BATTERY SYSTEM

Abstract

Battery system with a control unit and a solid-state lithium secondary battery comprising a cathode, an anode and a solid electrolyte layer arranged between the cathode and the anode, wherein the cathode comprises a cathode layer; wherein the cathode layer comprises a cathode active material; wherein the anode comprises a facing part and a non-facing part, the facing part being an area facing the cathode, and the non-facing part being an area not facing the cathode, wherein the control unit estimates a cathode end potential Ve2 from a voltage relaxation amount ΔV2, the cathode end potential Ve2 is a local potential of the end part of the cathode, and the voltage relaxation amount ΔV2 is generated by diffusion of lithium, which in a charged state was transferred from the cathode of the solid-state lithium secondary battery to the facing part of the anode, into the non-facing part of the anode, and wherein the control unit controls the execution and non-execution of the charging of the solid-state lithium secondary battery such that the cathode end potential Ve2 is less than or equal to a potential Vlimit at which a change in the crystal structure of the cathode active material occurs.

Description

TECHNICAL FIELD

[0001] The disclosure relates to a battery system. BACKGROUND

[0002] With the rapid proliferation of information and communication devices such as computers, video cameras, and mobile phones, the development of batteries used as power sources for these devices is becoming increasingly important. In the automotive industry, etc., the development of high-performance, high-capacity batteries for battery-electric vehicles or hybrid-electric vehicles is in full swing.

[0003] A solid-state battery has also attracted attention for the following reason: a solid electrolyte is used as the electrolyte between the cathode and the anode instead of an electrolyte solution containing an organic solvent.

[0004] Patent Literature 1 discloses a technique for preventing battery deterioration by estimating a positive electrode potential in a secondary battery system including a lithium-ion secondary battery, which is deterioration caused by the immobilization of lithium metal that begins to deposit in the anode.

[0005] Patent Literature 1: JP 2018-085789 A

[0006] The technique described in Patent Literature 1 can suppress lithium deposition in the anode. However, it cannot suppress the phenomenon of battery performance being reduced by a change in the crystal structure of the cathode active material due to an increase in the potential of the cathode itself.

[0007] In a solid-state lithium secondary battery, the electrode body cannot have a wound structure and thus has a laminated structure. Accordingly, a non-cathode-facing portion is likely to form in the anode. Once the non-cathode-facing portion is formed in the anode, the potential of the cathode end portion is likely to be high. SUMMARY

[0008] The disclosed embodiments have been achieved in view of the above circumstances. An object of the disclosed embodiments is to provide a battery system configured to suppress a decrease in battery performance caused by a change in the crystal structure of the cathode active material due to Li deposition.

[0009] In a first embodiment, a battery system is provided comprising a control unit and a solid-state lithium secondary battery having a cathode, an anode and a solid electrolyte layer disposed between the cathode and the anode, wherein the cathode comprises a cathode layer; wherein the cathode layer comprises a cathode active material; wherein the anode comprises a facing part and a non-facing part, the facing part being a region facing the cathode, and the non-facing part being a region not facing the cathode, wherein the control unit estimates a cathode end part potential Ve2 from a stress relaxation amount ΔV2, the cathode end part potential Ve2 is a local potential of an end part of the cathode, and the stress relaxation amount ΔV2 is generated by diffusion of lithium, which has been transferred in a charged state from the cathode of the all-solid-state lithium secondary battery into the facing part of the anode, into the non-facing part of the anode, and wherein the control unit controls the execution and non-execution of charging of the solid-state lithium secondary battery such that the cathode end-part potential Ve2 is less than or equal to a potential Vlimit at which a change in the crystal structure of the cathode active material occurs.

[0010] The battery system of the disclosed embodiments may be the battery system wherein the control unit detects a voltage V1 of the solid-state lithium secondary battery and calculates from the voltage V1 a cathode end part potential Ve1, which is a local potential of the end part of the cathode, wherein the control unit determines whether at the voltage V1 the cathode end potential Ve1 is less than or equal to the potential Vlimit or not, wherein, if it has been determined that at the voltage V1 the cathode end partial potential Ve1 is less than or equal to the potential Vlimit, the control unit sets the voltage at which the cathode end partial potential Ve1 is equal to the potential Vlimit to a first charge interruption voltage, and the control unit carries out a first charge, whereby the solid-state lithium secondary battery is charged until the first charge interruption voltage is reached, wherein the control unit suspends the charging and discharging of the solid-state lithium secondary battery for a certain period of time after the first charging, wherein the control unit measures the voltage relaxation amount ΔV2, estimates the cathode end potential Ve2 from the voltage relaxation amount ΔV2 and corrects the cathode end potential Ve1 to the cathode end potential Ve2, wherein the control unit detects a voltage V2 of the solid-state lithium secondary battery and determines whether or not, at the voltage V2, the cathode end potential Ve2 is less than or equal to the potential Vlimit, and wherein, when it is determined that the voltage V2 is the voltage at which the cathode end partial potential Ve2 is less than or equal to the potential Vlimit, the control unit sets the voltage at which the cathode end partial potential Ve2 is equal to the potential Vlimit to a second charge interruption voltage, and the control unit performs a second charging, thereby charging the all-solid-state lithium secondary battery until the second charge interruption voltage is reached.

[0011] The battery system of the disclosed embodiments may be the battery system wherein the control unit discharges the solid-state lithium secondary battery after the second charging, wherein the control unit detects a voltage V3 of the solid-state lithium secondary battery, wherein the control unit determines whether the voltage V3 is a voltage at which the cathode end part potential Ve2 is smaller than the potential Vlimit or not, and wherein, if it is determined that the voltage V3 is the voltage at which the cathode end part potential Ve2 is smaller than the potential Vlimit, the control unit resets the settings of the first and second charge interruption voltages.

[0012] According to the disclosed embodiments, a battery system configured to suppress a decrease in battery performance caused by a change in the crystal structure of the cathode active material is provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In the attached drawings, is Fig. 1 is a view illustrating the mechanism of generating a change in the structure of the cathode and illustrating the cathode potential with respect to the cathode position; is Fig. 2 is a flowchart of an example of control by the battery system of the disclosed embodiments; is Fig. 3 is a view showing an example of the relationship between the cell voltage and the cathode end potential Ve1; is Fig. 4 is a view showing an example of the relationship between the cell voltage and the cathode end potential Ve; is Fig. 5 is a view showing an example of the relationship between the elapsed time and the cell voltage; is Fig. 6 is a view showing an example of the relationship between the stress relaxation amount ΔV2 and the cathode end part potential Ve2; is Fig. 7 is a view showing an example of the relationship between the elapsed time of the control of the solid-state cell of the disclosed embodiments and the cell voltage, the cell being in the state where the amount of Li in the non-cathode-facing part of the anode is small, and showing an example of the relationship between the elapsed time and the cathode end-part potential Ve; is Fig. 8 is a view showing an example of the relationship between the elapsed time of the control of the solid-state cell of the disclosed embodiments and the cell voltage, the cell being in the state where Li is present in the non-cathode-facing part of the anode, and showing an example of the relationship between the elapsed time and the cathode end-part potential Ve; and is Fig. 9 is a view showing an example of the relationship between the elapsed time of the control of a conventional battery system and the cathode potential. DETAILED DESCRIPTION

[0014] The battery system of the disclosed embodiments is a battery system having a control unit and a solid-state lithium secondary battery comprising a cathode, an anode, and a solid electrolyte layer disposed between the cathode and the anode, wherein the cathode comprises a cathode layer; wherein the cathode layer comprises a cathode active material; wherein the anode comprises a facing part and a non-facing part; the facing part is a region facing the cathode, and the non-facing part is a region not facing the cathode; wherein the control unit estimates a cathode end part potential Ve2 from a stress relaxation amount ΔV2; the cathode end part potential Ve2 is a local potential of the end part of the cathode, and the stress relaxation amount ΔV2 is generated by diffusion of lithium, which has been transferred in a charged state from the cathode of the all-solid-state lithium secondary battery into the facing part of the anode, into the non-facing part of the anode, and wherein the control unit controls the execution and non-execution of charging of the solid-state lithium secondary battery such that the cathode end-part potential Ve2 is less than or equal to a potential Vlimit at which a change in the crystal structure of the cathode active material occurs.

[0015] In the disclosed embodiments, “solid-state lithium secondary battery” may be referred to as “battery,” “cell,” or the like for convenience.

[0016] In the disclosed embodiments, "lithium secondary battery" refers to a battery in which at least one of a lithium metal, a lithium alloy, and a lithium compound is used as the anode active material, and in which a lithium metal deposition-dissolution reaction is used as the anode reaction. Furthermore, "anode" in the disclosed embodiments refers to an electrode comprising an anode layer.

[0017] In the disclosed embodiments, the state of charge (SOC) refers to the percentage of charge capacity relative to the battery's full charge capacity. Full charge capacity is 100% SOC. For example, the SOC can be estimated from the open circuit voltage (OCV) of the solid-state battery.

[0018] An example of an anode active material is lithium titanate (LTO = Lithium Titanium Oxide). It is an electrode material that is more stable against expansion and contraction during charge and discharge than Si, carbon, etc. Compared with an electrolyte battery containing electrolyte-impregnated electrodes, in an all-solid-state battery, maintaining the connection between the electrodes affects battery performance deterioration. Accordingly, battery performance deterioration can be easily suppressed by using a low-expansion anode active material such as lithium titanate. Incidentally, lithium titanate has an anode potential of 1.5 V in a normal usage range. Accordingly, the potential of the cathode facing the anode is likely to be high, and a change in the crystal structure of the cathode active material is likely to occur.

[0019] According to the disclosed embodiments, by calculating the stress relaxation amount ΔV2 and setting a charge interruption voltage from the cathode end-part potential Ve2 based on the stress relaxation amount ΔV2 (the second charge interruption voltage), the charging of the battery can be precisely controlled to achieve a potential equal to or lower than the potential at which a change in the crystal structure of the cathode active material occurs, and a performance drop of the all-solid-state battery caused by a change in the crystal structure of the cathode active material due to Li deposition can be suppressed.

[0020] According to the disclosed embodiments, by calculating the voltage relaxation amount ΔV2 and, if necessary, correcting the first charge interruption voltage set from the initially set cathode end partial potential Ve1 to the second charge interruption voltage set from the cathode end partial potential Ve2 based on the voltage relaxation amount ΔV2, the charge of the battery can be more accurately controlled to achieve a potential equal to or lower than the potential at which a change in the crystal structure of the cathode active material occurs.

[0021] Fig. Figure 1 is a view illustrating the mechanism of generating a change in the structure of the cathode and illustrating the cathode potential with respect to the cathode position.

[0022] In Fig. 1 (1) shows the anode and cathode of the solid-state lithium secondary battery in the discharged state; (2) once the solid-state lithium secondary battery is charged, lithium is transferred from the cathode to the cathode-facing part of the anode; (3) lithium diffuses into the non-cathode-facing part of the anode; and (4) as the solid-state lithium secondary battery continues to be charged, (5) the structure of the cathode is changed, resulting in dissolution, reduction, etc., of the cathode metal. In (4) and (5), the cathode potential of the cathode end part reaches the cathode structure change limit value Vlimit or more.

[0023] Fig. 2 is a flowchart of an example of control by the battery system of the disclosed embodiments.

[0024] First, the cell voltage V1 is measured based on the data stored in the electric control unit (ECU) and the originally set value for the cathode end potential Ve1 is calculated.

[0025] Next, it is determined whether the measured cell voltage V1 is less than or equal to Vlimit (Ve1 ≤ Vlimit). Vlimit is the limiting potential at which the cathode structure changes. For example, the limiting potential at which the cathode structure changes can be the oxidation-reduction potential of a metal. The oxidation-reduction potential of Co is approximately 4.2 V, and the oxidation-reduction potential of Ni is approximately 4.3 V. If battery charging is controlled by the plane average potential of the cathode, there is a possibility that a potential equal to or greater than Vlimit will be reached, and a change in the cathode structure will occur.

[0026] If Ve1 is greater than Vlimit, battery discharge begins. If Ve1 is less than or equal to Vlimit, the voltage at which Ve1 reaches Vlimit is set as the first charge interrupt voltage, battery charging begins, and battery charging is interrupted (stopped) when the voltage at which Ve1 is equal to Vlimit (Ve1 = Vlimit) (first charge interrupt voltage) is reached (charge interrupt 1).

[0027] After the charge interruption 1, the charging and discharging of the battery is interrupted for a certain period of time (e.g., t = one minute (where t is the time required for measuring the voltage relaxation amount)) to measure the voltage relaxation amount ΔV2.

[0028] After the interruption of charging and discharging, the voltage relaxation amount ΔV2 is measured from the data stored in the electrical control unit and Ve2 (cathode end portion potential estimated from ΔV2) is calculated.

[0029] The cell voltage V2 is measured and it is determined whether the measured cell voltage V2 is less than or equal to Vlimit or not (Ve2 ≤ Vlimit).

[0030] If the measured cell voltage V2 is a voltage where Ve2 is greater than Vlimit, battery discharge is started. On the other hand, if the measured cell voltage V2 is a voltage where Ve2 is less than or equal to Vlimit, the voltage at which Ve2 reaches Vlimit is set as the second charge interruption voltage, and battery charging is started. Battery charging is interrupted (stopped) when the voltage at which Ve2 is equal to Vlimit (Ve2 = Vlimit) (second charge interruption voltage) is reached (charge interruption 2).

[0031] After charge interruption 2, the battery discharge is started; the cell voltage V3 is measured; and after the measured voltage V3 reaches the voltage at which Ve2 is less than Vlimit (Ve2 < Vlimit), the charge interruption voltage settings are reset and the control is terminated or repeated from the beginning.

[0032] The method for setting a worst-case assumption line passing through the cathode end portion potential Ve1 (the initially set cathode end portion potential value) is described here.

[0033] The Ve1 line can be selected appropriately depending on the current flowing through the battery and the temperature of the battery.

[0034] Fig. Figure 3 is a view showing an example of the relationship between the cell voltage and the cathode end potential Ve1.

[0035] The voltage usage range is set to a range of 1.5 V to 3 V and the limit value for the cathode structure change Vlimit is assumed to be 4.3 V.

[0036] Measurement 1: The battery is fully charged until a voltage of 3 V is reached. When the anode terminal is fully charged, the cathode terminal potential Ve1 is measured. If the cathode terminal potential Ve1 is then, for example, 4.7 V, this case is considered unfavorable.

[0037] Measurement 2: Since a potential of 4.7 V exceeds the cathode structural change limit Vlimit, the cell voltage is obtained when the non-cathode-facing part of the anode is charged at an extremely low rate in parallel with the facing part, so that a cathode end-part potential Ve1 of 4.3 V is reached. This voltage is stored in the ECU as the first charge interruption voltage (charge interruption voltage 1). For example, the voltage is 2.8 V and the cathode potential is 4.3 V. The first charge interruption voltage varies depending on the battery current and temperature.

[0038] The procedure for defining a stress relaxation maximum line or a stress relaxation maximum line is described here.

[0039] Fig. Figure 4 is a view showing an example of the relationship between the cell voltage and the cathode end potential Ve.

[0040] Measurement 3: The cell voltage at which the non-cathode-facing portion of the anode is charged at a high rate in the state where no lithium is present in the non-cathode-facing portion of the anode and when the cathode end-part potential reaches 4.3 V or less is obtained and stored in the ECU as the second charge interruption voltage (Charge Interruption 2). For example, the voltage and cathode potential may be 2.8 V and 4.3 V, respectively, or may be 2.95 V and 4.3 V, respectively. The second charge interruption voltage varies depending on the battery current and temperature.

[0041] The method for setting the time t required to measure the voltage relaxation amount ΔV2 after the battery charging and discharging is stopped is described here.

[0042] Fig. Figure 5 is a view showing an example of the relationship between elapsed time and cell voltage.

[0043] In Fig. 5, the time required to estimate the total ΔV is defined as “t”.

[0044] Furthermore, “t” is not necessarily the time required to stabilize the cell voltage.

[0045] For example, “t” can be set to one minute (t = one minute), and the total ΔV required to stabilize the cell voltage can be calculated from the voltages V 20s , V 40s and V 60s which occur 20 seconds, 40 seconds or 60 seconds after the battery charging or discharging is interrupted. ΔV=αV20s+βV40s+γV60s (where α,β and γ are constants).

[0046] The procedure for determining the stress relaxation amount ΔV2 is described here.

[0047] Fig. 6 is a view showing an example of the relationship between the stress relaxation amount ΔV2 and the cathode end-part potential Ve2.

[0048] Measurement 4: First, ΔV1 is obtained as a function of current, temperature, time, and SOC and stored in the ECU. Note that ΔV1 is a voltage return (cathode polarization + anode polarization) due to overvoltage. For example, a maximum ΔV1 can be 50 mV.

[0049] Measurement 5: The voltage relaxation amount ΔV2 as a function of temperature T and the ratio ΔC between the area of ​​the facing part of the anode and the area of ​​the non-facing part at the upper limit of the cell voltage is obtained and stored in the ECU. For example, a maximum ΔV2 can be 50 mV. The voltage relaxation amount ΔV2 is a voltage return (voltage decrease) due to Li diffusion into the non-cathode-facing part of the anode. The rate of voltage relaxation due to lithium diffusion is determined depending on the battery temperature and the area of ​​the non-facing portion into which lithium can diffuse.

[0050] A relationship line or line of relationship between ΔV2 and Ve2 can be chosen depending on the temperature of the battery and the area of ​​the unaddressed part into which Li can diffuse.

[0051] Fig. 7 is a view showing an example of the relationship between the elapsed time of controlling a solid-state cell of the disclosed embodiments and a cell voltage, the cell being in the state where the amount of Li in the non-facing part of the anode is small, and an example of the relationship between the elapsed time and the cathode end-part potential Ve.

[0052] First, the battery charging is stopped at the first charge interruption voltage, which is determined by the cathode potential of the worst-case line (charge interruption 1).

[0053] The stress relaxation amount ΔV2 is obtained and the cathode end potential Ve1 is corrected to the cathode end potential Ve2 until a current estimation line or a current estimated line is reached.

[0054] Using the current estimation line, the cell voltage (the second charge cut-off voltage) at which charging is allowed within a range where the cathode end partial potential Ve2 is not more than Vlimit (4.3 V), which corresponds to a voltage of 2.92 V, is calculated and set.

[0055] When the cell voltage reaches the second charge interruption voltage (2.92 V), the battery charging is stopped (charge interruption 2).

[0056] When the battery starts discharging, the charge interruption voltage settings are reset.

[0057] Fig. 8 is a view showing an example of the relationship between the elapsed time of controlling a solid-state cell of the disclosed embodiments and a cell voltage, the cell being in the state where Li is present in the non-cathode-facing part of the anode, and an example of the relationship between the elapsed time and the cathode end-part potential Ve.

[0058] In this case, the voltage relaxation value ΔV2 is 0 mV. The cathode end-part potential Ve is also not greater than Vlimit (4.3 V).

[0059] Fig. 9 is a view showing an example of the relationship between the elapsed time of control of a conventional battery system and a cathode potential.

[0060] A conventional battery system is controlled by the average potential of the cathode. Accordingly, there is a possibility that the cathode potential is equal to or greater than the threshold value Vlimit for cathode structure change, resulting in a change in the cathode structure.

[0061] The battery system of the disclosed embodiments includes a solid-state lithium secondary battery and a control unit.

[0062] The control unit may be an electronic control unit (ECU) or similar.

[0063] The ECU includes a central processing unit (CPU), memory, and an input / output buffer. Based on the signals received from the sensors and the maps and programs stored in the memory, the ECU controls the charging and discharging of the solid-state lithium secondary battery.

[0064] The control unit may include a voltage sensing unit. The voltage sensing unit may be a commonly known voltage sensor, a voltmeter, or the like.

[0065] The control unit estimates the cathode end-part potential Ve2 from the voltage relaxation amount ΔV2. The cathode end-part potential Ve2 is the local potential of the end part of the cathode, and the voltage relaxation amount ΔV2 is generated by the diffusion of lithium, which has been transferred in a charged state from the cathode of the all-solid-state lithium secondary battery to the facing part of the anode, into the non-facing part of the anode.

[0066] The control unit controls the execution and non-execution of charging of the solid-state lithium secondary battery so that the cathode end-part potential Ve2 is equal to or less than the potential Vlimit at which a change in the crystal structure of the cathode active material occurs. [First load]

[0067] The control unit can detect (measure) the voltage V1 of the solid-state lithium secondary battery and calculate the cathode end potential Ve1, which is the local potential of the cathode end, from the voltage V1. The control unit can determine whether the cathode end potential Ve1 is less than or equal to the potential Vlimit at the voltage V1. If it is determined that the voltage V1 is the voltage at which the cathode end potential is less than or equal to the potential Vlimit, the control unit can set the voltage at which the cathode end potential Ve1 is equal to the potential Vlimit to the first charge cut-off voltage, and the control unit can perform the first charge, charging the solid-state lithium secondary battery until the first charge cut-off voltage is reached.On the other hand, the control unit may perform discharging of the solid-state lithium secondary battery when it is determined that the voltage V1 is the voltage at which the cathode end partial potential Ve1 is greater than the potential Vlimit. [Interruption of loading and unloading]

[0068] After the initial charging, the control unit can suspend the charging and discharging of the solid-state lithium secondary battery for a certain time interval.

[0069] The specific time interval can be adequately set as the time t described above required to measure the stress relaxation amount ΔV2. [Second loading]

[0070] The control unit can measure the voltage relaxation amount ΔV2, can estimate the cathode end potential Ve2 from the voltage relaxation amount ΔV2, and can correct the cathode end potential Ve1 to the cathode end potential Ve2.

[0071] The control unit can detect the voltage V2 of the solid-state lithium secondary battery and determine whether the cathode end partial potential Ve2 is less than or equal to the potential Vlimit at the voltage V2. If it is determined that the voltage V2 is the voltage at which the cathode end partial potential Ve2 is less than or equal to the potential Vlimit, the control unit can set the voltage at which the cathode end partial potential Ve2 is less than or equal to the potential Vlimit to the second charge interruption voltage, and the control unit can perform a second charge in which the solid-state lithium secondary battery is charged until the second charge interruption voltage is reached. On the other hand, if it is determined that the voltage V2 is the voltage at which the cathode end partial potential Ve2 is greater than the potential Vlimit, the control unit can discharge the solid-state lithium secondary battery. [Deleting the charge interruption voltage settings]

[0072] The control unit can discharge the solid-state lithium secondary battery after the second charging.

[0073] The control unit can detect the voltage V3 of the solid-state lithium secondary battery and determine whether the cathode end potential Ve2 is lower than the potential Vlimit at voltage V3. If it is determined that the cathode end potential Ve2 is lower than the potential Vlimit at voltage V3, the control unit can clear (reset) the settings of the first and second charge cutoff voltages.

[0074] After the charge interrupt voltage settings have been cleared, the control unit can terminate the control or repeat the control from the beginning.

[0075] An all-solid-state lithium secondary battery of the disclosed embodiments includes a cathode, an anode, and a solid electrolyte layer disposed between the cathode and the anode. That is, the cathode, the solid electrolyte layer, and the anode are arranged in this order. [Cathode]

[0076] The cathode comprises a cathode layer. If necessary, it includes a cathode current collector. A cathode terminal may be connected to the cathode. The cathode current collector may be the cathode terminal. [cathode layer]

[0077] The cathode layer contains a cathode active material. If necessary, the cathode layer may contain a solid electrolyte, a conductive material, a binder, etc.

[0078] Examples of the cathode active material include lithium metal (Li), lithium alloy, LiCoO2, LiNi 0,8 Co 0,15 Al 0,05 O2, LiNi x Co1-x O2 (0 < x < 1), LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiMnO2, a Li-Mn spinel substituted with various elements, lithium titanate, lithium metal phosphate, LiCoN, Li2SiO3 and Li4SiO4, a transition metal oxide, TiS2, Si, SiO2, a Si alloy, and an intermetallic lithium storage compound, but are not limited to these. Examples of a spinel substituted with various elements include LiMn 1,5 Ni 0,5 O4, LiMn 1,5 Al 0,5 O4, LiMn 1,5 Mg 0,5 O 4, LiMn 1,5 Co 0,5 O 4, LiMn 1,5 Fe 0,5 O4 and LiMn 1,5 Zn 0,5 O4, but are not limited to these. Examples of lithium titanate include Li4Ti5O 12Examples of a lithium metal phosphate include, but are not limited to, LiFePO4, LiMnPO4, LiCoPO4, and LiNiPO4. Examples of a transition metal oxide include, but are not limited to, V2O5 and MoO3. Examples of a lithium storage compound include, but are not limited to, Mg2Sn, Mg2Ge, Mg2Sb, and Cu3Sb.

[0079] Examples of a lithium alloy include, but are not limited to, 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 a Si alloy include, but are not limited to, an alloy of Si and a metal such as Li, and an alloy of Si and at least one type of metal selected from the group consisting of Sn, Ge, and Al.

[0080] The shape of the cathode active material is not particularly limited. It can be particulate. If the cathode active material is in particulate form, the cathode active materials can be primary particles or secondary particles. The average particle diameter (D50) of the cathode active material can be 1 nm or more and 100 μm or less, or can be, for example, 10 nm or more and 30 μm or less.

[0081] A covering layer containing a lithium-ion-conducting oxide can be formed on the surface of the cathode active material. This can suppress a reaction between the cathode active material and the solid electrolyte.

[0082] Examples of a Li-ion conductive oxide include LiNbO3, Li4Ti5O 12and Li3PO4, but are not limited thereto. The thickness of the capping layer is, for example, 0.1 nm or more, and may be 1 nm or more. On the other hand, the thickness of the capping layer is, for example, 100 nm or less, and may be 20 nm or less. The coating rate of the capping layer on the surface of the cathode active material is, for example, 70% or more, and may be 90% or more.

[0083] Examples of a solid electrolyte include, but are not limited to, those exemplified below under [Solid Electrolyte Layer].

[0084] The amount of solid electrolyte contained in the cathode layer is not particularly limited. It can, for example, range from 1 wt% to 80 wt% of the total mass (100 wt%) of the cathode layer.

[0085] A known material such as a carbon material and metal particles can be used as the conductive material. Examples of the carbon material include, but are not limited to, at least one selected from the group consisting of acetylene black, furnace black, VGCF, carbon nanotubes, and carbon nanofibers. Among them, at least one selected from the group consisting of VGCF, carbon nanotubes, and carbon nanofibers can be used from the viewpoint of electronic conductivity. Examples of the metal particles include, but are not limited to, Ni, Cu, Fe, and stainless steel (SUS).

[0086] The amount of conductive material contained in the cathode layer is not particularly limited.

[0087] Examples of binders include acrylonitrile butadiene rubber (ABK), butadiene rubber (BK), polyvinylidene fluoride (PVdF), and styrene butadiene rubber (SBK). The amount of binder contained in the cathode layer is not particularly limited.

[0088] The thickness of the cathode layer is not particularly limited.

[0089] The cathode layer can be formed by a well-known method.

[0090] For example, the cathode active material and, if necessary, other components are added to a solvent and stirred to prepare a slurry for a cathode layer, the cathode layer slurry is coated on a surface of a support such as a cathode current collector, and the coated slurry is dried, thereby obtaining the cathode layer.

[0091] Examples of a solvent include, but are not limited to, butyl acetate, butyl butyrate, heptane, and N-methyl-2-pyrrolidone (NMP).

[0092] The method for applying the cathode layer slurry to a surface of the substrate, such as the cathode current collector, is not particularly limited. Examples of the method include, but are not limited to, a doctor blade method, a metal mask printing method, a static coating method, a dip coating method, a spread coating method, a roll coating method, a gravure coating method, and a screen printing method.

[0093] As a support, a support with self-supporting properties can be appropriately selected and used without any special restrictions. For example, a metal foil such as Cu and Al can be used.

[0094] As another method for forming the cathode layer, the cathode layer can be formed by compression molding a cathode mixed powder containing the cathode active material and other components if necessary. During compression molding of the cathode mixed powder, a compression pressure of approximately 1 MPa or more and 600 MPa or less is generally applied.

[0095] The method for applying the pressure is not particularly limited. Examples of the method include, but are not limited to, a method for applying the pressure using a platen press, a roller press, or the like. [Cathode current collector]

[0096] A known metal that can be used as a current collector of a battery can be used as the cathode current collector. Examples of a metal include, but are not limited to, a metal material containing one or more elements selected from the group consisting of Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Co, Cr, Zn, Ge, and In. Examples of a cathode current collector include, but are not limited to, stainless steel (SUS), aluminum, nickel, iron, titanium, and carbon.

[0097] The shape of the cathode current collector is not particularly limited. Examples of shapes include, but are not limited to, various shapes such as foil and mesh. The thickness of the cathode current collector varies depending on the shape. For example, it can be in a range of 1 µm to 50 µm or in a range of 5 µm to 20 µm.

[0098] The cathode current collector may be connected to the cathode terminal. The cathode current collector may be the cathode terminal. [Anode]

[0099] The anode comprises an anode layer. If necessary, it includes an anode current collector. An anode terminal can be connected to the anode. The anode current collector can be the anode terminal.

[0100] The anode comprises the facing part and the non-facing part. The facing part is an area facing the cathode (i.e., the cathode-facing part), and the non-facing part is an area not facing the cathode (i.e., the non-cathode-facing part). Accordingly, in a top view of the battery, the area of ​​the anode is larger than that of the cathode.

[0101] The ratio ΔC between the area of ​​the facing part and the area of ​​the non-facing part (ie, the area of ​​the facing part / the area of ​​the non-facing part) is not particularly limited. [anode layer]

[0102] The anode layer contains at least one anode active material. If necessary, it contains an electrically conductive material, a binder, a solid electrolyte, etc.

[0103] Examples of anode active material include, but are not limited to, lithium metal (Li) and lithium alloys. As long as the anode active material of the anode layer contains lithium metal or lithium alloys as the main component, the anode layer may contain another well-known anode active material. In the disclosed embodiments, a main component means a component of 50 wt% or more of the total mass (100 wt%) of the anode layer of a fully charged all-solid-state battery. Examples of known anode active materials include graphite, mesocarbon microbeads (MCMB), highly oriented pyrolytic graphite (HOPG), hard carbon, soft carbon, elemental Si, a Si alloy, and Li4Ti5O. 12(LTO), but are not limited to these. The materials exemplified above as cathode active materials can be used as lithium alloy and Si alloy.

[0104] The shape of the anode active material is not particularly limited. Examples of the shape include, but are not limited to, particle and plate shapes. If the anode active material is in particle form, the anode active material can be primary particles or secondary particles. The average particle diameter (D50) of the anode active material can be 1 nm or more and 100 μm or less, or, for example, 10 nm or more and 30 μm or less.

[0105] The electrically conductive material and binder used in the anode layer can be the same as those used above in the cathode layer. As the solid electrolyte used in the anode layer, the solid electrolyte exemplified below as the solid electrolyte used in the solid electrolyte layer can be used.

[0106] There are no particular restrictions on the thickness of the anode layer. For example, it can be between 10 µm and 100 µm.

[0107] The amount of anode active material contained in the anode layer is not particularly limited. It can range, for example, from 20 wt% to 90 wt%. [anode current collector]

[0108] The material for the anode current collector can be a material that is not alloyed with Li, such as stainless steel (SUS), Cu, and Ni. Examples of the shape of the anode current collector include, but are not limited to, a foil shape and a plate shape. Examples of the shape of the anode current collector in plan view include, but are not limited to, a circular shape, an ellipse shape, a rectangular shape, and any polygonal shape. The thickness of the anode current collector varies depending on the shape. For example, it may be in a range of 1 μm to 50 μm, or it may be in a range of 5 μm to 20 μm.

[0109] The anode current collector may be connected to the anode terminal. The anode current collector may be the anode terminal. [Solid electrolyte layer]

[0110] The solid electrolyte layer contains at least one solid electrolyte.

[0111] As the solid electrolyte in the solid electrolyte layer, a generally known solid electrolyte suitable for all-solid-state batteries, such as an oxide-based solid electrolyte or a sulfide-based solid electrolyte, can be suitably used.

[0112] Examples of a sulfide-based solid electrolyte include, but are not limited to, Li2S-P2S5, Li2S-SiS2, LiX-Li2S-SiS2, LiX-Li2S-P2S5, LiX-Li2O-Li2S-P2S5, LiX-Li2S-P2O5, LiX-Li3PO4-P2S5, and Li3PS4. Note that the term "Li2S-P2S" refers to a material composed of a raw material composition including Li2S and P2S5, and the same applies to other names. Furthermore, "X" of the LiX described above represents a halogen element. The raw material may contain one, two, or more types of LiX. When two or more types of LiX are included, the mixing ratio of the two or more types of LiX is not particularly limited.

[0113] The molar ratio of the elements in the sulfide-based solid electrolyte can be controlled by adjusting the amounts of the elements in the starting material. Furthermore, the molar ratio and composition of the elements in the sulfide-based solid electrolyte can be measured, for example, by ICP emission spectrometry.

[0114] The sulfide-based solid electrolyte can be a sulfide glass, a crystalline sulfide glass (glass-ceramic), or a crystalline material obtained by a solid-phase reaction treatment of the starting material.

[0115] The crystal state of the sulfide-based solid electrolyte can be obtained, for example, by powder X-ray diffraction measurement using CuK∝ radiation on the sulfide-based solid electrolyte.

[0116] The sulfide glass can be obtained by amorphizing the starting material, such as a mixture of Li2S and P2S5. Examples of amorphizing treatments include, but are not limited to, mechanical grinding.

[0117] A glass-ceramic can be obtained, for example, by heat treatment of a sulfide glass.

[0118] The heat treatment temperature can be higher than the crystallization temperature (Tc) determined by thermoanalytical measurement of the sulfide glass, and is generally 195 °C or higher. On the other hand, the upper limit of the heat treatment temperature is not particularly limited.

[0119] The crystallization temperature (Tc) of the sulfide glass can be measured by differential thermal analysis (DTA).

[0120] The heat treatment time is not particularly limited as long as the desired crystallinity of the glass-ceramic is maintained. For example, it ranges from one minute to 24 hours, and it can range from one minute to 10 hours.

[0121] The heat treatment method is not limited in any way. Examples of heat treatment methods include, but are not limited to, a heat treatment method using a kiln.

[0122] Examples of an oxide-based solid electrolyte include, but are not limited to, a substance with a garnet-type crystal structure containing, for example, a Li element, a La element, an A element (A is at least one of Zr, Nb, Ta, and Al), or an O element. The oxide-based solid electrolyte may, for example, contain Li 3+x PO 4-x N x (1 ≤ x ≤ 3).

[0123] The shape of the solid electrolyte can be a particle shape from the point of view of good handling.

[0124] The average particle diameter (D50) of the solid electrolyte particles is not specifically limited. The lower limit of the average particle diameter can be 0.5 µm or more, and the upper limit can be 2 µm or less.

[0125] In the disclosed embodiments, the average particle diameter is the value of a volume-based mean diameter (D50) measured by laser diffraction and scattering particle size distribution measurement, unless otherwise stated. In the disclosed embodiments, the median diameter (D50) is a diameter (volume-based average diameter) such that the cumulative volume of the particles is half (50%) of the total volume when the particles are arranged in order from smallest to largest particle diameter.

[0126] The solid electrolyte can be one type or two or more types of solid electrolytes. When two or more types of solid electrolytes are used, they can be mixed together or formed in layers to obtain a multilayer structure.

[0127] The amount of solid electrolyte in the solid electrolyte layer is not particularly limited. For example, it may be 50 wt% or more, may be within a range of 60 wt% or more and 100 wt% or less, may be within a range of 70 wt% or more and 100 wt% or less, or may be 100 wt%.

[0128] For example, to increase plasticity, a binder may also be included in the solid electrolyte layer. Examples of a binder include, but are not limited to, the materials used above as binders in the cathode layer. However, from the viewpoint of preventing excessive aggregation of the solid electrolyte and enabling the formation of the solid electrolyte layer in which the solid electrolyte is uniformly dispersed, thus facilitating high output, the binder content in the solid electrolyte layer may be 5 wt% or less.

[0129] Examples of the method for forming the solid electrolyte include compression molding of a solid electrolyte material powder containing a solid electrolyte. When compression molding the solid electrolyte powder, a compression pressure of about 1 MPa or more and 600 MPa or less is generally applied.

[0130] The method for applying pressure is not particularly limited. Examples of the method include the method for applying pressure during the formation of the cathode layer described above.

[0131] There are no specific restrictions on the thickness of the solid electrolyte layer. It is generally 0.1 µm or more and 1 mm or less.

[0132] If necessary, the solid-state lithium secondary battery includes an outer casing to accommodate the cathode layer, the anode layer, the solid electrolyte layer, etc.

[0133] The material for the outer casing is not particularly limited, as long as it is an electrolyte-stable material. Examples of materials include, but are not limited to, resins such as polypropylene, polyethylene, and acrylic resin.

[0134] Examples of the shape of the all-solid-state lithium secondary battery include, but are not limited to, a coin shape, a laminate shape, a cylindrical shape, and a square shape.

Claims

[1] A battery system comprising a control unit and a solid-state lithium secondary battery comprising a cathode, an anode and a solid electrolyte layer disposed between the cathode and the anode, wherein the cathode comprises a cathode layer; wherein the cathode layer comprises a cathode active material; wherein the anode comprises a facing part and a non-facing part, the facing part being a region facing the cathode, and the non-facing part being a region not facing the cathode, wherein the control unit estimates a cathode end part potential Ve2 from a stress relaxation amount ΔV2, the cathode end part potential Ve2 is a local potential of the end part of the cathode, and the stress relaxation amount ΔV2 is generated by diffusion of lithium, which has been transferred in a charged state from the cathode of the all-solid-state lithium secondary battery into the facing part of the anode, into the non-facing part of the anode, and wherein the control unit controls the execution and non-execution of charging of the solid-state lithium secondary battery such that the cathode end-part potential Ve2 is less than or equal to a potential Vlimit at which a change in the crystal structure of the cathode active material occurs. [2] Battery system according to claim 1, wherein the control unit detects a voltage V1 of the solid-state lithium secondary battery and calculates from the voltage V1 a cathode end part potential Ve1, which is a local potential of the end part of the cathode, wherein the control unit determines whether at the voltage V1 the cathode end potential Ve1 is less than or equal to the potential Vlimit or not, wherein, if it has been determined that at the voltage V1 the cathode end potential Ve1 is less than or equal to the potential Vlimit, the control unit sets the voltage at which the cathode end potential Ve1 is equal to the potential Vlimit to a first charge interruption voltage, and the control unit carries out a first charge by which the solid-state lithium secondary battery is charged until the first charge interruption voltage is reached, wherein the control unit suspends the charging and discharging of the solid-state lithium secondary battery for a certain period of time after the first charging, wherein the control unit measures the voltage relaxation amount ΔV2, estimates the cathode end potential Ve2 from the voltage relaxation amount ΔV2 and corrects the cathode end potential Ve1 to the cathode end potential Ve2, wherein the control unit detects a voltage V2 of the solid-state lithium secondary battery and determines whether or not the voltage V2 is a voltage at which the cathode end potential Ve2 is less than or equal to the potential Vlimit, and wherein, when it is determined that the voltage V2 is the voltage at which the cathode end partial potential Ve2 is less than or equal to the potential Vlimit, the control unit sets the voltage at which the cathode end partial potential Ve2 is equal to the potential Vlimit to a second charge interruption voltage, and the control unit performs a second charging by which the all-solid-state lithium secondary battery is charged until the second charge interruption voltage is reached. [3] Battery system according to claim 2, wherein the control unit discharges the solid-state lithium secondary battery after the second charging, wherein the control unit detects a voltage V3 of the solid-state lithium secondary battery, wherein the control unit determines whether the voltage V3 is a voltage at which the cathode end part potential Ve2 is smaller than the potential Vlimit or not, and wherein, if it is determined that the voltage V3 is the voltage at which the cathode end potential Ve2 is less than the potential Vlimit, the control unit resets the settings of the first and second charge interruption voltages.

Images