JP5326679B2 - Lithium ion secondary battery charge / discharge control method, secondary battery system, and hybrid vehicle - Google Patents

Description

  The present invention relates to a charge / discharge control method for a lithium ion secondary battery, a secondary battery system having a lithium ion secondary battery, and a hybrid vehicle having the secondary battery system.

  Secondary batteries such as nickel metal hydride storage batteries and lithium ion secondary batteries are in high demand as power sources for portable devices and as power sources for electric vehicles and hybrid vehicles. For this reason, in recent years, various charge / discharge control methods for secondary batteries have been proposed (see, for example, Patent Document 1).

JP 2003-9415 A

  Patent Document 1 proposes a charge / discharge control method for a nickel-metal hydride storage battery. Specifically, repeated charging / discharging without the memory effect (complete discharge (SOC is almost 0%) or full charge (SOC is almost 100%)) decreases the electromotive force value relative to the remaining capacity of the storage battery. Has been proposed.

By the way, in recent years, a lithium ion secondary battery using a lithium transition metal composite oxide having an olivine structure represented by a composition formula LiFePO ₄ or the like has been proposed as a positive electrode active material. 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. For this reason, a secondary battery having a positive electrode active material that performs charge and discharge in a two-phase coexistence type has recently attracted attention as a power source for hybrid vehicles and the like.

  However, when a lithium ion secondary battery having a positive electrode active material that performs charge and discharge in a two-phase coexistence type is mounted as a power source for driving a hybrid vehicle, charging and discharging are often repeated in a short time. In many cases, charging and discharging are repeated within a range of 60%. When such charge / discharge is repeated, localization of Li ions (a phenomenon in which Li ions are unevenly present in the positive electrode active material) occurs in the crystal of the positive electrode active material that performs charge and discharge in a two-phase coexistence type. End up. Due to this influence, the discharge capacity of the lithium ion secondary battery may be greatly reduced, and the performance of the lithium ion secondary battery may not be fully exploited.

  In addition, although localization of Li ion can be eliminated by performing refresh charging / discharging (complete charging or complete discharging is intentionally performed), since refresh charging / discharging requires time, time for operating as a secondary battery system This is not preferable.

  The present invention has been made in view of the present situation, and for a lithium ion secondary battery having a positive electrode active material that performs charge and discharge in a two-phase coexistence type, suppressing the localization of Li ions, battery performance An object of the present invention is to provide a charge / discharge control method for a lithium ion secondary battery, a secondary battery system, and a hybrid vehicle.

The solution is a method for controlling charging and discharging of a lithium ion secondary battery having a positive electrode active material that performs charge and discharge in a two-phase coexistence type, wherein the lithium ion secondary battery is charged with a discharge end charge depth SOC _D. use between charging end charging depth SOC _C and, the discharge termination charge depth SOC _D and charge end charging depth SOC _C, with the lower limit charging depth SOC _B and the upper limit charge depth SOC _T A charge / discharge control method for a lithium ion secondary battery that is sequentially changed, wherein the positive electrode active material is LiM1 _(1-X) M2 _X PO ₄ (M1 is Fe or Mn, and M2 is Mn, Cr, It is at least one of Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga, Mg, B, and Nb (however, when M1 is Mn, Mn is excluded), and 0 ≦ X ≦ 0.5 ) is a compound represented by the above lower limit charging depth SOC _B A value in the range of 15% to 30%, the upper limit charge depth SOC _T is a value within the range of 80% to 100%, and the discharge termination charge depth SOC _D and the charging end charging depth SOC _C Is a charge / discharge control method for a lithium ion secondary battery in which the difference is in the range of 10 to 50% .

The method of controlling charge and discharge of the lithium ion secondary battery of the present invention, a lithium ion secondary battery, used between the discharge termination charge depth SOC _D and charge end charging depth SOC _C. Here, the discharge cutoff charge depth, when viewed on a single discharge means the SOC value at the time of discharge termination (and SOC _D). Further, the end-of-charge charge depth refers to the SOC value (referred to as SOC _C ) at the end of charge when viewed with respect to one charge.

Furthermore, in the charge / discharge control method for a lithium ion secondary battery of the present invention, the end-of-discharge charge depth SOC _D and the end-of-charge charge depth SOC _C are set between the lower limit charge depth SOC _B and the upper limit charge depth SOC _T. Change sequentially. Here, the upper limit charge depth refers to the SOC value to prohibit the charging leading to no more SOC (State Of Charge) (a SOC _T). In addition, the lower limit charging depth refers to a SOC value (SOC _B ) that prohibits discharge to SOC below this level.

Specifically, for example, the lower limit charge depth SOC _{B is set} to 30%, the upper limit charge depth SOC _T is set to 90%, and the difference between the charge end charge depth SOC _C and the discharge end charge depth SOC _D is set to 10 There is a method in which SOC _D and SOC _C are sequentially changed between SOC _B and SOC _T (see FIG. 6). In this method, for example, in the first cycle, the discharge end charge depth SOC _D is 80% and the charge end charge depth SOC _C is 90% (same as SOC _T ), and the second cycle is SOC _B and SOC _C the first cycle of SOC _C less than, for example, 70% SOC _D, the charging and discharging of the SOC _C as 80% performed. Thus while reducing the SOC _B and SOC _C per cycle, charging and discharging until the discharge termination charge depth SOC _D is equivalent and lower charging depth SOC _B. Then, when it SOC _D is the same value and SOC _B, performed in the opposite turn, until SOC _C is SOC _T and equivalence, a significantly while charging and discharging the SOC _B and SOC _C per cycle.

Thus, for the lithium ion secondary battery having a positive electrode active material that performs charge and discharge in a two-phase coexistence type, the discharge end charge depth SOC _D and the charge end charge depth SOC _C are set to the lower limit charge depth SOC _B and the upper limit. by charging and discharging while sequentially varying between charging depth SOC _T, it is possible to suppress the localization of the Li ions in the positive electrode active material. Thereby, the fall of the discharge capacity of a lithium ion secondary battery is suppressed, and it becomes possible to fully draw out the performance of a lithium ion secondary battery.

Note that the SOC _D per cycle, (or even without regularly vertically are) irregularly is caused which may be varied. This is because, for example, when a lithium ion secondary battery is used as a main power source of a hybrid vehicle or the like, the regulation of SOC _C stays only at a reduction in regeneration efficiency, whereas the regulation of SOC _D is strictly performed, for example, This is because an instantaneous large current discharge cannot be performed in a low SOC region, and the function as a main power source of a hybrid vehicle or the like deteriorates.

  In addition, as the SOC (State Of Charge), for example, a value obtained by quantifying the percentage based on the battery capacity of the lithium ion secondary battery and the value obtained by integrating the charge / discharge current amount can be used.

The compound represented by the composition formula of LiM1 _(1-X) M2 _X PO ₄ is a positive electrode active material that performs charge and discharge in a two-phase coexistence type. Regarding the lithium ion secondary battery using this positive electrode active material, as described above, the end-of-discharge charge depth SOC _D and the end-of-charge charge depth SOC _C are set as the lower limit charge depth SOC _B and the upper limit charge depth SOC _T. By performing charging / discharging while sequentially changing between these, localization of Li ions in the positive electrode active material can be suppressed. Thereby, the fall of the discharge capacity of a lithium ion secondary battery is suppressed, and it becomes possible to fully draw out the performance of a lithium ion secondary battery.

Further, the charge and discharge control method of the present invention, the lower limit charging depth SOC _B to a value within the range of 15% to 30%, and the upper limit charge depth SOC _T to a value within the range of 80% to 100%.
In a lithium ion secondary battery using the compound represented by the above composition formula as a positive electrode active material, the battery voltage rapidly decreases when the SOC is less than 15% (see FIG. 7). Therefore, by setting the lower limit charging depth SOC _B to 15% or more, it is possible to prevent the battery voltage from being reduced, and thus the output characteristics of the lithium ion secondary battery can be improved.

Further, by setting the lower limit charge depth SOC _B to 30% or less and the upper limit charge depth SOC _T to 80% or more, the discharge end charge depth SOC _D and the charge end charge depth SOC _C are set to the lower limit charge depth. A sufficiently large variation can be made between the SOC _B and the upper limit charging depth SOC _T. Thereby, localization of Li ions in the positive electrode active material can be appropriately suppressed.

In addition, in the lithium ion secondary battery using the compound represented by the above composition formula as the positive electrode active material, the battery voltage hardly varies in the range of SOC 30% to 80%. Therefore, by setting SOC _B to 30% or less and SOC _T to 80% or more, a lithium ion secondary battery can be discharged with almost no change in battery voltage in a wide capacity range of SOC 30% to 80%. it can. Thereby, stable output characteristics can be obtained.

Further, the upper limit charge depth SOC _T by 100% or less, it is possible to prevent overcharging. As a result, it is possible to prevent problems due to overcharge (such as a decrease in electrolyte due to gas generation inside the battery and an early life span).
Furthermore, in the charge / discharge control method of the present invention, the difference between the charge end charge depth SOC _C and the discharge end charge depth SOC _D is set within a range of 10 to 50%. That is, the amount of electricity charged or discharged once is set to an amount of electricity corresponding to a value within the range of SOC 10% to 50%. In this way, SOC _D and SOC _C are set between the lower limit charge depth SOC _B (value in the range of 15 to 30%) and the upper limit charge depth SOC _T (value in the range of 80 to 100%). By performing charging / discharging while sequentially changing, the localization of Li ions in the positive electrode active material can be appropriately suppressed.

Furthermore, a method of controlling charge and discharge of the lithium ion secondary battery described above, the upper limit charge depth SOC _T is a method of controlling charge and discharge of the lithium ion secondary battery as a value in the range of 85% to 95% Is preferred.

By the upper limit charge depth SOC _T 85% or higher, it is possible to further suppress the localization of the Li ions in the positive electrode active material. Further, the upper limit charge depth SOC _T by 95% or less, it is possible to reliably prevent overcharging.

Furthermore, in any one of the above lithium ion secondary battery charge / discharge control methods, a difference between the end-of-charge charge depth SOC _C and the end-of-discharge charge depth SOC _D is in a range of 10 to 30%. It is preferable to use a charge / discharge control method for a lithium ion secondary battery.

  According to this charge / discharge control method, localization of Li ions in the positive electrode active material can be further suppressed.

Another solution is a secondary battery system comprising: a lithium ion secondary battery having a positive electrode active material that performs charge and discharge in a two-phase coexistence type; and a control device that controls charge and discharge of the lithium ion secondary battery. there are, the control device controls the charging and discharging between the lithium ion secondary battery with discharge cutoff charge depth SOC _D and charge end charging depth SOC _C, and, the end-of-discharge charge depths SOC _D and a charge termination charge depth SOC _C are secondary battery systems that perform control to sequentially vary between a lower limit charge depth SOC _B and an upper limit charge depth SOC _T , wherein the positive electrode active material is LiM1 _{( 1-X)} M2 _X PO ₄ (M1 is Fe or Mn, and M2 is at least one of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga, Mg, B, and Nb. Either (however, when M1 is Mn Except for Mn), and 0 ≦ X ≦ 0.5). The lower limit charge depth SOC _B is a value in the range of 15 to 30%, and the upper limit charge depth SOC _T Is a value in the range of 80 to 100% , and is a secondary battery system in which the difference between the charge end charge depth SOC _C and the discharge end charge depth SOC _D is in the range of 10 to 50% .

In the secondary battery system of the present invention, the control device performs control to charge and discharge the lithium ion secondary battery between the end-of-discharge charge depth SOC _D and the end-of-charge charge depth SOC _C , and the end-of-discharge charge. A positive electrode active material that performs charge and discharge in a two-phase coexistence type by sequentially varying the depth SOC _D and the end-of-charge charge depth SOC _C between the lower limit charge depth SOC _B and the upper limit charge depth SOC _T Controls charging and discharging of the lithium ion secondary battery. Thereby, about the lithium ion secondary battery which has a positive electrode active material which performs charge / discharge of 2 phase coexistence type, localization of Li ion in a positive electrode active material can be suppressed. Therefore, it is possible to suppress a decrease in the discharge capacity of the lithium ion secondary battery, and to fully draw out the performance of the lithium ion secondary battery.

The compound represented by the composition formula of LiM1 _(1-X) M2 _X PO ₄ is a positive electrode active material that performs charge and discharge in a two-phase coexistence type. Regarding the lithium ion secondary battery using this positive electrode active material, as described above, the end-of-discharge charge depth SOC _D and the end-of-charge charge depth SOC _C are set as the lower limit charge depth SOC _B and the upper limit charge depth SOC _T. By controlling charging / discharging while sequentially changing between, the localization of Li ions in the positive electrode active material can be suppressed. Thereby, the fall of the discharge capacity of a lithium ion secondary battery is suppressed, and it becomes possible to fully draw out the performance of a lithium ion secondary battery.

Furthermore, in the secondary battery system of the present invention, the lower limit charge depth SOC _B is a value within the range of 15 to 30% for the lithium ion secondary battery using the compound represented by the composition formula as a positive electrode active material. and then, and the upper limit charge depth SOC _T as a value in the range of 80% to 100%, control device, as described above, controls the charging and discharging of the lithium ion secondary battery.
By setting the lower limit charging depth SOC _B to 15% or more, the battery voltage can be prevented from becoming small, and the output characteristics of the lithium ion secondary battery can be improved.

Further, by setting the lower limit charge depth SOC _B to 30% or less and the upper limit charge depth SOC _T to 80% or more, the discharge end charge depth SOC _D and the charge end charge depth SOC _C are set to the lower limit charge depth. A sufficiently large variation can be made between the SOC _B and the upper limit charging depth SOC _T. Thereby, localization of Li ions in the positive electrode active material can be appropriately suppressed. In addition, stable output characteristics with small output fluctuations can be obtained.
Further, the upper limit charge depth SOC _T by 100% or less, it is possible to prevent overcharging.
Furthermore, in the secondary battery system of the present invention, the control device performs charging / discharging as described above by setting the difference between the charge end charge depth SOC _C and the discharge end charge depth SOC _D within a range of 10 to 50%. Control. Thereby, localization of Li ions in the positive electrode active material can be appropriately suppressed.

Further, in the above-described secondary battery system, the upper limit charge depth SOC _T is preferably a secondary battery system is a value in the range 85-95%.

By controlling the charge and discharge limit charging depth SOC _T as 85% or more, it is possible to further suppress the localization of the Li ions in the positive electrode active material. Further, by controlling the charging and discharging of the upper limit charge depth SOC _T as 95% or less, it is possible to reliably prevent overcharging.

Furthermore, the secondary battery system may be a secondary battery system in which a difference between the end-of-charge charge depth SOC _C and the end-of-charge charge depth SOC _D is within a range of 10 to 30%. preferable.

By controlling the charge / discharge as described above by setting the difference between the end-of-charge charge depth SOC _C and the end-of-discharge charge depth SOC _D within a range of 10 to 30%, the localization of Li ions in the positive electrode active material Can be further suppressed.

  Another solution is a hybrid vehicle, in which any of the secondary battery systems is mounted as a drive power supply system for the hybrid vehicle.

  The hybrid vehicle of the present invention is equipped with the above-described secondary battery system as a drive power supply system for the hybrid vehicle. Therefore, in the hybrid vehicle of the present invention, the localization of Li ions in the positive electrode active material can be suppressed for the lithium ion secondary battery that is the driving power source. Thereby, the fall of the discharge capacity of a lithium ion secondary battery can be suppressed, and the performance of a lithium ion secondary battery can fully be drawn out. Therefore, the hybrid vehicle of the present invention has good running performance.

It is the schematic of the hybrid vehicle concerning an Example. It is the schematic of the secondary battery system concerning an Example. It is sectional drawing of the lithium ion secondary battery concerning an Example. It is sectional drawing of the electrode body of a lithium ion secondary battery. It is a partial expanded sectional view of an electrode body, and is equivalent to the B section enlarged view of FIG. 1 is a schematic diagram illustrating a charge / discharge control method according to Example 1. FIG. It is a graph which shows the relationship between SOC of a lithium ion secondary battery concerning an Example, and battery voltage. It is a graph which shows the relationship between SOC of another lithium ion secondary battery, and battery voltage. 6 is a schematic diagram illustrating a charge / discharge control method according to Comparative Example 1. FIG.

Example 1
Next, Example 1 of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the hybrid vehicle 1 includes a vehicle body 2, an engine 3, a front motor 4, a rear motor 5, a secondary battery system 6, and a cable 7, and includes an engine 3, a front motor 4, and a rear motor 5. It is a hybrid car that is driven in combination. Specifically, the hybrid vehicle 1 is configured to be able to travel using the engine 3, the front motor 4, and the rear motor 5 using the secondary battery system 6 as a driving power source for the front motor 4 and the rear motor 5. .

  Among these, the secondary battery system 6 is attached to the vehicle body 2 of the hybrid 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 secondary battery system 6 includes a battery pack 10 in which a plurality of (for example, 100) lithium ion secondary batteries 100 are electrically connected in series to each other, a control device 30, and current detection. Device 50.

  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 positive electrode plate 155 has a positive electrode current collecting member 151 made of an aluminum foil and a positive electrode mixture 152 coated on the surface thereof. The negative electrode plate 156 has a negative electrode current collector 158 made of copper foil and a negative electrode mixture 159 coated on the surface thereof.

  The electrode body 150 is positioned at one end portion (right end portion in FIG. 3) in the axial direction (left and right direction in FIG. 3), and a positive electrode winding portion 155b in which only a part of the positive electrode current collecting member 151 overlaps in a spiral shape. The negative electrode winding portion 156b is located at the other end portion (left end portion in FIG. 3) and only a part of the negative electrode current collecting member 158 is spirally overlapped.

  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). The negative electrode plate 156 is coated with a negative electrode mixture 159 including a negative electrode active material 154 at a portion excluding 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.

In Example 1, LiFePO ₄ having an average primary particle diameter of 0.5 μm and an agglomerated secondary particle diameter of 2 μm is used as the positive electrode active material 153. LiFePO ₄ is an active material that performs charge and discharge in a two-phase coexistence type, and a charge and discharge reaction is performed in a state where two crystals having different crystal structures coexist. Further, a carbon material (natural graphite) is used as the negative electrode active material 154. Specifically, natural graphite having an average particle diameter of 20 μm, a lattice constant C0 of 0.67 nm, a crystallite size Lc of 27 nm, and a graphitization degree of 0.9 or more is used.

In Example 1, the positive electrode plate 155 was manufactured as follows. First, LiFePO ₄ (positive electrode active material 153), acetylene black (conducting aid) and polyvinylidene fluoride (binder resin) are mixed in a ratio of 85: 5: 10 (weight ratio), and N-methylpyrrolidone is mixed therewith. (Dispersion solvent) was mixed to prepare a positive electrode slurry. Next, this positive electrode slurry was applied to the surface of the positive electrode current collector 151 (aluminum foil), dried, and then pressed. Thereby, the positive electrode plate 155 in which the positive electrode mixture 152 was coated on the surface of the positive electrode current collecting member 151 was obtained.

In Example 1, the negative electrode plate 156 was manufactured as follows. First, 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 negative electrode current collector 158 (copper foil), dried, and then pressed. As a result, a negative electrode plate 156 in which the negative electrode mixture 159 was coated on the surface of the negative electrode current collector 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: 1.3.

Further, as the separator 157, a polypropylene / polyethylene / polypropylene three-layer structure composite porous sheet (thickness: 25 μm) is used. In addition, as a non-aqueous electrolyte, 1 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) is added to a solution obtained by mixing EC (ethylene carbonate) and DEC (diethyl carbonate) at a ratio of 4: 6 (volume ratio). What was melt | dissolved in the ratio is used.
The battery capacity of the lithium ion secondary battery 100 is 15 Ah.

  A current detection device 50 shown in FIG. 2 detects a current value flowing through the lithium ion secondary battery 100 constituting the assembled battery 10. In the current detection device 50, when the lithium ion secondary battery 100 is being charged, the current value I is detected as a positive value (I> 0), and when the discharge is being performed. The current value I is detected as a negative value (I <0).

The control device 30 includes a calculation unit 31, a control unit 32, and a storage unit 33. Among these, the calculating part 31 integrates the electric current value detected by the electric current detection apparatus 50 (electric current value x time), and calculates SOC (%) of the lithium ion secondary battery 100. The calculation unit 31 is connected to the control unit 32. The storage unit 33 stores a lower limit charge depth SOC _B , an upper limit charge depth SOC _T , and a difference between the charge end charge depth SOC _C and the discharge end charge depth SOC _D. The storage unit 33 is connected to the control unit 32.

The SOC (%) of the lithium ion secondary battery 100 calculated by the calculation unit 31 is sequentially sent to the control unit 32. The control unit 32 controls charging / discharging of the lithium ion secondary battery 100 based on the SOC of the lithium ion secondary battery 100 sent from the calculation unit 31. Specifically, the lithium ion secondary battery 100 is controlled to be charged / discharged between the end-of-discharge charge depth SOC _D and the end-of-charge charge depth SOC _C , and the end-of-discharge charge depth SOC _D and the end of charge are controlled. Control is performed to sequentially change the charging depth SOC _C between the lower limit charging depth SOC _B and the upper limit charging depth SOC _T.

Here, the charge / discharge control method according to the first embodiment will be described in detail with reference to FIG.
In the first embodiment, as shown in FIG. 6, the lower limit charge depth SOC _{B is set} to 30% and the upper limit charge depth SOC _T is set to 90%, and the charge end charge depth SOC _C and discharge end charge of each cycle are set. The control device 30 controls charging / discharging of the lithium ion secondary battery 100 by setting the difference from the depth SOC _D to 10%.

Specifically, in the first cycle, the discharge end charge depth SOC _{D is set} to 80% and the charge end charge depth so that the difference between the charge end charge depth SOC _C and the discharge end charge depth SOC _D is 10%. SOC _{C is set} to 90% (same as SOC _T ), and discharging and charging are controlled. Second cycle, SOC _B and SOC _C for 1 cycle of SOC _C less than, for example, 70% SOC _D, as 80% SOC _C, and controls the charging and discharging. Thus while reducing the SOC _B and SOC _C per cycle, and controls the charging and discharging until the discharge termination charge depth SOC _D is equivalent and lower charging depth SOC _B. When SOC _D becomes the same value as SOC _B (30% in this embodiment 1), on the contrary, every time until SOC _C becomes the same value as SOC _T (90% in this embodiment 1), on the contrary. Charge / discharge control is performed while increasing SOC _B and SOC _C. Thus, charging / discharging of the lithium ion secondary battery 100 is controlled so that the charging / discharging pattern shown in FIG. 6 is repeated.

In the secondary battery system 6 of the first embodiment, as described above, the SOC _D and the SOC _C are set to the lower limits while the difference between the charge end charge depth SOC _C and the discharge end charge depth SOC _D is 10%. The charging / discharging of the lithium ion secondary battery 100 is controlled by sequentially changing between the charging depth SOC _B and the upper limit charging depth SOC _T. Thus, the lithium ion secondary battery 100, it is possible to suppress the localization of the Li ions in the positive electrode active material (LiFePO _4). Therefore, a reduction in the discharge capacity of the lithium ion secondary battery 100 can be suppressed, and the performance of the lithium ion secondary battery 100 can be sufficiently extracted. Thereby, the running performance of the hybrid vehicle 1 is also improved.

  The lithium ion secondary battery 100 can be charged using, for example, an inverter that can convert kinetic energy of the internal combustion engine or frictional energy at the time of stopping into a charging current. In addition, it is efficient to use this inverter when converting electrical energy into kinetic energy during discharge.

(Example 2)
In Example 2, a secondary battery system and a hybrid vehicle were configured in the same manner as in Example 1 except that the difference between the end-of-charge charge depth SOC _C and the end-of-discharge charge depth SOC _D was set to 20%. .

(Examples 3 to 6)
In Examples 3 to 6, the lower limit charging depth SOC _B was set to 20%, and the upper limit charging depth SOC _T was set to 100%. Further, the difference between the end-of-charge charge depth SOC _C and the end-of-discharge charge depth SOC _D is 20% in Example 3, 30% in Example 4, 40% in Example 5, and 50% in Example 6. Set. Except these, it carried out similarly to Example 1, and comprised the secondary battery system and hybrid vehicle concerning Examples 3-6.

( Reference Example 1 and Examples 7 and 8 )
In Reference Example 1 and Examples 7 and 8, 80% upper limit charge depth SOC _T, setting the difference between the charging end charging depth SOC _C with discharge termination charge depth SOC _D 20%. Further, the lower limit charging depth SOC _B was set to 10% in Reference Example 1 , 20% in Example 7 , and 30% in Example 8 . Except for these, the secondary battery system and the hybrid vehicle according to Reference Example 1 and Examples 7 and 8 were configured in the same manner as Example 1 .

(Comparative Example 1)
As Comparative Example 1, a secondary battery system for controlling the lithium ion secondary battery 100 with the pattern shown in FIG. 9 was prepared. In Comparative Example 1, as in Example 4, the lower limit charge depth SOC _{B is set} to 20%, the upper limit charge depth SOC _T is set to 100%, the charge end charge depth SOC _C and the discharge end charge depth SOC. The difference from _D is set to 30%. However, unlike Example 4, the end-of-discharge charge depth SOC _D and the end-of-charge charge depth SOC _C are not changed between the lower limit charge depth SOC _B and the upper limit charge depth SOC _T, and the lithium ion concentration The charging / discharging of the secondary battery 100 is controlled. Specifically, with the SOC 50% as the control center, the end-of-discharge charge depth SOC _D is fixed at 35% and the end-of-charge charge depth SOC _C is fixed at 65% to control the charge / discharge of the lithium ion secondary battery 100. . Except for this, the secondary battery system of Comparative Example 1 was configured in the same manner as Example 1.

(Comparative Example 2)
In Comparative Example 2, an upper limit charge depth SOC _T 90%, setting the difference between the charging end charging depth SOC _C with discharge termination charge depth SOC _D 20%. Except for this, the secondary battery system of Comparative Example 2 was configured in the same manner as Comparative Example 1. Therefore, in this Comparative Example 2, discharge termination charge depth SOC _D and charge end charging depth SOC _C, without varying between a lower limit charging depth SOC _B and the upper limit charge depth SOC _T, the lithium ion secondary The charging / discharging of the secondary battery 100 is controlled. Specifically, with the SOC 50% as the control center, the end-of-discharge charge depth SOC _D is fixed at 40% and the end-of-charge charge depth SOC _C is fixed at 60% to control the charge / discharge of the lithium ion secondary battery 100. .

(Cycle charge / discharge)
In each of the secondary battery systems of Examples 1 to 8, Reference Example 1, and Comparative Examples 1 and 2, the lithium ion secondary battery 100 was repeatedly charged and discharged. Specifically, in each secondary battery system, the lithium ion secondary battery 100 was charged and discharged for 1000 cycles at a charge / discharge current of 50 A. The charge / discharge control methods and charge / discharge cycle patterns of the lithium ion secondary batteries 100 in Examples 1 to 8, Reference Example 1, and Comparative Examples 1 and 2 are as described above (see FIGS. 6 and 9).

(Check discharge capacity)
About each secondary battery system of Examples 1-8, Reference Example 1, and Comparative Examples 1 and 2, after performing the above-described 1000 cycles of charging and discharging, the lithium ion secondary battery 100 of each secondary battery system The discharge capacity was measured. Specifically, after charging and discharging for 1000 cycles, the lithium ion secondary battery 100 of each secondary battery system was charged to SOC 80% at a current value of 5A. Thereafter, discharging was performed to SOC 0% at a current value of 5 A, and the discharge capacity (referred to as discharge capacity A) at this time was measured.

  Subsequently, the lithium ion secondary battery 100 of each secondary battery system was subjected to refresh charge / discharge (the operation of charging to SOC 100% and then discharging to SOC 0% is repeated several times). Thereafter, as described above, the discharge capacity (discharge capacity B) when the lithium ion secondary battery 100 of each secondary battery system was discharged from SOC 80% to 0% was measured.

  In addition, about the lithium ion secondary battery 100 of each secondary battery system, by performing refresh charge / discharge, localization of Li ion produced by cycle charge / discharge can be eliminated. Therefore, the difference value (discharge capacity B−discharge capacity A) between the discharge capacity B after the refresh charge / discharge and the discharge capacity A before the refresh charge / discharge corresponds to the discharge capacity reduced by the localization of Li ions. That is, it can be said that the value of (discharge capacity B−discharge capacity A) is the amount of decrease in discharge capacity due to localization of Li ions.

  Accordingly, the ratio of (discharge capacity B−discharge capacity A) to the discharge capacity B, that is, the value of “{(discharge capacity B−discharge capacity A) / discharge capacity B} × 100 (%)” The degree of localization of the generated Li ions and the degree of capacity reduction were evaluated. Hereinafter, the value of {(discharge capacity B−discharge capacity A) / discharge capacity B} × 100 (%) is also referred to as a discharge capacity decrease rate. That is, it can be said that the larger the value of the discharge capacity decrease rate (%), the greater the degree of localization of Li ions generated by cycle charge / discharge, and the greater the discharge capacity decrease associated therewith. In other words, in a secondary battery system with a small discharge capacity reduction rate, localization of Li ions in the positive electrode active material can be suppressed, thereby reducing the discharge capacity of the lithium ion secondary battery. It can be said that it was able to be suppressed.

Here, for each of the secondary battery systems of Examples 1 to 8, Reference Example 1, and Comparative Examples 1 and 2, the value of the discharge capacity reduction rate (%) was calculated. When the discharge capacity reduction rate is less than 1%, the discharge capacity reduction is “none”, when 1% or more and less than 5%, the discharge capacity reduction is “present”, and when 5% or more, the discharge The capacity drop was evaluated as “significant”. These results are shown in Table 1.

As shown in Table 1, in Comparative Examples 1 and 2, a significant decrease in discharge capacity occurred. On the other hand, in Examples 1 to 8 and Reference Example 1 , it was possible to suppress a decrease in discharge capacity compared to Comparative Examples 1 and 2. For this reason, in the secondary battery systems of Examples 1 to 8 and Reference Example 1 , the performance of the lithium ion secondary battery 100 can be sufficiently obtained. From these results, in Examples 1 to 8 and Reference Example 1 , localization of Li ions in the positive electrode active material was suppressed for the lithium ion secondary battery 100 as compared with Comparative Examples 1 and 2. I can say that.

Therefore, regarding the lithium ion secondary battery having the positive electrode active material (LiFePO _{4 in} Examples 1 to 8 and Reference Example 1 ) that performs charge and discharge in a two-phase coexistence type, the discharge end charge depth SOC _D and the charge end charge depth By performing charge / discharge while sequentially varying the SOC _C between the lower limit charge depth SOC _B and the upper limit charge depth SOC _T , localization of Li ions in the positive electrode active material can be suppressed. It can be said. Thereby, it can be said that the fall of the discharge capacity of a lithium ion secondary battery can be suppressed, and the performance of a lithium ion secondary battery can fully be drawn out.

In the secondary battery systems of Examples 1 to 8 and Reference Example 1 , the lower limit charging depth SOC _B is set to a value of 30% or less, and the upper limit charging depth SOC _T is a value within the range of 80 to 100%. It is said. Further, in Examples 1 to 8 except Reference Example 1 , the lower limit charging depth SOC _B is set to a value of 15% or more (see Table 1).

Here, the graph which shows the relationship between SOC concerning lithium ion secondary battery 100 and battery voltage is shown in FIG. As shown in FIG. 7, in the lithium ion secondary battery 100, when the SOC becomes less than 15%, the battery voltage rapidly decreases (see FIG. 7). Accordingly, in Examples 1 to 8 in which the lower limit charging depth SOC _B is set to 15% or more, the battery voltage can be prevented from becoming small (about 3.3 V or less), so the output of the lithium ion secondary battery 100 Good characteristics can be achieved.

In addition, when SOC becomes less than 15%, the tendency of the battery voltage to rapidly decrease is LiM1 _(1-X) M2 _X PO ₄ (M1 is Fe or Mn, and M2 is Mn, Cr, Co, Cu, It is at least one of Ni, V, Mo, Ti, Zn, Al, Ga, Mg, B, and Nb (however, when M1 is Mn, Mn is excluded), and 0 ≦ X ≦ 0.5) It can be found in all lithium ion secondary batteries using a positive electrode active material as a positive electrode active material. For reference, FIG. 8 shows the relationship between the SOC and the battery voltage applied to a lithium ion secondary battery using LiMnPO ₄ as the positive electrode active material (only the positive electrode active material is different from the lithium ion secondary battery 100). A graph is shown. Therefore, for a lithium ion secondary battery using the compound represented by the above composition formula as the positive electrode active material, the battery voltage is reduced by controlling the charge / discharge with the lower limit charge depth SOC _B being 15% or more. It can be said that the output characteristics of the lithium ion secondary battery can be improved.

In the secondary battery systems of Examples 1 to 8 and Reference Example 1 , the lower limit charging depth SOC _{B is set} to 30% or less, and the upper limit charging depth SOC _{T is set} to 80% or more (see Table 1). Thus, discharge termination charge depth SOC _D and end-of-charge charge depth SOC _C, can be varied sufficiently large between the lower charge depth SOC _B and the upper limit charge depth SOC _T. For this reason, in the secondary battery systems of Examples 1 to 8 and Reference Example 1 , localization of Li ions in the positive electrode active material can be suppressed, and reduction in the discharge capacity of the lithium ion secondary battery 100 is suppressed. It can be said that it was possible. Therefore, the lithium ion secondary battery using the compound represented by the above composition formula as the positive electrode active material is charged / discharged with the lower limit charge depth SOC _B being 30% or less and the upper limit charge depth SOC _T being 80% or more. By controlling, it can be said that localization of Li ions in the positive electrode active material can be suppressed, and a decrease in discharge capacity of the lithium ion secondary battery 100 can be suppressed.

Moreover, as shown in FIGS. 7 and 8, in the lithium ion secondary battery using the compound represented by the above composition formula as the positive electrode active material, the battery voltage hardly varies in the range of SOC 30% to 80%. Therefore, by setting SOC _B to 30% or less and SOC _T to 80% or more, a lithium ion secondary battery can be discharged with almost no change in battery voltage in a wide capacity range of SOC 30% to 80%. it can. Thereby, stable output characteristics can be obtained.

Further, in the secondary battery system of Examples 1-8 and Reference Example 1, and the upper limit charge depth SOC _T is 100% or less (see Table 1). The upper limit charge depth SOC _T by 100% or less, it is possible to prevent overcharging. As a result, it is possible to prevent problems due to overcharge (such as a decrease in electrolyte due to gas generation inside the battery and an early life span).

Furthermore, in the secondary battery systems of Examples 1 to 8 and Reference Example 1 , the difference between the charge end charge depth SOC _C and the discharge end charge depth SOC _D is set to a value within a range of 10 to 50% (Table 1). That is, the amount of electricity charged or discharged once is set to an amount of electricity corresponding to a value within the range of SOC 10% to 50% (see FIG. 6). In this way, SOC _D and SOC _C are sequentially changed between the lower limit charging depth SOC _B (value of 30% or less) and the upper limit charging depth SOC _T (value in the range of 80 to 100%). However, by performing charging and discharging, localization of Li ions in the positive electrode active material can be appropriately suppressed. For this reason, in the secondary battery systems of Examples 1 to 8 and Reference Example 1 , localization of Li ions in the positive electrode active material can be suppressed, and reduction in the discharge capacity of the lithium ion secondary battery 100 is suppressed. It can be said that it was possible.

By the way, in Examples 5 and 6, although the discharge capacity fall could be suppressed, the discharge capacity fall became large compared with the other Examples (refer to Table 1). In other words, in Examples 1 to 4 , 7 and 8 , it was possible to further suppress the discharge capacity decrease compared to Examples 5 and 6. The reason is that in Examples 5 and 6, the difference between the end-of-charge charge depth SOC _C and the end-of-discharge charge depth SOC _D was 40% or more, whereas in Examples 1 to 4 , 7 , and 8 , This is probably because the difference between the end-of-charge charge depth SOC _C and the end-of-charge charge depth SOC _D is set to a value within the range of 10 to 30%. Accordingly, assuming that the difference between SOC _C and SOC _D is a value in the range of 10 to 30%, SOC _D and SOC _C are calculated as SOC _B (value of 30% or less) and SOC _T (in the range of 80 to 100%). It can be said that the localization of Li ions in the positive electrode active material can be further suppressed by charging and discharging while sequentially varying the value.

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

For example, in the secondary battery system 6 of Example 1, the lithium ion secondary battery 100 having LiFePO ₄ as the positive electrode active material was used. However, the positive electrode active material is not limited to LiFePO ₄ , and any positive electrode active material that performs charge and discharge in a two-phase coexistence type such as LiMnPO ₄ may be used.

DESCRIPTION OF SYMBOLS 1 Hybrid vehicle 6 Secondary battery system 10 Battery pack 30 Controller 100 Lithium ion secondary battery 153 Cathode active material

Claims (3)

A method for controlling charge / discharge of a lithium ion secondary battery having a positive electrode active material that performs charge / discharge of a two-phase coexistence type,
The lithium ion secondary battery is used between the end-of-discharge charge depth SOC _D and the end-of-charge charge depth SOC _C ,
The discharge termination charge depth SOC _D and end-of-charge charge depth SOC _C, met the charge and discharge control method for sequentially lithium ion secondary battery which vary between a lower limit charging depth SOC _B and the upper limit charge depth SOC _T And
The positive electrode active material is LiM1 _(1-X) M2 _X PO ₄ (M1 is Fe or Mn, M2 is Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga) , Mg, B, Nb (however, when M1 is Mn, Mn is excluded), and 0 ≦ X ≦ 0.5),
The lower limit charging depth SOC _B is a value within a range of 15 to 30%,
The upper limit charge depth SOC _T is a value within the range of 80% to 100%,
The difference between the end-of-charge charge depth SOC _C and the end-of-charge charge depth SOC _D is in the range of 10 to 50%.
A charge / discharge control method for a lithium ion secondary battery . A lithium ion secondary battery having a positive electrode active material that performs charge and discharge of two-phase coexistence type;
A control device that controls charging and discharging of the lithium ion secondary battery, and a secondary battery system comprising:
The control device
The lithium ion secondary battery is controlled to be charged / discharged between an end-of-discharge charge depth SOC _D and an end-of-charge charge depth SOC _C , and the end-of-discharge charge depth SOC _D and the end-of-charge charge depth SOC are controlled. _A secondary battery system that performs control to sequentially change _C between a lower limit charging depth SOC _B and an upper limit charging depth SOC _T ,
The positive electrode active material is LiM1 _(1-X) M2 _X PO ₄ (M1 is Fe or Mn, M2 is Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga) , Mg, B, Nb (however, when M1 is Mn, Mn is excluded), and 0 ≦ X ≦ 0.5),
The lower limit charging depth SOC _B is a value within a range of 15 to 30%,
The upper limit charge depth SOC _T is a value within the range of 80% to 100%,
The difference between the end-of-charge charge depth SOC _C and the end-of-charge charge depth SOC _D is in the range of 10 to 50%.
Secondary battery system. A hybrid car,
A hybrid vehicle comprising the secondary battery system according to claim 2 mounted as a drive power supply system for the hybrid vehicle.

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