JP2018206739A - Power storage device - Google Patents

Abstract

To suppress unevenness in a formation mode of a coating film and provide means for shortening a manufacturing time of a secondary battery.SOLUTION: There is provided a power storage device 1 including a secondary battery 50, power storage means 10, gas generation detection means 20, a first charge control unit 31, a second charge control unit 32, a third charge control unit 33, a first determination unit 34, and a second determination unit 35. There is provided a method of shortening a manufacturing time in which the following charge control is performed in order to shorten the manufacturing time. When the first charge control unit 31 carries out the 1C charging, the first determination unit 34 determines formation of a film on the surface of a negative electrode by the gas generation detection means 20, and the second charge control unit 32 reduces the charge rate with respect to 1C on the basis of the determination result. The second determination unit 35 reduces unevenness of the coating by again increasing the charge rate reduced by the third charge control unit 33 when it is determined by the gas generation detection means 20 that the film is no longer formed on the surface of the negative electrode.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power storage device that can be suitably charged in an equipped nonaqueous electrolyte secondary battery.

  Non-aqueous electrolyte secondary batteries, typified by lithium secondary batteries, are lighter and have higher energy density than existing batteries. So-called portable power sources such as personal computers and portable terminals, vehicle drive power sources, and residential power storage It is used as a device. Particularly in recent years, non-aqueous electrolytes have been used as high-output power sources for driving vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV) that charge and discharge at a high capacity and high rate. Secondary batteries are preferably used.

  When charging the secondary battery, it is known that an SEI film (Solid-Electrolyte Interface) is formed on the surface of the negative electrode. For example, when the negative electrode active material of a lithium ion secondary battery is a carbon-based material, the electrolyte component is easily decomposed at a predetermined potential or higher because of its high reactivity. The decomposed electrolyte component is deposited as a film on the surface of the negative electrode active material. This coating stabilizes and inactivates the surface of the carbon-based material and suppresses further decomposition of the electrolyte component. Therefore, for the purpose of forming a good-quality film with the negative electrode, a compound that forms a film by reductive decomposition during charging is also added to the non-aqueous electrolyte (see, for example, Patent Document 1). In this case, the coating is considered to be constituted by a reaction product of the electrolytic solution component and the above compound.

Such electrolyte components and compounds (hereinafter simply referred to as “film forming agent”) form a film during the initial charging of the secondary battery. Therefore, when manufacturing the secondary battery, a predetermined charging process is performed on the assembled battery, and an initial charging process is performed in which the battery is activated and an appropriate film is formed on the surface of the negative electrode. In the initial charging, gas such as H ₂ and CO is generated in the battery case as the film forming agent is decomposed. Further, it is known that the charging current (charging rate) in the initial charging is preferably suppressed to about 1 C or less because a more uniform SEI film can be formed. However, from the viewpoint of shortening the manufacturing time, it is desirable to complete the initial charging process in a short time. Therefore, for example, Patent Document 2 discloses that initial charging is performed at a high charging rate of 1.4 C or more and 6 C or less, and at least one minute rest period is provided in a voltage range in which the SEI film is formed on the negative electrode surface. ing. Thereby, it is described that the shortening of the initial charging time and the formation of a high-quality SEI film are possible.

Japanese Patent Laying-Open No. 2015-176771 Japanese Patent Laid-Open No. 2006-015280 JP 2014-044929 A

However, according to the study by the present inventors, there is a problem that even in the charging mode of Patent Document 2 described above, unevenness is likely to occur in the coating mode as compared with the case of charging at a low charging rate of 1C or less. It was.
The present invention was created in order to solve such a conventional problem, and its purpose is to suppress the occurrence of unevenness in the formation mode of the film and to charge the secondary battery in a shorter time. It is to provide a power storage device that can be used.

  In order to solve the above problems, a power storage device is provided by the present invention. The power storage device includes a battery case, a secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte housed in the battery case, a power storage unit that charges the secondary battery, and the non-aqueous electrolysis by charging by the power storage unit. Gas generation detecting means configured to detect the generation of gas occurring in the liquid based on the acoustic emission method, and a first battery for charging the secondary battery at a first charge rate of a high rate exceeding 1C by the power storage means. Based on the detection result of the charge control unit and the gas generation detection unit, the first determination unit that determines that the coating is formed on the negative electrode surface, and the charging by the power storage unit when the first determination unit determines the formation of the coating Based on the detection result by the second charge control unit for reducing the rate from the first charge rate to the second charge rate lower than the first charge rate, and the gas generation detection means A second determination unit that determines that a film is no longer formed on the surface of the negative electrode; and when the second determination unit determines that a film is no longer formed, the charge rate by the power storage means is greater than the second charge rate from the second charge rate. And a third charge control unit that increases the third charge rate.

  According to the above configuration, the timing of occurrence of film formation unevenness on the negative electrode and the timing at which film formation unevenness on the negative electrode becomes difficult to occur are accurately detected by detecting gas generation in the secondary battery by the acoustic emission method. It can be detected instantly well. And at these timings, the charge rate of the secondary battery can be appropriately controlled. As a result, the time required for charging as a whole can be shortened while more precisely suppressing the occurrence of coating unevenness of the negative electrode in the secondary battery.

  In this specification, acoustic emission (AE) is also referred to as acoustic emission. For example, when a material is deformed or a crack is generated, elastic energy (AE) is stored in the material. This is a phenomenon that is released as a wave. The acoustic emission method is a method for evaluating the process of change of the material by detecting an elastic wave emitted by the acoustic emission as an electric signal by a sensor and performing signal processing or the like. The AE wave mainly has a high frequency component in an ultrasonic region of several tens kHz to several MHz. Hereinafter, “acoustic emission” is simply abbreviated as “AE”.

Note that Patent Document 3 discloses a secondary battery including an AE sensor. However, this Patent Document 3 is different from the present invention in that the AE method is used to grasp the cumulative amount of gas generated in the battery case when the secondary battery is used.
Further, in this specification, “1C” means a current rate at which discharge is completed in exactly one hour when a secondary battery having a nominal capacity value is discharged with constant current. Further, the discharge or charge rate means a relative ratio of current during discharge or charge to the battery capacity.

It is the schematic which shows the structure of the electrical storage apparatus which concerns on one Embodiment. It is the graph which illustrated the waveform of AE signal. It is the graph which illustrated the waveform when the AE signal value of Drawing 2A was squared. It is the graph which showed the mode of charge control by the electrical storage apparatus which concerns on one Embodiment. It is a graph which shows the relationship between charging time and AE energy at the time of performing charging control shown in FIG. It is a cross-sectional schematic diagram explaining the mode of the film formed in a negative electrode active material layer when it charges by (a) low rate or (b) high rate. It is the graph which showed the mode of charge control in a prior art.

  Hereinafter, a power storage device according to the present invention will be described based on a preferred embodiment with appropriate reference to the drawings. Note that matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention (for example, a secondary battery structure that does not characterize the present invention) are based on prior art in this field. It can be grasped as a design matter of a person skilled in the art. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. In addition, dimensional relationships (length, width, thickness, etc.) in the drawings shown below do not necessarily reflect actual dimensional relationships. In addition, the notation “X to Y” indicating a range in the present specification means “X or more and Y or less” unless otherwise specified.

  In battery manufacture, for example, initial charging is performed on the assembled secondary battery. In the initial charging step, the assembled secondary battery is charged up to its operating upper limit potential (charging upper limit potential). When charging the secondary battery to a predetermined potential, the present inventors have studied in detail the relationship between the coating mode formed on the negative electrode and the charging mode, and obtained the following knowledge. First, FIGS. 5A and 5B are schematic cross-sectional views illustrating the state of the negative electrode during film formation when the secondary battery is a lithium ion secondary battery. In the drawing, the granular material represents the negative electrode active material, the aggregate (combined body) of the negative electrode active material represents the negative electrode active material layer, and the thicker portion of the contour (surface) portion of the negative electrode active material represents the coating film. The negative electrode active material layer is bonded to the surface of the sheet-like negative electrode current collector. When the secondary battery is charged, if the negative electrode potential is equal to or higher than the decomposition potential of the film forming agent, a film as a decomposition product is formed on the surface of the negative electrode active material. In the case of low-rate charging with a low charging rate, as shown in FIG. 5A, lithium ions and a film-forming agent component (hereinafter sometimes referred to as lithium ions) are outside (surface) of the negative electrode active material layer. To the inside (current collector and its vicinity) to form a film with a substantially uniform thickness in the thickness direction of the negative electrode active material layer. As a result, the charge / discharge characteristics of lithium ions are uniform in the thickness direction of the negative electrode active material layer, and the internal resistance of the secondary battery can be kept low. However, in charging at a low rate, the charging time to the charging upper limit potential becomes long. Here, the low rate means charging at a charging rate of about 2C or less (typically 1C or less). Further, the initial charging is performed with a current of about 0.01 C to 1 C, for example.

On the other hand, when the battery is charged at a high rate with a high charge rate, the negative electrode potential quickly reaches the decomposition potential such as lithium ions. Further, when charging at a high rate, lithium ions and the like move to the negative electrode side instantaneously and in large quantities. And there exists a situation that the formation rate of the film in the surface of a negative electrode active material becomes quick, so that a charge rate becomes high. Therefore, as shown in FIG. 5B, a large amount of lithium ions and the like that have reached the surface of the negative electrode active material layer react with the electrolyte components and the like on the surface of the negative electrode active material in order from the arrival. Form. That is, lithium ions and the like accumulate at a high concentration near the surface of the negative electrode active material layer before penetrating into the internal region, and start to form a film. Although the negative electrode active material layer has a porous structure, the path (path) for movement of lithium ions and the like is narrower than other parts, and is closer to the current collector than the vicinity of the surface in the thickness direction of the negative electrode active material layer Penetration to the inner area is difficult. Therefore, when a film is formed in the vicinity of the surface, lithium ions and the like are more difficult to penetrate into the internal region. As a result, a thick film is formed on the surface of the negative electrode active material in the vicinity of the surface of the negative electrode active material layer. On the other hand, in the other part of the negative electrode active material layer, that is, in the internal region, the thickness of the film on the surface of the negative electrode active material is reduced or almost no film is formed. That is, it has been confirmed that unevenness occurs in the formation mode of the film in the thickness direction of the negative electrode active material layer.
The high rate means a charging rate higher than the low rate. Typically, it includes a charge rate exceeding 1C, for example, means a current of 1.4C or higher, preferably 1.5C or higher, more preferably 2C or higher, particularly preferably 4C or higher. Although there is no upper limit to the high rate current, for example, about 100 C or less can be used as a guide.

  The unevenness of the film formation form is due to high-rate charging. For example, in charging at a high rate exceeding 1 C, the voltage range in which the film is formed for each battery is narrowed down accurately and specifically. Have difficulty. Therefore, for example, even when the technique of Patent Document 1 is applied, it is difficult to appropriately determine the timing at which a minute charging pause period is to be provided. As a result, as shown in FIG. 6, even if a minute rest period is provided in the middle of high-rate charging, high-rate charge / discharge can be performed in the film formation potential range before and after that, so that in the thickness direction of the negative electrode active material layer It is considered that there is still room for improvement in reducing the formation unevenness of the film. Therefore, in the present invention, when charging a secondary battery using a power storage device, the timing of occurrence of uneven film formation at the negative electrode and the timing at which uneven formation of film at the negative electrode are less likely to occur are more accurately determined. Based on the detection result, charging is performed at a charging rate suitable for the state of film formation.

  FIG. 1 is a conceptual diagram illustrating a configuration of a power storage device 1 according to an embodiment. The power storage device 1 includes a power storage unit 10, a gas generation detection unit 20, a control unit 30, and a secondary battery 50. The control unit 30 includes a first charge control unit 31, a second charge control unit 32, a third charge control unit 33, a first determination unit 34, and a second determination unit 35. In addition, the power storage device 1 of this example includes a voltmeter 11 and an ammeter 12 in order to confirm a charging potential and a charging current.

  Here, first, the configuration of the secondary battery 50 to be charged will be briefly described. Although not specifically illustrated, the secondary battery 50 is hermetically sealed in a battery case 51 in which a laminated electrode body that is a power generation element and a non-aqueous electrolyte are accommodated. In the laminated electrode body, a plurality of positive plates including a positive electrode current collector and a positive electrode active material layer and a plurality of negative electrode plates including a negative electrode current collector and a negative electrode active material layer are opposed to each other via a separator. Are stacked alternately. The active material layer is usually provided on both sides of the end current collector. One positive electrode active material layer on one surface of one positive electrode plate and the negative electrode active material layer on one surface of one negative electrode plate are overlapped with each other through one separator, thereby generating one power generation element. Composed. And the laminated electrode body is comprised by laminating | stacking two or more of these elements in order. The non-aqueous electrolyte includes, for example, a non-aqueous solvent, a supporting salt (for example, a lithium salt) that dissolves in the non-aqueous solvent to generate a charge carrier, and a film forming additive as necessary. The non-aqueous electrolyte is impregnated in the positive electrode active material layer, the negative electrode active material layer, and the separator in the multilayer electrode body. Further, the nonaqueous electrolytic solution is present in the space between the laminated electrode body and the battery case 51 in addition to the one impregnated in the laminated electrode body.

The positive electrode active material layer includes a positive electrode active material. As the positive electrode active material, a lithium-containing compound that can occlude and release lithium ions and includes a lithium element and one or more transition metal elements can be preferably used. For example, a preferred example is a lithium transition metal oxide having a layered rock salt type or spinel type crystal structure. Specifically, the lithium transition metal oxide includes a lithium nickel composite oxide (for example, LiNiO ₂ ), a lithium cobalt composite oxide (for example, LiCoO ₂ ), a lithium manganese composite oxide (for example, LiMn ₂ O ₄ ), or It may be a ternary lithium-containing composite oxide such as lithium nickel cobalt manganese composite oxide (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ). As the positive electrode current collector, aluminum or an aluminum alloy is preferably used.

  The negative electrode active material layer includes a negative electrode active material. As the negative electrode active material, one or more of various materials such as a carbon-based material, an oxide-based material, an alloy material, and an amorphous material that can occlude and release lithium ions can be used. Typical examples of the negative electrode active material include carbon materials such as graphite, non-graphitizable carbon, graphitizable carbon, and carbon nanotubes. Specifically, natural graphite and amorphous carbon-coated graphite obtained by coating natural graphite with amorphous carbon are preferable. As the negative electrode current collector, copper or a copper alloy is preferably used. In addition, the technique disclosed here can form a film uniformly by the thickness direction of this negative electrode active material layer. Therefore, it can be particularly preferably applied to a secondary battery having a thick negative electrode active material layer. Such a battery is, for example, a battery having a relatively large capacity and / or a high output except for a small secondary battery having an average thickness of the negative electrode active material layer of about 5 μm or less (in other words, the average thickness of the negative electrode active material layer is about Battery exceeding 5 μm (for example, 10 μm or more). Typically, a large-capacity battery for in-vehicle use corresponds to this.

As the nonaqueous electrolytic solution, typically, a support salt (for example, a lithium salt in a lithium ion secondary battery) dissolved or dispersed in a nonaqueous solvent may be employed. As the non-aqueous solvent, one or more of various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones can be used without particular limitation. For example, specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). As the supporting salt, one type or two or more types can be appropriately selected and used from various types used in general non-aqueous electrolyte secondary batteries. For example, the use of lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N, LiCF ₃ SO ₃ is exemplified. The supporting salt is preferably prepared so that the concentration in the non-aqueous electrolyte is within the range of 0.7 mol / L to 1.3 mol / L.

  The film forming additive is not essential, but is preferably used for forming a stable secondary battery. Although the film-forming additive is contained in the non-aqueous electrolyte during the manufacture of the battery, it is typically a variety of materials that can be decomposed on the surface of the electrode (typically the negative electrode) to form a film during the initial charging step. These compounds can be used. That is, in the secondary battery after the initial charging, the film forming additive does not have the original form. The decomposition potential of the film forming additive is not particularly limited, but it is preferably lower than the nonaqueous solvent and decomposed before the nonaqueous solvent is decomposed. As a preferred example, the battery voltage at which the film starts to be formed is lithium bis (oxalato) borate (LiBOB), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), which is about 3.5 V to 4 V, based on lithium. Examples thereof include fluoroethylene carbonate (FEC).

  Each of the positive electrode current collector and the negative electrode current collector is provided with a tab for current collection (see FIG. 1). The tab of the positive electrode current collector is superimposed on one end of the electrode body, and the tab of the negative electrode current collector is superimposed on the other end of the electrode body so as to protrude. The battery case 51 includes a case main body having an opening for inserting the multilayer electrode body, and a sealing body sealing the opening of the case main body. The sealing body is provided with a positive external terminal and a negative external terminal that electrically connect the inside and the outside of the battery case 51. When the battery case 51 is placed on a horizontal surface so that the sealing body is on the upper surface, the laminated electrode body is accommodated in the battery case 51 so that the surface of the electrode plate is in the vertical direction and the tab is positioned above. . The tab of the positive electrode current collector is electrically connected to an external positive electrode terminal provided on the sealing body. The tab of the negative electrode current collector is electrically connected to an external negative electrode terminal provided on the sealing body. The secondary battery 50 is charged by supplying electric power from the outside through the positive external terminal and the negative external terminal. Further, the secondary battery 50 can supply electric power to the outside through the positive external terminal and the negative external terminal.

  The power storage means 10 is a device that charges the secondary battery 50. The power storage unit 10 includes a power generation unit (not shown) and a connection unit that can be electrically connected to each of the positive electrode external terminal and the negative electrode external terminal of the secondary battery 50. In addition, about the electric power generation part, self may be provided with the electric power generation function, and the structural member for mounting an external power supply or connecting to an external power supply may be sufficient as it. The power storage means 10 is connected to the control unit 30. The operation of the power storage unit 10 is controlled by the control unit 30.

  The gas generation detection unit 20 detects the generation of gas that occurs in the non-aqueous electrolyte in the secondary battery 50 due to charging by the power storage unit 10 based on the AE method. When the gas is generated, an elastic wave having minute energy is emitted from the secondary battery 50. The gas generation detection means 20 detects the elastic wave resulting from this gas generation. The gas generation detection means 20 includes an AE sensor 21 and an amplifier 22. The gas generation detection unit 20 is connected to the control unit 30. The operation of the gas generation detection unit 20 is controlled by the control unit 30.

  The AE sensor 21 receives the elastic wave based on the gas generation, converts the acoustic wave into an electrical signal as an acoustic emission signal (AE signal), and outputs the electrical signal. The AE sensor 21 is configured by a piezoelectric element that detects a voltage signal corresponding to the received pressing force. The AE sensor 21 used in this embodiment is a ceramic piezoelectric element made of lead zirconate titanate (PZT). The AE sensor 21 has high sensitivity to elastic vibration in the ultrasonic band of 10 to 2000 kHz. The AE sensor 21 can detect an elastic wave accompanying gas generation instantaneously and with high accuracy. The AE sensor 21 can be directly fixed to the surface of the battery case 51 of the secondary battery 50 or can be fixed to a holding member that holds the secondary battery 50. The amplifier 22 amplifies the output signal of the AE sensor 21 (hereinafter referred to as “AE signal”). The AE signal amplified by the amplifier 22 is sent to the control unit 30.

  The control unit 30 is electrically connected to the power storage means 10 and the gas generation detection means 20, respectively, and comprehensively controls the overall operation of the power storage device 1. The configuration of the control unit 30 is not particularly limited. The control unit 30 is, for example, a microcomputer. The configuration of the microcomputer hardware is not particularly limited. Although the hardware configuration of the microcomputer is not specifically shown, for example, an interface that enables transmission and reception of data with an external device, and a central processing unit (CPU) that executes instructions of a control program ROM (read only memory) storing a program executed by the CPU, RAM (random access memory) used as a working area for developing the program, memory for storing various data such as the program and modeling data, etc. And a storage unit. The control unit 30 can receive information on the secondary battery 50 from a host computer or the like via the interface, and can output a detection result by the gas generation detection means 20 or the like. The first charging control unit 31, the second charging control unit 32, the third charging control unit 33, the first determination unit 34, and the second determination unit 35 included in the control unit 30 are all independent of hardware (for example, Circuit), or may be configured to be functionally realized by the CPU executing a computer program.

  The first determination unit 34 determines that a film is formed on the negative electrode surface of the secondary battery 50 based on the AE signal sent from the gas generation detection unit 20. The second determination unit 35 determines that no coating is formed on the negative electrode surface of the secondary battery 50 based on the AE signal sent from the gas generation detection unit 20. When the potential of the negative electrode becomes equal to or higher than the decomposition potential of the electrolyte and the film forming agent due to charging, the electrolyte and the film forming agent are decomposed to form a film. Formation of this film is accompanied by gas generation. Further, when the decomposition of all the film forming agents is completed by charging, no further film is formed and the generation of gas is stopped. Therefore, it can be determined whether or not the formation of the coating is proceeding based on the presence or absence of gas generation. From this, the 1st judgment part 34 can judge that the film was formed in the negative electrode surface with gas having generate | occur | produced inside a secondary battery based on AE signal. In addition, the second determination unit 35 forms a film on the negative electrode surface when the first determination unit 34 determines the formation of the film and the generation of gas inside the secondary battery is completed based on the AE signal. It can be judged that it was not done.

  Here, the AE signal will be briefly described. FIG. 2A is a graph in which the horizontal axis is time [μs] and the vertical axis is the value [V] of the AE signal. The vertical axis in FIG. 2A has a zero point at the center. The AE signal generated by the secondary battery 50 is almost zero or noise during the “normal period” in which bubbles are not generated due to gas generation. This is because charging / discharging of the secondary battery 50 is an electrochemical reaction and does not involve mechanical movement. However, when gas is generated in the secondary battery 50 and bubbles are generated, strain energy generated in the system due to this event is released as an elastic wave. When the gas generation detection means 20 detects this elastic wave, the value of the AE signal is larger than the normal period. For example, as shown in FIG. 2A, when the generation of one bubble is completed, the AE signal returns to the normal period again. In the present specification, the generation of one bubble is referred to as “one event”. For example, the amplitude time (duration) of the elastic wave with the occurrence of bubbles in the secondary battery as one event is, for example, about 1 microsecond to 4 microseconds. T1 on the vertical axis in FIG. 2A is a threshold value for identifying whether or not a target event has occurred. Since the elastic waveform may be considered to be symmetrical in a substantially positive / negative region, the threshold value T1 is provided only for positive signals in this example. Therefore, it can be determined that bubbles are generated when a signal that is smaller than the threshold T1 becomes larger than the threshold T1 as the AE signal. Moreover, it can be determined that the generation of bubbles has ended when a signal that is larger than the threshold T1 becomes smaller than the threshold T1 as the AE signal.

  Note that noise may be included in the AE signal. In general, bubbles are not only generated one by one but can be simultaneously generated. When a plurality of bubbles are generated, a waveform corresponding to one event in FIG. 2A is superimposed at each bubble generation timing, and the signal value increases. Therefore, the threshold value T1 may be set higher than the threshold value for detecting the occurrence of one bubble in order to determine that bubbles are generated reliably instead of noise. The absolute value of the threshold value T1 is appropriately set based on the accuracy of the AE sensor 21 so that the normal period and the period in which the event to be detected occurs can be properly distinguished in the waveform amplified by the amplifier 22 or the like. can do. Alternatively, when one signal (peak) whose AE signal exceeds the threshold value T1 is measured and the number of AE signals counted within a predetermined time exceeds the threshold value T2, bubbles are generated, that is, a film is formed. It may be determined that

Further, the AE signal can basically be converted into an energy value by squaring the voltage value. FIG. 2B shows the calculation of the square value [V ² ] of the AE signal value in FIG. 2A, that is, the energy value. Here, only the result for the region corresponding to one event where the AE signal is higher than the threshold value T1 in FIG. 2A is shown. Such an energy value of the AE signal makes it possible to more accurately and easily distinguish the normal period from the period in which the event to be detected occurs. For example, it is possible to determine the occurrence and end of bubbles by setting the threshold value T1 as having a higher frequency (here, the square value). Therefore, the generation and termination of bubbles based on the AE signal may be performed using the square value (energy value) of the AE signal. In other words, when the film is formed (becomes formed) on the negative electrode surface and when the film is not formed on the negative electrode surface, the square value (energy value) of the AE signal is used. You may judge. The calculation for these determinations may be performed by each of the first determination unit 34 and the second determination unit 35, or an AE signal processing unit (not shown) that processes the AE signal is provided separately. You may go.

  FIG. 3 is a graph in which the horizontal axis represents the charging time when the secondary battery 50 is charged by the power storage means 10, and the vertical axis represents the voltage [V] of the secondary battery 50. In this graph, t0 is the time when charging by the power storage means 10 is started. In addition, after the start of charging by the power storage means 10, the time when the first determination unit 34 determines that a film is formed (hereinafter referred to as the start of film formation) is set to t1. Then, after the film formation start time t1, the time when the second determination unit 35 determines that the film is no longer formed (hereinafter referred to as the film formation end time) is t2.

  A region indicated by I on the vertical axis in FIG. 3 is a period (t0 to t1) from when charging is started until a film is formed on the negative electrode. A region indicated by II on the vertical axis is a film formation period (t1 to t2) from when the film starts to be formed on the negative electrode to when the film formation is completed. A region indicated by III on the vertical axis is a period (t2) after the formation of the film on the negative electrode is completed. In regions I and III, no coating is formed. Therefore, there is no need to worry about uneven formation of the film in the thickness direction of the negative electrode active material layer. Therefore, the power storage device 1 can charge the secondary battery 50 at a high rate during the period from t0 to t1 which is the region I and the period after t2 which is the region III. On the other hand, a film is formed in region II. Therefore, the power storage device 1 is preferably charged at a charging rate that does not cause uneven coating formation in the thickness direction of the negative electrode active material layer. Therefore, the power storage device 1 can charge the secondary battery 50 at a charging rate that does not cause uneven coating formation during the period from t1 to t2 in the region II. The control unit 30 controls driving of the power storage means 10 so as to realize such charging.

  Specifically, first, the first charge control unit 31 is electrically connected to the power storage unit 10. The first charge control unit 31 controls the operation of the power storage unit 10. The first charge control unit 31 instructs the power storage means 10 to charge the secondary battery 50 at a high charge rate exceeding 1C. The first charging rate may be a value set in advance by the user. In the present embodiment, the first charging rate is 4C. Thereby, the electrical storage means 10 starts high-rate charging of the secondary battery 50 at the first charging rate.

  The second charge control unit 32 is electrically connected to the power storage means 10. The second charge control unit 32 controls the operation of the power storage unit 10. The second charging control unit 32 reduces the charging rate by the power storage means 10 from the first charging rate to the second charging rate at the coating formation start time t1 when the first determination unit 34 determines the formation of the coating. The second charge rate is a current value lower than the first charge rate. Thereby, the electrical storage means 10 switches to 2nd charge and charges the secondary battery 50 based on the instruction | indication of the 2nd charge control part 32 after the film formation start time t1. The second charging rate may be, for example, an arbitrary low rate that is predetermined at 2C or less. In the present embodiment, the second charge rate is set to 0.8C in advance. Thereby, the electrical storage means 10 starts low-rate charging of the secondary battery 50 at the second charging rate.

  The third charge control unit 33 is electrically connected to the power storage means 10. The third charging control unit 33 controls the operation of the power storage unit 10. The third charging control unit 33 increases the charging rate by the power storage means 10 from the second charging rate to the third charging rate at the end of film formation t2 when the second determination unit 35 determines that the coating is no longer formed. The third charging rate is a current value higher than the second charging rate. Thereby, the power storage means 10 charges the secondary battery 50 at the third charge rate based on the instruction from the third charge control unit 33 after the film formation end time t2. The third charging rate is not particularly limited as long as it exceeds 1C and is higher than the low rate. The third charging rate is, for example, 1.4C or higher, preferably 2C or higher (exceeding 2C), and may be an arbitrary high rate determined in advance in a range of, for example, about 6C or lower. In the present embodiment, the third charging rate is set to 4C in advance. Note that the third charging rate may be the same rate as the first charging rate or a rate different from the first charging rate, for example.

  According to the power storage device 1, charging can be performed while forming a good film on the secondary battery 50 in a short time by the following procedure. That is, first, the positive electrode connection portion and the negative electrode connection portion of the power storage device 1 are connected to the external positive electrode terminal and the external negative electrode terminal of the assembled secondary battery 50. Further, the AE sensor 21 of the gas generation detection means 20 is attached to the outer surface of the battery case 51 of the secondary battery 50. The AE sensor 21 is preferably attached to the approximate center of the widest surface of the flat rectangular battery case 51 so that the receiving surface is parallel to the electrode surface and located at the center of the electrode surface. Then, while the AE sensor 21 detects the AE signal generated in the secondary battery 50, charging of the secondary battery 50 is started by the power storage means 10. In this example, as shown in FIG. 3, the first charge control unit 31 starts charging at the charging start time t <b> 0 as 4 C high rate constant current charging as described above. Thereby, a large amount of lithium ions and the like contained in the electrolyte solution impregnated in the laminated electrode body of the secondary battery 50 starts moving from the positive electrode active material layer side toward the negative electrode active material layer. To do.

  FIG. 4 is a graph showing the AE energy obtained by amplifying the AE signal detected by the AE sensor 21 when the secondary battery is charged by the charging control shown in FIG. As shown in FIG. 4, the gas generation detection means 20 did not detect an AE signal exceeding the threshold T1 for a while from the time t0. The gas generation detection means 20 detected the AE signal at time t1. Thus, the first determination unit 34 determines that the potential of the secondary battery 50 has reached the film formation potential due to charging by the power storage device 1 and a film has started to be formed on the surface of the negative electrode. Then, the 2nd charge control part 32 controls the electrical storage means 10 so that the charge rate by the electrical storage means 10 may be reduced from 4C (1st charge rate) to low rate constant current charge of 0.8C (2nd charge rate). To do. The power storage means 10 starts charging at the second charging rate from time t1. This can reduce the rate at which a film is formed on the surface of the negative electrode. In the meantime, lithium ions and the like can sufficiently penetrate into the negative electrode active material layer. As a result, a coating derived from the decomposition product of the electrolyte is formed on the surface of the negative electrode active material constituting the negative electrode active material layer. This coating is formed so that the thickness is uniform in the thickness direction of the negative electrode active material layer.

  When the potential of the secondary battery 50 exceeds the film formation start potential, a large amount of film starts to be formed in the secondary battery 50. As a result, as shown in FIG. 4, the AE energy rapidly increases after the film formation start time t1. Thereafter, as the charging time elapses, the film-forming agent and the like continue to be decomposed, and the concentration in the non-aqueous electrolyte solution decreases. And the formation frequency of a film reduces. Along with this, the AE energy gradually decreases. At time t2, the gas generation detection unit 20 does not detect the AE signal. Thereby, the second determination unit 35 determines that the film is not formed on the surface of the negative electrode due to the charging by the power storage device 1. Then, the 3rd charge control part 33 controls the electrical storage means 10 so that the charge rate by the electrical storage means 10 may be increased from 0.8C (2nd charge rate) to the high rate constant current charge of 4C (3rd charge rate). To do. The power storage means 10 starts charging at the third charging rate from time t2. As a result, charging at a high rate can be started again. Note that the third charging rate can be appropriately set to a value higher than the second charging rate in consideration of the state of charge (SOC) of the secondary battery 50. At this time, it is preferable to set the third charging rate within a range in which lithium ions do not precipitate. This is because when the formation of the film is completed (t2), the SOC of the secondary battery may be in a high state to some extent. This is because, in such an SOC state, when the charge rate is set to a significantly high value (for example, 100 C), lithium ions accumulate at a high concentration on the surface of the negative electrode active material layer and metal lithium may be deposited. For example, the third charging rate may be 80C or lower, preferably 60C or lower, more preferably 40C or lower, for example 20C or lower, although it depends on the battery procedure and configuration. Further, the potential of the secondary battery 50 in FIG. 3 reaches the upper limit of the film formation potential range at time t2. The third charging control unit 33 performs charging by the power storage means 10 at the third charging rate after the time t2, for example, until the charging upper limit potential of the predetermined secondary battery 50 is reached (for example, 4.3 V based on lithium). To do.

  According to the above configuration, the power storage device 1 can charge the secondary battery 50 at a high rate in a voltage range in which a film can be formed on the surface of the negative electrode and at a high rate in other voltage ranges. This can reduce the film formation rate when a film is formed on the negative electrode, and can promote the penetration of lithium ions and the like into the internal region of the negative electrode active material layer. As a result, the thickness of the film formed on the surface of the active material can be made uniform in the thickness direction of the negative electrode active material layer. Further, the gas generation detection means 20 provided in the power storage device 1 can detect the generation of gas instantaneously and with high accuracy based on the AE method. Thereby, the charging time at the low rate can be shortened as much as possible, and the charging time can be effectively shortened as a whole.

  In the above embodiment, the charging rate is switched from the first charging rate to the second charging rate at time t1. That is, the reduction from the first charging rate to the second charging rate was performed at a time (in one step). However, the reduction from the first charge rate to the second charge rate need not be performed in one step. For example, specifically, the first charging rate may be gradually decreased in multiple stages while confirming the state of gas generation in the secondary battery 50 detected by the gas generation detection unit 20. In this case, when the gas generation detection unit 20 detects the gas generation in the secondary battery 50, the second charge control unit 32 is, for example, a second lower than the first charge rate by a predetermined decrease “−ΔC1”. Charge at the charge rate. If the gas generation detection unit 20 still detects gas generation in the secondary battery 50 after the predetermined time “Δt”, for example, the second charge control unit 32 sets the second charge rate to the first charge rate. Replace with 1 charge rate. Then, the second charge control unit 32 charges again at a second charge rate that is lower than the replaced first charge rate by a predetermined decrease “−ΔC1”. This can be continued until the gas generation detection means 20 no longer detects gas generation in the secondary battery 50 after a predetermined time “Δt1”. Alternatively, this can be continued until the second charge rate reaches a preset minimum low rate. When the second charging rate becomes the lowest low rate, the second charging rate may be fixed to the lowest low rate. Thereby, as soon as a film is formed, a charge rate can be reduced. In addition, a second charging rate suitable for the target secondary battery 50 can be adopted, and charging at an excessively low rate or charging at a rate that is not sufficiently reduced in the film formation potential range. Can be suppressed. The size of “−ΔC1” is not particularly limited. For example, “−ΔC1” is preferably −1C or more, more preferably −2C or more, and particularly preferably −3C or more. In addition, “−ΔC1” can be −5C or less, can be −4C or less, and can be −4.5C or less. Further, “Δt1” can be set to about 5 to 50 microseconds.

  In the above embodiment, the charging rate is switched from the second charging rate to the third charging rate at time t2. That is, the increase from the second charge rate to the third charge rate was performed at a time (in one step). However, the increase from the second charge rate to the third charge rate need not be performed in one step. For example, specifically, the third charge control unit 33 may increase the second charge rate while confirming the presence or absence of gas generation in the secondary battery 50 detected by the gas generation detection unit 20. . This is because, even when it is determined that the generation of gas in the secondary battery 50 is temporarily stopped, it is considered that the gas starts to be generated again after that. In this case, the third charge control unit 33 may preset the increment from the second charge rate to the third charge rate, for example, as “ΔC2”. Thereby, as soon as it is determined that the formation of the coating has been completed, the charge rate can be increased. The size of “ΔC2” is not particularly limited. For example, “ΔC2” is preferably 1C or more, more preferably 2C or more, and particularly preferably 3C or more. Further, “ΔC2” may be 5C or less, may be 4C or less, and may be 4.5C or less. Alternatively, the third charging control unit 33 does not start gas in the secondary battery 50 until the gas generation detection unit 20 stops detecting gas generation in the secondary battery 50 continuously for a predetermined time “Δt2”. It may be determined that the occurrence of has stopped. As a result, the charging rate can be increased as soon as the formation of the coating is completed.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. For example, in the above embodiment, a battery including a stacked electrode body is disclosed as a secondary battery to be charged, but the present invention is not limited to this. For example, a secondary battery including a wound electrode body in which a long positive electrode sheet and a negative electrode sheet are insulated and stacked by a long separator sheet and wound may be used as a charge target. The technology described in the claims of the present application includes various modifications and changes of the specific examples illustrated above.

DESCRIPTION OF SYMBOLS 1 Power storage device 10 Power storage part 20 Gas generation | occurrence | production detection means 21 AE sensor 30 Control part 31 1st charge control part 32 2nd charge control part 33 3rd charge control part 34 1st judgment part 35 2nd judgment part 50 Secondary battery

Claims (1)

A secondary battery comprising a battery case, and a positive electrode, a negative electrode and a non-aqueous electrolyte contained in the battery case;
Power storage means for charging the secondary battery;
Gas generation detection means configured to detect the generation of gas that occurs in the non-aqueous electrolyte due to charging by the power storage means, based on an acoustic emission method;
A first charge control unit configured to charge the secondary battery at a high charge first charge rate exceeding 1C by the power storage means;
A first determination unit configured to determine that a film is formed on the negative electrode surface based on a detection result by the gas generation detection unit;
A second charge control unit that reduces the charge rate by the power storage means from the first charge rate to a second charge rate lower than the first charge rate when the first determination unit determines the formation of a coating;
A second determination unit that determines that a film is no longer formed on the negative electrode surface based on a detection result by the gas generation detection unit;
A third charge control unit configured to increase the charge rate by the power storage means from the second charge rate to a third charge rate higher than the second charge rate when the second determination unit determines that the film is no longer formed; ,
A power storage device.

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