JP2020202083A - Lithium secondary battery control method, and control device, and lithium secondary battery system - Google Patents

Abstract

To provide means capable of improving charge/discharge rate characteristics in a lithium secondary battery using elemental sulfur or a reduction product thereof as a positive electrode active material.SOLUTION: When charging/discharging of a lithium secondary battery ia performed using sulfur alone or its reduction product as a positive electrode active material, the positive electrode equilibrium potential (vs. Li+/Li) is detected, and whether the detected value of the equilibrium potential is a value within the potential range of 0.7 to 1.9 [V] is determined, and when it is determined that the equilibrium potential is not within the potential range, the charging/the discharging is stopped.SELECTED DRAWING: Figure 4

Description

The present invention relates to a control method and a control device for a lithium secondary battery, and a lithium secondary battery system.

In recent years, there is an urgent need to reduce the amount of carbon dioxide in order to cope with global warming. In the automobile industry, expectations are high for the reduction of carbon dioxide emissions by introducing electric vehicles (EVs) and hybrid electric vehicles (HEVs), and non-water batteries such as secondary batteries for driving motors, which hold the key to their practical application. The development of secondary electrolyte batteries is being actively carried out.

The secondary battery for driving a motor is required to have extremely high output characteristics and high energy as compared with a consumer lithium secondary battery used in mobile phones, notebook computers, and the like. Therefore, the lithium secondary battery, which has the highest theoretical energy among all realistic batteries, is attracting attention and is currently being rapidly developed.

Here, the lithium secondary battery currently widely used uses a flammable organic electrolyte as an electrolyte. In such a liquid-based lithium secondary battery, safety measures against liquid leakage, short circuit, overcharge, etc. are required more strictly than other batteries.

Therefore, in recent years, research and development on an all-solid-state lithium secondary battery using an oxide-based or sulfide-based solid electrolyte as an electrolyte has been actively carried out. The solid electrolyte is a material composed mainly of an ionic conductor capable of conducting ions in a solid. Therefore, in the all-solid-state lithium secondary battery, various problems caused by the flammable organic electrolytic solution do not occur in principle unlike the conventional liquid-based lithium secondary battery. Further, in general, when a high potential / large capacity positive electrode material and a large capacity negative electrode material are used, the output density and energy density of the battery can be significantly improved. For example, elemental sulfur _{(S 8)} has a very large theoretical capacity of about 1670mAh / g, has the advantage of resources at a low cost is rich.

Taking advantage of such properties of elemental sulfur (S ₈ ), for example, Patent Document 1 proposes a lithium secondary battery using elemental sulfur (S ₈ ) or a reduction product thereof as a positive electrode active material.

Japanese Unexamined Patent Publication No. 2012-109223

Here, Patent Document 1 specifically states that a coin cell was produced using sulfur alone (S ₈ ) as the positive electrode active material of a lithium secondary battery, and a charge / discharge test was performed on this with a current density of 1 / 12C. Is disclosed. It is also disclosed that the charge / discharge voltage at the time of this charge / discharge test is in the range of 1.5 to 3.3 V. Since a lithium metal plate is used as the counter electrode (negative electrode) of the coin cell, the range of the charge / discharge voltage is equal to the range of the equilibrium potential (vs. Li + / Li) of the positive electrode.

According to the study by the present inventors, when charging / discharging is performed using the lithium secondary battery disclosed in Patent Document 1 described above, sufficient capacity cannot be taken out when charging / discharging at a high charge / discharge rate ( That is, the so-called rate characteristic is not sufficient).

Therefore, an object of the present invention is to provide a means capable of improving charge / discharge rate characteristics in a lithium secondary battery using sulfur alone or a reduction product thereof as a positive electrode active material.

The present inventors have conducted diligent studies to solve the above problems. As a result, by controlling the charging / discharging of such a lithium secondary battery so that the value of the equilibrium potential (vs. Li + / Li) of the positive electrode is within a predetermined potential range, the above-mentioned problem We have found that this can be solved, and have completed the present invention.

The method for controlling the lithium secondary battery according to one embodiment of the present invention includes a positive electrode including a positive electrode active material layer containing a single sulfur or a reduction product of sulfur containing lithium as a positive electrode active material, and a negative electrode active material. This is a control method for a lithium secondary battery including a power generation element having a negative electrode including a negative electrode active material layer and an electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer. Then, the control method detects the equilibrium potential (vs. Li + / Li) of the positive electrode when the lithium secondary battery is charged and / or discharged, and the detected equilibrium potential of the detected equilibrium potential. It is determined whether or not the value is within the potential range of 0.7 to 1.9 [V], and when it is determined that the equilibrium potential is not within the potential range, the charging is performed. It is characterized in that it includes stopping the processing and / or discharging processing.

The control device for the lithium secondary battery according to another embodiment of the present invention contains a positive electrode including a positive electrode active material layer containing sulfur alone or a reduction product of sulfur containing lithium as a positive electrode active material, and a negative electrode active material. It controls a lithium secondary battery having a power generation element having a negative electrode including a negative electrode active material layer and an electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer. Then, the control device has the positive electrode equilibrium potential detecting unit that detects the equilibrium potential (vs. Li + / Li) of the positive electrode, and the positive electrode equilibrium when performing the charging process and / or the discharging process of the lithium secondary battery. It is determined whether or not the value of the equilibrium potential detected by the potential detection unit is within the potential range of 0.7 to 1.9 [V], and the equilibrium potential is not a value within the potential range. It is characterized in that it includes a control unit that controls to stop the charging process and / or the discharging process when the determination is made.

The lithium secondary battery system according to still another embodiment of the present invention includes the above-mentioned lithium secondary battery and the above-mentioned lithium secondary battery control device.

According to the present invention, in a lithium secondary battery using elemental sulfur or a reduction product thereof as a positive electrode active material, the charge / discharge rate characteristics can be improved.

It is a block diagram for demonstrating the structure of the all-solid-state lithium secondary battery system which concerns on one Embodiment of this invention. A graph showing the change in the equilibrium potential (vs. Li + / Li) of the positive electrode (capacity to positive electrode) during charging and discharging of a lithium secondary battery containing a single sulfur or a reduction product of lithium containing lithium as a positive electrode active material. is there. It is a flowchart which shows the procedure of the charge process in a secondary battery system. It is sectional drawing which represented typically the bipolar type (bipolar type) all-solid-state lithium secondary battery (bipolar type secondary battery) which concerns on one Embodiment of this invention. It is a perspective view which showed the appearance of the flat lithium secondary battery which is a typical embodiment of a bipolar type secondary battery.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the technical scope of the present invention should be determined based on the description of the scope of claims, and is not limited to the following embodiments. The dimensional ratios in the drawings are exaggerated for convenience of explanation and may differ from the actual ratios. Hereinafter, the present invention will be described by taking as an example a bipolar (bipolar type) all-solid-state lithium secondary battery, which is a form of a secondary battery. As described above, the solid electrolyte constituting the all-solid-state lithium secondary battery is a material composed mainly of an ionic conductor capable of ionic conduction in the solid. Therefore, the all-solid-state lithium secondary battery has an advantage that various problems caused by the flammable organic electrolytic solution do not occur in principle unlike the conventional liquid-based lithium secondary battery. In general, using a high-potential, large-capacity positive electrode material and a large-capacity negative electrode material also has an advantage that the output density and energy density of the battery can be significantly improved.

[Secondary battery system]
FIG. 1 is a block diagram for explaining the configuration of an all-solid-state lithium secondary battery system according to an embodiment of the present invention.

This all-solid-state lithium secondary battery system (hereinafter, also referred to as "secondary battery system 1") includes an all-solid-state lithium secondary battery (hereinafter, also referred to as "secondary battery 2"). Then, a voltage sensor 3 that measures the cell voltage (voltage between terminals) of the secondary battery 2, a voltage / current adjusting unit 4 that supplies charging power to the secondary battery 2, and a current sensor that measures the charge / discharge current of the secondary battery 2. 5. A control unit 6 for controlling charging / discharging of the secondary battery 2 is provided. Further, the voltage / current adjusting unit 4 is connected to the external power source 7 and receives power during charging, while discharging to the external power source 9 side via the voltage / current adjusting unit 4 during discharging (details will be described later).

The details of each part will be described below.

The secondary battery 2 contains a positive electrode (hereinafter, also simply referred to as “sulfur-containing positive electrode”) containing a positive electrode active material layer containing a single sulfur or a reduction product of sulfur containing lithium as a positive electrode active material, and a negative electrode active material. The power generation element includes a negative electrode including a negative electrode active material layer containing the negative electrode, and a solid electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer. The details of the all-solid-state lithium secondary battery will be described later, but the equilibrium potential (vs.) of the positive electrode during charging and discharging of the lithium secondary battery containing a single sulfur or a reduction product of lithium containing lithium as a positive electrode active material. The change in Li + / Li) is shown in FIG. As shown in FIG. 2, the theoretical lower limit of the equilibrium potential (vs. Li + / Li) of the sulfur-containing positive electrode is 0.7 [V]. On the other hand, the theoretical upper limit of the equilibrium potential (vs. Li + / Li) of the sulfur-containing positive electrode is 3.0 [V], but in the secondary battery system 2 according to the present embodiment, the equilibrium potential (vs. The secondary battery 2 is charged and discharged so that Li + / Li) does not exceed 1.9 [V].

The voltage sensor 3 may be, for example, a voltmeter, and measures the cell voltage (voltage between terminals) between the positive electrode and the negative electrode of the secondary battery 2. The mounting position of the voltage sensor 3 is not particularly limited as long as it is a position where the cell voltage between the positive electrode and the negative electrode can be measured in the circuit connected to the secondary battery 2.

When charging the secondary battery 2, the voltage / current adjusting unit 4 adjusts the voltage and current of the electric power from the external power source 8 based on the command from the control unit 7, and supplies the electric power to the secondary battery 2. Further, when the secondary battery 2 is discharged, the voltage / current adjusting unit 4 discharges the electricity discharged from the secondary battery 2 to an external load (not shown).

Here, the external power source 8 is a power source for an electric vehicle used for charging an electric vehicle or the like, a so-called power grid or the like, and direct current is output. Such a power source for an electric vehicle is provided by converting commercial electric power (alternating current) into direct current having a voltage and a current required for charging the secondary battery 2. Further, the external power source 8 is provided with a power regeneration function, and when there is a discharge from the secondary battery 2, the direct current can be converted into an alternating current and regenerated to a commercial power source. As a device constituting such an external power source 8, a well-known power source having a power regeneration function may be used, and therefore detailed description thereof will be omitted here (as a power source having a power regeneration function, the power source has a power regeneration function. For example, Japanese Patent Application Laid-Open No. 7-222369, Japanese Patent Application Laid-Open No. 10-080067, etc.).

When the external power supply 8 is not connected to an external power supply device such as a commercial power supply, for example, when charging the secondary battery 2 using another secondary battery installed externally as a power source, the power discharged from the secondary battery 2 Is preferably stored in another secondary battery. This can reduce the waste of energy.

The current sensor 5 is, for example, an ammeter. The current sensor 5 measures the current value of the power supplied from the voltage / current adjusting unit 4 to the secondary battery 2 when charging the secondary battery 2, and is supplied from the secondary battery 2 to the voltage / current adjusting unit 4 when discharging. Measure the current value of power. The mounting position of the current sensor 5 is not particularly limited, as long as it is located in a circuit that supplies power from the voltage / current adjusting unit 4 to the secondary battery 2 and can measure the current value during charging / discharging. Good.

The control unit 6 is a so-called computer including, for example, a CPU 61 and a storage unit 62. The control unit 6 controls the conditions of the charge / discharge process when the secondary battery 2 is charged / discharged according to the procedure described later. As such a control unit 6, for example, an ECU (Electronic Control Unit) or the like may be used in an electric vehicle.

Here, the storage unit 62 is equipped with a non-volatile memory in addition to the RAM used by the CPU 61 as a working area. The non-volatile memory stores a program for controlling the charge / discharge processing conditions of the secondary battery 2 in the present embodiment.

Further, the storage unit 62 is a map showing the relationship between the charged state (SOC; State of Charge) of the secondary battery 2 and the equilibrium potential (vs. Li + / Li) of the positive electrode constituting the secondary battery 2. It also remembers the "first map"). Alternatively, the storage unit 62 stores a map (hereinafter, also referred to as “second map”) showing the relationship between the charge state (SOC; State of Charge) of the secondary battery 2 and the battery voltage of the secondary battery 2. You may be.

[Charging process]
The procedure of the charging process in the secondary battery system 1 configured in this way will be described.

This charging process is performed in a state where the secondary battery system 1 is connected to the external power source 7 and charging power can be supplied to the secondary battery 2. Further, the control of the charging process in the present embodiment is a constant current (CC) charging method in which the voltage of the secondary battery 2 reaches a predetermined voltage. However, the form of the charging process is not limited to this, and charging is performed by the constant current (CC) charging method, and after the voltage of the secondary battery 2 reaches a predetermined voltage, the constant voltage (CV) charging method is used. A current / constant voltage (CC-CV) charging method may be used.

In the charging process in the present embodiment, the equilibrium potential (vs. Li + / Li) of the positive electrode constituting the secondary battery 2 is detected, and the detected equilibrium potential value is 0.7 to 1.9 [V]. It is performed while determining whether or not the value is within the potential range. Then, when it is determined that the equilibrium potential is not within the potential range, the charging process is stopped. Unless otherwise specified, the control unit 7 controls the charging process. Hereinafter, the procedure of this charging process will be described with reference to FIG. FIG. 3 is a flowchart showing the procedure of the charging process in the secondary battery system 1.

First, the control unit 6 starts control for charging the secondary battery 2 (step S101). Specifically, electric power is introduced from the external power source 7 to the voltage / current adjusting unit 4 to start the charging process (in the present embodiment, constant current (CC) charging is started).

Subsequently, the control unit 6 acquires the charging current I from the current sensor 5 and the battery voltage V from the voltage sensor 3 (step S102). Then, in the present embodiment, the control unit 6 calculates the value of the charging state (SOC) of the secondary battery 2 based on the integrated value of the charging current I acquired from the current sensor 5 (step S103). After that, the control unit 6 shows the relationship between the “charged state (SOC) of the secondary battery 2 and the equilibrium potential (vs. Li + / Li) of the positive electrodes constituting the secondary battery 2” stored in the storage unit 62. The equilibrium potential (vs. Li + / Li) of the positive electrode is calculated from the SOC value of the secondary battery 2 calculated in step S103 with reference to the “map” (first map) (step S104).

Subsequently, the control unit 6 determines whether or not the value of the equilibrium potential (vs. Li + / Li) of the positive electrode calculated above is within the potential range of 0.7 to 1.9 [V]. (Step S105). As described above, since the theoretical lower limit of the equilibrium potential (vs. Li + / Li) of the sulfur-containing positive electrode is 0.7 [V], the above determination is based on the equilibrium potential (vs. Li + / Li) of the positive electrode. It is substantially synonymous with the determination of whether or not the value of Li + / Li) is 1.9 [V] or less. Here, if it is determined that the value of the equilibrium potential (vs. Li + / Li) of the positive electrode is within the potential range of 0.7 to 1.9 [V] (S105: YES), the control unit 6 will perform. , The control from step S102 is repeated. On the other hand, if it is determined that the value of the equilibrium potential (vs. Li + / Li) of the positive electrode is not within the potential range of 0.7 to 1.9 [V] (S105: NO), the control unit 6 determines. The charging process of the secondary battery 2 is completed (step S106).

By carrying out the control as described above, it is possible to improve the charge / discharge rate characteristics of a lithium secondary battery using elemental sulfur or a reduction product thereof as a positive electrode active material. The mechanism will be described below.

In order to identify the rate-determining step in the charge / discharge reaction in a lithium secondary battery containing a sulfur-containing positive electrode, the present inventors use the density functional theory, which is an electronic state calculation method based on density functional theory (DFT). The elementary reactions that make up the charge / discharge reaction were analyzed. Here, density functional theory (DFT) (density functional theory) is a kind of first-principles calculation that predicts physical properties and chemical reactions from Schrodinger equation (Dirac equation) without using experimental data and empirical parameters. There is a method of calculating the energy level of the generated energy Eg and the molecular orbital (orbital in which the electrons constituting the molecule can exist) for the molecular structure to be calculated.

Here, since the sulfur unit (S ₈ ) contained in the sulfur-containing positive electrode does not contain lithium, when this is viewed as the positive electrode active material, the lithium secondary battery containing the positive electrode active material is in the most charged state. It can be said. On the other hand, as the discharge of the lithium secondary battery progresses, the positive electrode active material sulfur alone (S ₈ ) gradually combines with lithium to pass through various reduction products, and finally becomes Li ₂ S. Become. That is, it can be said that the lithium secondary battery containing only Li ₂ S as the positive electrode active material is in the most discharged state.

Here, as the reduction product (intermediate) in which the molar ratios of sulfur atom and lithium atom are different between sulfur alone (S ₈ ) and Li ₂ S, (S ₈ ) → Li ₂ S ₈ → Li ₂ S ₇ → Li ₂ S ₆ → Li ₂ S ₅ → Li ₂ S ₄ → Li ₂ S ₃ → Li ₂ S ₂ → (Li ₂ S) can be assumed. Therefore, the present inventors have optimized the structure (positions of atoms constituting the molecule) based on DFT for each of elemental sulfur (S ₈ ) and Li ₂ S and their assumed reduction products (intermediate). Calculation to find the structure with the lowest generated energy by changing) was performed, and the generated energy with a stable atomic arrangement was calculated. The reactants and in all cases envisaged as a combination of products, the value obtained by subtracting the generated energy of the reaction product _{(E reactants)} from the generation energy of the product _{(E products)} the Gibbs free energy in the reaction ( It was regarded as ΔG). The detailed calculation conditions are as follows:
Simulation program: Vienna ab-initio simulation package (VASP)
Correlation functional: B3LYP
Cut-off energy: 400 [eV]
Pseudopotential: PAW GGA
Electronic relaxation algorithm: preconditioned residuum-minimization
Ion relaxation algorithm: RMM-DIIS.

Here, in the charging reaction, ΔG in each reaction is a positive value, and the product is energetically more unstable than the reactant. Therefore, in the charging reaction, it was determined that the reaction having the smallest ΔG among the reactions assumed when the reactant was fixed is actually proceeding. Table 1 below shows the results of actual calculations, assuming that the charging reaction of a lithium secondary battery containing Li ₂ S, which is the most discharged state, as the positive electrode active material proceeds. It shows the value rounded to the third place).

As shown in Table 1, for the Li ₂ S, for example, reaction producing _Li 2 _{S 2} and releasing lithium _{(2Li 2 S → Li 2 S} 2 + 2Li) is assumed. Generation energy generated energy _{(E reactants)} and the reaction product of reactants at this time _{(E products)} are each 14.41 [eV] and 15.44 [eV], the Gibbs free energy is calculated as the difference between these (ΔG = E _products −E _reactants ) is calculated as 1.02 [eV].

In addition to the above reactions, Li ₂ S reacts with Li ₂ S ₂ , Li ₂ S ₃ , Li ₂ S ₄ , Li ₂ S ₅ , Li ₂ S ₆ , and Li ₂ S _7. There is also a reaction that produces Li ₂ S ₃ , Li ₂ S ₄ , Li ₂ S ₅ , Li ₂ S ₆ , Li ₂ S ₇ , and Li ₂ S ₈ , respectively. The ΔG of each of these reactions is as shown in Table 1 above, but all of them are larger than the ΔG in the reaction that produces Li ₂ S ₂ . Therefore, in practice, the Li ₂ S, and it concluded that formation reaction of _Li 2 _{S 2} where ΔG is minimized progresses. In addition, the same analysis was carried out thereafter, and it was concluded that among the reactions assumed for each reactant, the reaction in which ΔG is the smallest value (shown in bold in Table 1) actually proceeds. It was. As a result, in the charging reaction, Li ₂ S produced Li ₂ S _2, and then Li ₂ S ₃ , Li ₂ S ₄ , Li ₂ S ₅ , Li ₂ S ₆ , Li ₂ S ₇ , Li ₂ S ₈ and S. _It was considered that ₈ was sequentially generated. Here, among the eight reactions from Li ₂ S to S ₈ , the one having the largest ΔG is the reaction for producing S ₈ from Li ₂ S in the final stage (Li ₂ S ₈ → S ₈ + 2 Li). Therefore, formation reaction of the S ₈ was considered the reaction rate in the charge reaction is the slowest reaction (rate-limiting reaction) (see Figure 2).

On the other hand, the discharge reaction, most charge a S ₈ is a state that has traveled on the assumption that the discharge reaction of the lithium secondary battery progresses containing as a positive electrode active material, the results of actual calculation table below Shown in 2. In the discharge reaction, ΔG in each reaction is a negative value, and the product is energetically more stable than the reactant. Therefore, in the discharge reaction, it was determined that the reaction with the maximum absolute value of ΔG is actually proceeding among the reactions assumed when the reactant is fixed.

As shown in Table 2, for S ₈ , only the reaction that produces Li ₂ S ₈ (S ₈ + 2 Li → Li ₂ S ₈ ) is assumed. After that, as the absolute value of ΔG is maximum (indicated in bold in Table 2), _Li 2 _{S 8} generates a _{Li 2 S 4 (Li 2 S} 8 + 2Li → 2Li 2 S 4), Li 2 S ₄ was considered to produce a _{Li 2 S 2 (Li 2 S} 4 + 2Li → 2Li 2 S 2), Li 2 S 2 generates a _{Li 2 S (Li 2 S 2} + 2Li → 2Li 2 S). Here, as described above, in the discharge reaction, the product is energetically more stable than the reactant. However, in order for the reaction to actually proceed, it is necessary to exceed the excitation energy in the reactant of each reaction. Therefore, the excitation energies of the reactants (S ₈ , Li ₂ S ₈ , Li ₂ S ₄ , Li ₂ S ₂ ) were calculated for each of the four reactions from S ₈ to Li ₂ S described above. Specifically, the energy level (E _LUMO ) and the Fermi level (existence of electrons) of the LUMO (minimum unoccupied molecular orbital; orbital with the lowest energy level among the molecular orbitals containing no electrons) of each reactant The excitation energy E ° was calculated according to the equation E ° = E _LUMO −E _fermi , assuming that the difference from the energy level (E _fermi ) having a probability of 50% corresponds to the excitation energy. As a result, the excitation energy E ° of each of the above four reactions was calculated as the value shown in Table 2 above. Here, among the four reactions from S ₈ to Li ₂ S, the one having the maximum excitation energy E ° is the reaction for forming Li ₂ S ₈ from S ₈ in the first stage (S ₈ + 2 Li → Li ₂ S _8). ). Therefore, formation reaction of Li ₂ S ₈ from S ₈ was considered the reaction rate in the discharge reaction is the slowest reaction (rate-limiting reaction) (see Figure 2).

From calculations based on DFT as described above, the rate limiting reaction in charging reaction of the lithium secondary battery comprising a sulfur-containing cathode is the formation reaction of _{S 8} from _{Li 2 S (Li 2 S 8} → S 8 + 2Li) Was identified. Similarly, the rate-limiting reaction in the discharge reaction of the lithium secondary battery comprising the sulfur-containing positive electrode was identified as a formation reaction of _Li 2 _{S 8} from _{S 8 (S 8 + 2Li →} Li 2 S 8). Based on these findings, the present inventors can control the charge and discharge of the lithium secondary battery so as not to utilize the above two rate-determining reactions, so that the reaction having a slow reaction rate does not need to be used. It was thought that the discharge rate characteristics could be improved. Here, referring to FIG. 2, the equilibrium potential of the positive electrode that can be reached only by utilizing the above two rate-determining reactions corresponds to a region larger than 1.9 [V]. Therefore, not utilizing the above two rate-determining reactions means that the equilibrium potential of the positive electrode is set to a potential range of 1.9 [V] or less (actually, the equilibrium potential of the equilibrium potential) during charging and discharging of the lithium secondary battery. It means that the value is maintained within the potential range of 0.7 to 1.9 [V] in consideration of the lower limit value. The present inventors have completed the present invention in this way.

Although the control according to the present invention has been described in detail above, the embodiment described with reference to the drawings is merely an example, and is appropriately modified within the scope of the technical idea of the invention described in the claims. The present invention may be carried out. For example, in the above-described embodiment, the determination of whether or not the value of the equilibrium potential of the positive electrode is within the potential range of 0.7 to 1.9 [V] is determined by the state of charge (SOC) of the lithium secondary battery 2. ) Is based on the value. Specifically, the control unit 6 determines whether or not the value of the equilibrium potential of the positive electrode is within the potential range of 0.7 to 1.9 [V] based on the integrated value of the charging current I. The SOC of the secondary battery 2 is calculated, and the value of the equilibrium potential of the positive electrode is calculated by referring to the first map. In this way, by performing the above determination based on the value of the state of charge (SOC) of the lithium secondary battery 2, the influence of overvoltage can be eliminated as compared with the case where the above determination is performed based on the battery voltage. There is an advantage that more precise control is possible. However, the determination based on the charge state (SOC) value of the lithium secondary battery 2 is not limited to such a form. For example, when the equilibrium potential of the positive electrode is in the range of 0.7 to 1.9 [V], the corresponding SOC range is obtained in advance, and it is calculated based on the integrated value of the charging current I in the same manner as above. By determining whether or not the SOC of the secondary battery 2 is within the range of the SOC obtained in advance, the value of the equilibrium potential of the positive electrode is in the potential range of 0.7 to 1.9 [V]. You may indirectly determine whether or not the value is within.

Further, in order to determine whether or not the value of the equilibrium potential of the positive electrode is within the potential range of 0.7 to 1.9 [V], the value of the charged state (SOC) of the lithium secondary battery 2 is calculated. You may go without it. Examples of such a method include a method of making the above determination based on the value of the battery voltage defined as the potential difference between the positive electrode and the negative electrode of the lithium secondary battery 2. According to such a method, since the value of the battery voltage detected by the voltage sensor 3 can be used, there is an advantage that the control can be performed by a simple method. The battery voltage is calculated as the potential difference between the equilibrium potential of the positive electrode and the equilibrium potential of the negative electrode. Therefore, when calculating the equilibrium potential of the positive electrode based on the battery voltage, the equilibrium potential of the negative electrode may be subtracted from the value of the battery voltage detected by the voltage sensor 3. Further, when the equilibrium potential of the negative electrode changes in the same manner according to the change of the battery voltage, the equilibrium potential of the positive electrode can be obtained from the value of the battery voltage detected by the voltage sensor 3 by referring to the second map described above. It may be calculated. As described above, when the above determination is performed based on the value of the battery voltage of the lithium secondary battery 2, the equilibrium potential of the positive electrode is calculated by the above method, and the calculated value is 0.7 to 1.9 [. It may be directly determined whether or not the value is within the potential range of [V]. Further, as in the case of SOC described above, the range of the battery voltage corresponding to the case where the equilibrium potential of the positive electrode is in the range of 0.7 to 1.9 [V] is obtained in advance and detected by the voltage sensor 3. By determining whether or not the value of the battery voltage is within the range of the battery voltage obtained in advance, the value of the equilibrium potential of the positive electrode is within the potential range of 0.7 to 1.9 [V]. It may be indirectly determined whether or not the value is.

According to another embodiment of the present invention, a lithium secondary battery control device for controlling the lithium secondary battery 2 described above is provided. The control device for the lithium secondary battery that controls the lithium secondary battery 2 is a positive electrode equilibrium potential detection unit (voltage sensor 3 and / / described above) that detects the equilibrium potential (vs. Li + / Li) of the positive electrode of the lithium secondary battery 2. Alternatively, the current sensor 5 and the control unit 6 correspond to this), and the value of the equilibrium potential detected by the positive electrode equilibrium potential detection unit when the lithium secondary battery 2 is charged and / or discharged. It is determined whether or not the value is within the potential range of 0.7 to 1.9 [V], and when it is determined that the equilibrium potential is not within the potential range, the charging process and / or the charging process and / or It includes a control unit (corresponding to the control unit 6 described above) that controls to stop the discharge process.

Further, according to still another embodiment of the present invention, a lithium secondary battery system including the above-mentioned lithium secondary battery 2 and the above-mentioned lithium secondary battery control device is also provided.

Hereinafter, the components of the all-solid-state lithium secondary battery system according to the present embodiment will be described. In the present specification, the bipolar all-solid-state lithium secondary battery may be simply referred to as a "bipolar secondary battery", and the electrode for a bipolar all-solid-state lithium secondary battery may be simply referred to as a "bipolar electrode". ..

<Bipolar secondary battery>
FIG. 4 is a sectional view schematically showing a bipolar type (bipolar type) all-solid-state lithium secondary battery (bipolar type secondary battery) according to an embodiment of the present invention. The bipolar secondary battery 10 shown in FIG. 4 has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminated film 29 which is a battery exterior.

As shown in FIG. 4, in the power generation element 21 of the bipolar secondary battery 10 of the present embodiment, a positive electrode active material layer 13 electrically bonded to one surface of the current collector 11 is formed, and the current collector 11 has a positive electrode active material layer 13. It has a plurality of bipolar electrodes 23 having an electrically coupled negative electrode active material layer 15 formed on the opposite surface. The bipolar electrodes 23 are laminated via the solid electrolyte layer 17 to form the power generation element 21. The solid electrolyte layer 17 has a structure in which the solid electrolyte is formed into layers. At this time, the positive electrode active material layer 13 of the one bipolar electrode 23 and the negative electrode active material layer 15 of the other bipolar electrode 23 adjacent to the one bipolar electrode 23 face each other via the solid electrolyte layer 17. , The bipolar electrodes 23 and the solid electrolyte layer 17 are alternately laminated. That is, the solid electrolyte layer 17 is sandwiched between the positive electrode active material layer 13 of the one bipolar electrode 23 and the negative electrode active material layer 15 of the other bipolar electrode 23 adjacent to the one bipolar electrode 23. Has been done. However, the technical scope of the present invention is not limited to the bipolar secondary battery as shown in FIG. 6, and a battery having a similar series connection structure as a result of a plurality of cell cell layers being electrically stacked in series. It may be.

The adjacent positive electrode active material layer 13, the solid electrolyte layer 17, and the negative electrode active material layer 15 constitute one cell cell layer 19. Therefore, it can be said that the bipolar secondary battery 10 has a configuration in which the single battery layers 19 are laminated. The positive electrode active material layer 13 is formed on only one side of the outermost layer current collector 11a on the positive electrode side located in the outermost layer of the power generation element 21. Further, the negative electrode active material layer 15 is formed on only one side of the outermost layer current collector 11b on the negative electrode side located in the outermost layer of the power generation element 21.

Further, in the bipolar secondary battery 10 shown in FIG. 4, a positive electrode current collector plate (positive electrode tab) 25 is arranged so as to be adjacent to the outermost layer current collector 11a on the positive electrode side, and this is extended to form a battery exterior. It is derived from the laminated film 29. On the other hand, the negative electrode current collector plate (negative electrode tab) 27 is arranged so as to be adjacent to the outermost layer current collector 11b on the negative electrode side, and is similarly extended and led out from the laminate film 29.

The number of times the cell cell layer 19 is laminated is adjusted according to a desired voltage. Further, in the bipolar type secondary battery 10, the number of times the single battery layer 19 is laminated may be reduced as long as a sufficient output can be secured even if the thickness of the battery is made as thin as possible. Even in the bipolar type secondary battery 10, in order to prevent external impact and environmental deterioration during use, the power generation element 21 is vacuum-sealed in the laminated film 29 which is the battery exterior, and the positive electrode current collector plate 25 and the negative electrode current collector are collected. It is preferable to have a structure in which the electric plate 27 is taken out from the laminated film 29.

Hereinafter, the main components of the above-mentioned bipolar secondary battery will be described.

[Current collector]
The current collector has a function of mediating the movement of electrons from one surface in contact with the positive electrode active material layer to the other surface in contact with the negative electrode active material layer. There are no particular restrictions on the materials that make up the current collector. As a constituent material of the current collector, for example, a metal or a resin having conductivity can be adopted.

Specific examples of the metal include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, and the like may be used. Further, the foil may be a metal surface coated with aluminum. Of these, aluminum, stainless steel, copper, and nickel are preferable from the viewpoints of electron conductivity, battery operating potential, adhesion of the negative electrode active material by sputtering to the current collector, and the like.

Further, as the latter resin having conductivity, a resin in which a conductive filler is added to a non-conductive polymer material as needed can be mentioned.

Examples of the non-conductive polymer material include polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE), etc.), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), and polyimide. (PI), Polyethyleneimide (PAI), Polyethylene (PA), Polytetrafluoroethylene (PTFE), Styrene-butadiene rubber (SBR), Polyacrylonitrile (PAN), Polymethylacrylate (PMA), Polymethylmethacrylate (PMMA) , Polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), polystyrene (PS) and the like. Such non-conductive polymer materials can have excellent potential resistance or solvent resistance.

A conductive filler may be added to the above-mentioned conductive polymer material or non-conductive polymer material, if necessary. In particular, when the resin used as the base material of the current collector is composed of only a non-conductive polymer, a conductive filler is inevitably indispensable in order to impart conductivity to the resin.

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. It preferably contains an alloy or metal oxide. Further, the conductive carbon is not particularly limited. Preferably, it is selected from the group consisting of acetylene black, vulcan (registered trademark), black pearl (registered trademark), carbon nanofiber, Ketjen black (registered trademark), carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene. It contains at least one species.

The amount of the conductive filler added is not particularly limited as long as it can impart sufficient conductivity to the current collector, and is generally 5 to 80% by mass with respect to 100% by mass of the total mass of the current collector. Is.

The current collector may have a single-layer structure made of a single material, or may have a laminated structure in which layers made of these materials are appropriately combined. From the viewpoint of reducing the weight of the current collector, it is preferable to include a conductive resin layer made of at least a conductive resin. Further, from the viewpoint of blocking the movement of lithium ions between the cell layers, a metal layer may be provided as a part of the current collector.

[Negative electrode active material layer]
The negative electrode active material layer contains 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 and the} like. Further, as the negative electrode active material, a metal containing Li may be used. Such a negative electrode active material is not particularly limited as long as it is a Li-containing active material, and examples thereof include Li metals and Li-containing alloys. Examples of the Li-containing alloy include alloys of Li and at least one of In, Al, Si and Sn.

In some cases, two or more kinds of negative electrode active materials may be used in combination. Needless to say, a negative electrode active material other than the above may be used.

Examples of the shape of the negative electrode active material include particulate (spherical, fibrous) and thin film. When the negative electrode active material has a particle shape, its average particle size (D ₅₀ ) is preferably in the range of, for example, 1 nm to 100 μm, more preferably in the range of 10 nm to 50 μm, and further preferably in the range of 100 nm. It is in the range of ~ 20 μm, and particularly preferably in the range of 1 to 20 μm. In the present specification, the value of the average particle size (D ₅₀ ) of the active material can be measured by the laser diffraction / scattering method.

The content of the negative electrode active material in the negative electrode active material layer is not particularly limited, but is preferably in the range of 40 to 99% by mass, preferably in the range of 50 to 90% by mass, for example. More preferred.

The negative electrode active material layer preferably further contains a solid electrolyte. Since the negative electrode active material layer contains a solid electrolyte, the ionic conductivity of the negative electrode active material layer can be improved. Examples of the solid electrolyte include a sulfide solid electrolyte and an oxide solid electrolyte, and a sulfide solid electrolyte is 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 O-LiI, 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- Z _m S _n (where m and n are positive numbers and Z is one of Ge, Zn or Ga), Li ₂ S-GeS ₂ , Li ₂ S-SiS ₂ -Li ₃ PO ₄ , Examples thereof include Li ₂ S-SiS ₂ -Li _x MO _y (where x and y are positive numbers, and M is any of P, Si, Ge, B, Al, Ga and In). .. 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 . Further, as the sulfide solid electrolyte having a Li ₄ P ₂ S ₇ skeleton, for example, a Li-PS-based solid electrolyte called LPS (for example, Li ₇ P ₃ S ₁₁ ) can be mentioned. 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. Furthermore, the sulfide solid electrolyte may contain halogens (F, Cl, Br, I).

When the sulfide solid electrolyte is Li ₂ SP ₂ S ₅ system, the ratio of Li ₂ S and P ₂ S ₅ is Li ₂ S: P ₂ S ₅ = 50: 50 to 100 in terms of molar ratio. 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). Further, as another example 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, Li LaZrO). , Li ₇ La ₃ Zr ₂ O ₁₂ ) and the like.

Examples of the shape of the solid electrolyte include a particle shape such as a true spherical shape and an elliptical spherical shape, and a thin film shape. When the solid electrolyte has a particle shape, its average particle size (D ₅₀ ) is not particularly limited, but is preferably 40 μm or less, more preferably 20 μm or less, and further preferably 10 μm or less. On the other hand, the average particle size (D ₅₀ ) is preferably 0.01 μm or more, and more preferably 0.1 μm or more.

The content of the solid electrolyte in the negative electrode active material layer is, for example, preferably in the range of 1 to 60% by mass, and more preferably in the range of 10 to 50% by mass.

The negative electrode active material layer may further contain at least one of a conductive auxiliary agent and a binder in addition to the negative electrode active material and the solid electrolyte described above.

Examples of the conductive auxiliary agent include metals such as aluminum, stainless steel (SUS), silver, gold, copper, and titanium, alloys or metal oxides containing these metals; carbon fibers (specifically, vapor-grown carbon fibers). (VGCF), polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, rayon-based carbon fiber, activated carbon fiber, etc.), carbon nanotube (CNT), carbon black (specifically, acetylene black, Ketjen black (registered trademark)) , Furness black, channel black, thermal lamp black, etc.), but is not limited to these. Further, a particulate ceramic material or a resin material coated with the above metal material by plating or the like can also be used as a conductive auxiliary agent. Among these conductive auxiliaries, from the viewpoint of electrical stability, it is preferable to contain at least one selected from the group consisting of aluminum, stainless steel, silver, gold, copper, titanium, and carbon, and aluminum, stainless steel. It is more preferable to contain at least one selected from the group consisting of silver, gold, and carbon, and it is further preferable to contain at least one carbon. Only one kind of these conductive auxiliaries may be used alone, or two or more kinds thereof may be used in combination.

The shape of the conductive auxiliary agent is preferably particulate or fibrous. 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. In the present specification, the “particle size of the conductive auxiliary agent” means the maximum distance L among the distances between any two points on the contour line of the conductive auxiliary agent. As the value of the "average particle size of the conductive auxiliary agent", the particle size of the particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The value calculated as the average value of is adopted.

When the negative electrode active material layer contains a conductive auxiliary agent, the content of the conductive auxiliary agent in the negative electrode active material layer is not particularly limited, but is preferably 0 to 10% by mass with respect to the total mass of the negative electrode active material layer. , More preferably 2 to 8% by mass, still more preferably 4 to 7% by mass. Within such a range, it is possible to form a stronger electron conduction path in the negative electrode active material layer, and it is possible to effectively contribute to the improvement of battery characteristics.

On the other hand, the binder is not particularly limited, and examples thereof include the following materials.

Polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are replaced with other halogen elements), polyethylene, polypropylene, polymethylpentene, polybutene, polyethernitrile, polytetrafluoroethylene, Polyacrylonitrile, polyimide, polyamide, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), ethylene-propylene-diene copolymer, styrene-butadiene-styrene block copolymer and its hydrogen additive , Fluoroplastic polymers such as styrene / isoprene / styrene block copolymers and their hydrogenated additives, tetrafluoroethylene / hexafluoropropylene copolymers (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymers (PFA) , Fluororesin such as ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), polyvinylfluoride (PVF), vinylidene fluoride- Hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-TFE-based fluororubber), vinylidene fluoride-pentafluoropropylene-based fluororubber (VDF-PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber) Examples thereof include vinylidene fluoride-based fluororubbers such as VDF-PFMVE-TFE-based fluororubbers, vinylidene fluoride-chlorotrifluoroethylene-based fluororubbers (VDF-CTFE-based fluororubbers), and epoxy resins. Of these, polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are more preferable.

The thickness of the negative electrode active material layer varies depending on the configuration of the target all-solid-state battery, but is preferably in the range of 0.1 to 1000 μm, for example.

[Positive electrode active material layer]
The positive electrode active material layer contains a positive electrode active material. The positive electrode of the lithium secondary battery according to an embodiment of the present invention, elemental sulfur (S ₈₎ or reduction products of sulfur containing lithium (either each compound of the above-mentioned _Li 2 _S 8 ~Li 2 _S) It is contained as a positive electrode active material. When the lithium secondary battery is provided in a charged state, it contains elemental sulfur (S ₈ ) as the positive electrode active material. Further, when the lithium secondary battery is provided in a discharged state, the content reduction product of sulfur containing lithium as a positive electrode active material (either each compound of the above-mentioned _Li 2 _S 8 ~Li 2 _S) To do.

Incidentally, the positive electrode active material layer, the positive electrode active material other than the (any of the compounds of _Li 2 _S 8 ~Li 2 _S described above) above elemental sulfur (S ₈₎ or reduction products of sulfur containing lithium It may be included. However, the ratio of sulfur alone or the reduction product of sulfur containing lithium to the positive electrode active material contained in the positive electrode active material layer is preferably 50 to 100% by mass, and more preferably 80 to 100% by mass. , More preferably 90 to 100% by mass, even more preferably 95 to 100% by mass, particularly preferably 98 to 100% by mass, and most preferably 100% by mass.

Examples of the positive electrode active material other than elemental sulfur or the reduction product of sulfur containing lithium include disulfide compounds, sulfur-modified polyacrylonitrile represented by the compounds described in WO 2010/0444437, and sulfur-modified polyisoprene. , Rubianic acid (dithiooxamide), polycarbon sulfide and the like. Inorganic sulfur compounds such as S-carbon composite, TiS ₂ , TiS ₃ , TiS ₄ , NiS, NiS ₂ , CuS, FeS ₂ , MoS ₂ , and MoS ₃ can also be used. Further, examples of the sulfur-free positive electrode active material include layered rock salt type active materials such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , and Li (Ni-Mn-Co) O ₂ , LiMn ₂ O ₄ , LiNi. Examples thereof include spinel-type active materials such as _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 . Examples of the oxide active material other than the above include Li ₄ Ti ₅ O ₁₂ . In some cases, two or more kinds of positive electrode active materials may be used in combination. Needless to say, a positive electrode active material other than the above may be used.

Examples of the shape of the positive electrode active material include particulate (spherical, fibrous) and thin film. When the positive electrode active material has a particle shape, its average particle size (D ₅₀ ) is preferably in the range of, for example, 1 nm to 100 μm, more preferably in the range of 10 nm to 50 μm, and further preferably in the range of 100 nm. It is in the range of ~ 20 μm, and particularly preferably in the range of 1 to 20 μm. In the present specification, the value of the average particle size (D ₅₀ ) of the active material can be measured by the laser diffraction / scattering method.

The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but is preferably in the range of 40 to 99% by mass, and preferably in the range of 50 to 90% by mass. More preferred.

[Solid electrolyte layer]
The solid electrolyte layer of the bipolar secondary battery according to the present embodiment contains a solid electrolyte as a main component and is a layer interposed between the positive electrode active material layer and the negative electrode active material layer described above. Since the specific form of the solid electrolyte contained in the solid electrolyte layer is the same as that described above, detailed description thereof will be omitted here.

The content of the solid electrolyte in the solid electrolyte layer 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 in the range of 90 to 100% by mass. Is more preferable.

The solid electrolyte layer may further contain a binder in addition to the solid electrolyte described above. Since the specific form of the binder that can be contained in the solid electrolyte layer is the same as that described above, detailed description thereof will be omitted here.

The thickness of the solid electrolyte layer varies depending on the configuration of the target bipolar secondary battery, but is preferably in the range of 0.1 to 1000 μm, preferably in the range of 0.1 to 300 μm. Is more preferable.

[Positive current collector plate and negative electrode current collector plate]
The material constituting the current collector plates (25, 27) is not particularly limited, and a known highly conductive material conventionally used as a current collector plate for a secondary battery can be used. As the constituent material of the current collector plate, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable. From the viewpoint of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable. The same material may be used or different materials may be used for the positive electrode current collector plate 27 and the negative electrode current collector plate 25.

[Positive lead and negative electrode lead]
Further, although not shown, the current collector 11 and the current collector plates (25, 27) may be electrically connected via a positive electrode lead or a negative electrode lead. As the constituent materials of the positive electrode and the negative electrode leads, materials used in known lithium secondary batteries can be similarly adopted. The part taken out from the exterior is heat-shrinkable with heat insulation so that it does not come into contact with peripheral devices or wiring and cause electric leakage and affect the product (for example, automobile parts, especially electronic devices). It is preferable to cover with a tube or the like.

[Battery exterior]
As the battery exterior, a known metal can case can be used, or a bag-shaped case using a laminated film 29 containing aluminum that can cover the power generation element as shown in FIG. 6 can be used. As the laminate film, for example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used, but the laminate film is not limited thereto. A laminated film is desirable from the viewpoint of high output and excellent cooling performance, and can be suitably used for batteries for large devices for EVs and HEVs. Further, the exterior body is more preferably a laminated film containing aluminum because the group pressure applied to the power generation element from the outside can be easily adjusted.

The bipolar secondary battery of this embodiment has a configuration in which a plurality of single battery layers are connected in series, so that it is excellent in output characteristics at a high rate. Therefore, the bipolar secondary battery of this embodiment is suitably used as a power source for driving EVs and HEVs.

FIG. 5 is a perspective view showing the appearance of a flat lithium secondary battery, which is a typical embodiment of a bipolar secondary battery.

As shown in FIG. 5, the flat bipolar secondary battery 50 has a rectangular flat shape, and positive electrode tabs 58 and negative electrode tabs 59 for extracting electric power are pulled out from both side portions thereof. There is. The power generation element 57 is wrapped by a battery exterior (laminate film 52) of the bipolar secondary battery 50, and the periphery thereof is heat-sealed. The power generation element 57 pulls out the positive electrode tab 58 and the negative electrode tab 59 to the outside. It is sealed in a closed state. Here, the power generation element 57 corresponds to the power generation element 21 of the bipolar secondary battery 10 shown in FIG. 4 described above. The power generation element 57 is formed by stacking a plurality of bipolar electrodes 23 via a solid electrolyte layer 17.

The lithium secondary battery is not limited to a laminated flat battery. The wound lithium secondary battery may have a cylindrical shape, or may be deformed into a rectangular flat shape. , There are no particular restrictions. The cylindrical shape is not particularly limited, for example, a laminated film may be used for the exterior body, or a conventional cylindrical can (metal can) may be used. Preferably, the power generation element is exteriorized with an aluminum laminate film. By this form, weight reduction can be achieved.

Further, the extraction of the tabs 58 and 59 shown in FIG. 5 is not particularly limited. The positive electrode tab 58 and the negative electrode tab 59 may be pulled out from the same side, or the positive electrode tab 58 and the negative electrode tab 59 may be divided into a plurality of each and taken out from each side, as shown in FIG. It is not limited to. Further, in the winding type lithium ion battery, the terminal may be formed by using, for example, a cylindrical can (metal can) instead of the tab.

[Battery set]
An assembled battery is formed by connecting a plurality of batteries. More specifically, it is composed of serialization, parallelization, or both by using at least two or more. By serializing and parallelizing, the capacitance and voltage can be adjusted freely.

It is also possible to connect a plurality of batteries in series or in parallel to form a small assembled battery that can be attached / detached. Then, by connecting a plurality of these detachable small assembled batteries in series or in parallel, a large capacity and a large capacity suitable for a vehicle driving power source or an auxiliary power source that require a high volume energy density and a high volume output density. It is also possible to form an assembled battery having an output. How many batteries are connected to make an assembled battery, and how many stages of small assembled batteries are stacked to make a large-capacity assembled battery depends on the battery capacity of the vehicle (electric vehicle) to be installed. It may be decided according to the output.

[vehicle]
The non-aqueous electrolyte secondary battery of this embodiment maintains the discharge capacity even after long-term use and has good cycle characteristics. In addition, the volumetric energy density is high. In vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles, higher capacity and larger size are required and longer life is required compared to electric and portable electronic device applications. .. Therefore, the non-aqueous electrolyte secondary battery can be suitably used as a power source for a vehicle, for example, a vehicle drive power source or an auxiliary power source.

Specifically, a battery or an assembled battery formed by combining a plurality of batteries can be mounted on the vehicle. In the present invention, a long-life battery having excellent long-term reliability and output characteristics can be configured. Therefore, when such a battery is installed, a plug-in hybrid electric vehicle having a long EV mileage or an electric vehicle having a long one-charge mileage can be configured. .. For example, in the case of automobiles, hybrid cars, fuel cell cars, electric cars (all four-wheeled cars (passenger cars, trucks, commercial cars such as buses, light cars, etc.)), as well as batteries or assembled batteries made by combining multiple of these. This is because it becomes a highly reliable automobile with a long life by using it for two-wheeled vehicles (including motorcycles) and three-wheeled vehicles. However, the application is not limited to automobiles, and can be applied to various power sources of other vehicles, for example, moving objects such as trains, and power supplies for mounting such as uninterruptible power supplies. It is also possible to use it as.

In the above description, the embodiment of the present invention has been described by taking a bipolar secondary battery as an example, but the type of the secondary battery to which the present invention can be applied is not particularly limited, and the single battery layer in the power generation element. For so-called parallel-stacked all-solid-state batteries in which the batteries are connected in parallel, and any conventionally known bipolar or non-bipolar (parallel-stacked) non-aqueous electrolyte secondary batteries (batteries that use an electrolyte). Applicable.

1 All-solid-state lithium secondary battery system,
2 All-solid-state lithium secondary battery,
3 Voltage sensor,
4 Voltage / current adjuster,
5 current sensor,
6 Control unit,
7 External power supply,
10,50 bipolar secondary battery,
11 Current collector,
11a Outermost layer current collector on the positive electrode side,
11b Outermost layer current collector on the negative electrode side,
13 Positive electrode active material layer,
15 Negative electrode active material layer,
17 Electrolyte layer,
19 Single battery layer,
21,57 Power generation elements,
23 Bipolar electrode,
25 Positive electrode current collector plate (positive electrode tab),
27 Negative electrode current collector plate (negative electrode tab),
29, 52 Laminated film,
58 Positive tab,
59 Negative tab,
61 CPU,
62 Memory.

Claims (6)

A positive electrode containing a positive electrode active material layer containing elemental sulfur or a reduction product of sulfur containing lithium as a positive electrode active material,
A negative electrode containing a negative electrode active material layer containing a negative electrode active material, and a negative electrode
An electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer,
It is a control method of a lithium secondary battery equipped with a power generation element having
When performing the charging process and / or the discharging process of the lithium secondary battery
Detecting the equilibrium potential (vs. Li + / Li) of the positive electrode and
Determining whether or not the detected equilibrium potential value is within the potential range of 0.7 to 1.9 [V], and
When it is determined that the equilibrium potential is not within the potential range, the charging process and / or the discharging process is stopped.
Methods of controlling lithium secondary batteries, including. The method for controlling a lithium secondary battery according to claim 1, wherein the determination is performed based on the value of the state of charge (SOC) of the lithium secondary battery. The method for controlling a lithium secondary battery according to claim 1, wherein the determination is made based on a value of a battery voltage defined as a potential difference between the positive electrode and the negative electrode. The method for controlling a lithium secondary battery according to any one of claims 1 to 3, wherein the lithium secondary battery is an all-solid-state lithium secondary battery. A positive electrode containing a positive electrode active material layer containing elemental sulfur or a reduction product of sulfur containing lithium as a positive electrode active material,
A negative electrode containing a negative electrode active material layer containing a negative electrode active material, and a negative electrode
An electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer,
It is a control device of a lithium secondary battery that controls a lithium secondary battery having a power generation element having a power generation element.
A positive electrode equilibrium potential detection unit that detects the equilibrium potential (vs. Li + / Li) of the positive electrode,
When the lithium secondary battery is charged and / or discharged, the value of the equilibrium potential detected by the positive electrode equilibrium potential detection unit is within the potential range of 0.7 to 1.9 [V]. A control unit that controls to stop the charging process and / or the discharging process when it is determined that the equilibrium potential is not within the potential range.
Lithium secondary battery control device, including. A positive electrode containing a positive electrode active material layer containing elemental sulfur or a reduction product of sulfur containing lithium as a positive electrode active material,
A negative electrode containing a negative electrode active material layer containing a negative electrode active material, and a negative electrode
An electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer,
Lithium secondary battery with power generation element,
A positive electrode equilibrium potential detection unit that detects the equilibrium potential (vs. Li + / Li) of the positive electrode,
The value of the equilibrium potential detected by the positive electrode equilibrium potential detection unit during the charging and / or discharging processing of the lithium secondary battery is within the potential range of 0.7 to 1.9 [V]. A control unit that controls to stop the charging process and / or the discharging process when it is determined that the equilibrium potential is not within the potential range.
Including lithium secondary battery system.