JP7240610B2 - Lithium-ion secondary battery control system - Google Patents

Description

The present invention relates to a control system for lithium ion secondary batteries.

For example, in JP-A-2018-137099, the amount of gas generated in the electrode body is estimated based on a pre-stored map, and when the amount of gas exceeds a threshold value, the degassing process is performed Lithium ion secondary battery is disclosed. According to the disclosure of Japanese Patent Application Laid-Open No. 2018-137099, when gas remains in the electrode body, lithium is likely to deposit on the electrode body. When lithium deposits on the electrode body, the lithium ions that contribute to the battery reaction decrease, which may cause the battery capacity to deteriorate. In the lithium-ion secondary battery control system disclosed in Japanese Patent Application Laid-Open No. 2018-137099, gas retained in the electrode body can be discharged out of the electrode body by repeatedly increasing and decreasing the pressing force that presses the battery. As a result, deposition of lithium on the electrode body can be suppressed.

JP 2018-137099 A

Here, we propose a new configuration for suppressing deposition of lithium on the electrode body.

The lithium-ion secondary battery control system proposed here includes a control device that controls charging and discharging of the lithium-ion secondary battery, and a detection device that detects the temperature and voltage of the lithium-ion secondary battery. . A lithium ion secondary battery includes a positive electrode on which a positive electrode active material layer containing a positive electrode active material is formed, a negative electrode on which a negative electrode active material layer containing a negative electrode active material is formed, and an electrolytic solution.
The negative electrode active material includes a first negative electrode active material and a second negative electrode active material having a higher operating potential than the first negative electrode active material and a large volume change rate due to absorption or release of lithium ions. . The second negative electrode active material is contained in an amount of 0.3 wt % or more with respect to the entire negative electrode active material and in a smaller amount than the first negative electrode active material.
The control device includes a calculation section, a storage section, a comparison section, and a discharge control section. The calculation unit calculates the gas generation amount of the lithium ion secondary battery based on the temperature and voltage detected by the detection device and the relationship between the temperature and voltage and the gas generation amount recorded in a predetermined map. do. The storage unit stores the threshold value of the gas generation amount. The comparison unit compares the gas generation amount calculated by the calculation unit with the threshold value stored in the storage unit. The discharge control unit discharges the lithium ion secondary battery in a region where the negative electrode potential is higher than the operating potential of the second negative electrode active material when the gas generation amount calculated by the calculation unit is greater than the threshold value.

According to the control system for the lithium ion secondary battery, when the calculated gas generation amount exceeds the threshold value, the second negative electrode active material is discharged, and lithium ions are released from the second negative electrode active material. . As a result, the volume of the second negative electrode active material, which has a large volume change rate due to absorption or release of lithium ions, is greatly reduced, and voids are generated in the negative electrode active material. Gas is discharged to the outside of the electrode assembly through this gap. By discharging the gas, deposition of lithium on the electrode body is suppressed.

FIG. 1 is a block diagram of a battery control system 10. As shown in FIG. FIG. 2 is a partial cross-sectional view of the lithium ion secondary battery 40. As shown in FIG. FIG. 3 is a table showing an example of physical property values of representative substances that can be used as the second negative electrode active material. FIG. 4 is a graph showing the relationship between the SOC of the lithium ion secondary battery 40 and the negative electrode potential. FIG. 5 is a flow chart showing a control process for discharging gas from the electrode body 50. As shown in FIG. FIG. 6 is a table showing the results of the gas emission test.

An embodiment of a lithium-ion secondary battery control system (hereinafter referred to as a battery control system) proposed here will be described below. The embodiments described herein are of course not intended to specifically limit the invention. The invention is not limited to the embodiments described herein unless specifically stated. In the figure, upper, lower, left and right are represented by U, D, L and R, respectively. However, up, down, left, and right are directions for convenience of explanation only, and do not limit the manner in which the lithium ion secondary battery or the battery control system is installed.

FIG. 1 is a block diagram of a battery control system 10. As shown in FIG. As shown in FIG. 1 , the battery control system 10 proposed here includes a control device 20 and a detection device 30 . The control device 20 is a device that controls charging and discharging of the lithium ion secondary battery 40 . The control device 20 is typically a computer, and includes a storage device (memory etc.) and an arithmetic device (CPU etc.). Each function of the battery control system 10 can be embodied appropriately through cooperation between physical components and control by the control device 20 based on the results of calculations performed according to a predetermined program. The detection device 30 is a device that detects the temperature and voltage of the lithium ion secondary battery 40 . The detection device 30 is connected to a lithium ion secondary battery 40 .

Lithium ion secondary battery 40 is, for example, a battery for a hybrid vehicle. In this embodiment, the battery control system 10 is installed in a hybrid vehicle. Here, a plurality of lithium ion secondary batteries 40 are provided and connected to form a battery pack. However, the lithium ion secondary battery 40 may be used as a single battery. The hybrid vehicle is equipped with a motor generator (not shown). The motor generator generates driving force for running the vehicle by discharging the battery pack of the lithium ion secondary battery 40, and converts kinetic energy associated with regenerative braking into electrical energy during regenerative braking of the hybrid vehicle. The electrical energy generated by regenerative braking charges the lithium ion secondary battery 40 . Since the hybrid vehicle is repeatedly charged and discharged in this way, the lithium ion secondary battery 40 is required to have a long service life for charging and discharging, in other words, to have little deterioration in input/output characteristics due to charging and discharging.

FIG. 2 is a partial cross-sectional view of the lithium ion secondary battery 40. As shown in FIG. As shown in FIG. 2, the lithium ion secondary battery 40 includes a case body 41, a lid body 42 joined to the case body 41, an electrode body 50, a positive electrode side take-out portion 60, and a negative electrode side take-out portion 70. , and an electrolyte 80 .

The case main body 41 accommodates the electrode body 50 and the electrolytic solution 80 . The case main body 41 is a substantially rectangular parallelepiped flat rectangular container. The case main body 41 has an open side surface between a pair of side surfaces forming wide surfaces facing each other. The case main body 41 is made of, for example, aluminum or an aluminum alloy. The lid 42 is attached so as to close the opening of the case body 41 . The lid 42 is welded to the periphery of the opening of the case body 41 . The lid 42 is also made of aluminum or an aluminum alloy, for example.

The electrode body 50 is housed in the case main body 41 while being covered with, for example, an insulating film (not shown). The electrode assembly 50 includes a positive electrode sheet 51 , a negative electrode sheet 52 , a first separator sheet 53 and a second separator sheet 54 . The positive electrode sheet 51, the negative electrode sheet 52, the first separator sheet 53, and the second separator sheet 54 are each a long belt-like member. The first separator sheet 53 , the positive electrode sheet 51 , the second separator sheet 54 , and the negative electrode sheet 52 are stacked in this order and wound inside the case body 41 .

A positive electrode active material layer 51 b containing a positive electrode active material is formed on the positive electrode sheet 51 . The positive electrode sheet 51 is formed by forming positive electrode active material layers 51b containing a positive electrode active material on both sides of a metal foil (for example, aluminum foil, hereinafter referred to as a positive electrode current collector foil 51a) having a predetermined width and thickness. It is a member. However, an unformed portion 51c in which the positive electrode active material layer 51b is not formed is set to a certain length at one end portion of the positive electrode current collector foil 51a. In the lithium ion secondary battery 40, the positive electrode active material is a material such as a lithium transition metal composite material that can release lithium ions during charging and absorb lithium ions during discharging.

A negative electrode active material layer 52 b containing a negative electrode active material is formed on the negative electrode sheet 52 . The negative electrode sheet 52 is formed by forming negative electrode active material layers 52b containing a negative electrode active material on both sides of a metal foil (e.g., copper foil, hereinafter referred to as negative electrode current collector foil 52a) having a predetermined width and thickness. It is a member. However, an unformed portion 52c in which the negative electrode active material layer 52b is not formed is set to a certain length at one end portion of the negative electrode current collector foil 52a.

In this embodiment, the negative electrode active material includes a first negative electrode active material and a second negative electrode active material. Both the first negative electrode active material and the second negative electrode active material are materials capable of absorbing lithium ions during charging and releasing the lithium ions absorbed during charging during discharging. The first negative electrode active material is graphite here. The first negative electrode active material accounts for most of the entire negative electrode active material. Preferably, the first negative electrode active material accounts for more than 95% and less than 99.7% of the total negative electrode active material. More preferably, the first negative electrode active material accounts for 97% or more and less than 99.7% of the entire negative electrode active material. However, the ratio of the first negative electrode active material to the entire negative electrode active material is not limited to the above. In this embodiment, the lithium ion secondary battery 40 is a battery for a hybrid vehicle, and is required to have a long life, in other words, to have little deterioration in input/output characteristics due to use. Therefore, the first negative electrode active material, which occupies most of the negative electrode active material, is made of graphite, which is excellent in input/output deterioration characteristics. However, various materials other than graphite have been proposed as materials that are suitable as the first negative electrode active material, and are not particularly limited.

The second negative electrode active material is a material that has a higher operating potential than the first negative electrode active material and a larger volume change rate due to absorption or release of lithium ions. The second negative electrode active material is contained in a smaller amount than the first negative electrode active material with respect to the entire negative electrode active material. The second negative electrode active material is contained in an amount of at least 0.3 wt % or more with respect to the entire negative electrode active material. Preferably, the content of the second negative electrode active material with respect to the entire negative electrode active material is 0.3 wt % or more and less than 5 wt %. More preferably, the content of the second negative electrode active material with respect to the entire negative electrode active material is 0.3 wt % or more and 3 wt % or less. However, the ratio of the second negative electrode active material to the entire negative electrode active material is not limited to the above. The second negative electrode active material is silicon here. However, the second negative electrode active material is not limited to silicon as long as it has a higher operating potential than the first negative electrode active material and a large volume change rate due to absorption or release of lithium ions. Bismuth, tin, antimony, or the like, for example, can be used as the second negative electrode active material.

FIG. 3 is a table showing an example of physical property values of representative substances that can be used as the second negative electrode active material. Specifically, FIG. 3 shows the operating potential of a representative material that can be used as the second negative electrode active material (operating potential based on lithium: V vs. Li/Li ⁺ ), and the volume due to absorption or release of lithium ions. An example of rate of change (%) is shown. As shown in FIG. 3, graphite (C) has a working potential of 0.05V relative to lithium, whereas silicon (Si), for example, has a working potential of 0.4V. The working potential of silicon is higher than that of graphite. Similarly, the working potentials of bismuth (Bi), tin (Sn), and antimony (Sb) are each higher than that of graphite. Each negative electrode active material absorbs or releases lithium ions in a region where the negative electrode potential is higher than the respective operating potential. The operating potential of the negative electrode active material is the lower limit negative electrode potential at which lithium ion absorption or desorption starts with respect to the negative electrode active material. Note that the operating potential of the negative electrode active material varies, and the average value of a plurality of operating potentials, for example, is used as the negative electrode potential of the practical negative electrode active material.

Further, as shown in FIG. 3, the volume change rate of silicon (Si) due to absorption or release of lithium ions is approximately 26 times that of graphite (C). As shown in FIG. 3, the volume change rates of bismuth (Bi), tin (Sn), and antimony (Sb) due to absorption or release of lithium ions are approximately 18 times, 21 times, and 17 times that of graphite (C), respectively. Double.

FIG. 4 is a graph showing the relationship between the SOC (State of Charge) of the lithium ion secondary battery 40 and the negative electrode potential. The horizontal axis of FIG. 4 is SOC (%). The vertical axis in FIG. 4 is the negative electrode potential (V vs. Li/Li ⁺ ). As shown in FIG. 4, the charge/discharge potential of the negative electrode of the lithium ion secondary battery 40 increases as the SOC decreases. Vc in FIG. 4 indicates the actuation potential of the graphite shown in FIG. When viewed from the SOC, the charge/discharge range of graphite is the range R1 in which the negative electrode potential is equal to or higher than the potential Vc. Vs in FIG. 4 indicates the operating potential of silicon shown in FIG. The charging/discharging range of silicon viewed from the SOC is a range R2 in which the negative electrode potential is equal to or higher than the potential Vs. As described above, silicon as the second negative electrode active material has a higher operating potential than graphite as the first negative electrode active material. Therefore, as shown in FIG. 4, charging and discharging of silicon starts from a region where the SOC is smaller than that of graphite and the negative electrode potential is higher.

For the first separator sheet 53 and the second separator sheet 54, for example, a porous resin sheet having required heat resistance and through which the electrolyte can pass is used. Various proposals have been made for the separator sheets 53 and 54, and there is no particular limitation.

The positive electrode sheet 51 wound inside the case main body 41 is taken out of the case main body 41 by the positive electrode side take-out portion 60 . As shown in FIG. 2 , the positive electrode extraction portion 60 includes a collector terminal 61 , a bolt terminal 62 and an insulating member 63 . The collector terminal 61 is welded to the non-formed portion 51 c of the positive electrode sheet 51 . The collector terminal 61 is connected to a bolt terminal 62 provided on the upper surface of the lid 42 . The positive collector terminal 61 and the bolt terminal 62 are made of, for example, aluminum or an aluminum alloy. The collector terminal 61 extends to the outside of the case body 41 through a through hole formed in the lid 42 . The collector terminal 61 and the bolt terminal 62 are electrically insulated from the lid 42 by an insulating member 63 . Although the material of the insulating member 63 is not particularly limited, it is, for example, resin.

The negative electrode sheet 52 is taken out of the case main body 41 by the negative electrode side extraction part 70 . The negative electrode extraction portion 70 has the same structure as the positive electrode extraction portion 60 . The negative electrode extraction portion 70 includes a collector terminal 71 , a bolt terminal 72 and an insulating member 73 . The collector terminal 71 and the bolt terminal 72 on the negative electrode side are made of, for example, copper or a copper alloy.

The electrolytic solution 80 is contained in the case main body 41 . The electrolytic solution 80 is sealed inside the case main body 41 by the lid 42 . For the electrolytic solution 80, for example, an organic solvent in which a lithium salt is dissolved is used. The electrolytic solution 80 is, for example, a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (for example, volume ratio 3:4:3) and LiPF ₆ at a concentration of about 1 mol/L. It is a non-aqueous electrolytic solution contained. However, various proposals have been made for the electrolytic solution 80, and the electrolytic solution 80 is not particularly limited.

The detection device 30 detects the temperature and voltage of the lithium ion secondary battery 40 . The detection device 30 is connected to a lithium ion secondary battery 40 . As shown in FIG. 1, the detection device 30 includes a temperature sensor 31 and a voltmeter 32 in this embodiment. In this embodiment, the temperature sensor 31 is attached to each of the plurality of lithium ion secondary batteries 40 . The temperature sensor 31 is attached at a predetermined position of the case body 41, for example. A temperature sensor 31 measures the temperature of each lithium ion secondary battery 40 . The voltmeter 32 is attached, for example, between the positive electrode side bolt terminal 62 and the negative electrode side bolt terminal 72 of the lithium ion secondary battery 40 . A voltmeter 32 measures the voltage between the positive electrode and the negative electrode of each lithium ion secondary battery 40 .

The control device 20 controls charging and discharging of the lithium ion secondary battery 40 . As shown in FIG. 1 , the control device 20 includes an SOC setting section 21 , a calculation section 22 , a storage section 23 , a comparison section 24 and a discharge control section 25 .

The SOC setting unit 21 sets the SOC range for normal use (so-called regular SOC). In other words, the SOC setting unit 21 sets the range of the negative electrode potential in normal use. An SOC range R3 in FIG. 4 indicates the normal SOC of the lithium-ion secondary battery 40 . The normal SOC is set within the charge/discharge range R1 of graphite and in a range where the SOC is higher and the negative electrode potential is lower than the charge/discharge range R2 of silicon. In normal use, discharge is controlled so that the SOC is lowered only to the lower limit of the normal SOC range R3.

The calculation unit 22 controls the gas generation of the lithium ion secondary battery 40 based on the temperature and voltage detected by the detection device 30 and the relationship between the temperature and voltage and the amount of gas generation recorded in a predetermined map. Calculate quantity. For example, as disclosed in Japanese Patent Application Laid-Open No. 2018-137099, in the lithium ion secondary battery 40, lithium may deposit on the surface of the electrode body 50 depending on the charging conditions. When lithium deposits on the electrode body 50, the amount of lithium ions that contribute to the battery reaction decreases, which may cause the battery capacity to deteriorate.

For example, as disclosed in Japanese Patent Application Laid-Open No. 2018-137099, the higher the temperature when the lithium ion secondary battery 40 is used and the higher the voltage, the more the electrolyte 80 decomposes. In this state, gas is likely to be generated within the electrode body 50 . When the gas is generated, part of it stays in the electrode body 50 (between the positive electrode sheet 51 and the negative electrode sheet 52). For example, as disclosed in Japanese Unexamined Patent Application Publication No. 2018-137099, lithium is likely to deposit on the electrode body 50 when gas remains in the electrode body 50 .

The calculation unit 22 stores a map in which the correlation between the temperature and potential of the lithium ion secondary battery 40 and the amount of gas staying in the electrode body 50 is recorded. Such a correlation is obtained through pre-performed tests and simulations. The calculation unit 22 calculates the gas generation amount of the lithium ion secondary battery 40 (hereinafter referred to as gas generation amount Q1) based on the map and the temperature and potential detected by the detection device 30 .

The storage unit 23 stores a threshold for the amount of gas generated (hereinafter referred to as threshold Q2). The comparison unit 24 compares the gas generation amount Q1 calculated by the calculation unit 22 and the threshold value Q2 stored in the storage unit 23 . The discharge control unit 25 performs control to promote discharge of gas from the electrode body 50 when the gas generation amount Q1 calculated by the calculation unit 22 exceeds the threshold value Q2.

When the gas generation amount Q1 calculated by the calculation unit 22 is larger than the threshold value Q2, the discharge control unit 25 sets the negative electrode potential higher than the operating potential of the second negative electrode active material (here, the operating potential Vs of silicon). is set so that the lithium-ion secondary battery 40 is discharged in a region where . In other words, the discharge control unit 25 discharges the lithium ion secondary battery 40 so as to reduce the SOC to within the charge/discharge range R2 of silicon in FIG. Details of control by the discharge control unit 25 and results thereof will be described below.

[Control process]
FIG. 5 is a flow chart showing a control process for discharging gas from the electrode body 50. As shown in FIG. As shown in FIG. 5, in this embodiment, the temperature and voltage of the lithium ion secondary battery 40 are detected in step S01. In step S02, gas generation amount Q1 is calculated based on the stored map and the detected temperature and voltage of lithium ion secondary battery 40 .

In step S03, the gas generation amount Q1 calculated in step S02 is compared with the stored threshold value Q2 of the gas generation amount. Here, both the gas generation amount Q1 and the threshold value Q2 are integrated values during the period of use. As shown in FIG. 5, when the calculated gas generation amount Q1 is equal to or less than the threshold value Q2 (when the result of step S03 is No), the battery control system 10, again in step S01, sets the temperature of the lithium ion secondary battery 40 to and voltage sensing. When the calculated gas generation amount Q1 exceeds the threshold value Q2 (when the result of step S03 is Yes), the lithium ion secondary battery 40 is discharged in step S04. In step S04, discharging is performed until the SOC reaches a predetermined value C1 that is smaller than the normal SOC.

The SOC value C1 in FIG. 4 is the SOC value reached by the discharge in step S04. The value C1 is predetermined. Predetermined value C1 is smaller than the lower limit of normal SOC range R3. The discharge control unit 25 discharges in a region where the SOC is lower than the lower limit of the normal SOC and the negative electrode voltage is higher than the negative electrode voltage at the lower limit of the normal SOC. The predetermined value C1 is also within the charging/discharging range R2 of silicon. The negative electrode potential V1 when the SOC is the predetermined value C1 is higher than the operating potential Vs of silicon. Therefore, in step S04, the lithium ions occluded by silicon are released.

In the process of step S04, when the lithium ions occluded in silicon are released, the volume of silicon rapidly decreases. As shown in FIG. 3, the volume change rate of silicon (Si) due to release of lithium ions is about 26 times that of graphite (C). Therefore, voids are generated in the negative electrode active material layer 52b. The generated gas is discharged to the outside of the electrode body 50 through this gap. As a result, retention of gas within the electrode body 50 is suppressed. As a result, deposition of lithium on the electrode body 50 is suppressed.

After the SOC drops to the predetermined value C1 in step S04, charging of the lithium ion secondary battery 40 is started in step S05, and the SOC returns to within the normal SOC range R3. After that, the process returns to step S01, and similar steps are repeated from the detection of the temperature and voltage of the lithium ion secondary battery 40. FIG. In this embodiment, the SOC is not held at the predetermined value C1 for a certain period of time in step S04, but may be held.

It should be noted that, if discharge is frequently performed such that the SOC becomes smaller than the normal SOC range R3, for example, there is a risk that the battery life will be deteriorated. This is the case where the quantity Q1 exceeds the threshold Q2, and its frequency is low. Therefore, there is little possibility that the battery life will be deteriorated.

[Test results]
The results of gas discharge tests conducted by the inventors of the present application are shown below. FIG. 6 is a table showing the results of the gas emission test. In this test, a large rectangular lithium ion secondary battery is used. The negative electrode sheet is manufactured by applying a paste obtained by mixing graphite with a predetermined ratio of silicon to the negative electrode current collector foil. After applying the paste to the negative electrode current collector foil, the paste is dried and pressed. The added amount (%) of silicon in FIG. 6 is the ratio of silicon to the entire negative electrode active material.

Specifically, the gas discharge operation of FIG. 6 is an operation of discharging until the SOC reaches a predetermined value within the charge/discharge range R2 of silicon. All samples except sample 8 were degassed. For Sample 8, no degassing operation was performed. Sample 8 is a sample for confirming the effect of the gas discharge operation.

Prior to the outgassing operation, each sample was subjected to a cycle test and a lithium deposition test. A cycle test is a test in which a charge/discharge cycle is repeated for a predetermined number of cycles under predetermined temperature and current conditions. The lithium deposition test is a test in which charging is performed for a predetermined number of cycles (that is, overcharging) under predetermined temperature and current conditions. After that, each sample except sample 8 is subjected to a gas discharge operation.

Each sample was evaluated on two points: the capacity retention rate and the presence or absence of lithium deposition. In the evaluation of the capacity retention rate, the rate of decrease in battery capacity of each sample in the cycle test and lithium deposition test was compared with Sample 1 to which silicon was not added (0% silicon addition rate) as a reference. In FIG. 6, the capacity decrease rates of the samples having acceptable capacity retention rates are within a predetermined allowable range with respect to the capacity decrease rate of sample 1 as a reference. In FIG. 6, the capacity decrease rates of the samples having failed capacity retention rates are outside the predetermined allowable range with the capacity decrease rate of Sample 1 as a reference.

Silicon, which is added to the negative electrode active material as the second negative electrode active material, is a material that causes contradictory effects such as deterioration of battery capacity and increased resistance, for example. As shown in FIG. 3, the volume change rate of silicon due to absorption or release of lithium ions is much higher than that of graphite. problems such as shortened battery life. In addition, silicon has a large resistance and poor input/output characteristics. In the conventionally known technology, silicon has a large capacity as a negative electrode active material, so it is sometimes used in batteries where large battery capacity is important, such as secondary batteries for electric vehicles. It is not usually used for batteries where life and input/output characteristics are important, such as secondary batteries.

In order to avoid the trade-off effect, the normal SOC is set outside the charging/discharging range R2 of silicon. In this case, silicon is not charged or discharged in the normal SOC range R3. Therefore, the volume of silicon does not change in the normal SOC range R3. Also, the doping rate of silicon is set to be very small. These suppress the anti-reactive action of silicon. Samples whose capacity retention rate is rejected in FIG. 6 are samples in which the amount of silicon added is too large and the contradictory effect exceeds the allowable range.

The presence or absence of lithium deposition is confirmed by disassembling each sample and checking whether lithium is deposited on the negative electrode. In FIG. 6, the samples for which lithium deposition was accepted are samples in which lithium deposition was not observed on the negative electrode. Samples for which lithium deposition was rejected in FIG. 6 are samples in which deposition of lithium was observed on the negative electrode.

Sample 1 is a sample with a silicon addition rate of 0% (no addition). Sample 2 is a sample with a silicon addition rate of 0.1%. Sample 3 is a sample with a silicon addition rate of 0.3%. Sample 4 is a sample with a silicon addition rate of 0.5%. Sample 5 is a sample with a silicon addition rate of 1%. Sample 6 is a sample with a silicon addition rate of 3%. Sample 7 is a sample with a silicon addition rate of 5%. Sample 8 is a sample in which the addition rate of silicon is 3% and no gas discharge operation is performed.

As shown in FIG. 6, in samples 1 and 2, lithium is deposited on the negative electrode. In other words, when the addition rate of silicon is 0.1% or less, the effect of suppressing deposition of lithium cannot be confirmed. In samples 3 to 7, lithium was not deposited on the negative electrode. In other words, when the addition rate of silicon is 0.3% or more, the effect of suppressing deposition of lithium can be confirmed. In Sample 8, lithium is deposited on the negative electrode. From the results of sample 8, it can be seen that the effect of suppressing lithium deposition does not appear unless discharge is performed so as to lower the SOC to the charge/discharge range R2 of silicon.

In addition, as shown in FIG. 6, Sample 7 fails the capacity retention rate. The capacity retention rate of the other samples is acceptable. In other words, when the addition rate of silicon is 5% or more, the contradictory effect of deterioration of battery capacity exceeds the allowable range. When the addition rate of silicon is 3% or less, the contradictory effect of deterioration of battery capacity is within the allowable range. However, the acceptance/rejection boundary value of 3%/5% silicon addition rate is the result based on the allowable value determined in the test by the inventor of the present application, and will change if the allowable value is changed. Therefore, the upper limit of the addition rate of silicon is not necessarily between 3% and 5% with respect to the entire negative electrode active material.

As described above, the battery control system 10 according to the present embodiment includes the control device 20 that controls charging and discharging of the lithium ion secondary battery 40, and the detection device 30 that detects the temperature and voltage of the lithium ion secondary battery 40. , is equipped with In addition, the negative electrode active material includes a first negative electrode active material (for example, graphite) and a second negative electrode active material having a higher operating potential than the first negative electrode active material and a large volume change rate due to absorption or release of lithium ions. a substance (eg, silicon); The second negative electrode active material is contained in an amount of 0.3 wt % or more with respect to the entire negative electrode active material and in a smaller amount than the first negative electrode active material. The battery control system 10 detects gas in the lithium ion secondary battery 40 based on the temperature and voltage detected by the detector 30 and the relationship between the temperature and voltage and the amount of gas generated recorded in a predetermined map. A generation amount Q1 is calculated. Furthermore, the battery control system 10 compares the calculated gas generation amount Q1 and the stored threshold value Q2, and if the calculated gas generation amount Q1 is larger than the threshold value Q2, the second negative electrode active material is It is configured to discharge the lithium ion secondary battery 40 in the region R2 where the negative electrode potential is higher than the operating potential (for example, the operating potential Vs of silicon).

According to the battery control system 10, when the calculated gas generation amount Q1 exceeds the threshold value Q2, the second negative electrode active material is discharged and lithium ions are released from the second negative electrode active material. . As a result, the volume of the second negative electrode active material having a large volume change rate due to absorption or release of lithium ions is greatly reduced, and voids are generated in the negative electrode active material layer 52b. The gas is discharged to the outside of the electrode body 50 through this gap. The discharge of the gas suppresses deposition of lithium on the electrode body 50 .

In addition, in the battery control system 10 according to the present embodiment, the normal SOC is set to the region R3 where the negative electrode potential is lower than the operating potential of the second negative electrode active material (for example, the operating potential Vs of silicon). Therefore, the second negative electrode active material is not charged or discharged under normal usage conditions. Therefore, it is possible to suppress the contradictory effect of the second negative electrode active material (for example, the deterioration of the battery life due to the difference in the volume change rate related to the absorption and discharge of lithium ions between the first negative electrode active material and the first negative electrode active material). .

Various descriptions have been made above regarding the control system for the lithium-ion secondary battery proposed herein. Unless otherwise specified, the embodiments of the lithium-ion secondary battery control system and the like given here do not limit the present invention.

10 Battery control system 20 Control device 21 SOC setting unit 22 Calculation unit 23 Storage unit 24 Comparison unit 25 Discharge control unit 30 Detecting device 31 Temperature sensor 32 Voltmeter 40 Lithium ion secondary battery 41 Case main body 42 Lid 50 Electrode 51 Positive electrode Sheet 51a Positive electrode current collector foil 51b Positive electrode active material layer 51c Unformed portion 52 Negative electrode sheet 52a Negative electrode current collector foil 52b Negative electrode active material layer 52c Unformed portion 53 First separator sheet 54 Second separator sheet 60 Positive electrode side extraction portion 61 Current collector Terminal 62 Bolt terminal 63 Insulating member 70 Negative electrode extraction portion 71 Current collecting terminal 72 Bolt terminal 73 Insulating member 80 Electrolyte solution Q1 Calculated gas generation amount Q2 Gas generation amount threshold value R1 Graphite charging/discharging range R2 Silicon charging/discharging range R3 Normal SOC range C1 SOC in gas exhaust
Vc Operating potential of graphite Vs Operating potential of silicon V1 Negative electrode potential during discharge

Claims (1)

Control charge/discharge of a lithium ion secondary battery including a positive electrode having a positive electrode active material layer containing a positive electrode active material, a negative electrode having a negative electrode active material layer containing a negative electrode active material, and an electrolyte. a controller;
a detection device that detects the temperature and voltage of the lithium ion secondary battery;
with
The negative electrode active material is
a first negative electrode active material;
a second negative electrode active material having a higher operating potential than the first negative electrode active material and having a large volume change rate due to absorption or release of lithium ions;
including
The second negative electrode active material is 0.3 wt% or more with respect to the entire negative electrode active material and is contained in a smaller amount than the first negative electrode active material,
The control device is
Calculation for calculating the gas generation amount of the lithium ion secondary battery based on the temperature and voltage detected by the detection device and the relationship between the temperature and voltage and the gas generation amount recorded in a predetermined map Department and
a storage unit that stores a threshold value for the amount of gas generated;
a comparison unit that compares the gas generation amount calculated by the calculation unit with the threshold value stored in the storage unit;
A discharge control unit that discharges the lithium ion secondary battery in a region where the negative electrode potential is higher than the operating potential of the second negative electrode active material when the gas generation amount calculated by the calculation unit is greater than the threshold value. and,
is equipped with
Control system for lithium-ion secondary batteries.

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