Battery System

Abstract

The object of the present invention is to provide a battery system capable of suppressing the degradation of battery performance caused by the change of the crystal structure of the positive electrode active material. The battery system comprises a solid lithium secondary battery and a control unit, wherein the control unit estimates the local potential of the positive terminal, i.e., the end positive electrode potential Ve2, based on the voltage relaxation amount ΔV2, wherein the voltage relaxation amount ΔV2 is generated by the diffusion of lithium from the opposite part of the positive electrode to the negative electrode after the solid lithium secondary battery is charged to the non-opposite part of the negative electrode, and the control unit controls whether the solid lithium secondary battery is charged in such a way that the end positive electrode potential Ve2 is below the potential Vlimit that causes the crystal structure change of the positive electrode active material.

Description

Technical Field

[0001] The present disclosure relates to a battery system. Background Art

[0002] In recent years, with the rapid popularization of information-related devices and communication devices such as personal computers, cameras and mobile phones, the development of batteries used as their power sources has received attention. In addition, the automotive industry is also promoting the development of high-output and high-capacity batteries for electric vehicles and hybrid vehicles.

[0003] In addition, solid batteries have attracted much attention because they use solid electrolytes as electrolytes between the positive electrode and the negative electrode instead of electrolyte solutions containing organic solvents.

[0004] Patent Document 1 discloses a technology for preventing battery degradation caused by fixation of metallic lithium that has begun to precipitate at a negative electrode by estimating a positive electrode potential in a secondary battery system including a lithium ion secondary battery.

[0005] Prior Art Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2018-085789 Summary of the invention

[0007] The technology described in Patent Document 1 can suppress the deposition of lithium at the negative electrode, but cannot suppress the phenomenon in which the battery performance is reduced due to the change in the crystal structure of the positive electrode active material caused by the high potential of the positive electrode itself.

[0008] In a solid lithium secondary battery, the electrode body is not wound but stacked, so it is easy to have a negative electrode portion that is not facing the positive electrode. If a negative electrode portion that is not facing the positive electrode is formed, the positive terminal portion is likely to have a high potential.

[0009] The present disclosure has been made in view of the above-mentioned situation, and a main object of the present disclosure is to provide a battery system capable of suppressing the degradation of battery performance caused by the change in the crystal structure of the positive electrode active material accompanying Li precipitation.

[0010] The battery system disclosed herein is characterized in that it comprises a solid lithium secondary battery and a control unit, wherein the solid lithium secondary battery has a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode.

[0011] The positive electrode comprises a positive electrode layer,

[0012] The positive electrode layer contains a positive electrode active material.

[0013] The negative electrode includes an opposing portion and a non-opposing portion, wherein the opposing portion is a region opposing the positive electrode, and the non-opposing portion is a region not opposing the positive electrode.

[0014] The control unit estimates the local potential at the end of the positive electrode, i.e., the end positive electrode potential Ve2, based on the voltage relaxation amount ΔV2, which is caused by the diffusion of lithium that moves from the positive electrode to the opposing part of the negative electrode to the non-opposing part of the negative electrode after the solid lithium secondary battery is charged.

[0015] The control unit controls whether charging of the solid lithium secondary battery is executed or not (i.e., execution or non-execution) so that the end positive electrode potential Ve2 is lower than a potential Vlimit causing a change in the crystal structure of the positive electrode active material.

[0016] In the battery system of the present disclosure, the control unit may detect a voltage V1 of the solid lithium secondary battery, calculate a local potential at the end of the positive electrode, namely, an end positive electrode potential Ve1, based on the voltage V1.

[0017] The control unit determines whether the voltage V1 is a voltage at which the end positive electrode potential Ve1 is equal to or lower than the potential Vlimit,

[0018] When the control unit determines that the voltage V1 is a voltage at which the end positive electrode potential Ve1 is equal to or lower than the potential Vlimit, the control unit sets the voltage at which the end positive electrode potential Ve1 reaches the potential Vlimit as a first charge prohibition voltage, and performs a first charge of charging the solid lithium secondary battery until the first charge prohibition voltage is reached.

[0019] The control unit stops the power supply to the solid lithium secondary battery for a predetermined time after the first charge.

[0020] The control unit measures the voltage relaxation amount ΔV2, estimates the end positive electrode potential Ve2 based on the voltage relaxation amount ΔV2, corrects the end positive electrode potential Ve1 to the end positive electrode potential Ve2,

[0021] The control unit detects the voltage V2 of the solid lithium secondary battery and determines whether the voltage V2 is a voltage at which the end positive electrode potential Ve2 is equal to or lower than the potential Vlimit.

[0022] When the control unit determines that the voltage V2 is a voltage equal to or lower than the potential Vlimit of the end positive electrode potential Ve2, the control unit sets the voltage at which the end positive electrode potential Ve2 reaches the potential Vlimit as a second charge prohibition voltage, and performs a second charge on the solid lithium secondary battery until the second charge prohibition voltage is reached.

[0023] In the battery system of the present disclosure, the control unit may discharge the solid lithium secondary battery after the second charging.

[0024] The control unit detects the voltage V3 of the solid lithium secondary battery.

[0025] The control unit determines whether the voltage V3 is a voltage corresponding to the end positive electrode potential Ve2 and smaller than the potential Vlimit.

[0026] When the control unit determines that the voltage V3 is a voltage corresponding to the end positive electrode potential Ve2 and lower than the potential Vlimit, the control unit resets the settings of the first charge inhibition voltage and the second charge inhibition voltage.

[0027] The present disclosure can provide a battery system capable of suppressing degradation of battery performance caused by changes in the crystal structure of a positive electrode active material. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a diagram explaining the mechanism of the positive electrode structural change and the positive electrode potential relative to the positive electrode position.

[0029] Figure 2 This is a flowchart showing an example of control performed by the battery system of the present disclosure.

[0030] Figure 3 This is a diagram showing an example of the relationship between the cell voltage and the end positive electrode potential Ve1.

[0031] Figure 4 This is a diagram showing an example of the relationship between the cell voltage and the end positive electrode potential Ve.

[0032] Figure 5 This is a diagram showing an example of the relationship between the elapsed time and the cell voltage.

[0033] Figure 6 1 is a diagram showing an example of the relationship between the voltage relaxation amount ΔV2 and the end positive electrode potential Ve2.

[0034] Figure 7 This is a diagram showing an example of the relationship between the elapsed time, the battery voltage, and the end positive electrode potential Ve during control of a solid battery in a state where the amount of Li in the negative electrode non-opposing portion is small.

[0035] Figure 8 This is a diagram showing an example of the relationship between the elapsed time, the battery voltage, and the end positive electrode potential Ve during control of a solid battery in a state where Li is present in the negative electrode non-opposing portion.

[0036] Fig. 9 This is a diagram showing an example of the relationship between the elapsed time and the positive electrode potential in the control of the conventional battery system. DETAILED DESCRIPTION

[0037] The battery system disclosed herein is characterized in that it comprises a solid lithium secondary battery and a control unit, wherein the solid lithium secondary battery has a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode.

[0038] The positive electrode comprises a positive electrode layer,

[0039] The positive electrode layer contains a positive electrode active material.

[0040] The negative electrode includes an opposing portion and a non-opposing portion, wherein the opposing portion is a region opposing the positive electrode, and the non-opposing portion is a region not opposing the positive electrode.

[0041] The control unit estimates the local potential at the end of the positive electrode, i.e., the end positive electrode potential Ve2, based on the voltage relaxation amount ΔV2, which is caused by the diffusion of lithium that moves from the positive electrode to the opposing part of the negative electrode to the non-opposing part of the negative electrode after the solid lithium secondary battery is charged.

[0042] The control unit controls whether or not to charge the solid lithium secondary battery so that the end positive electrode potential Ve2 is equal to or lower than a potential Vlimit that causes a change in the crystal structure of the positive electrode active material.

[0043] In the present disclosure, for convenience, a solid lithium secondary battery is sometimes simply referred to as a battery, a single cell, or the like.

[0044] In the present disclosure, a lithium secondary battery refers to a battery that uses at least one selected from metallic lithium, lithium alloys, and lithium compounds as a negative electrode active material and utilizes the precipitation-dissolution reaction of metallic lithium as a negative electrode reaction. In addition, in the present disclosure, the so-called negative electrode refers to an electrode containing a negative electrode layer.

[0045] In the present disclosure, SOC (State of Charge) indicates the ratio of the charge capacity to the full charge capacity of the battery, and the full charge capacity is SOC 100%. SOC can be estimated from the open circuit voltage (OCV) of the solid battery, for example.

[0046] Lithium titanate (LTO), which is a negative electrode active material, is an electrode material that has less expansion and contraction caused by charge and discharge than Si and carbon. Compared with electrolyte-based batteries immersed in electrodes, the maintenance of the bonding between electrodes in solid batteries affects the degradation of battery performance, so low-expansion negative electrode active materials such as lithium titanate can easily inhibit electrode degradation. On the other hand, since the negative electrode potential in the area where lithium titanate is usually used is 1.5V, the opposite positive electrode is prone to high potential, and the crystal structure of the positive electrode active material is prone to change.

[0047] According to the present disclosure, by calculating the voltage relaxation amount ΔV2, the charging prohibition voltage (the second charging prohibition voltage) is set according to the end positive electrode potential Ve2 taking into account the voltage relaxation amount ΔV2, thereby enabling high-precision control of charging so that it becomes below the potential at which the crystal structure change of the positive electrode active material occurs, thereby suppressing the degradation of solid battery performance caused by the crystal structure change of the positive electrode active material accompanying Li precipitation.

[0048] In addition, according to the present disclosure, by calculating the voltage relaxation amount ΔV2, the first charging prohibition voltage set by the initially set end positive electrode potential Ve1 is corrected to the second charging prohibition voltage set by the end positive electrode potential Ve2 taking the voltage relaxation amount ΔV2 into consideration, as needed, thereby enabling the charging to be controlled more accurately to be below the potential at which the crystal structure of the positive electrode active material changes.

[0049] Figure 1 This is a diagram explaining the mechanism of the positive electrode structural change and the positive electrode potential relative to the positive electrode position.

[0050] First, (1) from the discharge state, (2) when charging the solid lithium secondary battery, lithium moves from the positive electrode to the negative electrode facing the positive electrode, (3) lithium diffuses to the negative electrode not facing the positive electrode, (4) when charging is continued, (5) the positive electrode structure changes, resulting in dissolution and reduction of the positive electrode metal, etc. In the above (4) and (5), the positive electrode potential at the positive terminal reaches or exceeds the positive electrode structure change threshold value Vlimit.

[0051] Figure 2 This is a flowchart showing an example of control performed by the battery system of the present disclosure.

[0052] First, the battery (cell) voltage V1 is measured based on the ECU internal data, and the end positive electrode potential Ve1 of the initial setting value is calculated.

[0053] Then, it is determined whether the measured single-cell voltage V1 is a voltage where Ve1 ≤ Vlimit. Vlimit is the threshold value of the potential at which the positive electrode structure changes. The threshold value of the potential at which the positive electrode structure changes can be, for example, the oxidation / reduction potential of a metal. For Co, it is approximately 4.2 V, and for Ni, it is approximately 4.3 V. If the charging is controlled by the surface average potential of the positive electrode, a potential above Vlimit may occur, and the structure of the positive electrode may change.

[0054] When Ve1 exceeds Vlimit, the battery discharge is started. On the other hand, when Ve1 is below Vlimit, the voltage at which Ve1 becomes Vlimit is set as the first charge prohibition voltage, and the battery charging is started. When the voltage reaches Ve1 = Vlimit (the first charge prohibition voltage), the battery charging is prohibited (stopped) (charge prohibition 1).

[0055] After charge prohibition 1, in order to measure the voltage relaxation amount ΔV2, the energization of the battery is stopped for a predetermined time (for example, t = 1 minute, where t is the time required to measure the voltage relaxation amount).

[0056] After the energization is stopped, the voltage relaxation amount ΔV2 is measured through the data built in the ECU, and Ve2 (the end positive electrode potential estimated from ΔV2) is calculated.

[0057] The single-cell voltage V2 is measured, and it is determined whether the measured single-cell voltage V2 is a voltage where Ve2 ≤ Vlimit.

[0058] When the measured battery voltage V2 is a voltage where Ve2 exceeds Vlimit, the battery discharge is started. On the other hand, when the measured single-cell voltage V2 is a voltage where Ve2 is below Vlimit, the voltage at which Ve2 becomes Vlimit is set as the second charge prohibition voltage, and the battery charging is started. When the voltage reaches Ve2 = Vlimit (the second charge prohibition voltage), the battery charging is prohibited (stopped) (charge prohibition 2).

[0059] After charge prohibition 2, the battery discharge is started, the single-cell voltage V3 is measured. After the measured battery voltage V3 reaches a voltage where Ve2 < Vlimit, the setting of the charge prohibition voltage is reset, and the control ends or the repeated control is performed again from the beginning.

[0060] The following describes the method for setting the worst-case assumption line of the end positive electrode potential Ve1 (the end positive electrode potential of the initial setting value).

[0061] The Ve1 line can be appropriately selected according to the current flowing through the battery and the temperature of the battery.

[0062] Figure 3 It is a diagram showing an example of the relationship between the single-cell voltage and the end positive electrode potential Ve1.

[0063] The voltage use range is set to 1.5V to 3V, and the positive electrode structure change threshold Vlimit is assumed to be 4.3V.

[0064] Measurement 1: The battery was fully charged until the voltage reached 3 V, and the end positive electrode potential Ve1 was measured in a state where the battery was fully charged to the negative end. For example, if the end positive electrode potential Ve1 was 4.7 V, it was NG (bad).

[0065] Measurement 2: 4.7V exceeds the positive electrode structure change threshold Vlimit, so the negative electrode non-opposing part and the opposing part are charged at an extremely low rate in parallel, and the single cell voltage when the end positive electrode potential Ve1 is below 4.3V is obtained and stored in the ECU as the first charge prohibition voltage (charge prohibition 1). For example, the voltage is 2.8V and the positive electrode potential is 4.3V. The first charge prohibition voltage varies according to the battery current and temperature.

[0066] Next, a method of setting a line with the maximum voltage relaxation will be described.

[0067] Figure 4 This is a diagram showing an example of the relationship between the cell voltage and the end positive electrode potential Ve.

[0068] Measurement 3: High rate charging is performed in a state where there is no lithium in the non-opposing part of the negative electrode that is not opposed to the positive electrode, and the single cell voltage when the end positive electrode potential is below 4.3V is obtained, and it is stored in the ECU as the second charge prohibition voltage (charge prohibition 2). For example, it can be a voltage of 2.8V and a positive electrode potential of 4.3V, or it can be a voltage of 2.95V and a positive electrode potential of 4.3V. The second charge prohibition voltage varies according to the current and temperature of the battery.

[0069] Next, a method of setting the time t required to measure the voltage relaxation amount ΔV2 after the energization is stopped will be described.

[0070] Figure 5 This is a diagram showing an example of the relationship between the elapsed time and the cell voltage.

[0071] Will Figure 5 The time necessary for the total ΔV to be estimated is defined as t.

[0072] t does not necessarily need to be set as the time until the cell voltage stabilizes.

[0073] For example, t can be set to 1 minute, and the voltage V can be calculated 20 seconds, 40 seconds, and 60 seconds after the energization is stopped. 20s 、V 40s 、V 60s The total ΔV until the single cell voltage stabilizes.

[0074] ΔV=αV20s+ βV 40s +γV 60s (α, β, γ are constants)

[0075] Next, a method of setting the voltage relaxation amount ΔV2 will be described.

[0076] Figure 6 1 is a diagram showing an example of the relationship between the voltage relaxation amount ΔV2 and the end positive electrode potential Ve2.

[0077] Measurement 4: Obtain ΔV1 corresponding to current, temperature, time and SOC and store it in the ECU. ΔV1 is the voltage return (positive polarization + negative polarization) caused by overvoltage. For example, the maximum value of ΔV1 can be 50mV.

[0078] Measurement 5: Obtain the ratio of the negative electrode's opposing area / non-opposing area ΔC and the voltage relaxation amount ΔV2 corresponding to the temperature T at the upper limit cell voltage and store them in the ECU. For example, the maximum value of ΔV2 can be 50 mV. The voltage relaxation amount ΔV2 is the voltage return (voltage drop) caused by the diffusion of Li to the negative electrode non-opposing part. The voltage relaxation rate caused by lithium diffusion is determined based on the non-opposing area where lithium can diffuse and the battery temperature.

[0079] The relationship line between ΔV2 and Ve2 can be selected according to the area of ​​the non-opposing portion in which Li can diffuse and the battery temperature.

[0080] Figure 7 This is a diagram showing an example of the relationship between the elapsed time, the cell voltage, and the end positive electrode potential Ve during control of a solid battery in a state where the amount of Li in the negative electrode non-opposing portion is small.

[0081] First, charging is stopped at a first charge inhibition voltage set at the positive electrode potential of the line in the worst case (charge inhibition 1).

[0082] The voltage relaxation amount ΔV2 is obtained, and the end positive electrode potential Ve1 is corrected to the end positive electrode potential Ve2 until reaching the actual estimated line.

[0083] Using the actual estimated curve, the cell voltage (second charge inhibition voltage) of 2.92 V that is allowable for charging within a range where the end positive electrode potential Ve2 does not exceed Vlimit (4.3 V) is calculated and applied.

[0084] When the cell voltage reaches 2.92 V, which is a second charge inhibition voltage, charging is stopped (charge inhibition 2).

[0085] After discharging starts, the charge inhibit setting is reset.

[0086] Figure 8This is a diagram showing an example of the relationship between the elapsed time, the cell voltage, and the end positive electrode potential Ve during control of a solid battery in a state where Li is present in the negative electrode non-opposing portion.

[0087] In this case, the voltage relaxation amount ΔV2 is 0 mV. In addition, the end positive electrode potential Ve does not exceed Vlimit (4.3 V).

[0088] Fig. 9 This is a diagram showing an example of the relationship between the elapsed time and the positive electrode potential in the control of the conventional battery system.

[0089] Conventional battery systems are controlled by the average surface potential of the positive electrode, so the positive electrode potential may sometimes exceed the positive electrode structure change threshold Vlimt, which may cause a positive electrode structure change.

[0090] A battery system disclosed in the present disclosure includes a solid lithium secondary battery and a control unit.

[0091] The control unit may be an electronic control unit (ECU) or the like.

[0092] The ECU includes a CPU (Central Processing Unit), a memory, and an input / output buffer. The ECU controls the charging and discharging of the solid lithium secondary battery based on signals received from various sensors and maps and programs stored in the memory.

[0093] The control unit may include a voltage detection unit. The voltage detection unit may be a conventionally known voltage sensor, voltmeter, or the like.

[0094] The control unit estimates the local potential at the end of the positive electrode, namely the end positive electrode potential Ve2, based on the voltage relaxation amount ΔV2, which is caused by the diffusion of lithium that has moved from the positive electrode to the opposing part of the negative electrode of the charged solid lithium secondary battery to the non-opposing part of the negative electrode.

[0095] The control unit controls whether or not to charge the solid lithium secondary battery so that the end positive electrode potential Ve2 is equal to or lower than the potential Vlimit at which the crystal structure of the positive electrode active material changes.

[0096] [1st charge]

[0097] The control unit detects (measures) the voltage V1 of the solid lithium secondary battery, calculates the local potential of the positive terminal, i.e., the end positive electrode potential Ve1, from the voltage V1, and determines whether the voltage V1 is a voltage below the end positive electrode potential Ve1 equivalent to the potential Vlimit. When it is determined that the voltage V1 is a voltage below the end positive electrode potential Ve1 equivalent to the potential Vlimit, the voltage at which the end positive electrode potential Ve1 becomes the potential Vlimit can be set as the first charge prohibition voltage, and the solid lithium secondary battery is charged until the first charge prohibition voltage is reached. On the other hand, when the control unit determines that the voltage V1 is a voltage at which the end positive electrode potential Ve1 exceeds the potential Vlimit, the solid lithium secondary battery can be discharged.

[0098] [Power off]

[0099] After the first charge, the control unit may stop the energization of the solid lithium secondary battery for a predetermined time.

[0100] The predetermined time can be appropriately set to the time t required to measure the voltage relaxation amount ΔV2.

[0101] [2nd charge]

[0102] The control unit may measure the voltage relaxation amount ΔV2, estimate the end positive electrode potential Ve2 from the voltage relaxation amount ΔV2, and correct the end positive electrode potential Ve1 to the end positive electrode potential Ve2.

[0103] The control unit detects the voltage V2 of the solid lithium secondary battery, determines whether the voltage V2 is a voltage below the end positive electrode potential Ve2 equivalent to the potential Vlimit, and when it is determined that the voltage V2 is a voltage below the end positive electrode potential Ve2 equivalent to the potential Vlimit, the voltage at which the end positive electrode potential Ve2 becomes the potential Vlimit can be set as the second charge prohibition voltage, and the solid lithium secondary battery is charged until the second charge prohibition voltage is reached. On the other hand, when the control unit determines that the voltage V2 is a voltage at which the end positive electrode potential Ve2 exceeds the potential Vlimit, the solid lithium secondary battery can be discharged.

[0104] [Release the setting of the charging inhibition voltage]

[0105] After the second charge, the control unit discharges the solid lithium secondary battery.

[0106] The control unit detects the voltage V3 of the solid lithium secondary battery and determines whether the voltage V3 is a voltage equivalent to the end positive electrode potential Ve2 and less than the potential Vlimit. When it is determined that the voltage V3 is a voltage equivalent to the end positive electrode potential Ve2 and less than the potential Vlimit, the settings of the first charging prohibition voltage and the second charging prohibition voltage can be released (reset).

[0107] The control unit may terminate the control after canceling the setting of the charge inhibition voltage, or may repeat the control again from the beginning.

[0108] The solid lithium secondary battery disclosed in the present invention comprises a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode, wherein the positive electrode, the solid electrolyte layer, and the negative electrode are disposed in this order.

[0109] [positive electrode]

[0110] The positive electrode includes a positive electrode layer and, if necessary, a positive electrode current collector. A positive electrode terminal may be connected to the positive electrode, and the positive electrode current collector may be a positive electrode terminal.

[0111] [Positive electrode layer]

[0112] The positive electrode layer contains a positive electrode active material, and may contain a solid electrolyte, a conductive material, a binder, and the like as optional components.

[0113] Examples of positive electrode active materials include metallic lithium (Li), lithium alloys, LiCoO2, LiNi 0.8 Co 0.15 Al 0.05 O2、LiNi x Co 1-x O2(0 <x<1)、LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiMnO2, heterogeneous element substituted Li-Mn spinel, lithium titanate, lithium metal phosphate, LiCoN, Li2SiO3 and Li4SiO4, transition metal oxides, TiS2, Si, SiO2, Si alloys and lithium storage metal compounds. Heterogeneous element substituted Li-Mn spinel, such as LiMn 1.5 Ni 0.5 O4、LiMn 1.5 Al 0.5 O4、LiMn 1.5 Mg 0.5 O4、LiMn 1.5 Co 0.5 O4、LiMn 1.5 Fe 0.5 O4 and LiMn 1.5 Zn 0.5 O4, etc. Lithium titanate is, for example, Li4Ti5O 12 Examples of lithium metal phosphates include LiFePO4, LiMnPO4, LiCoPO4, and LiNiPO4. Examples of transition metal oxides include V2O5 and MoO3. Examples of lithium storage intermetallic compounds include Mg2Sn, Mg2Ge, Mg2Sb, and Cu3Sb.

[0114] Examples of lithium alloys include Li-Au, Li-Mg, Li-Sn, Li-Si, Li-Al, Li-B, Li-C, Li-Ca, Li-Ga, Li-Ge, Li-As, Li-Se, Li-Ru, Li-Rh, Li-Pd, Li-Ag, Li-Cd, Li-In, Li-Sb, Li-Ir, Li-Pt, Li-Hg, Li-Pb, Li-Bi, Li-Zn, Li-Tl, Li-Te, and Li-At. Examples of Si alloys include alloys with metals such as Li, and alloys with at least one metal selected from Sn, Ge, and Al.

[0115] The shape of the positive electrode active material is not particularly limited, and may be granular. When the positive electrode active material is granular, the positive electrode active material may be a primary particle or a secondary particle. The average particle size (D50) of the positive electrode active material may be, for example, greater than 1 nm and less than 100 μm, or greater than 10 nm and less than 30 μm.

[0116] A coating layer containing a Li ion conductive oxide may be formed on the surface of the positive electrode active material because this can suppress the reaction between the positive electrode active material and the solid electrolyte.

[0117] Examples of Li ion conductive oxides include LiNbO3, Li4Ti5O 12 and Li3PO4, etc. The thickness of the coating layer is, for example, greater than 0.1 nm, or greater than 1 nm. On the other hand, the thickness of the coating layer is, for example, less than 100 nm, or less than 20 nm. The coverage of the coating layer on the surface of the positive electrode active material is, for example, greater than 70%, or greater than 90%.

[0118] As the solid electrolyte, the same substances as exemplified in the solid electrolyte layer can be exemplified.

[0119] The content of the solid electrolyte in the positive electrode layer is not particularly limited, and may be, for example, in the range of 1% to 80% by mass when the total mass of the positive electrode layer is 100% by mass.

[0120] As the conductive material, known materials can be used, for example, carbon materials and metal particles can be mentioned. As the carbon material, for example, at least one selected from acetylene black, furnace black, VGCF, carbon nanotubes and carbon nanofibers can be mentioned. Wherein, from the viewpoint of electronic conductivity, it can be at least one selected from VGCF, carbon nanotubes and carbon nanofibers. As the metal particles, particles of Ni, Cu, Fe and SUS can be mentioned.

[0121] The content of the conductive material in the positive electrode layer is not particularly limited.

[0122] Examples of the binder (adhesive) include acrylonitrile-butadiene rubber (ABR), butadiene rubber (BR), polyvinylidene fluoride (PVdF), styrene-butadiene rubber (SBR), etc. The content of the binder in the positive electrode layer is not particularly limited.

[0123] The thickness of the positive electrode layer is not particularly limited.

[0124] The positive electrode layer can be formed by a conventionally known method.

[0125] For example, a positive electrode active material and other components as required are added to a solvent and stirred to prepare a positive electrode layer slurry, and the positive electrode layer is obtained by applying the positive electrode layer slurry onto one side of a support such as a positive electrode current collector and drying it.

[0126] Examples of the solvent include butyl acetate, butyl butyrate, heptane, and N-methyl-2-pyrrolidone (NMP).

[0127] The method for coating the positive electrode layer slurry on one side of a support such as a positive electrode current collector is not particularly limited, and examples thereof include doctor blade coating, metal mask printing, electrostatic coating, dip coating, spray coating, roll coating, gravure coating, and screen printing.

[0128] As the support, a self-supporting support can be appropriately selected and used without particular limitation, and for example, metal foil of Cu, Al, etc. can be used.

[0129] In addition, as another method for forming the positive electrode layer, the positive electrode layer can be formed by press-forming the positive electrode mixture powder containing the positive electrode active material and other components contained as needed. In the case of press-forming the powder of the positive electrode mixture, a pressing pressure of 1 MPa or more and 600 MPa or less is usually loaded.

[0130] The pressurizing method is not particularly limited, and examples thereof include a method of applying pressure using a flat plate press, a roll press, and the like.

[0131] [Positive electrode collector]

[0132] As the positive electrode current collector, a known metal that can be used as a current collector of a battery can be used. As such a metal, a metal material containing one or more elements selected from Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Co, Cr, Zn, Ge and In can be exemplified. As the positive electrode current collector, for example, SUS, aluminum, nickel, iron, titanium and carbon can be cited.

[0133] The form of the positive electrode current collector is not particularly limited, and may be in various forms such as foil and mesh. The thickness of the positive electrode current collector varies depending on the shape, and may be, for example, in the range of 1 μm to 50 μm or in the range of 5 μm to 20 μm.

[0134] The positive electrode current collector may be connected to the positive electrode terminal, or the positive electrode current collector may be the positive electrode terminal.

[0135] [negative electrode]

[0136] The negative electrode includes a negative electrode layer and, if necessary, a negative electrode current collector. A negative electrode terminal may be connected to the negative electrode, and the negative electrode current collector may be the negative electrode terminal.

[0137] The negative electrode includes a facing portion, which is a region facing the positive electrode, and a non-facing portion, which is a region not facing the positive electrode. Therefore, when the battery is viewed from above, the area of ​​the negative electrode is larger than that of the positive electrode.

[0138] The ratio ΔC of the area of ​​the facing portion to the area of ​​the non-facing portion (the area of ​​the facing portion / the area of ​​the non-facing portion) is not particularly limited.

[0139] [Negative electrode layer]

[0140] The negative electrode layer contains at least a negative electrode active material and, if necessary, contains a conductive material, a binder, a solid electrolyte, and the like.

[0141] As the negative electrode active material, metallic lithium (Li) and lithium alloys can be cited. The negative electrode layer can contain metallic lithium or lithium alloy as the main component as the negative electrode active material, and can also contain conventionally known negative electrode active materials. In the present disclosure, the main component refers to a component containing 50% by mass or more when the total mass of the negative electrode layer of the solid battery is 100% by mass when the solid battery is fully charged. As conventionally known negative electrode active materials, graphite, mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, soft carbon, Si single substance, Si alloy and Li4Ti5O 12 (LTO), etc. As the lithium alloy and the Si alloy, the same materials as those exemplified in the positive electrode active material can be used.

[0142] The shape of the negative electrode active material is not particularly limited, and examples thereof include granular and plate-like shapes. When the negative electrode active material is granular, the negative electrode active material may be a primary particle or a secondary particle. In addition, the average particle size (D50) of the negative electrode active material may be, for example, greater than 1 nm and less than 100 μm, or greater than 10 nm and less than 30 μm.

[0143] The shape of the negative electrode active material is not particularly limited, and examples thereof include a particle shape and a plate shape.

[0144] The conductive material and binder used in the negative electrode layer may be the same as those exemplified in the positive electrode layer. The solid electrolyte used in the negative electrode layer may be the same as those exemplified in the solid electrolyte layer.

[0145] The thickness of the negative electrode layer is not particularly limited, and may be, for example, 10 to 100 μm.

[0146] The content of the negative electrode active material in the negative electrode layer is not particularly limited, and may be, for example, 20% by mass to 90% by mass.

[0147] [Negative electrode current collector]

[0148] The material of the negative electrode collector can be a material that does not alloy with Li, for example, SUS, Cu and Ni can be mentioned. As the form of the negative electrode collector, for example, foil and plate can be mentioned. The top view shape of the negative electrode collector is not particularly limited, for example, a circle, an ellipse, a rectangle and any polygon can be mentioned. In addition, the thickness of the negative electrode collector varies depending on the shape, for example, it can be in the range of 1μm to 50μm, and it can also be in the range of 5μm to 20μm.

[0149] The negative electrode current collector may be connected to the negative electrode terminal, and the negative electrode current collector may be the negative electrode terminal.

[0150] [Solid electrolyte layer]

[0151] The solid electrolyte layer contains at least a solid electrolyte.

[0152] As the solid electrolyte contained in the solid electrolyte layer, a known solid electrolyte that can be used in a solid battery can be used as appropriate, and examples thereof include oxide-based solid electrolytes and sulfide-based solid electrolytes.

[0153] As sulfide-based solid electrolysis, for example, Li2S-P2S5, Li2S-SiS2, LiX-Li2S-SiS2, LiX-Li2S-P2S5, LiX-Li2O-Li2S-P2S5, LiX-Li2S-P2O5, LiX-Li3PO4-P2S5 and Li3PS4 can be cited. Furthermore, the above-mentioned "Li2S-P2S5" refers to a material obtained using a raw material composition containing Li2S and P2S5, and the same applies to other records. In addition, the "X" of the above-mentioned LiX represents a halogen element. In the raw material composition containing the above-mentioned LiX, LiX can contain one or more than two kinds. When containing two or more kinds of LiX, the mixing ratio of the two or more kinds is not particularly limited.

[0154] The molar ratio of each element in the sulfide-based solid electrolyte can be controlled by adjusting the content of each element in the raw material. In addition, the molar ratio and composition of each element in the sulfide-based solid electrolyte can be measured by, for example, ICP emission spectrometry.

[0155] The sulfide-based solid electrolyte may be sulfide glass, crystallized sulfide glass (glass ceramic), or a crystalline material obtained by subjecting a raw material composition to a solid phase reaction treatment.

[0156] The crystal state of the sulfide-based solid electrolyte can be confirmed by, for example, performing powder X-ray diffraction measurement of the sulfide-based solid electrolyte using CuKα rays.

[0157] Sulfide glass can be obtained by subjecting a raw material composition (for example, a mixture of Li2S and P2S5) to amorphization. Examples of amorphization treatment include mechanical polishing.

[0158] Glass ceramics can be obtained, for example, by heat treating sulfide glass.

[0159] The heat treatment temperature may be higher than the crystallization temperature (Tc) observed by thermal analysis of the sulfide glass, and is usually 195° C. or higher. On the other hand, the upper limit of the heat treatment temperature is not particularly limited.

[0160] The crystallization temperature (Tc) of sulfide glass can be measured by differential thermal analysis (DTA).

[0161] The heat treatment time is not particularly limited as long as it is a time that can obtain the desired crystallinity of the glass ceramics, and is, for example, in the range of 1 minute to 24 hours, particularly, in the range of 1 minute to 10 hours.

[0162] The method of heat treatment is not particularly limited, and an example thereof includes a method using a sintering furnace.

[0163] As the oxide-based solid electrolyte, for example, there can be mentioned a substance having a garnet-type crystal structure of Li element, La element, A element (A is at least one of Zr, Nb, Ta and Al) and O element. As the oxide-based solid electrolyte, for example, Li 3+x PO 4-x N x (1≤x≤3) etc.

[0164] From the viewpoint of good handling properties, the solid electrolyte may be in the form of particles.

[0165] The average particle size (D50) of the particles of the solid electrolyte is not particularly limited, but the lower limit may be 0.5 μm or more and the upper limit may be 2 μm or less.

[0166] In the present disclosure, unless otherwise specified, the average particle size of particles is the value of the volume-based median diameter (D50) obtained by laser diffraction / scattering particle size distribution measurement. In addition, in the present disclosure, the median diameter (D50) refers to the diameter (volume average diameter) at which the cumulative volume of the particles becomes half (50%) of the total volume when the particles are arranged in order from the smallest particle size.

[0167] The solid electrolyte may be used alone or in combination of two or more. When two or more solid electrolytes are used, the two or more solid electrolytes may be mixed, or two or more solid electrolyte layers may be formed to obtain a multilayer structure.

[0168] The proportion of the solid electrolyte in the solid electrolyte layer is not particularly limited, and may be, for example, 50 mass % or more, 60 mass % or more and 100 mass % or less, 70 mass % or more and 100 mass % or less, or 100 mass %.

[0169] From the viewpoint of embodying plasticity, etc., the solid electrolyte layer may contain a binder. As such a binder, the material exemplified as the binder used in the positive electrode layer can be exemplified. However, in order to easily achieve high output, from the viewpoint of preventing excessive aggregation of the solid electrolyte and being able to form a solid electrolyte layer with a uniformly dispersed solid electrolyte, etc., the binder contained in the solid electrolyte layer can be 5% by mass or less.

[0170] The method of forming the solid electrolyte layer includes a method of press-molding a solid electrolyte material powder containing a solid electrolyte, etc. When the solid electrolyte material powder is press-molded, a press pressure of about 1 MPa to 600 MPa is usually applied.

[0171] The pressurizing method is not particularly limited, and the pressurizing methods exemplified in the formation of the positive electrode layer may be mentioned.

[0172] The thickness of the solid electrolyte layer is not particularly limited, but is usually 0.1 μm or more and 1 mm or less.

[0173] The solid lithium secondary battery includes an outer casing that accommodates a positive electrode layer, a negative electrode layer, a solid electrolyte layer, and the like, as necessary.

[0174] The material of the outer casing is not particularly limited as long as it is stable to the electrolyte, and examples thereof include resins such as polypropylene, polyethylene, and acrylic resin.

[0175] Examples of the shape of the solid lithium secondary battery include a coin shape, a laminate shape, a cylindrical shape, and a square shape.

Claims

1. A battery system, characterized in that: A solid lithium secondary battery and a control unit are provided, wherein the solid lithium secondary battery has a positive electrode, a negative electrode, and a solid electrolyte layer arranged between the positive electrode and the negative electrode. The positive electrode comprises a positive electrode layer, The positive electrode layer contains a positive electrode active material. The negative electrode includes an opposing portion and a non-opposing portion, wherein the opposing portion is a region opposing the positive electrode, and the non-opposing portion is a region not opposing the positive electrode. The control unit estimates the local potential at the end of the positive electrode, i.e., the end positive electrode potential Ve2, based on the voltage relaxation amount ΔV2, wherein the voltage relaxation amount ΔV2 is the amount of voltage drop of the solid lithium secondary battery caused by the diffusion of lithium from the positive electrode to the opposing part of the negative electrode to the non-opposing part of the negative electrode after the solid lithium secondary battery is charged, The control unit controls whether or not to charge the solid lithium secondary battery so that the end positive electrode potential Ve2 is below a potential Vlimit that causes a change in the crystal structure of the positive electrode active material. The control unit detects a voltage V1 of the solid lithium secondary battery, and calculates an end positive electrode potential Ve1 which is a local potential at the end of the positive electrode based on the voltage V1. The control unit determines whether the voltage V1 is a voltage at which the end positive electrode potential Ve1 is equal to or lower than the potential Vlimit, When the control unit determines that the voltage V1 is a voltage at which the end positive electrode potential Ve1 is equal to or lower than the potential Vlimit, the control unit sets the voltage at which the end positive electrode potential Ve1 reaches the potential Vlimit as a first charge prohibition voltage, and performs a first charge of charging the solid lithium secondary battery until the first charge prohibition voltage is reached. The control unit stops the power supply to the solid lithium secondary battery for a predetermined time after the first charge. The control unit measures the voltage relaxation amount ΔV2, estimates the end positive electrode potential Ve2 based on the voltage relaxation amount ΔV2, corrects the end positive electrode potential Ve1 to the end positive electrode potential Ve2, The control unit detects the voltage V2 of the solid lithium secondary battery and determines whether the voltage V2 is a voltage at which the end positive electrode potential Ve2 is equal to or lower than the potential Vlimit. When the control unit determines that the voltage V2 is a voltage equal to or lower than the potential Vlimit of the end positive electrode potential Ve2, the control unit sets the voltage at which the end positive electrode potential Ve2 reaches the potential Vlimit as a second charge prohibition voltage, and performs a second charge on the solid lithium secondary battery until the second charge prohibition voltage is reached.

2. The battery system according to claim 1, The control unit discharges the solid lithium secondary battery after the second charging. The control unit detects a voltage V3 of the solid lithium secondary battery. The control unit determines whether the voltage V3 is a voltage corresponding to the end positive electrode potential Ve2 and smaller than the potential Vlimit. When the control unit determines that the voltage V3 is a voltage corresponding to the end positive electrode potential Ve2 and lower than the potential Vlimit, the control unit resets the settings of the first charge inhibition voltage and the second charge inhibition voltage.

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