Charging method and charging control device for all-solid-state batteries

Abstract

In a method for charging an all-solid-state battery provided with a solid electrolyte layer and a negative electrode containing lithium metal, an impedance measurement device for measuring impedance in all-solid-state batteries is used to measure the impedance value at the interface between the negative electrode and the solid electrolyte layer, a determination is made as to whether or not the measured impedance value is within an allowable impedance range, and charging of the all-solid-state battery is allowed if the measured impedance value is within the allowable impedance range. The allowable impedance range is determined by using: an allowable impedance map in which charging current densities are associated with the allowable impedance values at which charging is allowed; and the charging current density for charging the all-solid-state battery.

Description

[Technical Field]

[0001] The present invention relates to a charging method and a charging control device for an all-solid-state battery. This application claims priority based on Japanese Patent Application No. 2021-207116 filed on December 21, 2021, and for designated states where incorporation by reference of documents is permitted, the contents of the above application are incorporated by reference into this application and made part of the description of this application. [Background technology]

[0002] A method for estimating an internal short circuit state has been known for measuring the AC impedance of an all-solid-state lithium-ion secondary battery and estimating the possibility of an internal short circuit (Patent Document 1). In the method for estimating an internal short circuit state described in Patent Document 1, an electrolyte resistance component and a reaction resistance component are calculated from the AC impedance, and the internal resistance coordinates are obtained by plotting the electrolyte resistance component as one axis component and the reaction resistance component as the other axis component on a plane coordinate system consisting of two axis components. Next, an approximate line is obtained using multiple internal resistance coordinates, and the approximate line is compared with a map showing the normal region, internal short circuit region, and possible short circuit region for the internal resistance coordinates to calculate the distance between the intersection of the possible short circuit region and the approximate line and the internal resistance coordinates. If the calculated distance is equal to or less than a predetermined threshold, it is estimated that there is a possibility of an internal short circuit in the all-solid-state lithium-ion secondary battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-167069 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the estimation method of the above-described conventional technology cannot detect the possibility of an internal short circuit occurring when the contact area at the interface between the lithium negative electrode and the solid electrolyte layer is excessive, and therefore, there is a possibility that the all-solid-state battery will be charged in a state where the contact area is excessive.

[0005] The problem to be solved by the present invention is to provide a charging method and a charge control device that can estimate whether the contact area at the interface between the negative electrode and the solid electrolyte layer is in an excessive state, and can charge an all-solid-state battery while preventing a short circuit. [Means for solving the problem]

[0006] The present invention solves the above problem by measuring an impedance value at the interface between the negative electrode and the solid electrolyte layer of an all-solid-state battery, determining whether the impedance value is within an allowable impedance range determined by an allowable impedance map and a charging current density, and permitting charging of the all-solid-state battery when the measured impedance value is within the allowable impedance range. [Effects of the Invention]

[0007] According to the present invention, it is possible to charge an all-solid-state battery while preventing short circuits. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram showing a charging control system for a secondary battery according to this embodiment. [Figure 2] FIG. 2 is a plan view of the secondary battery according to this embodiment. [Figure 3] FIG. 3 is a cross-sectional view of the secondary battery taken along line III-III in FIG. [Figure 4] FIG. 4 is a schematic diagram of the contact state at the negative electrode interface. [Figure 5] FIG. 5(a) is a graph showing the relationship between the double layer capacity at the negative electrode interface and the chargeable capacity, and FIG. 5(b) is a graph showing the relationship between the reaction resistance at the negative electrode interface and the chargeable capacity. [Figure 6]Figure 6(a) is a graph showing the relationship between the double layer capacity of the negative electrode interface and the chargeable capacity as a function of the charging current density, and Figure 6(b) is a graph showing the relationship between the reaction resistance of the negative electrode interface and the chargeable capacity as a function of the charging current density. [Figure 7] FIG. 7 is a flowchart showing the procedure of the control process in the charge control system according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] FIG. 1 is a diagram showing the configuration of a charge control system for an all-solid-state battery according to this embodiment. The charge control system according to this embodiment measures the impedance value at the negative electrode interface of the all-solid-state battery, determines whether the impedance value is within an allowable impedance range, and permits and carries out charging of the all-solid-state battery according to the determination result. As shown in FIG. 1, the charge control system 1 includes a secondary battery 2, a voltage sensor 3, a temperature sensor 4, a voltage / current adjustment unit 5, a current sensor 6, an impedance measuring device 7, a controller 8, and an external power supply 9. The charge control system shown in FIG. 1 is a system for determining whether charging is possible before and / or during charging, and charging the secondary battery 2 with power from the external power supply 9.

[0010] An all-solid-state lithium-ion secondary battery will be described as an example of the secondary battery 2 in this embodiment. The secondary battery 2 is an all-solid-state battery and includes a power generating element having a positive electrode including a positive electrode active material layer containing a positive electrode active material capable of absorbing and releasing lithium ions, a negative electrode including a negative electrode active material layer containing a negative electrode active material capable of absorbing and releasing lithium ions, and a solid electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer. In addition to the power generating element, the secondary battery 2 also has an electrode tab and an exterior member that houses the electrode tab and the power generating element. The detailed structure and materials of the secondary battery will be described later.

[0011] The voltage sensor 3 is a sensor for detecting the input / output voltage of the secondary battery 2, and detects the cell voltage (terminal voltage) between the positive and negative electrodes of the secondary battery 2. There are no particular restrictions on the connection position of the voltage sensor 3, as long as it is located in a circuit connected to the secondary battery 2 where the cell voltage between the positive and negative electrodes can be detected.

[0012] The temperature sensor 4 measures the external surface temperature (environmental temperature) of the secondary battery 2. The temperature sensor 4 is attached to the surface of the case (exterior body, housing) of the secondary battery 2, for example.

[0013] The voltage / current adjusting unit 5 is a circuit for adjusting the battery current and cell voltage when charging and / or discharging the secondary battery 2, and adjusts the current / voltage of the secondary battery 2 based on commands from the controller 8. The voltage / current adjusting unit 5 has a voltage conversion circuit and the like for converting the power output from an external power source into a charging voltage for the secondary battery.

[0014] 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 adjustment unit 5 to the secondary battery 2 when the secondary battery 2 is being charged, and detects the current supplied from the secondary battery 2 to the voltage / current adjustment unit 5 when the secondary battery 2 is being discharged.

[0015] The impedance measuring device 7 is connected to the secondary battery 2. It applies an AC perturbation current as an input signal to the secondary battery 2 and measures the AC impedance (complex impedance) of the secondary battery 2 by acquiring a response voltage corresponding to the AC signal (AC current). The impedance measuring device 7 may be selected from among commonly used devices for measuring AC impedance. For example, the impedance measuring device 7 may measure the AC impedance of the secondary battery 2 by changing the frequency of the AC perturbation current over time using an AC impedance method. Alternatively, the impedance measuring device 7 may be capable of simultaneously applying multiple AC perturbation currents with different frequencies. The method for measuring AC impedance using the AC impedance method is not particularly limited. For example, analog methods such as the Lissajous method and the AC bridge method, and digital methods such as the digital Fourier integration method and the fast Fourier transform method using noise injection may be appropriately employed. In this embodiment, multiple AC perturbation currents with different frequencies are applied to the secondary battery 2 to measure the AC impedance. The multiple frequencies may be within a range that allows the reaction resistance component of the secondary battery 2 to be calculated from a graph (Nyquist plot; Cole-Cole plot) in which the real component Z' and imaginary component Z" that make up the AC impedance Z measured by the impedance measuring instrument 7 are plotted on complex plane coordinates. There are no particular restrictions on the amplitude of the waveform (e.g., sine wave) of the AC perturbation current applied to the battery, and it may be set arbitrarily. The measurement result of the AC impedance measured by the impedance measuring instrument 7 is sent to the controller 8 as the output of the impedance measuring instrument 7.

[0016] The controller 8 has a CPU 81, a storage unit 82, etc. The controller 8 is a control device that determines whether or not lithium is deposited in the secondary battery 2 based on the reaction resistance of the secondary battery 2 measured by the impedance measuring device 7. The controller 8 also controls the charging of 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.

[0017] The external power supply 9 is a power supply for charging the secondary battery 2. For example, a three-phase 200V AC power supply is used as the power supply. The external power supply 9 may also be a single-phase 100V or single-phase 200V AC power supply. Furthermore, the external power supply 9 is not limited to AC, and may also be a DC power supply.

[0018] Next, the structure of the secondary battery (all-solid-state lithium ion secondary battery) 2 will be described with reference to Fig. 2 and Fig. 3. Fig. 2 shows a plan view of the secondary battery 2 according to this embodiment, and Fig. 3 shows a cross-sectional view of the secondary battery 2 taken along line III-III in Fig. 2.

[0019] As shown in FIGS. 2 and 3 , the secondary battery 2 is composed of a power generating element 101 having three positive electrode layers 102, seven electrolyte layers 103, and three negative electrode layers 104, positive electrode tabs 105 connected to the three positive electrode layers 102, respectively, negative electrode tabs 106 connected to the three negative electrode layers 104, and an upper exterior member 107 and a lower exterior member 108 that accommodate and seal the power generating element 101, positive electrode tabs 105, and negative electrode tabs 106.

[0020] The numbers of the positive electrode layers 102, the electrolyte layers 103, and the negative electrode layers 104 are not particularly limited, and the power generating element 101 may be configured with one positive electrode layer 102, three electrolyte layers 103, and one negative electrode layer 104, or the numbers of the positive electrode layers 102, the electrolyte layers 103, and the negative electrode layers 104 may be appropriately selected as needed.

[0021] The positive electrode layer 102 constituting the power generating element 101 includes a positive electrode current collector 102a extending to the positive electrode tab 105, and positive electrode active material layers formed on both main surfaces of a portion of the positive electrode current collector 102a. The positive electrode current collector 102a constituting the positive electrode layer 102 can be made of an electrochemically stable metal foil such as aluminum foil, aluminum alloy foil, copper-titanium foil, or stainless steel foil. Metals such as nickel, iron, and copper may also be used for the positive electrode current collector 102a. Other materials that may be used include a clad material of nickel and aluminum, a clad material of copper and aluminum, and the like.

[0022] Instead of metal, a conductive resin may be used for the positive electrode current collector 102a. The conductive resin may be a resin obtained by adding a conductive filler to a non-conductive polymeric material as needed. Examples of non-conductive polymeric materials include polyethylene (PE; high-density polyethylene (HDPE), low-density polyethylene (LDPE), etc.), polypropylene (PP), and polyethylene terephthalate (PET), which have excellent potential resistance. The conductive filler can be any conductive material. Examples of materials with excellent conductivity, potential resistance, or lithium ion blocking properties include metals and conductive carbon. Examples of metals include, but are not limited to, at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, and Sb, or alloys or metal oxides containing these metals.

[0023] The positive electrode active material layer constituting the positive electrode layer 102 is not particularly limited, but may be a layered rock salt active material such as LiCoO2, LiMnO2, LiNiO2, LiVO2, or Li(Ni-Mn-Co)O2; LiMn2O4, LiNi 0.5 Mn 1.5 Examples of oxide active materials include spinel-type active materials such as LiFePO4 and LiMnPO4, olivine-type active materials such as LiFeSiO4 and LiMnSiO4, and Si-containing active materials such as LiFeSiO4 and LiMnSiO4. 12 A composite oxide containing lithium and nickel is preferably used, and more preferably Li(Ni-Mn-Co)O2 or an oxide in which part of the transition metal is replaced with another element (hereinafter, also simply referred to as "NMC composite oxide").

[0024] The positive electrode active material layer may contain a sulfur-based positive electrode active material, such as particles or a thin film of an organic sulfur compound or an inorganic sulfur compound, as long as the material is capable of releasing lithium ions during charging and absorbing lithium ions during discharging by utilizing the oxidation-reduction reaction of sulfur.

[0025] The positive electrode active material layer may further contain at least one of a solid electrolyte, a conductive additive, and a binder, as necessary. Examples of the solid electrolyte include a sulfide solid electrolyte and an oxide solid electrolyte, and examples of the solid electrolyte that can constitute the electrolyte layer 103 described later can be used.

[0026] Each of the positive electrode current collectors 102a constituting the three positive electrode layers 102 is joined to a positive electrode tab 105. The positive electrode tab 105 may be made of aluminum foil, aluminum alloy foil, copper foil, nickel foil, or the like.

[0027] The negative electrode layer 104 constituting the power generating element 101 has a negative electrode side current collector 104a extending to the negative electrode tab 106 and a negative electrode active material layer formed on each of the two main surfaces of a portion of the negative electrode side current collector 104a.

[0028] The negative electrode side current collector 104a of the negative electrode layer 104 is made of an electrochemically stable metal foil such as nickel foil, copper foil, stainless steel foil, or iron foil.

[0029] The negative electrode layer 104 is formed of a layer containing a negative electrode active material. The type of negative electrode active material is not particularly limited, but examples thereof include carbon materials, metal oxides, and metal active materials. Examples of carbon materials include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon. Examples of metal oxides include Nb2O5, Li4Ti5O 12 , SiO, etc. Furthermore, examples of the metal active material include simple metals such as In, Al, Si, and Sn, and alloys such as TiSi and La3Ni2Sn7.

[0030] The negative electrode active material may be a lithium alloy containing Li. Examples of lithium alloys include alloys of lithium and at least one metal selected from gold (Au), magnesium (Mg), aluminum (Al), calcium (Ca), zinc (Zn), tin (Sn), and bismuth (Bi). The lithium alloy may also be an alloy of lithium and two or more of the above-mentioned metals. Specific examples of lithium alloys include lithium-gold alloy (Li-Au), lithium-magnesium alloy (Li-Mg), lithium-aluminum alloy (Li-Al), lithium-calcium alloy (Li-Ca), lithium-zinc alloy (Li-Zn), lithium-tin alloy (Li-Sn), and lithium-bismuth alloy (Li-Bi). The negative electrode active material layer may be any material containing a lithium alloy, and its configuration is not particularly limited.

[0031] In the secondary battery 2 of this 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. That is, in the secondary battery 2 of this embodiment, each negative electrode layer 104 is joined to a single common negative electrode tab 106.

[0032] The electrolyte layer 103 of the power generating element 101 prevents a short circuit between the above-described positive electrode layer 102 and negative electrode layer 104. The electrolyte layer 103 contains a solid electrolyte as a main component and is interposed between the above-described positive electrode active material layer and negative electrode active material layer. Examples of the solid electrolyte include a sulfide solid electrolyte, an oxide solid electrolyte, and a polymer solid electrolyte. The solid electrolyte layer 103 may further contain a binder.

[0033] As shown in FIG. 3, the positive electrode layers 102 and the negative electrode layers 104 are alternately stacked with the electrolyte layers 103 interposed therebetween, and the electrolyte layers 103 are stacked on the top and bottom layers, respectively, thereby forming the power generating element 101.

[0034] The power generating element 101 configured as described above is housed in and sealed in an upper exterior member 107 and a lower exterior member 108 (sealing means). The upper exterior member 107 and the lower exterior member 108 for sealing the power generating element 101 are formed of a flexible material, such as a resin film of polyethylene, polypropylene, or the like, or a resin-metal thin film laminate material in which both sides of a metal foil such as aluminum are laminated with a resin such as polyethylene or polypropylene, and by heat-sealing the upper exterior member 107 and the lower exterior member 108, the power generating element 101 is sealed with the positive electrode tab 105 and the negative electrode tab 106 protruding to the outside.

[0035] Note that, in the portions of the positive electrode tab 105 and the negative electrode tab 106 that come into contact with the upper exterior member 107 and the lower exterior member 108, sealing films 109 are provided to ensure adhesion with the upper exterior member 107 and the lower exterior member 108. The sealing film 109 is not particularly limited, but can be made of, for example, a synthetic resin material that has excellent electrolyte resistance and heat-sealing properties, such as polyethylene, modified polyethylene, polypropylene, modified polypropylene, or ionomer.

[0036] Next, the relationship between the contact state of the interface between the solid electrolyte layer and the negative electrode (hereinafter also referred to as the negative electrode interface) in a secondary battery (all-solid-state battery) 2 and dendrites will be described with reference to FIG. 4. FIG. 4 is a schematic diagram of the contact state of the negative electrode interface. (a) represents a state in which the contact at the negative electrode interface is too small, (b) represents a state in which the contact at the negative electrode interface is normal (normal cell), and (c) represents a state in which the contact at the negative electrode interface is excessive. In (a) and (c), the upper diagrams show the state before dendrite formation, and the lower diagrams show the state after dendrite formation.

[0037] As shown in Figure 4(a), if the contact between the solid electrolyte layer and the negative electrode is insufficient, the solid electrode and the negative electrode will be partially in contact. In such a case, lithium ions and electrons will gather at the contacting part of the negative electrode interface, causing the current density to be higher than that of a normal cell. Lithium will then precipitate as metal and form dendrites (see the bottom diagram of Figure 4(a)). If the dendrites further break through the solid electrolyte layer, a short circuit will occur within the secondary battery 2.

[0038] As shown in Figure 4(c), when there is excessive contact between the solid electrolyte layer and the negative electrode, lithium metal penetrates into the solid electrolyte layer. In such cases, the lithium reaction is concentrated in a certain area, causing the lithium metal to extend into the solid electrolyte layer, forming dendrites (see the bottom diagram in Figure 4(c)). On the other hand, when the contact at the negative electrode interface is good, dendrites are less likely to form than when there is insufficient or excessive contact.

[0039] That is, as shown in Figures 4(a) and (c), the unevenness of contact at the negative electrode interface increases with the application of current. Therefore, to prevent dendrite formation, it is necessary to be able to detect both insufficient and excessive contact at the negative electrode interface. In the case of insufficient contact at the negative electrode interface, when dendrites form, the cell voltage gradually increases as the charge capacity increases. When dendrites penetrate the solid electrolyte layer and short-circuit, the cell voltage becomes almost zero. In other words, an insufficient contact state can be detected from a change in cell voltage. On the other hand, when the negative electrode interface is in an excessive contact state, even if dendrites form, the increase in cell voltage is small, and the voltage drop upon short-circuiting is also small. Therefore, it is difficult to detect an excessive contact state from the cell voltage. Furthermore, it is also difficult to directly detect the contact state (contact area) at the negative electrode interface. In this embodiment, as a method for indirectly detecting the contact state at the negative electrode interface, the impedance value at the negative electrode interface is measured and the contact state at the negative electrode interface is estimated from the measured impedance value.

[0040] In this embodiment, the double layer capacitance and / or reaction resistance at the negative electrode interface are measured as indicators for detecting the insufficient contact state and the excessive contact state at the negative electrode interface. The double layer capacitance and / or reaction resistance at the negative electrode interface correspond to the impedance value at the negative electrode interface.

[0041] The general formula for double layer capacitance is given by the following formula (1):

number

[0042] Then, the double layer capacity of the negative electrode interface in the used secondary battery 2 is C dl ’ and the surface area is A ’ Then, the relationship of the following formula (2) holds.

number

[0043] From equations (1) and (2), once the materials used in the secondary battery 2 and the battery shape are determined, the double layer capacity (C dl ) is proportional to the contact area of ​​the negative electrode interface. In other words, using the double layer capacity in the initial state of the secondary battery 2 as a reference, the larger the double layer capacity, the larger the contact area of ​​the negative electrode interface, and the smaller the double layer capacity, the smaller the contact area of ​​the negative electrode interface. The contact area of ​​the negative electrode interface after battery use can be estimated from the difference between the double layer capacity when the contact area at the negative electrode interface is normal (full contact state) and the double layer capacity after battery use.

[0044] Similarly to the double layer capacity, the contact area of ​​the negative electrode interface can also be estimated from the reaction resistance. The reaction resistance in the initial state of the secondary battery 2 is R ct , the contact area is A, and the reaction resistance in the secondary battery 2 after use is Rct ’ , contact area is A ’ Then, the relation is expressed by the following equation (3).

number

[0045] From equation (3), the reaction resistance is inversely proportional to the contact area of ​​the negative electrode interface. Using the reaction resistance in the initial state of the secondary battery 2 as a reference, the smaller the reaction resistance, the larger the contact area of ​​the negative electrode interface. Reaction Resistance The larger the value, the smaller the contact area at the negative electrode interface.The contact area at the negative electrode interface after battery use can be estimated from the difference between the reaction resistance when the contact area at the negative electrode interface is normal (perfect contact state) and the reaction resistance after battery use.In this way, in this embodiment, the contact state (contact area) at the negative electrode interface is indirectly estimated from the double layer capacity and / or reaction resistance at the negative electrode interface.

[0046] The impedance value required to estimate the contact area at the negative electrode interface can be measured as follows. The impedance measuring instrument 7 applies AC signals at multiple frequency values ​​within a predetermined frequency band and measures the real axis component value (Z') and imaginary axis component value (-Z") of the AC impedance for each frequency value. The predetermined frequency band includes at least the frequency for measuring the reaction resistance. On a complex plane coordinate system where the real and imaginary axes are perpendicular to each other, the real axis component value is plotted as the real axis component of the complex plane coordinate system, and the imaginary axis component value is plotted as the imaginary axis component of the complex plane coordinate system. The graph obtained by plotting is a complex impedance plot (Nyquist plot; Cole-Cole plot) containing a circular arc locus. In the case of an all-solid-state battery, the Nyquist plot has three arcs, and the size of the arcs indicates, from the high-frequency side, the bulk resistance of the electrolyte, the resistance of the electrolyte grain boundary, and the reaction resistance. The reaction resistance at the negative electrode interface can be calculated from the diameter of the lowest-frequency arc of the three arcs in the Nyquist plot. The electrolyte resistance (R sep ) can be calculated from the combined resistance of the bulk resistance of the electrolyte and the resistance of the grain boundaries of the electrolyte.

[0047] The impedance measuring instrument 7 measures a specific AC impedance characteristic at a specific frequency. Impedance The negative electrode reaction resistance of the secondary battery 2 is calculated based on the resistance of the solid electrolyte and negative electrode contained in the secondary battery 2. The resistance of the negative electrode is calculated based on the electric double layer capacity (C dl ) and reaction resistance ( R аct ) in a parallel circuit with the electrolyte resistance (R sep ) can be expressed as an equivalent circuit in which they are connected in series. Then, from the impedance of the equivalent circuit, the imaginary part (Z im ) is extracted, the following equation (4) is derived. Note that ω is the angular frequency determined by the frequency of the AC signal.

[0048]

number

[0049] Furthermore, by transforming equation (4), the following equation (5) is derived.

number

[0050] In equation (5), -1 / (ωZ im ) on the vertical axis, and 1 / ω 2 If we plot a graph with the horizontal axis as the axis, we get 1 / C dl R аct 2 is the slope, and C dl The intercept is a straight line. The electric double layer capacity of the negative electrode (C dl ) and calculate the slope (1 / C dl R аct 2 ) to obtain the negative electrode reaction resistance (R аct ) can be calculated.

[0051] Furthermore, in this embodiment, in order to estimate the contact state (contact area) of the negative electrode interface, the impedance value of the negative electrode interface is measured, and then the measured impedance value is compared with an allowable impedance value to determine whether charging is possible. The allowable impedance value is the impedance value at which charging is allowed, and the range of allowable impedance values ​​(allowable impedance range) indicates the range of impedance values ​​at which the secondary battery 2 can be charged to a desired chargeable capacity without short-circuiting when charged at the charging current density set during charging. The allowable impedance range is experimentally determined according to the charging current density. Specifically, the allowable impedance range is determined from an allowable impedance map that corresponds charging current density to allowable impedance values, and from the charging current density.

[0052] Figure 5(a) is a graph showing the relationship between the double layer capacity of the negative electrode interface and the chargeable capacity, and Figure 5(b) is a graph showing the relationship between the reaction resistance of the negative electrode interface and the chargeable capacity. In Figure 5, the vertical axis of each graph is the chargeable capacity (mAh cm -2 ) where the horizontal axis of (a) represents the double layer capacity (F) of the negative electrode interface, and the horizontal axis of (b) represents the reaction resistance (Ω) of the negative electrode interface. The evaluation conditions for obtaining the characteristics of Figure 5 were a state in which a certain pressure was applied while the solid electrolyte layer and the negative electrode were in contact (for example, 1.5 MPa ), and at a constant temperature (e.g., 25°C), a constant charging current density (1 mA / cm 2 Then, using a reference battery equivalent to the all-solid-state battery, current is passed through it under evaluation conditions to experimentally obtain the impedance value (double layer capacity / reaction resistance) and chargeable capacity of the negative electrode interface.

[0053] The chargeable capacity represents the capacity that can be charged until a dendrite-induced short circuit occurs when the secondary battery 2 is charged at a charging current density under evaluation conditions, depending on the contact area of ​​the negative electrode interface (double layer capacity / reaction resistance). Then, under the specified evaluation conditions, the chargeable capacity according to the contact area of ​​the negative electrode interface is measured, and the experimental values ​​are plotted with the contact state of the negative electrode interface (double layer capacity / reaction resistance) and the chargeable capacity on the horizontal and vertical axes, respectively. The characteristics obtained from the experimental values ​​are shown as an upward-convex graph (dotted line graph), as shown in Figure 5(a, b).

[0054] As shown in Figure 5(a), when the double layer capacitance is equivalent to the contact state of a normal cell, the chargeable capacity is large. When the double layer capacitance is equivalent to insufficient contact (when the double layer capacitance is smaller than the contact state of a normal cell), the chargeable capacity is smaller as the double layer capacitance is smaller. When the double layer capacitance is equivalent to excessive contact (when the double layer capacitance is larger than the contact state of a normal cell), the chargeable capacity is smaller as the double layer capacitance is larger.

[0055] Also, as shown in Figure 5(b), when the reaction resistance is equivalent to the contact state of a normal cell, the chargeable capacity is large. When the reaction resistance is equivalent to the contact state of an insufficient cell (when the reaction resistance is smaller than the contact state of a normal cell), the reaction resistance is small The smaller the charge capacity, the smaller the Reaction Resistance When the magnitude corresponds to excessive contact (when the reaction resistance is greater than the magnitude corresponding to the contact state of a normal cell), big In this case, the larger the reaction resistance, the smaller the chargeable capacity.

[0056] In this embodiment, an allowable impedance map having the characteristics of the graphs of FIG. 5(a) and / or FIG. 5(b) is experimentally obtained, and is stored in the storage unit of the controller 8. 82 The allowable impedance map is a map corresponding to the magnitude of the charging current density, and is a mapping of experimental values ​​obtained from a reference battery equivalent to the secondary battery 2.

[0057] For example, when charging the secondary battery 2 with the charging current density that gives the characteristics shown in Figure 5(a), the required chargeable capacity after charging is 2.5 (mAh cm -2 In this case, in the graph of Figure 5(a), within the range enclosed by the upward convex dotted line, the chargeable capacity is 2.5 (mAh cm -2 The range of double layer capacity where the impedance is equal to or greater than E1 and equal to or less than E2 in Figure 5(a) corresponds to the allowable impedance range. Furthermore, if the chargeable capacity required after completion of charging is set to a large value, the chargeable capacity will be small if the contact area of ​​the negative electrode interface is too small or too large, and the required chargeable capacity after completion of charging cannot be obtained. As a result, the allowable impedance range becomes narrower.

[0058] For example, when charging the secondary battery 2 with the charging current density that gives the characteristics in Figure 5(b), the required chargeable capacity after charging is 1.0 (mAh cm -2 In the graph in Figure 5(b), the area enclosed by the upward-convex dotted line graph is the area where the chargeable capacity is 1.0 (mAh cm -2 ) or more (Figure 5( b The range of R1 or more and R2 or less of the above (R1 or more and R2 or less) corresponds to the allowable impedance range. As with double layer capacitance, the allowable impedance range for reactive resistance becomes narrower as the required chargeable capacity after charging is set larger.

[0059] The allowable impedance range also varies depending on the charging current density. Figure 6(a) is a graph showing the relationship between the double layer capacity at the negative electrode interface and the chargeable capacity as a function of the charging current density. Figure 6(b) is a graph showing the relationship between the reaction resistance at the negative electrode interface and the chargeable capacity as a function of the charging current density. The vertical and horizontal axes in Figures 6(a) and 6(b) are the same as those in Figures 5(a) and 5(b). Each graph in Figure 6(a) and 6(b) shows the characteristics when the charging current density is set to three levels. The solid line graph shows the characteristics when the charging current density is the highest, the dotted line graph shows the characteristics when the charging current density is the second highest, and the dashed line graph shows the characteristics when the charging current density is the lowest.

[0060] The allowable impedance range represents the range of impedance values ​​that allows charging to a capacity equal to or greater than the desired cell capacity (chargeable capacity). In the graphs of Figure 6 (a, b), the area enclosed by the desired cell capacity (chargeable capacity) value and each graph corresponding to the charging current density represents the range in which charging is permitted. In the example shown in Figure 6, where there are three levels of charging current density, when the charging current density is at its highest, area S corresponds to the range in which charging is permitted. As the charging current density increases, the allowable impedance range narrows, and the range in which charging is permitted also narrows.

[0061] The controller 8 identifies an allowable impedance map from the charging current density of the secondary battery 2 and determines an allowable impedance range by collating the identified allowable impedance map. The controller 8 uses the impedance measuring device 7 to measure the impedance value of the all-solid-state battery 2 before charging of the secondary battery 2 starts and / or during charging. The controller 8 determines whether the measured impedance value is within the allowable impedance range. If the controller 8 determines that the measured impedance value is within the allowable impedance range, the controller 8 permits charging of the secondary battery 2. On the other hand, if the controller 8 determines that the measured impedance value is outside the allowable impedance range, the controller 8 does not start charging if charging has not yet started, or stops charging if charging is currently in progress.

[0062] In this embodiment, the contact state (contact area) of the negative electrode interface is thus indirectly estimated from the impedance value of the secondary battery 2. An allowable impedance range is determined from the allowable impedance map and the charging current density, and it is determined whether the measured impedance value is within the allowable impedance range. If the measured impedance value is within the allowable impedance range, charging of the secondary battery 2 is permitted, and if the measured impedance value is outside the allowable impedance range, charging of the secondary battery 2 is not permitted.

[0063] Next, a method for determining whether or not to permit charging of the secondary battery 2 and a method for controlling charging will be described. Fig. 7 is a flowchart showing the procedure of the determination process and the procedure of the charging process in the charge control system.

[0064] In step S1, the controller 8 measures the impedance value of the secondary battery 2 using the impedance measuring instrument 7 before starting charging of the secondary battery 2. In step S2, the controller 8 determines an allowable impedance range from the charging current density and an allowable impedance map. The charging current density is a current density set between steps S5 to S9, which will be described later. The charging current density is determined in advance according to the charging sequence of the secondary battery 2. The controller 8 identifies a corresponding allowable impedance map from the charging current density set when charging the secondary battery 2. Then, the controller 8 determines, on the identified allowable impedance map, an impedance range that satisfies the chargeable capacity required for charging the secondary battery 2 (desired chargeable capacity).

[0065] In step S3, the controller 8 determines whether the measured impedance value is within the allowable impedance range. If the measured impedance value is within the allowable impedance range, the controller 8 permits charging in step S4. If the measured impedance value is outside the allowable impedance range, the controller 8 determines in step S10 that charging is not permitted.

[0066] In step S5, controller 8 teeth Charging of the secondary battery 2 begins. In step S6, the controller 8 measures the impedance value of the secondary battery 2 using the impedance measuring device 7 while the secondary battery 2 is being charged. Step S 7 In step S, the controller 8 determines the allowable impedance range. 8In step S9, the controller 8 determines whether the measured impedance value is within the allowable impedance range. If the measured impedance value is within the allowable impedance range, the controller 8 continues charging and determines whether to terminate charging of the secondary battery 2. For example, if the charge capacity of the secondary battery 2 reaches a target value, the controller 8 determines that charging has terminated. If charging has not terminated, the controller 8 executes the control flow from step S6 onwards. If it is determined that charging has terminated, the controller 8 terminates the control flow.

[0067] If it is determined in step S8 that the measured impedance value is outside the allowable impedance range, the controller 8 determines that charging is not possible in step S10. If it is determined that charging is not possible, the controller 8 ends the control flow.

[0068] As described above, in this embodiment, the controller 8 measures the impedance value at the negative electrode interface using the impedance measuring device 7, determines whether the measured impedance value is within the allowable impedance range, and allows charging of the secondary battery 2 if the measured impedance value is within the allowable impedance range. The allowable impedance range is determined by an allowable impedance map that corresponds the charging current density with the allowable impedance value at which charging is allowed, and the charging current density for charging the secondary battery 2. This makes it possible to determine the contact area at the negative electrode interface from the impedance value, and to charge the secondary battery 2 while preventing short circuits.

[0069] In this embodiment, the measured impedance value is the double layer capacity and / or reaction resistance of the negative electrode interface, which allows the contact area of ​​the negative electrode interface to be determined from the impedance value, and allows the secondary battery 2 to be charged while preventing short circuits.

[0070] In this embodiment, the allowable impedance map is a mapping of experimental values ​​obtained from a reference battery equivalent to the secondary battery 2, and the allowable impedance range indicates the range of impedance values ​​that can be charged to the desired chargeable capacity without short-circuiting when the secondary battery 2 is charged at the charging current density set during charging. This allows the secondary battery 2 to be charged while preventing short-circuiting after determining the allowable range of impedance values ​​for determining whether charging is possible. [Example]

[0071] The present invention will be described below in more detail with reference to examples. Not limited.

[0072] <Production of prototype (example)> 100 mg of sulfide solid electrolyte was weighed, placed in a McCol tube, clamped between hard Cr-plated SLD pins, and pressed at 400 MPa for 1 minute at room temperature to obtain an electrolyte pellet (solid electrolyte layer). A 0.2 mm thick Li foil and a 10 μm thick SUS430 foil were placed on both sides of the electrolyte pellet, and the pellet was pressed at 20 MPa for 1 second at room temperature to produce a Li symmetric cell. The confining pressure during cell assembly was 4 MPa.

[0073] <Charging conditions> A charging test was carried out on the prototype (Li symmetric cell) of the example obtained above. Under a pressure of 1.5 MPa, the measurement temperature was 25°C, and the charging current density was 1 mA / cm. 2 The evaluation device used was TOSCAT manufactured by Toyo Systems Co., Ltd.

[0074] <Electrochemical measurement (impedance measurement)> Impedance measurements were performed on the Li symmetric cell. The measurement temperature was 25°C, and the evaluation device was a Solartron 1260A. The measurement frequency was 10 MHz to 0.05 Hz, and the amplitude was 10 mV.

[0075] <Evaluation of Examples> When the impedance value (double layer capacitance / reaction resistance) and the chargeable capacity value obtained from the evaluation results of the above prototype were plotted, the characteristics shown in Figure 5 were obtained.

[0076] Although the embodiments and examples of the present invention have been described above, these embodiments and examples are described to facilitate understanding of the present invention and are not described to limit the present invention. Therefore, each element disclosed in the above embodiments is intended to include all design modifications and equivalents that fall within the technical scope of the present invention. [Explanation of symbols]

[0077] 1… Charging Control System 2…Secondary battery 3...Voltage sensor 4...Temperature sensor 5...Voltage and current adjustment section 6...Current sensor 7. Impedance measuring instrument 8...Controller 9…External power supply

Claims

1. A method for charging an all-solid-state battery including a negative electrode containing lithium metal and a solid electrolyte layer, comprising: using an impedance measuring device for measuring the impedance of the all-solid-state battery, measuring the double layer capacity of the interface and / or the reaction resistance of the interface as the impedance value at the interface between the negative electrode and the solid electrolyte layer; determining an allowable impedance range from an allowable impedance map in which a charging current density corresponds to an allowable impedance value at which charging is allowed, and a charging current density for charging the all-solid-state battery; determining whether the measured impedance value is within the allowable impedance range; permitting charging of the all-solid-state battery when the measured impedance value is within the allowable impedance range; The allowable impedance range is: In the characteristic of the chargeable capacity relative to the double layer capacity, the range of the double layer capacity where the chargeable capacity is equal to or greater than a predetermined value, and in the characteristic of the chargeable capacity relative to the reaction resistance, the range of the double layer capacity where the chargeable capacity is equal to or greater than a predetermined value, The characteristics of the chargeable capacity relative to the double layer capacity are such that, when the double layer capacity is smaller than the magnitude corresponding to the contact state of a normal cell, the smaller the double layer capacity, the smaller the chargeable capacity; and, when the double layer capacity is larger than the magnitude corresponding to the contact state of a normal cell, the larger the double layer capacity, the smaller the chargeable capacity. A charging method in which the characteristics of the chargeable capacity with respect to the reaction resistance are such that, when the reaction resistance is smaller than the magnitude corresponding to the contact state of a normal cell, the smaller the reaction resistance, the smaller the chargeable capacity, and, when the reaction resistance is larger than the magnitude corresponding to the contact state of a normal cell, the larger the reaction resistance, the smaller the chargeable capacity.

2. The charging method according to claim 1, The allowable impedance map is a mapping of experimental values ​​obtained from a reference battery equivalent to the all-solid-state battery, a charging method in which the allowable impedance range indicates a range of impedance values ​​that can charge the all-solid-state battery to a desired chargeable capacity without causing a short circuit when the all-solid-state battery is charged at the charging current density set during charging.

3. A charge control device for controlling charging of an all-solid-state battery including a negative electrode containing lithium metal and a solid electrolyte layer, an impedance measuring instrument for measuring a double layer capacitance and / or a reaction resistance of the interface between the negative electrode and the solid electrolyte layer as an impedance value at the interface; a controller that determines whether or not the all-solid-state battery can be charged; The controller determining an allowable impedance range from an allowable impedance map in which a charging current density corresponds to an allowable impedance value at which charging is allowed, and a charging current density for charging the all-solid-state battery; determining whether the impedance value measured by the impedance measuring instrument is within the allowable impedance range; permitting charging of the all-solid-state battery when the measured impedance value is within the allowable impedance range; The allowable impedance range is: In the characteristic of the chargeable capacity relative to the double layer capacity, the range of the double layer capacity where the chargeable capacity is equal to or greater than a predetermined value, and in the characteristic of the chargeable capacity relative to the reaction resistance, the range of the double layer capacity where the chargeable capacity is equal to or greater than a predetermined value, The characteristics of the chargeable capacity relative to the double layer capacity are such that, when the double layer capacity is smaller than the magnitude corresponding to the contact state of a normal cell, the smaller the double layer capacity, the smaller the chargeable capacity; and, when the double layer capacity is larger than the magnitude corresponding to the contact state of a normal cell, the larger the double layer capacity, the smaller the chargeable capacity. A charging control device in which the characteristics of the chargeable capacity with respect to the reaction resistance are such that, when the reaction resistance is smaller than the magnitude corresponding to the contact state of a normal cell, the smaller the reaction resistance, the smaller the chargeable capacity, and, when the reaction resistance is larger than the magnitude corresponding to the contact state of a normal cell, the larger the reaction resistance, the smaller the chargeable capacity.

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