (R _sep) (R _sep) are ions move in the electrolyte It is a composite value of the resistance and the resistance when electrons move in the electrode and wiring. The distance between the point H and the point L, that is, the diameter of the arc locus indicates the magnitude of the _{reaction resistance (R r).} The point L is a point where the arc locus extends in an arc shape on the low frequency side and intersects with the actual axis. Thus, from the Nyquist plot shown in FIG. 4, the electrolyte resistance (R _sep ) and the reaction resistance (R sep) and the reaction resistance ( R _r ) can be obtained.

The impedance measuring instrument 7 calculates the negative electrode reaction resistance of the secondary battery 2 based on the identification at a specific frequency among the characteristics of the AC impedance. FIG. 5 is a circuit diagram showing an equivalent circuit of an electrolyte and a negative electrode contained in the secondary battery 2. R _act indicates the negative electrode reaction resistance, and C _dl indicates the electric double layer capacity of the negative electrode. _{When only the imaginary part (Zim} ) is extracted from the impedance of the equivalent circuit shown in FIG. 5, the following equation (3) is derived. Note that ω is an angular frequency determined by the frequency of the AC signal.

Further, by modifying the equation (3), the following equation (4) is derived.

In equation (4), with -1 / (ωZ _im ) on the vertical axis and 1 / ω ² on the horizontal axis, and drawing a graph, 1 / C _dl R _аct ² is the slope and C _dl is the intercept. It becomes a straight line. Then, calculates the negative electrode capacity _{(C dl)} of sections from the slope ^{_{(1 / C dl R аct 2}} ) and capacitance _{(C dl),} it calculates the negative electrode reaction resistance _(R аct).

Further, the impedance measuring instrument 7 can calculate the negative electrode reaction resistance from the actual part of the impedance of the equivalent circuit shown in FIG. _{When only the real part (Z re} ) is extracted from the impedance of the equivalent circuit shown in FIG. 5, the following equation (5) is derived.

Further, by modifying the equation (5), the following equation (6) is derived.

In equation (6), with 1 / (Z _re- R _sep ) on the vertical axis and ω ² on the horizontal axis, and drawing a graph, C _dl ² R _аct is the slope and 1 / R _аct is the intercept. It becomes a straight line. Then, the negative electrode reaction resistance (R _аct ) can be calculated from the intercept. Although the negative electrode reaction resistance has been described in the above calculation method, the positive electrode reaction resistance can also be calculated by the above calculation method.

In order to distinguish between the positive electrode reaction resistance and the negative electrode reaction resistance, the impedance measuring instrument 7 applies an AC signal having a specific frequency and calculates the positive electrode reaction resistance and the negative electrode reaction resistance based on the impedance characteristics at the specific frequency. doing.

FIG. 6 is a graph showing the frequency characteristics of the overall reaction resistance, the positive electrode reaction resistance, and the negative electrode reaction resistance of the secondary battery 2. The vertical axis is "reaction resistance (R _аct ), and the horizontal axis is frequency. Graph а shows the characteristics of the negative electrode reaction resistance, graph b shows the characteristics of the positive electrode reaction resistance, and graph c shows the characteristics of the total reaction resistance. Shows the characteristics.

As shown in the graph а, the negative electrode reaction resistance peaks at the _{frequency (f а).} As shown in graph b, the positive electrode reaction resistance has a peak value at the _{frequency (f b).} As shown in the graph of FIG. 6, the frequency characteristics of the reaction resistance are different between the positive electrode and the negative electrode. Therefore, for example, in order to measure the reaction resistance of the negative electrode, a specific frequency having a high positive electrode reaction resistance and a low negative electrode reaction resistance is selected, and an AC signal of the selected specific frequency is used as a secondary battery. Apply to 2. At this time, since it is difficult for a current to flow through the reaction resistance of the positive electrode, the change in the reaction resistance of the negative electrode can be measured from the AC impedance of the secondary battery when the AC signal is passed through the secondary battery 2. In the example of FIG. 6, the impedance measuring instrument 7 sets a specific frequency to _fа , applies an AC signal to the secondary battery 2, and calculates the reaction resistance of the negative electrode from the characteristics of the AC impedance. Further, the impedance measuring instrument 7 sets a specific frequency to f _b , applies an AC signal to the secondary battery 2, and calculates the reaction resistance of the positive electrode from the characteristics of the AC impedance. That is, the specific frequency (f _а ) is the frequency for measuring the negative electrode reaction resistance (frequency for measuring the negative electrode), and the specific frequency ( _{b b} ) is the frequency for measuring the positive electrode reaction resistance (frequency for measuring the positive electrode). ). The specific frequency (f _а ) on the negative electrode side is set to a frequency higher than the specific frequency (f _b ) on the positive electrode side, preferably within the range of 100 Hz or more and 20 kHz or less, or 300 Hz or more and 3 kHz or less. It is set within the range. _{The specific frequency (b b} ) on the positive electrode side is set in the range of, for example, 20 Hz or more and 80 Hz or less. Since the frequency characteristics of the reaction resistance differ depending on the material used for the secondary battery 2, the temperature, and the like, specific frequencies on the positive electrode side and the negative electrode side may be obtained experimentally. For example, in order to grasp the frequency band in which the reaction resistance of the negative electrode appears, an AC signal having a large number of frequency values within a predetermined frequency band is applied to the secondary battery 2 into which the reference electrode is inserted, and for each frequency. Measure the AC impedance. Then, a frequency suitable for measuring the reaction resistance is specified from the characteristics of the imaginary part of the measured AC impedance. The specific frequency of the positive electrode may be specified in the same manner.

While charging the secondary battery 2, the controller 8 calculates the change in the negative electrode reaction resistance per unit time based on the reaction resistance of the negative electrode measured by the impedance measuring device 7, and determines the presence or absence of lithium precipitation. When the secondary battery 2 is being charged, the reaction resistance of the secondary battery 2 changes in a normal charging reaction, but when lithium precipitation occurs, the reaction resistance of the secondary battery 2 is the precipitation of lithium. It also changes depending on. Therefore, when the reaction resistance of the secondary battery 2 changes, it is possible to identify that the precipitation of lithium has occurred if it is possible to distinguish whether the change in the reaction resistance is due to a normal charging reaction or a precipitation of lithium.

FIG. 7 is a graph showing the temporal transition of the reaction resistance when lithium precipitation occurs. FIG. 7 (а) shows the characteristics of the negative electrode reaction resistance, and FIG. 7 (b) shows the characteristics of the positive electrode reaction resistance. The vertical axis "a reaction resistance, and the horizontal axis indicates the charging time. The time _(t а) at the time of, it is assumed that lithium deposition has occurred. Secondary battery 2 charging start time from the time _(t а ), The amount of change in the reaction resistance of the negative electrode is small. If _{lithium precipitates at the time (t а} ), the reaction resistance of the negative electrode is greatly reduced, and the reaction resistance of the negative electrode is the time (t _b ). On the other hand, the reaction resistance of the positive electrode does not decrease even if lithium precipitation occurs. That is, when lithium precipitation occurs, the negative electrode reaction resistance decreases significantly, but the positive electrode reaction resistance increases. The controller 8 detects a change in the negative electrode reaction resistance during charging of the secondary battery 2, and determines that lithium is deposited when the negative electrode reaction resistance decreases by a predetermined value or more per unit time.

Further, in the present embodiment, in order to further improve the determination accuracy of the presence or absence of lithium precipitation, a specific frequency for measuring the negative electrode reaction resistance is set according to the temperature of the secondary battery 2. FIG. 8 is a graph for explaining the temperature transition of the Nyquist plot of the imaginary part component constituting the AC impedance Z. In FIG. 8, the vertical axis is the imaginary part value (−Z ”) of the AC impedance and the horizontal axis is the frequency. (а) is _{the characteristic at the battery temperature (TL} ), and (b) is the battery temperature. _{(T M)} is a characteristic in the case of, are higher in the order of a characteristic of a. the temperature of the rechargeable _{battery, T L, T M, T} H when (c) is the battery temperature _{(T H).} In each graph, the point P on the graph is the apex of the arc representing the magnitude of the reaction resistance of the battery in the Nyquist plot. As shown in FIG. 8, the frequency at which the apex of the arc representing the magnitude of the reaction resistance appears is As the temperature rises, _{the frequency increases in the order of f L} , f _M , and f _{H. From} this, it can be seen that the frequency suitable for measuring the magnitude of the reaction resistance becomes higher as the temperature rises. ..

The specific frequency for measuring the reaction resistance of the negative electrode is also set to a higher frequency as the temperature is higher. Specifically, the AC impedance when lithium precipitation is generated in the secondary battery 2 at a plurality of different temperatures can be measured at a plurality of frequencies, and lithium precipitation can be detected at each temperature (decrease in reaction resistance can be captured). Determine the frequency band and set it within the range of that frequency band.

With reference to FIG. 9, the frequency set when the battery temperature is 25 ° C. will be described as an example. FIG. 9 is a graph showing the characteristics of the negative electrode reaction resistance for each frequency. The vertical axis is the reaction resistance and the horizontal axis is time. The graphs а to f show the characteristics at 200 Hz, 300 Hz, 400 Hz, 3.2 kHz, 5.4 kHz, and 6.6 kHz, respectively. The characteristics of graphs а to f are calculated by calculating the reaction resistance when lithium is deposited at a battery temperature of 25 ° C. from impedances of a plurality of frequencies. In the example of FIG. 9, as shown in the graph A, in the case of setting the frequency to 200Hz, the time period before the time point of time the reaction resistance is reduced significantly (t _p) (K-9 Part), the reaction resistance is reduced. Since the reaction resistance decreases before lithium precipitation due to the influence of the behavior of the positive electrode, the behavior is as shown in Graph а. Further, even when the frequency is lower than 200 Hz, the reaction resistance is affected by the behavior of the positive electrode as in the behavior shown in Graph а, and the reaction resistance decreases before lithium precipitation. That is, in the example of FIG. 9, when the frequency is set to 200 Hz or less, it is difficult to distinguish whether the decrease in reaction resistance is due to lithium precipitation or the influence of the behavior of the positive electrode. The frequency of is not preferable as a specific frequency for measuring the negative electrode reaction resistance.

Further, in the example of FIG. 9, as shown in the graph f, when the frequency is set to 6.6 kHz, the reaction resistance hardly decreases. Even when it is higher than 6.6 kHz, the characteristic of the reaction resistance shows that the reaction resistance hardly decreases as in the behavior as shown in the graph f. Therefore, a frequency in the frequency band of 6.6 kHz or higher is not preferable as a specific frequency for measuring the decrease in reaction resistance. Therefore, in the example of FIG. 9, when the battery temperature is 25 ° C., the frequency that can be set as the specific frequency is in the range higher than 200 Hz and lower than 6.6 kHz.

If there is a frequency band that can be set as a specific frequency and there is a specific frequency that can be set in common at any temperature, the specific frequency may be fixed with respect to the temperature. Also, if there is a frequency band that can be set as a specific frequency, and if it becomes a noise source for other devices in some of the frequency bands, avoid that frequency band and set the specific frequency. You may.

The impedance measuring instrument 7 may set a frequency included in a frequency band in which the change in the negative electrode reaction resistance according to the battery temperature is small to a specific frequency. The temperature characteristics of the negative electrode reaction resistance described with reference to FIG. 8 vary depending on the material used for the secondary battery 2 and the like. Then, when the change in the negative electrode reaction resistance is small with respect to the temperature change of the secondary battery 2 and there is a frequency in which the negative electrode reaction resistance greatly decreases when lithium precipitation occurs, such a frequency is used. The frequency may be set to a specific frequency. This makes it possible to improve the determination accuracy of lithium precipitation with respect to changes in battery temperature.

The impedance measuring device 7 sets a specific frequency for measuring the positive electrode reaction resistance according to the battery temperature of the secondary battery 2. The setting method of the specific frequency may be the same as the setting method for the negative electrode described above.

Further, in the present embodiment, in order to further improve the accuracy of determining the presence or absence of lithium precipitation, the possibility of lithium precipitation occurring is detected based on the state of the secondary battery 2. Then, when there is a possibility that lithium precipitation may occur, the controller 8 determines the presence / absence of lithium precipitation, and when there is no possibility of lithium precipitation occurring, the controller 8 determines the presence / absence of lithium precipitation. do not. Hereinafter, a method for detecting the possibility of lithium precipitation will be described.

FIG. 10 is a graph showing the frequency characteristics of the reaction resistance of the secondary battery 2. In FIG. 10, the vertical axis represents the reaction resistance and the horizontal axis represents the frequency. Graph а shows the characteristics of the negative electrode reaction resistance, graph b shows the characteristics of the positive electrode reaction resistance, and graph c shows the characteristics of the overall reaction resistance. (А) Is the characteristic in the charged state (SOC: System of Charge) (SOC _L ), (b) is the characteristic in the charged state (SOC _M ), and (c) is the characteristic in the charged state (SOC _H). ) Is the characteristic. The charge state of the secondary battery increases in the order of _{SOC L} , SOC _M , and SOC _H. As shown in FIG. 10, the reaction resistance of the negative electrode is affected by the SOC change. Then, in a state where the SOC is likely to be biased in the secondary battery 2 such as when the C rate is high during battery charging, it is possible to distinguish whether the decrease in reaction resistance is due to the SOC change or the occurrence of lithium precipitation. It can be difficult. Furthermore, the effect of such SOC bias is also noticeable when the battery temperature is low.

Therefore, in the present embodiment, the condition that lithium precipitation does not occur is experimentally obtained by using the correlation between the temperature, the charging current, and the charging state of the secondary battery 2, and the experimental data is used as an electrodeposition map in the memory of the controller 8. It is stored in. As a method of acquiring experimental data, for example, in a secondary battery 2 having a reference electrode inserted, charging is performed while measuring the negative electrode potential using the reference electrode. Then, the negative electrode potential when lithium precipitation occurs is recorded as a precipitation point. Recording of such precipitation points is carried out at different C rates and temperatures, respectively. The recorded data can represent the relationship between the temperature of the secondary battery 2 and the charging current and the magnitude of the cell voltage which is the precipitation point. The experimental data for deriving the precipitation point may be a method of disassembling and analyzing the secondary battery 2 after charging to confirm the presence or absence of lithium precipitation.

FIG. 11 is a graph for explaining the relationship between the temperature of the secondary battery 2, the charging current, and the cell voltage at the precipitation point. In FIG. 11, the vertical axis represents the cell voltage and the horizontal axis represents the current (C rate) during charging. Since the cell voltage has a correlation with the charging state (SOC), the vertical axis corresponds to the charging state. Each graph shown in FIG. 11 shows the voltage at the precipitation point with respect to the charging current. For example, the temperature of the secondary battery 2 is T _A, when charged at a charge current (I _A), the cell voltage of the deposition point becomes V _A. Then, when charging at a charge current (I _A), as the temperature of the secondary battery 2 is high, the cell voltage of the deposition point is high. The precipitation point corresponds to the point at which lithium precipitation starts.

The controller 8 detects the possibility of lithium precipitation based on the detected temperature of the temperature sensor 4, the detected current of the current sensor 6, and the detected voltage of the voltage sensor 3. Specifically, the controller 8 acquires the map (deposition map) shown in FIG. 11 from the memory, and specifies the correlation between the current and the cell voltage corresponding to the current battery temperature on the map. For example, when the detected temperature of the temperature sensor 4 is T _A identifies the graph shown by the arrow T _A in FIG. 11. Secondary battery 2 charging current when (corresponding to the detection current of the current sensor 6) is I _A, the controller 8 on the identified graph, the cell voltage of the deposition point corresponding to the current I _A (V _A) To identify. Begins charging in the temperature of the secondary battery 2 (T _A) and the charging current (I _A), as charging proceeds, SOC of the secondary battery 2 becomes higher. If the cell voltage of the secondary battery 2 is _VA or less, there is no possibility of lithium precipitation. On the other hand, if the cell voltage of the secondary battery 2 _{becomes higher than VA,} there is a possibility of lithium precipitation.

The controller 8 uses the electrodeposition map, the temperature of the secondary battery 2 (T _A) and the charging current (I _A) After identifying the voltage (V _A) of the deposition point from the secondary battery 2 of the cell voltage ( (Corresponding to the detection voltage of the voltage sensor 3) and the cell voltage ( _VA ) at the precipitation point are compared. Then, when the cell voltage of the secondary battery 2 _{is equal to or lower than the cell voltage (VA} ) at the precipitation point, the controller 8 determines that there is no possibility of lithium precipitation. On the other hand, when the cell voltage of the secondary battery 2 _{is higher than the cell voltage (VA} ) at the precipitation point, the controller 8 determines that there is a possibility of lithium precipitation. Then, in a state where there is a possibility of lithium precipitation, the controller 8 determines whether or not lithium precipitation has occurred based on the negative electrode reaction resistance. Thereby, the determination accuracy of lithium precipitation can be improved.

In this embodiment, a change in the positive electrode reaction resistance may be used in order to detect the possibility of lithium precipitation occurring based on the state of the secondary battery 2. As described with reference to FIG. 7, when lithium precipitation occurs, the negative electrode reaction resistance may decrease, but the positive electrode reaction resistance may not decrease. Therefore, utilizing this characteristic, the controller 8 determines whether or not the positive electrode reaction resistance has decreased in correspondence with the timing at which the negative electrode reaction resistance has decreased. Then, if the positive electrode reaction resistance does not decrease, the controller 8 determines that lithium precipitation may occur. On the other hand, when the positive electrode reaction resistance also decreases in correspondence with the timing when the negative electrode reaction resistance decreases, there is a high possibility that the decrease in the negative electrode reaction resistance is a factor other than the determination of lithium precipitation. It is not necessary to determine the presence or absence of lithium precipitation. The case where the positive electrode reaction resistance does not decrease is not limited to the case where the positive electrode reaction resistance does not decrease at all. If the decrease in the positive electrode reaction resistance is less than a predetermined value, it may be determined that the positive electrode reaction resistance has not decreased, and if the decrease in the positive electrode reaction resistance is greater than or equal to the predetermined value, the positive electrode reaction resistance decreases. It may be determined that it is.

Next, a method for determining lithium precipitation in the secondary battery 2 and a method for controlling charging of the secondary battery 2 will be described. FIG. 12 is a flowchart showing the procedure of the determination process and the procedure of the charge process in the lithium precipitation determination system. The control flow of FIG. 12 is repeatedly executed for a predetermined cycle while the secondary battery 2 is being charged.

In step S1, the controller 8 measures the battery temperature using the temperature sensor 4, and measures the cell voltage (voltage of the secondary battery 2) using the voltage sensor 3. In step S2, the impedance measuring instrument 7 sets a specific frequency (f _{а ) for measuring the negative electrode reaction resistance and a specific frequency (f b} ) for measuring the positive electrode reaction resistance, respectively, according to the battery temperature. .. In step S3, the controller 8 starts charging the secondary battery 2. Further, the impedance measuring device 7 _{applies an} AC signal to the secondary battery 2 by superimposing an AC signal (impedance measuring current) including a specific frequency (f а) and a specific frequency (f _{b) on the charging current.} ..

In step S4, the controller 8 compares the cell voltage with the specified voltage value. The specified voltage value indicates the upper limit voltage for switching from CC charging to CV charging. When the cell voltage is higher than the specified voltage value, in step S5, the controller 8 charges the secondary battery 2 by CV charging (constant voltage charging). In step S6, the controller 8 compares the charging current with the specified end current value (cutoff current value). The charging current may be measured using the current sensor 6. When the charging current is equal to or greater than the end current specified value, the controller 8 executes the control flow in step S8. When the charging current is less than the end current specified value, the controller 8 stops charging the secondary battery 2 and ends the control flow.

After the determination process in step S4, if the cell voltage is equal to or lower than the specified voltage value, the controller 8 charges the secondary battery 2 by CC charging (constant current charging) in step S7. In step S9, the controller 8 determines whether or not a predetermined time has elapsed from the time when the superimposed current starts to flow. Immediately after the start of the superimposed current, it is affected by the transient current change. Therefore, in order to avoid such an influence, the control flow in step S9 is performed. If a predetermined time has not elapsed from the time when the superimposed current starts to flow, the control flow shown in FIG. 12 is temporarily terminated, and the control flow of step S1 is executed again. That is, if a predetermined time has not passed from the time when the superimposed current is started to flow, the data measured by the impedance measuring instrument 7 is not used for the presence or absence of lithium precipitation.

When a predetermined time has elapsed from the time when the superimposed current starts to flow, in step S10, the impedance measuring instrument 7 reacts with the positive electrode and the negative electrode based on the AC impedance at _{a specific frequency (f а} , _bb). Are measured respectively. In step S11, the controller 8 detects the possibility that lithium precipitation may occur based on the battery state of the secondary battery 2. When there is no possibility that lithium precipitation occurs, the control flow shown in FIG. 12 is temporarily terminated, and the control flow of step S1 is executed again.

If there is a possibility that lithium precipitation may occur, in step S12, the controller 8 determines the presence or absence of lithium precipitation. FIG. 13 is a flowchart showing a subflow of the control process in step S12. The controller 8 executes the control process of step S12 shown in FIG. 12 by executing the control flow shown in FIG.

In step S21, the controller 8 performs a filtering process on the reaction resistance measured by the impedance measuring device 7 to remove noise. For example, a low-pass filter is used as the filter. In step S22, the slope of the negative electrode reaction resistance is calculated in order to measure the change in the negative electrode reaction resistance per unit time. The slope can be calculated by dividing the sampling period from the difference between the previous value of the negative electrode reaction resistance (R _{аct (k-1)} ) and the current value of the negative electrode reaction resistance (R _{аct (k)).} The slope indicates the amount of decrease (decrease rate) of the negative electrode reaction resistance per unit time. However, k is a natural number. The sampling cycle corresponds to the measurement cycle of the impedance measuring device 7. In order to lengthen the unit time, the sampling cycle may be longer than the measurement cycle of the impedance measuring device 7 so as to include a plurality of measurement timings of the impedance measuring device 7. In other words, the sampling period may be set so that the measured values of the reaction resistance include, for example, 2 to 10 within the period corresponding to the difference in the negative electrode reaction resistance.

In step S23, the controller 8 compares the calculated slope with the preset judgment threshold, and when the slope is equal to or greater than the judgment threshold, that is, the reduction width of the negative electrode reaction resistance per unit time is the judgment threshold. If it is larger, the controller 8 determines in step S24 that there is lithium precipitation. On the other hand, when the slope is less than the determination threshold value, that is, when the reduction width of the negative electrode reaction resistance per unit time is smaller than the determination threshold value, the controller 8 determines that lithium is not deposited in step S25. That is, the controller 8 detects whether or not the negative electrode reaction resistance is lowered by a predetermined value or more per unit time by executing the control processing of steps S23 to S25, and the negative electrode reaction resistance is lowered by a predetermined value or more per unit time. If this is the case, it is determined that lithium is deposited, and if the negative electrode reaction resistance does not decrease by a predetermined value or more per unit time, it is determined that there is no lithium precipitation.

Then, the controller 8 ends the control flow shown in FIG. 13 and executes the control flow of step S13 shown in FIG. The control process in step S13 is a control process for branching the following control flow according to the determination result in the control process in step S12.

If it is determined in the control process of step S12 that lithium precipitation is present, the process proceeds to "Yes" from the control process of step S13. In step S14, the controller 8 sets the charging current to a value lower than the current current. Set. The charging current may be set to zero to stop the charging current. Then, the control flow shown in FIG. 12 ends.

If it is determined in the control process of step S12 that there is no lithium precipitation, the process proceeds from the control process of step S13 to "No", the control flow shown in FIG. 12 is temporarily terminated, and the control flow of step S1 is executed again. To do.

As described above, in the present embodiment, the AC impedance of the lithium ion secondary battery 2 is measured, and the negative electrode reaction of the secondary battery 2 is based on the characteristics of the AC impedance of the secondary battery 2 at a specific frequency. The resistance is calculated, and when the negative electrode reaction resistance drops by a predetermined value or more per unit time during charging of the secondary battery 2, it is determined that lithium is deposited. Thereby, the determination accuracy of lithium precipitation can be improved.

Further, in the present embodiment, the specific frequency is set within the range of 100 Hz or more and 20 kHz or less. This makes it possible to measure the reaction resistance of the negative electrode in a state where it is not easily affected by other factors such as the positive electrode.

Further, in the present embodiment, the higher the temperature detected by the temperature sensor 4, the higher the specific frequency is set. As a result, the negative electrode reaction resistance can be accurately measured even if the temperature of the secondary battery 2 changes.

Further, in the present embodiment, the negative electrode reaction resistance is calculated based on the impedance of at least one of the real part and the imaginary part of the AC impedance. Thereby, the reaction resistance of the designated frequency band can be calculated.

Further, in the present embodiment, the possibility of lithium precipitation is detected based on the state of the secondary battery 2, and when there is a possibility of lithium precipitation, the presence or absence of lithium precipitation is determined, and lithium is used. If there is no possibility that the precipitation of lithium will occur, the presence or absence of the precipitation of lithium is not determined. Thereby, the determination accuracy of lithium precipitation can be improved.

Further, in the present embodiment, the charge state (SOC) of the secondary battery 2 is calculated based on the detected values of the voltage sensor 3 and / or the current sensor 6 (corresponding to the “voltage / current sensor” of the present invention), and the temperature sensor is used. Based on the temperature detected by No. 4, the current of the secondary battery 2, and the state of charge, the possibility of lithium precipitation is detected. Thereby, the determination accuracy of lithium precipitation can be improved.

Further, in the present embodiment, among the characteristics of the AC impedance of the secondary battery 2, the positive electrode reaction resistance of the secondary battery 2 is calculated based on the characteristics at a frequency lower than the specific frequency, and the positive electrode reaction resistance does not decrease. In this case, the presence or absence of lithium precipitation is determined. Thereby, the determination accuracy of lithium precipitation can be improved.

Further, in the present embodiment, when it is determined that lithium is deposited, the charging current of the secondary battery 2 is lowered. This makes it possible to prevent the precipitation of lithium from proceeding.

In the present embodiment, the controller 8 calculates the slope of the negative electrode reaction resistance in the control flow of steps S22 and S23, and compares the calculated slope with the determination threshold value. The difference (decrease in the negative electrode reaction resistance) may be calculated, and the difference may be compared with the judgment threshold. The difference between the negative electrode reaction resistances is the k-th value of the negative electrode reaction resistance and the kn-th value of the negative electrode reaction resistance. However, n is a natural number, which is the number of samplings corresponding to a unit time. The determination resistance may be set in advance so as to correspond to the difference. When the difference between the negative electrode reaction resistances is equal to or greater than the determination threshold value, it corresponds to a decrease in the negative electrode reaction resistance by a predetermined value or more per unit time. Further, when the difference of the negative electrode reaction resistance is less than the determination threshold value, it corresponds to that the negative electrode reaction resistance does not decrease by a predetermined value or more per unit time.

In the above-described embodiment, the lithium precipitation determination device may be provided with at least an impedance measuring device 7 and a controller 8.

Although the embodiments of the present invention have been described above, these embodiments are described for facilitating the understanding of the present invention, and are not described for limiting the present invention. Therefore, each element disclosed in the above-described embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

1 ... Lithium precipitation determination system 2 ... Secondary battery 3 ... Voltage sensor 4 ... Temperature sensor 5 ... Voltage / current adjusting unit 6 ... Current sensor 7 ... Impedance measuring device 8 ... Controller 9 ... External power supply

Claims (9)

It is a determination device that determines the precipitation of lithium contained in a lithium ion secondary battery.
The measuring instrument is provided with a measuring instrument for measuring the AC impedance of the secondary battery and a controller for determining the presence or absence of precipitation of lithium, and the measuring instrument is based on the characteristics of the AC impedance of the secondary battery at a specific frequency. Calculate the negative electrode reaction resistance of the secondary battery and calculate
The controller is a determination device for determining that lithium is deposited when the negative electrode reaction resistance drops by a predetermined value or more per unit time during charging of the secondary battery. The determination device according to claim 1.
The determination device in which the specific frequency is set within the range of 100 Hz or more and 20 kHz or less. The determination device according to claim 1 or 2.
A temperature sensor for detecting the temperature of the secondary battery is provided.
The measuring instrument is a determination device that sets the specific frequency to a higher frequency as the temperature detected by the temperature sensor increases. The determination device according to any one of claims 1 to 3.
The measuring instrument is a determination device that calculates the negative electrode reaction resistance based on the impedance of at least one of the real part and the imaginary part of the AC impedance. The determination device according to any one of claims 1 to 4.
The controller
Based on the state of the secondary battery, the possibility of the precipitation of lithium is detected, and
When there is a possibility that the lithium precipitation may occur, the presence or absence of the lithium precipitation is determined.
A determination device that does not determine the presence or absence of precipitation of lithium when there is no possibility that precipitation of lithium will occur. The determination device according to claim 5.
A temperature sensor that detects the temperature of the secondary battery and
A voltage / current sensor for detecting the cell voltage and / or current of the secondary battery is provided.
The controller
Based on the detected value of the voltage / current sensor, the charge state of the secondary battery is calculated.
A determination device that detects the possibility of lithium precipitation based on the temperature detected by the temperature sensor, the current of the secondary battery, and the charging state. The determination device according to claim 5.
The measuring instrument calculates the positive electrode reaction resistance of the secondary battery based on the characteristics of the AC impedance of the secondary battery at a frequency lower than the specific frequency for measuring the negative electrode.
The controller
A determination device for determining the presence or absence of precipitation of lithium when the positive electrode reaction resistance has not decreased. The determination device according to any one of claims 1 to 7.
The controller is a determination device that lowers the charging current of the secondary battery when it is determined that the lithium is deposited. This is a method for determining the precipitation of lithium contained in a lithium ion secondary battery.
Measure the AC impedance of the secondary battery and
Among the characteristics of the AC impedance of the secondary battery, the negative electrode reaction resistance of the secondary battery is calculated based on the characteristics at a specific frequency.
A method for determining that lithium is deposited when the negative electrode reaction resistance drops by a predetermined value or more per unit time during charging of the secondary battery.

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