JP2011018547A - Lithium ion secondary battery and battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery and a battery system capable of obtaining stable output characteristics and can prevent at least either over-discharge or overcharge.SOLUTION: For the lithium ion secondary battery and the battery system characterized by the appearance of a first discharge flat part FDA1, a voltage lowering part DV, and a second discharge flat part FDB2 in a battery voltage fluctuation curve in discharging, a cathode active material contains a first cathode active material (LiMnPO) carrying out the charge and discharge of a two-phase coexisting type as a main ingredient, and a second cathode active material (LiFePO) carrying out the charge and discharge of a two-phase coexisting type as a sub ingredient.

Description

  The present invention relates to a lithium ion secondary battery and a battery system including the lithium ion secondary battery.

Lithium ion secondary batteries are attracting attention as power sources for portable devices and as power sources for electric vehicles and hybrid vehicles. Currently, as a lithium ion secondary battery, a positive electrode active material made of LiMO ₂ (M is Co, Ni, Mn, V, Al, Mg, etc.), a negative electrode active material made of a carbon material, Li salt and non-aqueous What has the nonaqueous electrolyte solution which consists of a solvent has become mainstream (for example, refer patent documents 1-3). This lithium ion secondary battery has the advantage of exhibiting a high discharge voltage and high output.

JP 2005-336000 A JP 2003-100300 A JP 2003-059489 A JP 2003-36889 A JP 2006-12613 A

  By the way, the lithium ion secondary batteries disclosed in Patent Documents 1 to 3 have characteristics that the battery voltage gradually increases as the battery is charged during charging, and conversely the battery voltage gradually decreases as the battery discharges during discharging. have. For this reason, since the change of the battery voltage at the time of charging / discharging becomes large, the output fluctuation is large, and there is a problem that the output characteristics change depending on the state of charge (discharge depth) of the battery and it is difficult to use.

On the other hand, Patent Documents 4 and 5 propose secondary batteries using, as a positive electrode active material, a lithium transition metal composite oxide having an olivine structure represented by a composition formula LiFePO ₄ or the like. The lithium transition metal composite oxide having an olivine structure represented by LiFePO ₄ or the like has a substantially constant charge / discharge potential even during charge / discharge, and hardly changes even when lithium ions are desorbed and occluded. The reason is, for example, lithium transition metal composite oxide having an olivine structure represented by LiFePO _4, when absorption and desorption of Li, believed to be because the two-phase coexistence state between LiFePO ₄ and FePO ₄ .

Therefore, by using a positive electrode active material that performs charge and discharge in a two-phase coexistence type, such as LiFePO ₄ , a lithium secondary battery that has little change in input density and output density due to change in charge state and stable output characteristics is configured. It becomes possible to do. However, such a lithium ion secondary battery has a very small change in battery voltage during charge and discharge.
Specifically, when such a lithium ion secondary battery is discharged, the battery voltage value hardly changes until the end of discharge. For this reason, at the time of discharge, it is difficult to detect the end of discharge (or that the end of discharge is approaching) based on the battery voltage, and there is a possibility of overdischarge.
Further, when such a lithium ion secondary battery is charged, the battery voltage value hardly changes until the end of charging. For this reason, it is difficult to detect the end of charge (or approaching the end of charge) based on the battery voltage during charging. In addition, at the end of charging, the battery voltage value suddenly rises and immediately reaches a fully charged state. For this reason, based on the battery voltage, it is difficult to detect the end of charging before reaching the fully charged state, and there is a possibility of overcharging.

  The present invention has been made in view of the current situation, and is a lithium ion secondary battery capable of obtaining stable output characteristics, and is at least one of overdischarge and overcharge of the lithium ion secondary battery. And a lithium ion secondary battery capable of obtaining stable output characteristics, and at least one of overdischarge and overcharge of the lithium ion secondary battery It is an object of the present invention to provide a battery system capable of preventing the above-described problem.

  (1) One embodiment of the present invention is a lithium ion secondary battery including a positive electrode active material and a negative electrode active material, and the positive electrode active material performs charge and discharge in a two-phase coexistence type as a main component. A first positive electrode active material, and a second positive electrode active material that performs charge and discharge in a two-phase coexistence type as an auxiliary component, wherein the first positive electrode active material includes the first positive electrode active material and the negative electrode active material. In the battery voltage fluctuation curve when the first lithium ion secondary battery using the battery is discharged, the first positive electrode active material is discharged out of the range of the electric capacity up to the theoretical electric capacity that can be theoretically stored at the maximum. Over the range of 50% or more of the whole up to the end stage, the first discharge flat line has a characteristic in which the fluctuation of the battery voltage value is 0.2 V or less, and the second positive electrode active material is the second positive electrode Second lithium ion using active material and negative electrode active material In the battery voltage fluctuation curve when the secondary battery is discharged, the total 50 up to the end of discharge is within the range of the electric capacity up to the theoretical electric capacity that the second positive electrode active material can theoretically accumulate to the maximum. %, A second discharge flat line having a battery voltage value variation of 0.2 V or less appears, and the average voltage value of the second discharge flat line is higher than the average voltage value of the first discharge flat line. The lithium ion secondary battery has a lower characteristic, and the battery voltage fluctuation curve when the lithium ion secondary battery is discharged excludes an end portion on the discharge end side of the first discharge flat line. A first discharge flat portion corresponding to a portion and a second discharge flat portion corresponding to an end portion on the discharge end side of the second discharge flat line, and located on a discharge end side with respect to the first discharge flat portion. A second discharge flat portion showing a voltage value lower than the voltage value of the first discharge flat portion, and a voltage reduction portion in which the battery voltage decreases over a range from the first discharge flat portion to the second discharge flat portion. And it is a lithium ion secondary battery which has the characteristic that the voltage reduction part where a battery voltage falls large compared with the said 1st discharge flat part and the said 2nd discharge flat part appears.

  The above-described lithium ion secondary battery includes a first positive electrode active material that performs charge and discharge in a two-phase coexistence type as a main component (for example, 80 wt%) of the positive electrode active material. %) Includes a second positive electrode active material that performs charge and discharge in a two-phase coexistence type.

  In the first lithium ion secondary battery using only the first positive electrode active material as the positive electrode active material and the negative electrode active material equivalent to the above-described lithium ion secondary battery as the negative electrode active material, the first lithium ion secondary battery is used. In the battery voltage fluctuation curve when the battery is discharged, 50% or more of the total capacity until the end of discharge is reached in the range of the electric capacity with the upper limit of the theoretical electric capacity that the first positive electrode active material can theoretically accumulate to the maximum. Over the above range (for example, a capacity range corresponding to 95% to 5% of the theoretical electric capacity), the first discharge flat line in which the fluctuation of the battery voltage value is 0.2 V or less appears. Thus, in the first lithium ion secondary battery in which the fluctuation of the battery voltage value is 0.2 V or less over a wide capacity range, stable output characteristics with a small output fluctuation can be obtained.

  In the second lithium ion secondary battery using only the second positive electrode active material as the positive electrode active material and using the negative electrode active material equivalent to the above-described lithium ion secondary battery as the negative electrode active material, the second lithium ion secondary battery is used. In the battery voltage fluctuation curve when the battery is discharged, 50% or more of the total capacity up to the end of the discharge is within the range of the electric capacity up to the theoretical electric capacity that the second positive electrode active material can theoretically accumulate to the maximum. Over the above range (for example, a capacity range corresponding to 95% to 5% of the theoretical electric capacity), the second discharge flat line in which the fluctuation of the battery voltage value is 0.2 V or less appears. Thus, in the second lithium ion secondary battery in which the fluctuation of the battery voltage value is 0.2 V or less over a wide capacity range, stable output characteristics with a small output fluctuation can be obtained.

  However, in the first lithium ion secondary battery and the second lithium ion secondary battery, the capacity range of 50% or more of the whole until the end of discharge (for example, the capacity range corresponding to 95% to 5% of the theoretical electric capacity) ), The fluctuation of the battery voltage value is 0.2 V or less. That is, the battery voltage value hardly changes from the middle of discharge to the end of discharge. For this reason, at the time of discharge, it is difficult to detect the end of discharge (or that the end of discharge is approaching) based on the battery voltage, and there is a possibility of overdischarge.

  In contrast, the above-described lithium ion secondary battery includes a first positive electrode active material that performs charge and discharge in a two-phase coexistence type as a main component (for example, 80 wt%) of the positive electrode active material, For example, the second positive electrode active material that performs charge and discharge in a two-phase coexistence type is included as 20 wt%). Such a lithium ion secondary battery is a first voltage corresponding to a portion of the first discharge flat line excluding the end portion on the discharge end side in the battery voltage fluctuation curve when the lithium ion secondary battery is discharged. A discharge flat portion and a second discharge flat portion corresponding to an end portion on the discharge end side of the second discharge flat line, located on the discharge end side with respect to the first discharge flat portion, and a voltage of the first discharge flat portion A second discharge flat portion having a voltage value lower than the first value, and a voltage reduction portion in which the battery voltage decreases over a range from the first discharge flat portion to the second discharge flat portion, the first discharge flat portion and Compared with the second discharge flat part, a voltage drop part in which the battery voltage is greatly reduced appears.

  In the voltage reduction part located between the first discharge flat part and the second discharge flat part, the battery voltage is greatly reduced as compared with the first discharge flat part and the second discharge flat part. When the battery is discharged, it can be easily detected that the battery voltage has been reached by detecting the battery voltage. A voltage drop part is a site | part close | similar to the end of discharge among battery voltage fluctuation curves. For this reason, at the time of discharge of the above-mentioned lithium ion secondary battery, by detecting the battery voltage value of the voltage drop part (for example, a specific voltage value within the range of the voltage drop part), it is approaching the end of discharge. Can be detected. As a result, it becomes possible to perform processing for preventing overdischarge (for example, processing for warning that the remaining amount of battery power is low, processing for stopping discharge, etc.), and appropriately overloading the lithium ion secondary battery. It becomes possible to prevent discharge.

  In addition, in the above-described lithium ion secondary battery, the battery voltage value varies 0.2 V over a wide capacity range including the first discharge flat portion (for example, a capacity range corresponding to 95% to 25% of the theoretical electric capacity). Therefore, stable output characteristics with small output fluctuations can be obtained.

(2) Further, in the above lithium ion secondary battery, the positive electrode active material includes LiMO ₂ (M includes at least one of Ni, Co, and Mn) as a subcomponent, and the first In the battery voltage fluctuation curve when the first lithium ion secondary battery is charged, the positive electrode active material is 50% or more of the total capacity up to the end of charging in the range of the electric capacity with the theoretical electric capacity as the upper limit. The first charging flat line in which the variation of the battery voltage value is 0.2V or less over the range, and the terminal stage of charging adjacent to the first charging flat line, the battery voltage value compared to the first charging flat line And the first charging end line in which the first charging flat line has an average voltage value of 4.5 V or less when the carbon material is used as the negative electrode active material. two In the battery voltage fluctuation curve when the lithium ion secondary battery is charged, the battery is a first portion corresponding to a portion of the first charge flat line excluding an end portion on the charge initial side and an end portion on the end stage of charge. A charge flat portion and a second charge end portion adjacent to the first charge flat portion, the battery voltage value gradually increasing over a wide capacity range as compared with the first charge end portion. A lithium ion secondary battery having the appearing characteristics is preferable.

  In the first lithium ion secondary battery, in the battery voltage fluctuation curve when charged, the first positive electrode active material reaches the end of charging out of the range of electric capacity up to the theoretical electric capacity that can theoretically be accumulated to the maximum. The first charging flat line in which the fluctuation of the battery voltage value is 0.2 V or less appears over a range of 50% or more (for example, a capacity range corresponding to 5% to 95% of the theoretical electric capacity). Therefore, in the first lithium ion secondary battery, the battery voltage value hardly changes from the middle of charging to the end of charging. For this reason, it is difficult to detect the end of charge (or approaching the end of charge) based on the battery voltage during charging. Moreover, in the first lithium ion secondary battery, in the battery voltage fluctuation curve when charged, the battery voltage value rises rapidly compared to the first charging flat line, at the end of charging adjacent to the first charging flat line. The first charge end stage appears. That is, at the end of charging, the battery voltage value rapidly rises and immediately reaches a fully charged state. For this reason, based on the battery voltage, it is difficult to detect the end of charging before reaching the fully charged state, and there is a possibility of overcharging.

On the other hand, in the above-described lithium ion secondary battery, the first positive electrode active material is included as the main component of the positive electrode active material, and LiMO ₂ is added as a subcomponent of the positive electrode active material in addition to the second positive electrode active material (for example, 1 to 5 wt%). Such a lithium ion secondary battery excludes the end part on the charge initial side and the end part on the end of charge side of the first charge flat line in the battery voltage fluctuation curve when the lithium ion secondary battery is charged. A first charging flat portion corresponding to the portion, and a charging end portion adjacent to the first charging flat portion, and a second charging end portion in which the battery voltage value gradually increases over a wider capacity range than the first charging end portion Part has a characteristic of appearing.

  At the end of charging of the above-described lithium ion secondary battery (second charging end), the battery voltage value gradually decreases over a wide capacity range compared to the end of charging of the first lithium ion secondary battery (first charging end). To rise. That is, at the end of charging, the battery voltage value does not rapidly increase and reaches a fully charged state relatively slowly. For this reason, at the time of charge of the above-mentioned lithium ion secondary battery, it can be easily detected that the second charge end stage has been reached by detecting the battery voltage. Therefore, when the above-described lithium ion secondary battery is charged, the battery voltage value at the end of the second charge (for example, a specific voltage value within the range of the end of the second charge) is detected to approach the fully charged state. Can be detected. This makes it possible to perform processing for preventing overcharging (for example, charging stop processing) and appropriately prevent overcharging of the lithium ion secondary battery.

Moreover, in the above-described lithium ion secondary battery, the battery voltage value varies 0.2 V over a wide capacity range including the first discharge flat portion (for example, a capacity range corresponding to 25% to 95% of the theoretical electric capacity). Therefore, stable output characteristics with small output fluctuations can be obtained.
Note that LiMO ₂ (M includes at least one of Ni, Co, and Mn) includes, as M, at least one element of Ni, Co, and Mn (a combination of one or more), Furthermore, other elements different from Ni, Co, and Mn (for example, V, Al, Mg, etc.) may be included.

(3) Another aspect of the present invention is a lithium ion secondary battery comprising a positive electrode active material and a negative electrode active material, wherein the positive electrode active material is charged and discharged in a two-phase coexistence type as a main component. A first positive electrode active material to be performed, and LiMO ₂ (M includes at least one of Ni, Co, and Mn) as a subcomponent, and the first positive electrode active material includes the first positive electrode active material and In the battery voltage fluctuation curve when the first lithium ion secondary battery using the negative electrode active material is charged, the electric capacity of the upper limit is the theoretical electric capacity that the first positive electrode active material can theoretically store to the maximum. The first charging flat line in which the fluctuation of the battery voltage value is 0.2V or less over the range of 50% or more of the entire range up to the end of charging in the range, and the end stage of charging adjacent to the first charging flat line Compared to the first charging flat wire And a first charging end stage in which the battery voltage value rapidly rises, and when the carbon material is used as the negative electrode active material, the average voltage value of the first charging flat line is 4.5 V or less. The lithium ion secondary battery is a first charging flat corresponding to a portion of the first charging flat line excluding a portion at the end of charging in the battery voltage fluctuation curve when the lithium ion secondary battery is charged. And a second end-of-charge portion adjacent to the first charge flat portion, the second end-of-charge portion where the battery voltage value gradually increases over a wide capacity range as compared to the first end-of-charge portion. A lithium ion secondary battery having

The above-described lithium ion secondary battery includes a first positive electrode active material that performs charge and discharge in a two-phase coexistence type as a main component (for example, 95 wt%) of the positive electrode active material, and a subcomponent (for example, 5 wt%) of the positive electrode active material. %) Includes LiMO ₂ .

  In the first lithium ion secondary battery using only the first positive electrode active material as the positive electrode active material and the negative electrode active material equivalent to the above-described lithium ion secondary battery as the negative electrode active material, the first lithium ion secondary battery is used. In the battery voltage fluctuation curve when the battery is charged, 50% or more of the total capacity until the end of charging is reached in the range of the electric capacity up to the theoretical electric capacity that the first positive electrode active material can theoretically accumulate to the maximum. Over the range (for example, a capacity range corresponding to 5% to 95% of the theoretical electric capacity), the first charging flat line in which the fluctuation of the battery voltage value is 0.2 V or less appears. Thus, in the first lithium ion secondary battery in which the fluctuation of the battery voltage value is 0.2 V or less over a wide capacity range, stable output characteristics with a small output fluctuation can be obtained.

  However, in the first lithium ion secondary battery, in the battery voltage fluctuation curve when charged, the battery voltage value fluctuation is 0.2 V or less over the entire capacity range of 50% or more until the end of charging. That is, the battery voltage value hardly changes from the middle of charging to the end of charging. For this reason, it is difficult to detect the end of charge (or approaching the end of charge) based on the battery voltage during charging. Moreover, in the first lithium ion secondary battery, in the battery voltage fluctuation curve when charged, the battery voltage value rises rapidly compared to the first charging flat line, at the end of charging adjacent to the first charging flat line. The first charge end stage appears. That is, at the end of charging, the battery voltage value rapidly rises and immediately reaches a fully charged state. For this reason, based on the battery voltage, it is difficult to detect the end of charging before reaching the fully charged state, and there is a possibility of overcharging.

In contrast, the above-described lithium ion secondary battery includes a first positive electrode active material that performs charge and discharge in a two-phase coexistence type as a main component (for example, 95 wt%) of the positive electrode active material, For example, LiMO ₂ is contained as 5 wt%). Such a lithium ion secondary battery has a first charging flat corresponding to a portion of the first charging flat line excluding a portion at the end of charging in the battery voltage fluctuation curve when the lithium ion secondary battery is charged. And a second charge end portion that is a charge end portion adjacent to the first charge flat portion, and in which the battery voltage value gradually rises over a wide capacity range as compared to the first charge end portion. .

At the end of charging of the above-described lithium ion secondary battery (second charging end), the battery voltage value gradually decreases over a wide capacity range compared to the end of charging of the first lithium ion secondary battery (first charging end). To rise. That is, at the end of charging, the battery voltage value does not rapidly increase and reaches a fully charged state relatively slowly. For this reason, at the time of charge of the above-mentioned lithium ion secondary battery, it can be easily detected that the second charge end stage has been reached by detecting the battery voltage. Therefore, when the above-described lithium ion secondary battery is charged, the fully charged state is approached by detecting the voltage value at the end of the second charge (for example, a specific voltage value within the range of the end of the second charge). Can be detected. This makes it possible to perform processing for preventing overcharging (for example, charging stop processing) and appropriately prevent overcharging of the lithium ion secondary battery.

  In addition, in the above-described lithium ion secondary battery, the fluctuation of the battery voltage value is 0.2 V over a wide capacity range including the first charging flat portion (for example, a capacity range corresponding to 25% to 95% of the theoretical electric capacity). It becomes as follows. In such a lithium ion secondary battery, stable output characteristics with small output fluctuations can be obtained.

  (4) Further, in the above lithium ion secondary battery, the positive electrode active material includes a second positive electrode active material that performs charge and discharge in a two-phase coexistence type as a subcomponent, and the first positive electrode active material includes In the battery voltage fluctuation curve when the first lithium ion secondary battery is discharged, over a range of 50% or more of the total capacity up to the end of discharge in the range of the electric capacity with the theoretical electric capacity as the upper limit, The second positive electrode active material has a characteristic in which a first discharge flat line having a battery voltage fluctuation of 0.2 V or less appears, and the second positive electrode active material is a second lithium using the second positive electrode active material and the negative electrode active material. In the battery voltage fluctuation curve when the ion secondary battery is discharged, the entire range up to the end of discharge in the range of the electric capacity up to the theoretical electric capacity that the second positive electrode active material can theoretically store to the maximum. 50% or more of A second discharge flat line appears with a fluctuation of the battery voltage value of 0.2 V or less, and the average voltage value of the second discharge flat line is lower than the average voltage value of the first discharge flat line. And the lithium ion secondary battery corresponds to a portion of the first discharge flat line excluding an end portion on a discharge end side in a battery voltage fluctuation curve when the lithium ion secondary battery is discharged. A first discharge flat portion and a second discharge flat portion corresponding to an end portion on a discharge end side of the second discharge flat line, the first discharge flat portion being located on a discharge end side with respect to the first discharge flat portion; A second discharge flat portion having a voltage value lower than the voltage value of the discharge flat portion, and a voltage reduction portion in which the battery voltage decreases over a range from the first discharge flat portion to the second discharge flat portion. It, may be a lithium ion secondary battery having a characteristic that the voltage drop unit cell voltage is greatly reduced in comparison with the first discharge flat portion and the second discharge flat portion appears.

  In the first lithium ion secondary battery and the second lithium ion secondary battery, when discharged, the capacity range of 50% or more of the total capacity until the end of discharge is reached out of the range of electric capacity with the theoretical electric capacity as the upper limit ( For example, the variation of the battery voltage value is 0.2 V or less over a capacity range corresponding to 5% to 95% of the theoretical electric capacity. That is, the battery voltage value hardly changes from the middle of discharge to the end of discharge. For this reason, in the first lithium ion secondary battery and the second lithium ion secondary battery, it is difficult to detect the end of discharge (or approaching the end of discharge) based on the battery voltage at the time of discharge. There was a risk of becoming.

In contrast, the above-described lithium ion secondary battery includes a first positive electrode active material that performs charge and discharge in a two-phase coexistence type as a main component of the positive electrode active material, and in addition to LiMO ₂ as a sub main component of the positive electrode active material. And a second positive electrode active material that performs charge and discharge in a two-phase coexistence type (for example, 5 to 20 wt%). Such a lithium ion secondary battery is a battery voltage fluctuation curve when the lithium ion secondary battery is discharged, except for an end portion on the initial discharge side and an end portion on the final discharge side of the first discharge flat line. A first discharge flat portion corresponding to the first discharge flat portion and a second discharge flat portion corresponding to an end portion on the discharge end side of the second discharge flat line, which is located on the discharge end side of the first discharge flat portion, A second discharge flat portion showing a voltage value lower than a voltage value of the first discharge flat portion, and a voltage reduction portion in which the battery voltage decreases over a range from the first discharge flat portion to the second discharge flat portion. And a voltage drop portion where the battery voltage is greatly reduced as compared with the first discharge flat portion and the second discharge flat portion.

  In the voltage reduction part located between the first discharge flat part and the second discharge flat part, the battery voltage is greatly reduced as compared with the first discharge flat part and the second discharge flat part. When the battery is discharged, it can be easily detected that the battery voltage has been reached by detecting the battery voltage. A voltage drop part is a site | part close | similar to the end of discharge among battery voltage fluctuation curves. For this reason, at the time of discharge of the above-described lithium ion secondary battery, it is detected that the end of the discharge is approaching by detecting the voltage value of the voltage drop part (for example, a specific voltage value within the range of the voltage drop part). can do. As a result, it becomes possible to perform processing for preventing overdischarge (for example, processing for warning that the remaining amount of battery power is low, processing for stopping discharge, etc.), and appropriately overloading the lithium ion secondary battery. It becomes possible to prevent discharge.

  Moreover, in the above-described lithium ion secondary battery, the battery voltage value varies 0.2 V over a wide capacity range including the first discharge flat portion (for example, a capacity range corresponding to 25% to 95% of the theoretical electric capacity). Therefore, stable output characteristics with small output fluctuations can be obtained.

(5) Further, in any of the lithium ion secondary batteries, the first positive electrode active material is LiFePO ₄ , and the second positive electrode active material is Li ₃ Fe ₂ (PO ₄ ) ₃ . A lithium ion secondary battery is preferable.

In the above-described lithium ion secondary battery, LiFePO ₄ is included as a main component (first positive electrode active material) of the positive electrode active material, and Li ₃ Fe ₂ (PO ₄ ) is used as a subcomponent (second positive electrode active material) of the positive electrode active material. Includes in _three . Further, LiMO ₂ (M includes at least one of Ni, Co, and Mn) is also included as a subcomponent of the positive electrode active material.

  Such a lithium ion secondary battery has a characteristic in which a first discharge flat portion, a voltage drop portion, and a second discharge flat portion appear in a battery voltage fluctuation curve when discharged. For this reason, at the time of discharge of a lithium ion secondary battery, by detecting the voltage value of the voltage drop part (for example, a specific voltage value within the range of the voltage drop part), detecting that the end of discharge is approaching Can do. As a result, it becomes possible to perform processing for preventing overdischarge (for example, processing for warning that the remaining amount of battery power is low, processing for stopping discharge, etc.), and appropriately overloading the lithium ion secondary battery. It becomes possible to prevent discharge.

  Furthermore, this lithium ion secondary battery has a characteristic in which a first charge flat portion and a second charge end portion appear in a battery voltage fluctuation curve when charged. For this reason, at the time of charge of a lithium ion secondary battery, it is approaching a fully charged state by detecting the voltage value (for example, specific voltage value within the range of the 2nd charge end part) of the 2nd charge end part. Can be detected. This makes it possible to perform processing for preventing overcharging (for example, charging stop processing) and appropriately prevent overcharging of the lithium ion secondary battery.

  Moreover, in the above-described lithium ion secondary battery, the battery voltage value varies 0.2 V over a wide capacity range including the first discharge flat portion (for example, a capacity range corresponding to 25% to 95% of the theoretical electric capacity). Therefore, stable output characteristics with small output fluctuations can be obtained.

  (6) Moreover, the other aspect of this invention is the battery voltage value of the lithium ion secondary battery as described in said (1), (2), (4) or (5), and the said lithium ion secondary battery. The voltage detection device for detecting the battery voltage value of the lithium ion secondary battery in the voltage drop unit is stored in advance, and the voltage detected by the voltage detection device when the lithium ion secondary battery is discharged. A battery system comprising: a processing device that performs a predetermined process for preventing overdischarge of the lithium ion secondary battery based on a battery voltage value of a lowering portion.

  The battery system described above includes the lithium ion secondary battery described in (1), (2), (4), or (5) described above. As described above, these lithium ion secondary batteries have a characteristic in which a first discharge flat portion, a voltage drop portion, and a second discharge flat portion appear in a battery voltage fluctuation curve when discharged. Moreover, in these lithium ion secondary batteries, as described above, the battery voltage value has a wide capacity range including the first discharge flat portion (for example, a capacity range corresponding to 95% to 25% of the theoretical electric capacity). The fluctuation is 0.2V or less. For this reason, in the battery system described above, stable output characteristics with small output fluctuations can be obtained.

  Furthermore, the battery system described above is configured to prevent a lithium ion secondary battery from overdischarge based on the battery voltage value of the voltage drop unit detected by the voltage detection device when the lithium ion secondary battery is discharged. A processing device for processing is provided. Accordingly, when the end of discharge of the lithium ion secondary battery is approaching, a predetermined processing (for example, a process for warning that the remaining amount of electricity in the battery is low) is prevented by the processing device. , Discharge stop processing, etc.). Thereby, it becomes possible to prevent overdischarge of the lithium ion secondary battery.

  (7) Further, in the above battery system, the battery system is mounted on the electric vehicle as a power supply system for driving the electric vehicle, and the processing device is configured to discharge the lithium ion secondary battery. It is determined whether the battery voltage value of the lithium ion secondary battery detected by the voltage detection device has reached the battery voltage value of the voltage reduction unit, and is determined to have reached the battery voltage value of the voltage reduction unit In this case, the predetermined process may be a battery system that performs a process of warning that the remaining amount of electricity of the lithium ion secondary battery is small.

  The battery system described above is mounted on an electric vehicle as a drive power supply system for the electric vehicle. In this battery system, when the processing apparatus determines that the battery voltage value of the lithium ion secondary battery has reached the battery voltage value of the voltage drop portion during discharging of the lithium ion secondary battery, the remaining amount of the lithium ion secondary battery is determined. Processing for warning that the amount of electricity is small (for example, processing for turning on a warning lamp) is performed. By this warning, the driver of the electric vehicle can know that the remaining electricity amount of the lithium ion secondary battery is small. Thereby, the driver of the electric vehicle can stop the electric vehicle and charge the lithium ion secondary battery while electricity remains in the lithium ion secondary battery. Therefore, according to the battery system described above, overdischarge of the lithium ion secondary battery can be prevented.

  (8) In the battery system, the battery system is mounted on the vehicle as a power supply system for a plug-in hybrid vehicle including a motor and an engine, and the vehicle drives the engine. Either an EV mode that travels by driving the motor using electric power supplied by the discharge of the lithium ion secondary battery, or an HV mode that travels by a combination of driving of the motor and driving of the engine The processing device is configured to be able to run, and the processing device is configured to detect the lithium ion secondary detected by the voltage detection device when the lithium ion secondary battery is discharged after the automobile starts running in the EV mode. Determine whether the battery voltage value of the secondary battery has reached the battery voltage value of the voltage drop portion, When it is determined to have reached the battery voltage of the serial voltage drop unit, so that the vehicle travels by the HV mode, as the predetermined processing, may be a battery system that performs processing for starting the engine.

  The battery system described above is mounted on a plug-in hybrid vehicle as a drive power supply system for the plug-in hybrid vehicle including a motor and an engine. A plug-in hybrid vehicle is a hybrid vehicle having a configuration in which a lithium ion secondary battery included in a battery system mounted on the vehicle can be charged using electric power supplied from an external power source. This plug-in hybrid vehicle has an EV mode (electric vehicle mode) that runs by driving a motor using electric power supplied by discharging a lithium ion secondary battery without driving the engine, and driving of the motor and engine The vehicle is configured to be able to travel in any one of HV modes (hybrid vehicle mode) that travels by a combination of driving.

  In the battery system described above, after the plug-in hybrid vehicle starts running in the EV mode, when the processing device discharges the lithium ion secondary battery, the battery voltage value of the lithium ion secondary battery is the battery voltage value of the voltage reduction unit. When it is determined that the engine has reached, the engine is started so that the plug-in hybrid vehicle travels in the HV mode. As a result, the plug-in hybrid vehicle travels by a combination of the motor drive and the engine drive, so that the discharge of the lithium ion secondary battery is suppressed (and the lithium ion secondary battery is charged). Can do. Thereby, the overdischarge of a lithium ion secondary battery can be prevented.

  (9) Furthermore, in any one of the battery systems, the lithium ion secondary battery is the lithium ion secondary battery according to (2), (4), or (5), and the processing apparatus. Stores in advance the battery voltage value of the lithium ion secondary battery at the second charge end stage, and the second charge end part detected by the voltage detection device when the lithium ion secondary battery is charged. Based on the battery voltage value, a battery system that performs a predetermined process for preventing overcharging of the lithium ion secondary battery is preferable.

  The battery system described above includes the lithium ion secondary battery described in (2), (4), or (5) above. As described above, these lithium ion secondary batteries have a characteristic that the first charging flat portion and the second charging end portion appear in the battery voltage fluctuation curve when charged.

  Further, in the battery system described above, the processing device performs overcharge of the lithium ion secondary battery based on the battery voltage value at the end of the second charge detected by the voltage detection device when charging the lithium ion secondary battery. A predetermined process is performed to prevent this. Therefore, when the end of charging of the lithium ion secondary battery is reached, the processing device performs a predetermined process (for example, a charge stop process) for preventing overcharging of the lithium ion secondary battery. Thereby, it is possible to prevent overcharge of the lithium ion secondary battery.

  (10) Further, in the battery system, the processing device may be configured such that a battery voltage value of the lithium ion secondary battery detected by the voltage detection device when the lithium ion secondary battery is charged is the second voltage. It is determined whether or not the battery voltage value at the end of charging has been reached, and when it is determined that the battery voltage value at the end of second charging has been reached, the lithium ion secondary battery is charged as the predetermined process. A battery system that performs a process of stopping is preferable.

  In the battery system described above, when the processing apparatus determines that the battery voltage value of the lithium ion secondary battery has reached the battery voltage value at the end of the second charge during charging of the lithium ion secondary battery, the lithium ion secondary battery Processing to stop charging the battery is performed. Thereby, the overcharge of a lithium ion secondary battery can be prevented.

(11) Moreover, the other aspect of this invention is the voltage detection apparatus which detects the battery voltage value of the lithium ion secondary battery in any one of said (2)-(5), and the said lithium ion secondary battery. And the battery voltage value of the lithium ion secondary battery in the second charge end stage is stored in advance, and the second charge end part detected by the voltage detector when the lithium ion secondary battery is charged. And a processing device that performs a predetermined process for preventing overcharging of the lithium ion secondary battery based on the battery voltage value.

  The above-described battery system includes the lithium ion secondary battery according to any one of the above (2) to (5). As described above, these lithium ion secondary batteries have a characteristic that the first charging flat portion and the second charging end portion appear in the battery voltage fluctuation curve when charged. In addition, as described above, in these lithium ion secondary batteries, the battery voltage value is increased over a wide capacity range including the first discharge flat portion (for example, a capacity range corresponding to 25% to 95% of the theoretical electric capacity). The fluctuation is 0.2V or less. For this reason, in the battery system described above, stable output characteristics with small output fluctuations can be obtained.

  Furthermore, the battery system described above is for preventing overcharging of the lithium ion secondary battery based on the battery voltage value at the end of the second charge detected by the voltage detection device when charging the lithium ion secondary battery. A processing device for performing predetermined processing is provided. Therefore, when the end of charging of the lithium ion secondary battery is reached, the processing device performs a predetermined process (for example, a charge stop process) for preventing overcharging of the lithium ion secondary battery. Thereby, it is possible to prevent overcharge of the lithium ion secondary battery.

  (12) Further, in the battery system described above, the processing device may be configured such that the battery voltage value of the lithium ion secondary battery detected by the voltage detection device when the lithium ion secondary battery is charged is the second voltage. It is determined whether or not the battery voltage value at the end of charging has been reached, and when it is determined that the battery voltage value at the end of second charging has been reached, the lithium ion secondary battery is charged as the predetermined process. A battery system that performs a process of stopping is preferable.

  In the battery system described above, when the processing apparatus determines that the battery voltage value of the lithium ion secondary battery has reached the battery voltage value at the end of the second charge during charging of the lithium ion secondary battery, the lithium ion secondary battery Processing to stop charging the battery is performed. Thereby, the overcharge of a lithium ion secondary battery can be prevented.

  (13) Furthermore, in any one of the battery systems described above, the lithium ion secondary battery is the lithium ion secondary battery according to (2), (4), or (5), and the processing apparatus. The battery voltage value of the lithium ion secondary battery in the voltage drop unit is stored in advance, and the battery voltage value of the voltage drop unit detected by the voltage detection device during the discharge of the lithium ion secondary battery Based on the above, it is preferable that the battery system performs a predetermined process for preventing overdischarge of the lithium ion secondary battery.

  The battery system described above includes the lithium ion secondary battery described in (2), (4), or (5) above. As described above, these lithium ion secondary batteries have a characteristic in which a first discharge flat portion, a voltage drop portion, and a second discharge flat portion appear in a battery voltage fluctuation curve when discharged.

  Furthermore, in the battery system described above, the processing device prevents overdischarge of the lithium ion secondary battery based on the battery voltage value of the voltage drop portion detected by the voltage detection device when the lithium ion secondary battery is discharged. Predetermined processing is performed. Accordingly, when the end of discharge of the lithium ion secondary battery is approaching, a predetermined processing (for example, a process for warning that the remaining amount of electricity in the battery is low) is prevented by the processing device. , Discharge stop processing, etc.). Thereby, it becomes possible to prevent overdischarge of the lithium ion secondary battery.

  (14) Further, in the battery system described above, the battery system is mounted on the electric vehicle as a power supply system for driving the electric vehicle, and the processing apparatus is configured to discharge the lithium ion secondary battery. It is determined whether the battery voltage value of the lithium ion secondary battery detected by the voltage detection device has reached the battery voltage value of the voltage reduction unit, and is determined to have reached the battery voltage value of the voltage reduction unit In this case, the predetermined process may be a battery system that performs a process of warning that the remaining amount of electricity of the lithium ion secondary battery is small.

  The battery system described above is mounted on an electric vehicle as a drive power supply system for the electric vehicle. In this battery system, when the processing apparatus determines that the battery voltage value of the lithium ion secondary battery has reached the battery voltage value of the voltage drop portion during discharging of the lithium ion secondary battery, the remaining amount of the lithium ion secondary battery is determined. Processing to warn that the amount of electricity is low. By this warning, the driver of the electric vehicle can know that the remaining electricity amount of the lithium ion secondary battery is small. Thereby, the driver of the electric vehicle can stop the electric vehicle and charge the lithium ion secondary battery while electricity remains in the lithium ion secondary battery. Therefore, according to the battery system described above, overdischarge of the lithium ion secondary battery can be prevented.

  (15) In the battery system, the battery system is mounted on the vehicle as a power supply system for a plug-in hybrid vehicle including a motor and an engine, and the vehicle drives the engine. Either an EV mode that travels by driving the motor using electric power supplied by the discharge of the lithium ion secondary battery, or an HV mode that travels by a combination of driving of the motor and driving of the engine The processing device is configured to be able to run, and the processing device is configured to detect the lithium ion secondary detected by the voltage detection device when the lithium ion secondary battery is discharged after the automobile starts running in the EV mode. It is determined whether the battery voltage value of the secondary battery has reached the battery voltage value of the voltage drop portion. When it is determined to have reached the battery voltage value of the voltage drop unit, so that the vehicle travels by the HV mode, as the predetermined processing, it may be a battery system that performs processing for starting the engine.

  The battery system described above is mounted on a plug-in hybrid vehicle as a drive power supply system for the plug-in hybrid vehicle including a motor and an engine. In this battery system, after the plug-in hybrid vehicle starts running in the EV mode, when the processing device discharges the lithium ion secondary battery, the battery voltage value of the lithium ion secondary battery becomes the battery voltage value of the voltage reduction unit. When it is determined that the engine has reached, the engine is started so that the plug-in hybrid vehicle travels in the HV mode. As a result, the plug-in hybrid vehicle travels by a combination of the motor drive and the engine drive, so that the discharge of the lithium ion secondary battery is suppressed (and the lithium ion secondary battery is charged). Can do. Thereby, the overdischarge of a lithium ion secondary battery can be prevented.

It is the schematic of an electric vehicle. 1 is a schematic diagram of a battery system according to Example 1. FIG. 1 is a cross-sectional view of a lithium ion secondary battery according to Example 1. FIG. It is sectional drawing of the electrode body of the lithium ion secondary battery. It is a partial expanded sectional view of the electrode body, and is equivalent to the B section enlarged view of FIG. It is a battery voltage fluctuation curve when the other lithium ion secondary battery A is discharged. It is a battery voltage fluctuation curve when the other lithium ion secondary battery A is charged. It is a battery voltage fluctuation curve when the other lithium ion secondary battery B is discharged. It is a battery voltage fluctuation curve when the other lithium ion secondary battery B is charged. It is a battery voltage fluctuation curve when the lithium ion secondary battery concerning Example 1 was discharged. 3 is a flowchart illustrating a flow of discharge control according to the first embodiment. 1 is a schematic view of a plug-in hybrid vehicle. 6 is a schematic diagram of a battery system according to Example 2. FIG. 6 is a flowchart illustrating a flow of discharge control according to the second embodiment.

Example 1
Next, Example 1 of the present invention will be described with reference to the drawings.
The battery system 6 of the first embodiment is mounted on the electric vehicle 1 as a drive power supply system for the electric vehicle 1 (see FIG. 1). As shown in FIG. 1, the electric vehicle 1 includes a vehicle body 2, a front motor 4, a rear motor 5, a battery system 6, a cable 7, and a power plug 8. Specifically, the electric vehicle 1 is configured so that the battery system 6 is mounted as a driving power source for the front motor 4 and the rear motor 5 and can be driven by driving the front motor 4 and the rear motor 5.

  The battery system 6 is attached to the vehicle body 2 of the electric vehicle 1 and is connected to the front motor 4 and the rear motor 5 by a cable 7. As shown in FIG. 2, the battery system 6 includes an assembled battery 30, a conversion device 44, a processing device 70, and a voltage detection device 50. The assembled battery 30 includes a plurality (for example, 100) of lithium ion secondary batteries 100 electrically connected in series. In addition, the charge state of all the lithium ion secondary batteries 100 which comprise the assembled battery 30 is made equal.

  The voltage detection device 50 detects one lithium ion secondary battery 100 battery voltage value (terminal voltage value) selected from the plurality of lithium ion secondary batteries 100 constituting the assembled battery 30. In the first embodiment, the terminal voltage between the positive terminal 120 and the negative terminal 130 of the lithium ion secondary battery 100 is detected as the battery voltage value of the lithium ion secondary battery 100.

  The processing device 70 includes a ROM, a CPU, a RAM, and the like (not shown), and is electrically connected to the assembled battery 30 via switches 41 and 42. The processing device 70 controls the discharge of the assembled battery 30 with the switches 41 and 42 turned on. For example, during operation of the electric vehicle 1, power supply from the assembled battery 30 to the inverter (motor) is controlled. The processing device 70 is connected to a control unit 60 (see FIG. 2) that controls the electric vehicle 1, and transmits and receives electrical signals to and from the control unit 60.

  In addition, the processing device 70 inputs the battery voltage value of the lithium ion secondary battery 100 detected by the voltage detection device 50. The ROM (not shown) of the processing device 70 stores in advance the battery voltage value of the lithium ion secondary battery 100 in a voltage drop unit DV (see FIG. 10) described later. In Example 1, 3.7 V is selected as the battery voltage value of the voltage drop unit DV from the battery voltage range in the voltage drop unit DV (a range of about 3.9 V to 3.4 V, see FIG. 10). And stored in a ROM (not shown) of the processing device 70.

  Furthermore, the processing device 70 inputs the battery voltage value of the lithium ion secondary battery 100 detected by the voltage detection device 50 at every predetermined timing when the lithium ion secondary battery 100 is discharged. Then, it is determined whether or not the battery voltage value of the lithium ion secondary battery 100 has reached the battery voltage value of the voltage drop unit DV (3.7 V in the first embodiment). When it is determined that the battery voltage value of the lithium ion secondary battery 100 has reached the battery voltage value of the voltage drop portion DV (3.7 V in the first embodiment), overdischarge of the lithium ion secondary battery 100 is prevented. Process to do. Specifically, a process of warning that the remaining amount of electricity of the lithium ion secondary battery 100 is small is performed. Specifically, a process of turning on a warning lamp 47 (see FIG. 2) for warning that the remaining amount of electricity of the lithium ion secondary battery 100 is small is performed.

  The warning lamp 47 is disposed at a position (for example, an instrument panel) that can be visually recognized by the driver of the electric vehicle 1. For this reason, the driver of the electric vehicle 1 can know that the remaining amount of electricity of the lithium ion secondary battery 100 is small by confirming that the warning lamp 47 is turned on. Thus, the driver of the electric vehicle 1 can stop the electric vehicle 1 and charge the lithium ion secondary battery 100 while electricity remains in the lithium ion secondary battery 100. Therefore, according to the battery system 6 of the first embodiment, overdischarge of the lithium ion secondary battery 100 constituting the assembled battery 30 can be prevented.

  The converter 44 is configured by an AC / DC converter, and can convert the voltage of the commercial power supply 46 into a DC constant voltage having a constant voltage value. The conversion device 44 is electrically connected to the power plug 8 through a cable 71 included in the cable 7. Further, the conversion device 44 is electrically connected to the assembled battery 30 via the switch 43.

  The power plug 8 is configured to be electrically connectable to the commercial power source 46. The power plug 8 is electrically connected to the conversion device 44. Therefore, the converter 44 and the commercial power source 46 can be electrically connected through the power plug 8. In the first embodiment, the cable 71 can be pulled out of the electric vehicle 1 together with the power plug 8, and the power plug 8 can be connected to a commercial power source 46 separated from the electric vehicle 1.

  For this reason, in the electric vehicle 1 of the first embodiment, the electric power supplied from the commercial power source 46 is used by electrically connecting the power plug 8 to the commercial power source 46 while the electric vehicle 1 is stopped. The lithium ion secondary battery 100 constituting the assembled battery 30 can be charged. When the processing device 70 monitors the conversion device 44 and detects that power is supplied from the commercial power supply 46 to the conversion device 44 through the power plug 8, the processing device 70 turns off the switches 41 and 42 and turns on the switch 43. To. Thereby, the lithium ion secondary battery 100 which comprises the assembled battery 30 can be charged using the electric power supplied from the commercial power supply 46. FIG. Specifically, the battery pack 30 converts the electric power supplied from the commercial power supply 46 through the converter 44 while converting the voltage of the commercial power supply 46 into a DC constant voltage having a predetermined constant voltage value by the converter 44. Is supplied to the lithium ion secondary battery 100 constituting the.

  As shown in FIG. 3, the lithium ion secondary battery 100 is a rectangular sealed lithium ion secondary battery including a rectangular parallelepiped battery case 110, a positive electrode terminal 120, and a negative electrode terminal 130. Among these, the battery case 110 is made of metal, and includes a rectangular housing portion 111 that forms a rectangular parallelepiped housing space, and a metal lid portion 112. An electrode body 150, a positive current collecting member 122, a negative current collecting member 132, and the like are accommodated in the battery case 110 (rectangular accommodation portion 111).

  The electrode body 150 is an oblong cross section, and is a flat wound body formed by winding a sheet-like positive electrode plate 155, a negative electrode plate 156, and a separator 157 (see FIGS. 4 and 5). The electrode body 150 is located at one end (right end in FIG. 3) in the axial direction (left and right in FIG. 3), and a positive winding part 155b in which only a part of the positive electrode plate 155 overlaps in a spiral shape, It is located at the other end (left end in FIG. 3) and has a negative electrode winding part 156b in which only a part of the negative electrode plate 156 overlaps in a spiral shape. The positive electrode plate 155 is coated with a positive electrode mixture 152 including a positive electrode active material 153 at a portion other than the positive electrode winding portion 155b (see FIG. 5). Similarly, a negative electrode mixture 159 including a negative electrode active material 154 is applied to the negative electrode plate 156 at portions other than the negative electrode winding portion 156b (see FIG. 5). The positive electrode winding part 155 b is electrically connected to the positive electrode terminal 120 through the positive electrode current collecting member 122. The negative electrode winding part 156 b is electrically connected to the negative electrode terminal 130 through the negative electrode current collecting member 132.

The lithium ion secondary battery 100 of Example 1 includes a first positive electrode active material that performs charge and discharge in a two-phase coexistence type as a main component (specifically, 80 wt%) of the positive electrode active material 153, and includes a positive electrode active material. As a subcomponent of the substance 153 (specifically, 20 wt%), a second positive electrode active material that performs charge and discharge in a two-phase coexistence type is included. In Example 1, LiMnPO ₄ is used as the first positive electrode active material, and LiFePO ₄ is used as the second positive electrode active material. Therefore, the positive electrode active material 153 is composed of 80 wt% LiMnPO ₄ and 20 wt% LiFePO ₄ .
Further, a carbon material (specifically, natural graphite) is used as the negative electrode active material 154.

Here, unlike the lithium ion secondary battery 100 of Example 1, only LiMnPO ₄ (first positive electrode active material of Example 1) was used as the positive electrode active material, and negative electrode active material 154 (natural graphite) was used as the negative electrode active material. ) Will be described. FIG. 6 shows a battery voltage fluctuation curve (curve representing the relationship between the depth of discharge and the battery voltage value) when the lithium ion secondary battery A is discharged. FIG. 7 shows a battery voltage fluctuation curve (curve representing the relationship between the charged state and the battery voltage value) when the lithium ion secondary battery A is charged.

As shown in FIG. 6, in the lithium ion secondary battery A, the theoretical electric capacity that LiMnPO ₄ (the first positive electrode active material of Example 1) can theoretically accumulate to the maximum in the battery voltage fluctuation curve when discharged. In the range of the electric capacity up to the upper limit (in the range of 0 to 100% of the discharge depth in FIG. 6), the range of 50% or more of the whole until the end of the discharge (specifically, 98% to 6% of the theoretical capacity) A discharge flat line FDA in which the fluctuation of the battery voltage value is 0.2 V or less (specifically, about 0.1 V) appears over a capacity range corresponding to 1 (range of discharge depth of 2 to 94% in FIG. 6). Thus, in the lithium ion secondary battery A in which the fluctuation of the battery voltage value is 0.2 V or less (specifically about 0.1 V) over a wide capacity range, stable output characteristics with small output fluctuation can be obtained.

Further, unlike the lithium ion secondary battery 100 of Example 1, only LiFePO ₄ (second positive electrode active material of Example 1) is used as the positive electrode active material, and negative electrode active material 154 (natural graphite) is used as the negative electrode active material. A lithium ion secondary battery B using the above will be described. FIG. 8 shows a battery voltage fluctuation curve (curve representing the relationship between the depth of discharge and the battery voltage value) when the lithium ion secondary battery B is discharged. Further, FIG. 9 shows a battery voltage fluctuation curve (curve representing the relationship between the charged state and the battery voltage value) when the lithium ion secondary battery B is charged.

As shown in FIG. 8, in the lithium ion secondary battery B, the theoretical electric capacity that LiFePO ₄ (second positive electrode active material of Example 1) can theoretically accumulate to the maximum in the battery voltage fluctuation curve when discharged. In the range of the electric capacity up to the upper limit (in the range of 0 to 100% of the discharge depth in FIG. 8), the range of 50% or more of the whole until the end of the discharge (specifically, 98% to 6% of the theoretical capacity) A discharge flat line FDB in which the fluctuation of the battery voltage value is 0.2 V or less (specifically, about 0.1 V) appears over a capacity range corresponding to (a range of discharge depth of 2 to 94% in FIG. 8). Thus, in the lithium ion secondary battery B in which the fluctuation of the battery voltage value is 0.2 V or less (specifically about 0.1 V) over a wide capacity range, stable output characteristics with small output fluctuation can be obtained. Note that the average voltage value (3.35 V) of the discharge flat line FDB is lower than the average voltage value (4.0 V) of the discharge flat line FDA (see FIGS. 6 and 8).

  In the above example, the lithium ion secondary battery A corresponds to the first lithium ion secondary battery, and the lithium ion secondary battery B corresponds to the second lithium ion secondary battery. Further, the discharge flat line FDA corresponds to the first discharge flat line, and the discharge flat line FDB corresponds to the second discharge flat line.

  By the way, in the lithium ion secondary batteries A and B, as shown in FIGS. 6 and 8, the battery voltage value hardly changes from the beginning of discharge (discharge depth 2%) to the end of discharge (discharge depth 94%). . For this reason, in the lithium ion secondary batteries A and B, at the time of discharging, it is difficult to detect the end of discharge (or approaching the end of discharge) based on the battery voltage value, which may cause overdischarge. .

  Next, FIG. 10 shows a battery voltage fluctuation curve (curve representing the relationship between the depth of discharge and the battery voltage value) when the lithium ion secondary battery 100 of Example 1 was discharged. As shown in FIG. 10, in the lithium ion secondary battery 100, in the battery voltage fluctuation curve when discharged, the first discharge flat part FDA1, the second discharge flat part FDB2, and the first discharge flat part FDA1 A voltage drop portion DV in which the battery voltage value falls over a range up to the two-discharge flat portion FDB2 appears.

  Here, the 1st discharge flat part FDA1 is corresponded to the part except the edge part (part whose discharge depth is 72% or more in FIG. 6) of the discharge flat line FDA (refer FIG. 6) at the end stage of discharge. The second discharge flat portion FDB2 corresponds to an end portion (portion at a discharge depth of 80 to 94% in FIG. 8) of the discharge flat line FDB (see FIG. 8), and discharges more than the first discharge flat portion FDA1. It is located on the end side (the side with the larger discharge depth) and has a voltage value lower than the voltage value of the first discharge flat part FDA1 (see FIG. 10). The voltage drop part DV has a battery voltage value that is significantly lower than that of the first discharge flat part FDA1 and the second discharge flat part FDB2.

The reason why such a battery voltage fluctuation curve appears is that, in the lithium ion secondary battery 100, as described above, LiMnPO ₄ (first positive electrode active material) is used as the main component (specifically, 80 wt%) of the positive electrode active material 153. This is because LiFePO ₄ (second positive electrode active material) is included as a subcomponent of the positive electrode active material 153 (specifically, 20 wt%).

  In the voltage drop part DV located between the first discharge flat part FDA1 and the second discharge flat part FDB2, the battery voltage is greatly lowered compared to the first discharge flat part FDA1 and the second discharge flat part FDB2. For this reason, when the lithium ion secondary battery 100 is discharged, the voltage detector 50 detects the battery voltage value of the lithium ion secondary battery 100 to easily detect that the voltage drop unit DV has been reached. . Specifically, as described above, the battery voltage value of the lithium ion secondary battery 100 detected by the voltage detection device 50 by the processing device 70 is the battery voltage value of the voltage drop unit DV (3 in the first embodiment). .7V), it can be determined whether or not the voltage drop portion DV has been reached.

  By the way, the voltage reduction part DV is a site | part close | similar to the terminal stage of discharge among battery voltage fluctuation curves, as shown in FIG. For this reason, when the lithium ion secondary battery 100 is discharged by the processing device 70, the battery voltage value of the lithium ion secondary battery 100 reaches the battery voltage value of the voltage drop portion DV (3.7 V in the first embodiment). It can be determined that the end of discharge is approaching. Therefore, at this time, the processing device 70 performs a process of warning that the remaining amount of electricity of the lithium ion secondary battery 100 is small (a process of turning on the warning lamp 47). It becomes possible to prevent the secondary battery 100 from being overdischarged.

  Moreover, in the lithium ion secondary battery 100, a wide capacity range including the first discharge flat portion FDA1 (specifically, a capacity range corresponding to 98% to 28% of the theoretical electric capacity, in FIG. The battery voltage value fluctuation is 0.1 V or less over a range of 72%), so that stable output characteristics with small output fluctuation can be obtained.

Next, the manufacturing method of the lithium ion secondary battery 100 of the first embodiment will be described.
First, LiMnPO ₄ and LiFePO ₄ are prepared. Next, a conductive carbon film is formed on the surface of LiMnPO ₄ . Similarly, a conductive carbon film is formed on the surface of LiFePO ₄ . In addition, the formation method of a carbon film can use the method currently disclosed by Unexamined-Japanese-Patent No. 2008-311067, for example. Next, LiMnPO ₄ and LiFePO ₄ having a carbon coating are mixed at a ratio (weight ratio) of 80:20 to obtain a positive electrode active material mixture (corresponding to the positive electrode active material 153). Thereafter, the positive electrode active material 153, acetylene black (conducting aid) and polyvinylidene fluoride (binder resin) were mixed at a ratio of 85: 5: 10 (weight ratio), and N-methylpyrrolidone (dispersing solvent) was mixed therewith. Were mixed to prepare a positive electrode slurry. Next, this positive electrode slurry was applied to the surface of the aluminum foil 151, dried, and then pressed. Thereby, the positive electrode plate 155 in which the positive electrode mixture 152 was coated on the surface of the aluminum foil 151 was obtained (see FIG. 5).

Further, natural graphite (negative electrode active material 154), styrene-butadiene copolymer (binder resin), and carboxymethyl cellulose (thickener) are used in a ratio of 95: 2.5: 2.5 (weight ratio). A negative electrode slurry was prepared by mixing in water. Next, this negative electrode slurry was applied to the surface of the copper foil 158, dried, and then pressed. Thereby, the negative electrode plate 156 in which the negative electrode mixture 159 was coated on the surface of the copper foil 158 was obtained (see FIG. 5).
In Example 1, the coating amounts of the positive electrode slurry and the negative electrode slurry are adjusted so that the ratio between the theoretical capacity of the positive electrode and the theoretical capacity of the negative electrode is 1: 1.5.

  Next, a positive electrode plate 155, a negative electrode plate 156, and a separator 157 were laminated and wound to form an electrode body 150 having an oval cross section (see FIGS. 4 and 5). However, when the positive electrode plate 155, the negative electrode plate 156, and the separator 157 are stacked, an uncoated portion of the positive electrode plate 155 that is not coated with the positive electrode mixture 152 protrudes from one end portion of the electrode body 150. Thus, the positive electrode plate 155 is arranged. Furthermore, the negative electrode plate 156 is arranged so that an uncoated portion of the negative electrode plate 156 not coated with the negative electrode mixture 159 protrudes from the opposite side of the positive electrode plate 155 from the uncoated portion. . Thereby, the electrode body 150 (refer FIG. 3) which has the positive electrode winding part 155b and the negative electrode winding part 156b is formed. In Example 1, a polypropylene / polyethylene / polypropylene three-layer structure composite porous membrane is used as the separator 157.

Next, the positive electrode winding part 155 b of the electrode body 150 and the positive electrode terminal 120 are connected through the positive electrode current collecting member 122. Further, the negative electrode winding portion 156 b of the electrode body 150 and the negative electrode terminal 130 are connected through the negative electrode current collecting member 132. Then, this was accommodated in the square accommodating part 111, the square accommodating part 111 and the cover body 112 were welded, and the battery case 110 was sealed. Next, after injecting an electrolyte through an injection port (not shown) provided in the lid 112, the injection port is sealed, whereby the lithium ion secondary battery 100 of Example 1 is completed. . In Example 1, as the electrolytic solution, lithium hexafluorophosphate (LiPF ₆ ) was used in a solution in which EC (ethylene carbonate) and DEC (diethyl carbonate) were mixed at a volume ratio of 4: 6.
Is used at a rate of 1 mol / L.

Next, the discharge control of the assembled battery 30 (lithium ion secondary battery 100) according to the first embodiment will be described.
For example, when the driver of the electric vehicle 1 depresses the accelerator pedal, the control unit 60 transmits a command (signal) for discharging the assembled battery 30 (the lithium ion secondary battery 100) to the processing device 70. When the processing device 70 receives an instruction to discharge the assembled battery 30 (lithium ion secondary battery 100) from the control unit 60, the processing apparatus 70 turns on the assembled battery 30 (lithium ion secondary battery 100) with the switches 41 and 42 turned on. ) Is discharged to supply power to the inverter (motor). As a result, the electric vehicle 1 travels by driving the front motor 4 and the rear motor 5.

  When the processing device 70 starts discharging the assembled battery 30 (lithium ion secondary battery 100), as shown in FIG. 11, the battery voltage of the lithium ion secondary battery 100 detected by the voltage detection device 50 in step S1. Enter (detect) a value. Subsequently, it progresses to step S2, and the processing apparatus 70 judges whether the battery voltage value of the lithium ion secondary battery 100 has reached 3.7V (battery voltage value of the voltage reduction part DV). If it is determined that the battery voltage value of the lithium ion secondary battery 100 has not reached 3.7 V (No), the process returns to step S1 again, and the above-described processing is performed.

  On the other hand, if it is determined in step S2 that the battery voltage value of the lithium ion secondary battery 100 has reached 3.7V (Yes), the process proceeds to step S3, and the processing device 70 determines that the lithium ion secondary battery 100 has A warning lamp 47 is lit to warn that the amount of remaining electricity is small. The driver of the electric vehicle 1 can know that the remaining electricity amount of the lithium ion secondary battery 100 is small by confirming that the warning lamp 47 is turned on. Accordingly, the driver of the electric vehicle 1 can stop the electric vehicle 1 and charge the lithium ion secondary battery 100 while electricity remains in the lithium ion secondary battery 100. In this way, the warning lamp 47 is turned on to prompt the driver of the electric vehicle 1 to charge the lithium ion secondary battery 100, thereby over-discharging the lithium ion secondary battery 100 constituting the assembled battery 30. It becomes possible to prevent.

  Then, it progresses to step S4 and the processing apparatus 70 judges whether discharge of the lithium ion secondary battery 100 has stopped. When the processing device 70 receives an instruction to stop the discharge of the assembled battery 30 (lithium ion secondary battery 100) from the control unit 60 and stops the discharge of the lithium ion secondary battery 100, the lithium ion secondary battery It can be determined that the discharge of the battery 100 is stopped. When it is determined that the discharge of the lithium ion secondary battery 100 is stopped (Yes), the series of processes is terminated. In addition, when the processing apparatus 70 receives the instruction | command which stops the discharge of the assembled battery 30 (lithium ion secondary battery 100) from the control unit 60, when the discharge of the lithium ion secondary battery 100 is stopped, for example, driving | operation A case where the person takes his / her foot off the accelerator pedal and stops the electric vehicle 1 can be mentioned.

  On the other hand, when the processing device 70 determines that the discharge of the lithium ion secondary battery 100 is not stopped (No), the processing device 70 proceeds to step S5 and newly detects the lithium ion secondary battery detected by the voltage detection device 50. 100 battery voltage values are input (detected). Subsequently, it progresses to step S6 and it is judged whether the battery voltage value of the lithium ion secondary battery 100 has reached 3.0V. If it is determined that the battery voltage value of the lithium ion secondary battery 100 has not reached 3.0V (No), the process returns to step S4, and again whether or not the discharge of the lithium ion secondary battery 100 is stopped. to decide. In this way, the processes in steps S4 to S6 are repeated until it is confirmed that the lithium ion secondary battery 100 has stopped discharging.

  As shown in FIG. 10, when the battery voltage value of the lithium ion secondary battery 100 reaches 3.0 V, the end of discharge (discharge depth 98%) has been reached, and the lithium ion secondary battery 100 is no longer discharged. If it continues, it will be overdischarged. Therefore, when the processing device 70 determines in step S6 that the battery voltage value of the lithium ion secondary battery 100 has reached 3.0 V (Yes), the processing device 70 proceeds to step S7, and the lithium ion secondary battery 100 is processed. Stop discharging. Thereby, the over discharge of the lithium ion secondary battery 100 which comprises the assembled battery 30 can be prevented.

(Example 2)
Next, Embodiment 2 of the present invention will be described with reference to the drawings. Here, the description will focus on the points different from the first embodiment, and the description of the same points as in the first embodiment will be omitted or simplified.

  The battery system 16 of the second embodiment is mounted on the plug-in hybrid vehicle 11 as a drive power supply system for the plug-in hybrid vehicle 11 (see FIG. 12). As shown in FIG. 12, the battery system 16 includes a vehicle body 2, an engine 3, a front motor 4, a rear motor 5, a battery system 16, a cable 7, and a power plug 8. The plug-in hybrid vehicle 11 includes a motor (a front motor 4 and a rear motor 5) using electric power supplied by discharging an assembled battery 30 (lithium ion secondary battery 100) constituting the battery system 16 without driving the engine 3. ) And an HV mode that travels by a combination of driving of the motor (front motor 4 and rear motor 5) and driving of the engine 3.

As shown in FIG. 13, the battery system 16 includes an assembled battery 30, a conversion device 44, a processing device 270, and a voltage detection device 50.
The processing device 270 includes a ROM, a CPU, a RAM, and the like (not shown), and is electrically connected to the assembled battery 30 via the switches 41 and 42. The processing device 270 controls charging / discharging of the assembled battery 30 in a state where the switches 41 and 42 are turned on. For example, during operation of the plug-in hybrid vehicle 11, the exchange of electric power between the assembled battery 30 and the inverter (motor) is controlled. The processing device 270 is connected to the control unit 260 that controls the plug-in hybrid vehicle 11, and transmits and receives electrical signals to and from the control unit 260.

  Further, the processing device 270 inputs the battery voltage value of the lithium ion secondary battery 100 detected by the voltage detection device 50. The ROM (not shown) of the processing device 270 stores the battery voltage value of the lithium ion secondary battery 100 in the voltage drop unit DV (see FIG. 10) in advance. In the second embodiment, as in the first embodiment, 3.7 V is selected as the battery voltage value of the voltage drop unit DV and stored in the ROM (not shown) of the processing device 270.

  Furthermore, after the plug-in hybrid vehicle 11 starts running in the EV mode, the processing device 270 is configured to detect the lithium ion secondary detected by the voltage detection device 50 at predetermined timing when the lithium ion secondary battery 100 is discharged. The battery voltage value of the battery 100 is input. Then, it is determined whether or not the battery voltage value of the lithium ion secondary battery 100 has reached the battery voltage value (3.7 V in the second embodiment) of the voltage drop unit DV. When it is determined that the battery voltage value of the lithium ion secondary battery 100 has reached the battery voltage value of the voltage drop portion DV (3.7 V in the present embodiment 2), the lithium ion secondary battery 100 is prevented from being overdischarged. Process to do. Specifically, a process of starting the engine 3 is performed so that the plug-in hybrid vehicle 11 travels in the HV mode.

  As a result, the plug-in hybrid vehicle 11 travels by a combination of driving of the motors (front motor 4 and rear motor 5) and driving of the engine 3, thereby suppressing discharge of the lithium ion secondary battery 100 (and further The lithium ion secondary battery 100 can be charged). Thereby, the overdischarge of the lithium ion secondary battery 100 can be prevented.

  In the plug-in hybrid vehicle 11 of the second embodiment, the power supplied from the commercial power supply 46 can be obtained by electrically connecting the power plug 8 to the commercial power supply 46 during the stop period of the plug-in hybrid vehicle 11. It is possible to charge the lithium ion secondary battery 100 that constitutes the assembled battery 30. When the processing device 270 monitors the conversion device 44 and detects that power is supplied from the commercial power supply 46 to the conversion device 44 through the power plug 8, the processing device 270 turns off the switches 41 and 42 and turns on the switch 43. To. Thereby, the lithium ion secondary battery 100 which comprises the assembled battery 30 can be charged using the electric power supplied from the commercial power supply 46 similarly to the electric vehicle 1 of Example 1. FIG.

Next, the discharge control of the assembled battery 30 (lithium ion secondary battery 100) according to the second embodiment will be described.
For example, after the charging of the assembled battery 30 (lithium ion secondary battery 100) mounted on the plug-in hybrid vehicle 11 using the power supplied from the commercial power supply 46 as described above, the plug-in When the main power source (main switch) of the hybrid vehicle 11 is turned on, the EV mode is selected by the control unit 260. After that, when the driver of the plug-in hybrid vehicle 11 depresses the accelerator pedal, the processing device 270 discharges the assembled battery 30 (lithium ion secondary battery 100) with the switches 41 and 42 turned on, and the inverter Supply power to the (motor). As a result, the plug-in hybrid vehicle 11 travels by driving the front motor 4 and the rear motor 5. In the EV mode, the engine 3 is not driven.

  When the processing device 270 starts discharging the assembled battery 30 (lithium ion secondary battery 100), as shown in FIG. 13, the battery voltage of the lithium ion secondary battery 100 detected by the voltage detection device 50 in step T1. Enter (detect) a value. Next, the process proceeds to Step T2, and the processing device 270 determines whether or not the battery voltage value of the lithium ion secondary battery 100 has reached 3.7V (battery voltage value of the voltage drop unit DV). When it is determined that the battery voltage value of the lithium ion secondary battery 100 has not reached 3.7 V (No), the process returns to step T1 again and the above-described processing is performed.

  On the other hand, when it is determined in step T2 that the battery voltage value of the lithium ion secondary battery 100 has reached 3.7 V (Yes), the process proceeds to step T3, and the processing device 270 starts the engine 3. At this time, the control unit 260 switches from the EV mode to the HV mode. As a result, the plug-in hybrid vehicle 11 travels by a combination of driving of the motors (front motor 4 and rear motor 5) and driving of the engine 3, thereby suppressing discharge of the lithium ion secondary battery 100 (further, lithium ion The secondary battery 100 can be charged). Thereby, the overdischarge of the lithium ion secondary battery 100 can be prevented.

  In the above, the present invention has been described with reference to the first and second embodiments. However, the present invention is not limited to the above-described embodiment, and it can be applied as appropriate without departing from the scope of the present invention. Nor.

DESCRIPTION OF SYMBOLS 1 Electric vehicle 3 Engine 4 Front motor 5 Rear motor 6, 16 Battery system 11 Plug-in hybrid vehicle 30 Battery 50 Voltage detection apparatus 70,270 Processing apparatus 100 Lithium ion secondary battery 153 Positive electrode active material 154 Negative electrode active material DV Voltage reduction part FDA1 first discharge flat part FDB2 second discharge flat part

Claims (15)

A lithium ion secondary battery comprising a positive electrode active material and a negative electrode active material,
The positive electrode active material is
A first positive electrode active material that performs charge and discharge in a two-phase coexistence type as a main component;
A second positive electrode active material that performs charge and discharge in a two-phase coexistence type as a subcomponent,
The first positive electrode active material is
In the battery voltage fluctuation curve when the first lithium ion secondary battery using the first positive electrode active material and the negative electrode active material is discharged, the theoretical electricity that the first positive electrode active material can theoretically accumulate to the maximum extent is possible. Over the range of 50% or more of the total capacity until the end of discharge in the range of electric capacity with the capacity as the upper limit, the first discharge flat line having a fluctuation of the battery voltage value of 0.2 V or less appears,
The second positive electrode active material is
In the battery voltage fluctuation curve when the second lithium ion secondary battery using the second positive electrode active material and the negative electrode active material is discharged, the theoretical electricity that the second positive electrode active material can theoretically accumulate to the maximum extent is possible. A second discharge flat line in which the fluctuation of the battery voltage value is 0.2 V or less appears in a range of 50% or more of the entire capacity up to the end of discharge in the range of electric capacity with the upper limit of capacity, and the second discharge The flat line has an average voltage value lower than the average voltage value of the first discharge flat line,
The lithium ion secondary battery is
In the battery voltage fluctuation curve when the lithium ion secondary battery is discharged,
A first discharge flat portion corresponding to a portion of the first discharge flat wire excluding an end portion on a discharge end side;
A second discharge flat portion corresponding to an end portion on the discharge end side of the second discharge flat line, located on a discharge end side with respect to the first discharge flat portion, and from a voltage value of the first discharge flat portion A second discharge flat portion having a low voltage value;
A voltage reduction unit in which a battery voltage decreases over a range from the first discharge flat unit to the second discharge flat unit, wherein the battery voltage is higher than that of the first discharge flat unit and the second discharge flat unit. A lithium ion secondary battery having a characteristic that a voltage drop portion that greatly decreases. The lithium ion secondary battery according to claim 1,
The positive electrode active material is
As an auxiliary component, LiMO ₂ (M includes at least one of Ni, Co, and Mn),
The first positive electrode active material is:
In the battery voltage fluctuation curve when charging the first lithium ion secondary battery,
A first charging flat line in which the fluctuation of the battery voltage value is 0.2 V or less over a range of 50% or more of the entire capacity up to the end of charging in the range of the electric capacity with the theoretical electric capacity as an upper limit;
A first charging end line adjacent to the first charging flat line, and a first charging end section where the battery voltage value rapidly increases compared to the first charging flat line,
When the carbon material is used as the negative electrode active material, the first charging flat wire has an average voltage value of 4.5 V or less,
The lithium ion secondary battery is
In the battery voltage fluctuation curve when the lithium ion secondary battery is charged,
A first charging flat portion corresponding to a portion of the first charging flat line excluding an end portion on an initial charging side and an end portion on an end charging side;
Lithium having a characteristic that an end-of-charge portion adjacent to the first charge flat portion and a second end-of-charge portion in which a battery voltage value gradually increases over a wide capacity range as compared with the first end-of-charge portion Ion secondary battery. A lithium ion secondary battery comprising a positive electrode active material and a negative electrode active material,
The positive electrode active material is
A first positive electrode active material that performs charge and discharge in a two-phase coexistence type as a main component;
LiMO ₂ (M includes at least one of Ni, Co, and Mn) as a subcomponent,
The first positive electrode active material is
In the battery voltage fluctuation curve when charging the first lithium ion secondary battery using the first positive electrode active material and the negative electrode active material,
The fluctuation of the battery voltage value is 0.00% over a range of 50% or more of the total capacity up to the end of charging, within the range of the electric capacity up to the theoretical electric capacity that the first positive electrode active material can theoretically store to the maximum. A first charging flat wire of 2V or less;
A first charging end line adjacent to the first charging flat line and a battery voltage value rapidly rising compared to the first charging flat line,
When the carbon material is used as the negative electrode active material, the first charging flat wire has an average voltage value of 4.5 V or less,
The lithium ion secondary battery is
In the battery voltage fluctuation curve when the lithium ion secondary battery is charged,
A first charging flat portion corresponding to a portion of the first charging flat wire excluding a portion at the end of charging;
Lithium having a characteristic that an end-of-charge portion adjacent to the first charge flat portion and a second end-of-charge portion in which a battery voltage value gradually increases over a wide capacity range as compared with the first end-of-charge portion Ion secondary battery. The lithium ion secondary battery according to claim 3,
The positive electrode active material is
As a secondary component, including a second positive electrode active material that performs charge and discharge in a two-phase coexistence type,
The first positive electrode active material is:
In the battery voltage fluctuation curve when the first lithium ion secondary battery is discharged, the battery covers over 50% or more of the range up to the end of discharge in the range of the capacity with the theoretical capacity as the upper limit. A first discharge flat line having a voltage value fluctuation of 0.2 V or less appears,
The second positive electrode active material is
In the battery voltage fluctuation curve when the second lithium ion secondary battery using the second positive electrode active material and the negative electrode active material is discharged, the theoretical electricity that the second positive electrode active material can theoretically accumulate to the maximum extent is possible. A second discharge flat line in which the fluctuation of the battery voltage value is 0.2 V or less appears in a range of 50% or more of the entire capacity up to the end of discharge in the range of electric capacity with the upper limit of capacity, and the second discharge The flat line has an average voltage value lower than the average voltage value of the first discharge flat line,
The lithium ion secondary battery is
In the battery voltage fluctuation curve when the lithium ion secondary battery is discharged,
A first discharge flat portion corresponding to a portion of the first discharge flat wire excluding an end portion on a discharge end side;
A second discharge flat portion corresponding to an end portion on the discharge end side of the second discharge flat line, located on a discharge end side with respect to the first discharge flat portion, and from a voltage value of the first discharge flat portion A second discharge flat portion having a low voltage value;
A voltage reduction unit in which a battery voltage decreases over a range from the first discharge flat unit to the second discharge flat unit, wherein the battery voltage is higher than that of the first discharge flat unit and the second discharge flat unit. A lithium ion secondary battery having a characteristic that a voltage drop portion that greatly decreases. The lithium ion secondary battery according to claim 2 or 4,
The first positive electrode active material is LiFePO ₄ ,
The lithium ion secondary battery in which the second positive electrode active material is Li ₃ Fe ₂ (PO ₄ ) ₃ . The lithium ion secondary battery according to claim 1, claim 2, claim 4, or claim 5,
A voltage detection device for detecting a battery voltage value of the lithium ion secondary battery;
The battery voltage value of the lithium ion secondary battery in the voltage reduction unit is stored in advance, and based on the battery voltage value of the voltage reduction unit detected by the voltage detection device when the lithium ion secondary battery is discharged. And a processing device that performs a predetermined process for preventing overdischarge of the lithium ion secondary battery. The battery system according to claim 6,
The battery system is mounted on the electric vehicle as a drive power system for the electric vehicle,
The processing device determines whether or not a battery voltage value of the lithium ion secondary battery detected by the voltage detection device has reached a battery voltage value of the voltage reduction unit when the lithium ion secondary battery is discharged. And when it is judged that the battery voltage value of the said voltage reduction part has been reached, the battery system which performs the process which warns that the remaining electricity amount of the said lithium ion secondary battery is small as said predetermined process. The battery system according to claim 6,
The battery system includes:
As a drive power supply system for a plug-in hybrid vehicle equipped with a motor and an engine, it is installed in the vehicle,
The above car
EV mode that travels by driving the motor using power supplied by discharging the lithium ion secondary battery without driving the engine, and HV that travels by a combination of driving the motor and driving the engine It is configured to be able to run according to any of the modes,
The processor is
After the automobile starts running in the EV mode, the battery voltage value of the lithium ion secondary battery detected by the voltage detection device when the lithium ion secondary battery is discharged is the battery voltage value of the voltage reduction unit. The process of starting the engine as the predetermined process so that the vehicle travels in the HV mode when it is determined that the battery voltage value of the voltage drop unit has been reached. Do the battery system. The battery system according to any one of claims 6 to 8,
The lithium ion secondary battery is the lithium ion secondary battery according to claim 2, claim 4, or claim 5,
The processing device stores in advance a battery voltage value of the lithium ion secondary battery at the second end of charging, and the second voltage detected by the voltage detection device during charging of the lithium ion secondary battery. A battery system that performs a predetermined process for preventing overcharging of the lithium ion secondary battery based on the battery voltage value at the end of charging. The battery system according to claim 9,
Whether the battery voltage value of the lithium ion secondary battery detected by the voltage detection device has reached the battery voltage value at the end of the second charge at the time of charging the lithium ion secondary battery. When the battery voltage value at the end of the second charge has been reached, the battery system performs a process for stopping the charging of the lithium ion secondary battery as the predetermined process. The lithium ion secondary battery according to any one of claims 2 to 5,
A voltage detection device for detecting a battery voltage value of the lithium ion secondary battery;
The battery voltage value of the lithium ion secondary battery at the second charge end stage is stored in advance, and the battery at the second charge end stage detected by the voltage detector when the lithium ion secondary battery is charged. A battery system comprising: a processing device that performs a predetermined process for preventing overcharging of the lithium ion secondary battery based on a voltage value. The battery system according to claim 11,
Whether the battery voltage value of the lithium ion secondary battery detected by the voltage detection device has reached the battery voltage value at the end of the second charge at the time of charging the lithium ion secondary battery. When the battery voltage value at the end of the second charge has been reached, the battery system performs a process for stopping the charging of the lithium ion secondary battery as the predetermined process. The battery system according to claim 11 or 12,
The lithium ion secondary battery is the lithium ion secondary battery according to claim 2, claim 4, or claim 5,
The processing device stores in advance a battery voltage value of the lithium ion secondary battery in the voltage reduction unit, and the voltage reduction unit detected by the voltage detection device when the lithium ion secondary battery is discharged. A battery system that performs a predetermined process for preventing overdischarge of the lithium ion secondary battery based on a battery voltage value. The battery system according to claim 13,
The battery system is mounted on the electric vehicle as a drive power system for the electric vehicle,
The processing device determines whether or not a battery voltage value of the lithium ion secondary battery detected by the voltage detection device has reached a battery voltage value of the voltage reduction unit when the lithium ion secondary battery is discharged. And when it is judged that the battery voltage value of the said voltage reduction part has been reached, the battery system which performs the process which warns that the remaining electricity amount of the said lithium ion secondary battery is small as said predetermined process. The battery system according to claim 13,
The battery system includes:
As a drive power supply system for a plug-in hybrid vehicle equipped with a motor and an engine, it is installed in the vehicle,
The above car
EV mode that travels by driving the motor using power supplied by discharging the lithium ion secondary battery without driving the engine, and HV that travels by a combination of driving the motor and driving the engine It is configured to be able to run according to any of the modes,
The processor is
After the automobile starts running in the EV mode, the battery voltage value of the lithium ion secondary battery detected by the voltage detection device when the lithium ion secondary battery is discharged is the battery voltage value of the voltage reduction unit. The process of starting the engine as the predetermined process so that the vehicle travels in the HV mode when it is determined that the battery voltage value of the voltage drop unit has been reached. Do the battery system.

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