JP5841827B2 - Secondary battery system and control method of secondary battery system - Google Patents

Description

  The present invention includes a positive electrode capable of inserting and extracting lithium ions, a negative electrode made of amorphous carbon capable of inserting and extracting lithium ions, a separator disposed between the positive electrode and the negative electrode, an organic electrolyte, TECHNICAL FIELD The present invention relates to a battery system using a lithium ion secondary battery having a battery and a method for controlling the secondary battery system.

  From the viewpoint of environmental protection and energy saving, a hybrid electric vehicle (HEV) that uses an engine and a motor as a power source has been developed and commercialized. In the future, a plug-in hybrid electric vehicle (PHEV) having a system capable of supplying electric power from an electric plug is being developed. As an energy source of this hybrid electric vehicle, a secondary battery capable of repeatedly charging and discharging electricity is used. In particular, lithium ion secondary batteries are advantageous in that they have a higher operating voltage and higher output than other secondary batteries such as nickel metal hydride batteries, and are increasingly important as power sources for hybrid electric vehicles in the future. It is thought to increase.

International Publication No. 2010/079595

  In a hybrid electric vehicle, a strong assist force is required to assist the acceleration force of the vehicle with a motor drive, and a high output of a battery serving as a power source is required. Further, when the vehicle is running, depending on the control method of the hybrid system, charging and discharging of the battery with a large current having a maximum current value of 10C or more is repeated instantaneously. High output performance is required to be maintained even under such usage conditions.

  In such a secondary battery system using a lithium ion secondary battery, a deterioration phenomenon is known in which the internal resistance of the battery gradually increases due to a charge / discharge cycle. Such a deterioration phenomenon is likely to occur in the case of a charge / discharge cycle having a large current and a large capacity, and is further likely to occur by performing a charge / discharge cycle in a low temperature environment.

  Patent Document 1 discloses a non-electrolyte liquid type lithium ion secondary battery system that prevents the uneven distribution of the salt concentration of the electrolyte, avoids an increase in internal resistance, and improves the durability of the non-electrolyte liquid type lithium ion secondary battery. And the technology of the control method is disclosed. It is suggested that the cause of the increase in internal resistance is due to the electrode and the salt concentration, but it does not occur individually as a cause of the increase in resistance. Are correlated, and the non-uniform salt concentration distribution is considered to vary depending on electrode parameters, that is, electrode active material, electrode density, and the like. Therefore, in order to suppress the increase in internal resistance of the lithium ion battery, it is necessary to take measures for the battery as a whole in consideration of electrode parameters, and there is room for further improvement.

  The present invention provides a secondary battery system that suppresses an increase in internal resistance by suppressing an increase in internal resistance of a lithium ion secondary battery within an appropriate range and is excellent in cycle characteristics.

As a result of studying the control method of the lithium ion secondary battery, the inventors discovered that there is a correlation between an increase in internal resistance and a voltage drop associated with the increase in internal resistance, thereby completing the present invention. That is, the gist of the present invention is as follows.
(1) A positive electrode including a positive electrode active material capable of inserting and extracting lithium ions, a negative electrode including amorphous carbon capable of inserting and extracting lithium ions, a separator disposed between the positive electrode and the negative electrode, and organic electrolysis A secondary battery system comprising a lithium ion secondary battery, wherein the maximum current value during charging / discharging in the lithium ion secondary battery is a time rate of 5C or more; Charge / discharge control means for controlling discharge, internal resistance calculation means for calculating internal resistance of the lithium ion secondary battery, and internal resistance of the lithium ion secondary battery calculated by the internal resistance calculation means exceeds the internal resistance threshold value Ds1 The internal resistance rise detecting means for detecting the fact that the battery resistance of the lithium ion secondary battery is 25 ° C. or lower by the internal resistance calculating means from the internal resistance threshold value Ds1. When the calculated internal resistance of the lithium ion secondary battery increases, the charge / discharge current value of the lithium ion secondary battery being charged / discharged is the charge / discharge current before the internal resistance of the lithium ion secondary battery exceeds the internal resistance threshold Ds1. A secondary battery system comprising: deterioration determination means for making the value smaller than the value.
(2) In the above, battery state detection means for detecting the battery surface temperature of the lithium ion secondary battery, and internal resistance threshold value setting means for setting the internal resistance threshold value Ds1 according to the battery surface temperature detected by the battery state detection means; A secondary battery system.
(3) In the above, when the internal resistance of the lithium ion secondary battery calculated by the internal resistance calculation means is larger than the internal resistance threshold value Ds1, the deterioration determination means determines the charge / discharge current value of the lithium ion secondary battery being charged / discharged. Is a secondary battery system that controls the current below a predetermined current value.
(4) In the above, when the internal resistance of the lithium ion secondary battery calculated by the internal resistance calculation means becomes larger than the internal resistance threshold value Ds1, the deterioration determination means stops charging / discharging of the lithium ion secondary battery being charged / discharged. Secondary battery system.
(5) In the above, after the deterioration determination means makes the charge / discharge current value of the lithium ion secondary battery being charged / discharged smaller than the charge / discharge current value before the internal resistance of the lithium ion secondary battery exceeds the internal resistance threshold value Ds1 When the internal resistance of the lithium ion secondary battery becomes smaller than the internal resistance threshold value Ds2 preset by the internal resistance calculating means, the charge / discharge current value of the lithium ion secondary battery module being charged / discharged by the deterioration judging means is changed to the lithium ion secondary battery. The secondary battery system which controls to the charging / discharging current value before the internal resistance of a secondary battery exceeds internal resistance threshold value Ds1.
(6) A positive electrode including a positive electrode active material capable of inserting and extracting lithium ions, a negative electrode including amorphous carbon capable of inserting and extracting lithium ions, a separator disposed between the positive electrode and the negative electrode, and organic electrolysis A secondary battery system comprising a lithium ion secondary battery, wherein the maximum current value at the time of charging and discharging in the lithium ion secondary battery is 5C or more, and the lithium ion secondary battery Charge / discharge control means for controlling charge / discharge of the battery, internal resistance calculation means for calculating the internal resistance of the lithium ion secondary battery, and the internal resistance of the lithium ion secondary battery calculated by the internal resistance calculation means is an internal resistance threshold value. The internal resistance rise detecting means for detecting that Ds1 has been exceeded, and the internal resistance threshold value Ds1 when the battery surface temperature of the lithium ion secondary battery is 25 ° C. or lower. When the internal resistance of the lithium ion secondary battery calculated by the means is increased, the charge / discharge current value of the lithium ion secondary battery being charged / discharged is charged before the internal resistance of the lithium ion secondary battery exceeds the internal resistance threshold Ds1. A method for controlling a secondary battery system, comprising: deterioration determination means for making the discharge current value smaller than the discharge current value.

  According to the present invention, by calculating or estimating the internal resistance, it is possible to suppress a rapid voltage drop caused by an increase in the internal resistance, and thus excellent cycle characteristics of the lithium ion secondary battery can be expected. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is a one-side cross-section schematic diagram of the winding type lithium ion secondary battery to which the present invention is applied. It is a schematic block diagram of a secondary battery system. FIG. 3 is a system flow diagram of the secondary battery system according to the first embodiment. It is the relationship between internal resistance and cycle discharge lower limit voltage. It is the relationship between environmental temperature and internal resistance. 6 is a system flow diagram of a secondary battery system according to Embodiment 2. FIG. This is the relationship between the internal resistance and the fitting result. It is the relationship between the internal resistance of Example 1, and a charging / discharging waveform. It is the relationship between the internal resistance of Example 2, and a charging / discharging waveform.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description shows specific examples of the contents of the present invention, and the present invention is not limited to these descriptions. Various modifications by those skilled in the art are within the scope of the technical idea disclosed in this specification. Changes and modifications are possible. In all the drawings for explaining the present invention, components having the same function are denoted by the same reference numerals, and repeated description thereof may be omitted.

  As a result of studying the control method of the lithium ion secondary battery, the present inventors have found that there is a correlation between an increase in internal resistance and a voltage drop associated with the increase in internal resistance. Specifically, it has been found that the voltage drop is caused after the internal resistance increases with the progress of the cycle. Therefore, by providing a threshold value for the internal resistance, it is possible to estimate and suppress a rapid voltage drop due to an internal resistance increase that occurs thereafter.

  The increase in internal resistance is caused by performing a high rate charge / discharge with a maximum current value of 5C or more at the time of charge / discharge in the lithium ion secondary battery. Further, the increase in internal resistance does not appear remarkably at a high temperature such as 50 ° C. It appears more prominently at 25 ° C or lower. High-rate charge / discharge causes an uneven concentration of lithium ions in the electrolytic solution held between the positive electrode and the negative electrode. For example, when a bias of lithium ions occurs and the lithium ion concentration is high on the negative electrode side and low on the positive electrode side, less lithium ions reach the positive electrode during discharge. As a result, the electrons that should have been combined with lithium ions are left. The surplus electrons decompose the electrolyte component. The electrolytic solution decomposition component is deposited on the positive electrode surface as an organic substance and an inorganic substance, and inhibits lithium ion deinsertion. It is assumed that the charge / discharge cycle repeats the bias of lithium ions and the deposition of organic and inorganic substances on the surface of the positive electrode, further increasing the internal resistance.

  This internal resistance increase mechanism has been confirmed when amorphous carbon is used for the negative electrode. For example, when graphite is used for the negative electrode, cracks occur between the active materials due to the expansion and contraction of the graphite during the cycle, the graphite particles are isolated, and the negative electrode utilization rate decreases. Therefore, the battery capacity is reduced. Since the isolation of the graphite particles does not return to the original, the electrode deterioration mechanism is different, which is different from the above-described resistance increase of amorphous carbon.

  In addition, the present inventors have discovered a phenomenon in which internal resistance decreases in a lithium-ion secondary battery having increased internal resistance by bringing the internal resistance to an unloaded state after increasing the internal resistance. This decrease in internal resistance is thought to be caused by the separation or dissolution of the electrolyte decomposition component deposited on the positive electrode surface and the elimination of the lithium ion bias.

  The present invention has been made based on such knowledge, and by controlling the internal resistance of the lithium ion secondary battery, the internal resistance of the battery is within an appropriate range, and good cycle characteristics can be obtained.

  In the method of estimating the internal resistance of a lithium ion secondary battery, necessary parameters include battery voltage, charge / discharge current, charge / discharge electricity quantity, battery temperature, and the like. The battery voltage indicates the state of charge of the lithium ion secondary battery. Generally, when the battery voltage is high, the lithium ion self-discharge proceeds on the negative electrode side, and the lithium ions are lost, so that the deterioration is accelerated. In addition, it is considered that when the battery temperature increases, decomposition / generation of the electrolytic solution in the lithium ion secondary battery proceeds, and the deterioration is accelerated. The charge / discharge current and the amount of charge / discharge indicate the speed and amount of lithium ions desorbed / inserted into the electrode, and it is considered that deterioration proceeds when both values are large.

Next, Embodiment 1 of the present invention will be described with reference to the drawings.
FIG. 1 shows an embodiment of a lithium ion secondary battery to which the present invention is applied, and shows a schematic cross-sectional side view of a wound lithium ion secondary battery 100.

  The lithium ion secondary battery 100 uses lithium as an electrode reactant. The lithium ion secondary battery 100 is a so-called cylindrical type, and a pair of strip-shaped positive electrode 3, strip-shaped negative electrode 6, and separator 7 are wound inside a substantially hollow cylindrical negative electrode battery can 13. The positive electrode 3 and the negative electrode 6 are disposed to face each other with a separator 7 interposed therebetween, and an electrolytic solution is injected therein.

  The negative electrode battery can 13 is made of, for example, iron (Fe) plated with nickel (Ni), and has one end closed and the other end open. A pair of positive electrode insulating material 10 and negative electrode insulating material 11 are arranged inside the negative electrode battery can 13 so as to be perpendicular to the wound peripheral surface so as to sandwich the wound electrode group.

  A positive electrode battery lid 12 is attached to the open end of the negative electrode battery can 13 by caulking through a gasket 14, and the inside of the negative electrode battery can 13 is sealed. The positive battery lid 12 is made of the same material as the negative battery can 13, for example.

  A positive electrode lead 8 made of, for example, aluminum (Al) is connected to the positive electrode 3 of the wound electrode group, and a negative electrode lead 9 made of, for example, nickel (Ni) is connected to the negative electrode 6. The positive electrode lead 8 is electrically connected to the positive electrode battery lid 12, and the negative electrode lead 9 is welded and electrically connected to the negative electrode battery can 13.

  The shape of the electrode winding group in the present invention does not necessarily need to be a true cylindrical shape, and may be a long cylindrical shape whose winding group cross section is an ellipse or a prismatic shape such as a rectangular winding cross section. As a typical use form, a cylindrical battery can with a bottom is filled with an electrode winding group and an electrolytic solution, and a tab for taking out current from the electrode plate is sealed in a state welded to the lid and the battery can. Although the form is preferable, it is not particularly limited to this form.

  Moreover, the negative electrode battery can 13 filling the electrode winding group is not particularly limited. However, the battery can made of iron plated for corrosion resistance, the stainless steel battery can, etc. Those excellent in workability are preferred. It is also possible to reduce the weight by using an aluminum alloy or various engineering plastics, and various engineering plastics and metals can be used in combination.

  Below, the positive electrode of a battery, a negative electrode, electrolyte solution, and a separator are demonstrated.

<Positive electrode>
First, the positive electrode will be described. The positive electrode 3 can be obtained by applying a positive electrode paste containing a positive electrode active material, a conductive material, a binder and the like to the surface of the positive electrode current collector 1 to provide the positive electrode layer 2.

  A positive electrode material paste is prepared using a positive electrode active material, a conductive material, graphite, and a binder in consideration of the solid weight during drying and using a solvent. After applying this positive electrode material paste to the aluminum foil used as the positive electrode current collector 1, it was dried at 80 ° C., pressed with a pressure roller, and dried at 120 ° C. to form the positive electrode layer 2 as the positive electrode current collector 1. To form.

Note that the cathode material in the composition formula _{LiMn x M1 y M2 z O 2} ( wherein, M1 is at least one selected Co, from Ni, M2 is, Co, Ni, Al, B , Fe, Mg, Cr And at least one selected from x + y + z = 1, 0.2 ≦ x ≦ 0.6, 0.2 ≦ y ≦ 0.6, 0.05 ≦ z ≦ 0.4) is preferable. .

In particular, LiMn _0.4 Ni _0.4 Co _0.2 O ₂ , LiMn _1/3 Ni _1/3 Co _1/3 O ₂ , LiMn _0.3 Ni _0.4 Co _0.3 O ₂ , LiMn _0.35 Ni _0.3 Co _0.3 Al _0.05 O ₂ , LiMn _0.35 Ni _0.3 Co _0.3 B _0.05 O ₂ , LiMn _0.35 Ni _0.3 Co _0.3 Fe _0.05 O ₂ , LiMn _0.35 Ni _0.3 Co _0.3 Mg _0.05 O _{2 and the} like can be used. In some cases, these are generally referred to as positive electrode active materials. In the composition, increasing Ni increases the capacity, increasing Co increases the output at low temperature, and increasing Mn can suppress the material cost. In particular, LiMn _1/3 Ni _1/3 Co _1/3 O ₂ has high low-temperature characteristics and high cycle stability, and is suitable as a lithium ion battery material for a hybrid vehicle (HEV). In addition, the additive element is effective in stabilizing the cycle characteristics. In addition, the general formula LiM _x PO ₄ (M: Fe or Mn, 0.01 ≦ x ≦ 0.4) or LiMn _1-x M _x PO ₄ (M: divalent cation other than Mn, 0.01 ≦ It may be an orthorhombic phosphate compound having symmetry of the space group Pnma where x ≦ 0.4).

  The positive electrode binder may be any material as long as the material constituting the positive electrode and the positive electrode current collector are in close contact with each other. For example, a homopolymer or copolymer such as vinylidene fluoride, tetrafluoroethylene, acrylonitrile, ethylene oxide, styrene- Examples thereof include butadiene rubber.

  The conductive material is, for example, a carbon material such as carbon black, graphite, carbon fiber, and metal carbide, and each may be used alone or in combination.

<Negative electrode>
Subsequently, the negative electrode will be described. The negative electrode 6 can be obtained by applying a negative electrode paste obtained by mixing a negative electrode active material, a conductive material, a binder, and the like to the surface of the negative electrode current collector 4 and providing the negative electrode layer 5.

  A negative electrode material paste, a conductive material, and a binder are used, and a negative electrode material paste is prepared using a solvent in consideration of the solid content weight during drying. The negative electrode material paste is applied to the copper foil used as the negative electrode current collector 4, dried at 80 ° C., pressed with a pressure roller, and dried at 120 ° C. to form the negative electrode layer 5 on the negative electrode current collector 4. Form.

The negative electrode material is an amorphous carbon material, has high conductivity, and is excellent in terms of low temperature characteristics and cycle stability. Hexagonal carbon layer spacing d ₀₀₂ is less than 0.39 nm, sometimes referred to as pseudo-anisotropic carbon. A material having a wide carbon network plane distance _d002 is excellent in rapid charge / discharge and low temperature characteristics, and is suitable. However, since a material with a wide d ₀₀₂ may have a reduced capacity and a low charge / discharge efficiency at the initial stage of charging, d ₀₀₂ is preferably 0.39 nm or less. Furthermore, a carbonaceous material having high conductivity such as graphite, amorphous, activated carbon or the like may be mixed to constitute the electrode.

  The negative electrode binder may be any material as long as the material constituting the negative electrode and the negative electrode current collector are in close contact with each other. For example, a homopolymer or copolymer such as vinylidene fluoride, tetrafluoroethylene, acrylonitrile, ethylene oxide, styrene- Examples thereof include butadiene rubber.

  The conductive agent is, for example, a carbon material such as carbon black, graphite, carbon fiber, and metal carbide, and each may be used alone or in combination.

<Electrolyte>
Next, the electrolytic solution will be described. The electrolytic solution is composed of a solvent, an additive, and an electrolyte. The electrolytic solution of a lithium ion secondary battery that can be operated in a wide voltage range in principle is required to have a withstand voltage characteristic, and an organic electrolytic solution using an organic compound as a solvent is used. An electrolyte having a lithium salt as an electrolyte and carbonate as a solvent can be made highly conductive, and is widely used as an electrolyte for a lithium ion secondary battery in that it has a wide potential window.

  It is known that an electrolytic solution composed of a lithium salt and a carbonate solvent reacts on the negative electrode surface of a lithium ion secondary battery. In order to suppress these electrode reactions and make the battery highly resistant to long-term storage and continuous charge / discharge of the battery, an additive having a reduction reaction potential higher than that of the solvent is often added to the electrolyte. These additives themselves undergo reductive decomposition to form an inactive film on the electrode surface. And the film formed on the electrode surface suppresses the continued electrode reaction.

As an electrolyte, LiPF ₆ is preferable because of its high quality stability and high ion conductivity in a carbonate solvent. The concentration of the electrolyte is preferably 0.5 mol / l to 2 mol / l with respect to the total amount of the solvent and the additive. If this concentration is too low, the electrical conductivity of the organic electrolyte may be insufficient. If the concentration is too high, the electrical conductivity will decrease due to an increase in viscosity, and the lithium ion secondary using the organic electrolyte will be reduced. Battery performance may be reduced.

  As the additive, vinylene carbonate (VC), methyl vinylene carbonate (MVC), dimethyl vinylene carbonate (DMVC), ethyl vinylene carbonate (EVC), diethyl vinylene carbonate (DEVC) or the like can be used. VC has a low molecular weight and is considered to form a dense electrode film. MVC, DMVC, EVC, DEVC, and the like in which an alkyl group is substituted for VC are considered to form an electrode film having a low density in accordance with the size of the alkyl chain, and are considered to act effectively to improve low-temperature characteristics. The additive preferably has a composition ratio of 0.01 wt% to 5 wt% with respect to the solvent. More desirably, 0.1 wt% to 2 wt% is preferable. If the composition ratio is high, the resistance of the electrolytic solution may be increased.

  As the solvent, an aprotic organic solvent such as ethylene carbonate (EC), dimethyl carbonate (DMC), or propylene carbonate, or a solvent of two or more mixed organic compounds is used. Lithium ion secondary batteries have good discharge characteristics during charge / discharge cycles, low temperature and high current discharge characteristics, long-term storage, and long-term high-temperature storage characteristics. Therefore, there is a demand for an organic electrolyte that satisfies these requirements. In order to satisfy the above various requirements, it is difficult to use a solvent composed of only one kind of compound, and it is necessary to mix two or more kinds of compounds and use them as a solvent.

  Specifically, for example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc., which improve the dissociation degree of the lithium salt and improve the ionic conductivity can be mentioned. Of these, EC is preferred because it has the highest dielectric constant, can improve the dissociation degree of the lithium salt, and can provide a highly ionic conductive electrolyte. Dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) and the like can be used.

  DMC is a highly compatible solvent and is suitable for use in a mixture with EC or the like. DEC has a melting point lower than that of DMC, and is suitable for improving the low temperature characteristics of −30 ° C. EMC is suitable for improving low-temperature characteristics because of its asymmetric molecular structure and low melting point. Among them, a mixed solvent of EC and DMC that can ensure battery characteristics in a wide temperature range is preferable.

<Separator>
The separator 7 is not particularly limited as long as it can withstand the range of use of the lithium ion secondary battery, but it is common to use a single or composite of microporous films of olefin resins such as polyethylene and polypropylene. It is also preferable as an embodiment. Although it is not limited to the thickness of this separator, 10-40 micrometers is preferable.

  Next, FIG. 2 shows a secondary battery system. The lithium ion secondary battery module 21 combines a plurality of batteries shown in FIG. 1 in series, parallel, or series / parallel. A plurality of lithium ion secondary battery modules 21 are connected in parallel to form an assembled battery.

  In order to detect each state of the lithium ion secondary battery module 21, a battery controller 26 is provided. The secondary battery system includes a voltage measurement unit 22 that measures the battery voltage of the lithium ion secondary battery module 21 as a battery state detection unit, a current measurement unit 23 that measures charge / discharge current, and a temperature measurement unit 24 that measures the battery surface temperature. , And a time measuring unit 25 for detecting the charge / discharge time. The battery controller 26 has internal resistance calculation means. The internal resistance is detected from the voltage measuring unit 22, the current measuring unit 23, the temperature measuring unit 24, and the time measuring unit 25. Further, the battery controller 26 includes an internal resistance increase detection means, a deterioration determination means, and an internal resistance threshold value setting means. A rise in internal resistance is detected from the voltage measurement unit 22, current measurement unit 23, temperature measurement unit 24, and time measurement unit 25, and compared with a set internal resistance threshold value to determine deterioration.

  The battery controller 26 has a CPU, a ROM, and a RAM, and includes a microcomputer that operates according to a predetermined program. Based on the detection values obtained from the voltage measurement unit 22, current measurement unit 23, temperature measurement unit 24, and time measurement unit 25, the charge / discharge of the lithium ion secondary battery module 21 is performed by the charge / discharge control means in the battery controller 26. Take control.

  The voltage measurement unit 22, which is one of battery state detection means, detects the voltage of the lithium ion secondary battery module 21. The battery voltage to be detected may be the voltage of one battery constituting the lithium ion secondary battery module 21, or a battery group in which a plurality of batteries are connected in series, and an assembled battery in which a plurality of batteries are connected in series and parallel. The battery voltage to be measured is not particularly limited.

  Next, the current measuring unit 23 detects the value of the charge / discharge current. As a detection method, a galvanometer, a galvanometer using a shunt resistor, a clamp meter, and the like can be considered, but the present invention is not limited to this, and any means can be used as long as it is a means for detecting a current value. Can do.

  Next, the temperature measurement unit 24 detects the temperature of the lithium ion secondary battery module 21. A means for detecting the temperature may be a thermocouple, a thermistor, or the like, but is not particularly limited. Further, the temperature detection location may be the battery surface, the inside of the battery, the surface temperature of the casing in which the lithium ion secondary battery is housed, and the ambient temperature of the lithium ion secondary battery module 21.

  Next, the time measuring unit 25 measures the time related to charging / discharging of the lithium ion secondary battery module 21. For example, the elapsed time after the start of discharge is measured.

  For example, in the case of an automobile, the electric load 27 may be a heater, an electric brake, an electric power steering, or an electric motor.

  As described above, according to the present embodiment, in the secondary battery system in which a plurality of lithium ion secondary battery modules 21 are connected in parallel, the battery controller 26 is provided for the lithium ion secondary battery module 21. . Further, in the battery controller 26, charging of the lithium ion secondary battery module 21 according to the detected value obtained by the voltage measuring unit 22, the current measuring unit 23, the temperature measuring unit 24, and the time measuring unit 25 and the state of the electric load 27, Control discharge, pause, etc.

Next, a charge / discharge control method of the battery controller 26 will be described.
FIG. 3 is a flowchart of the secondary battery system according to the first embodiment of the present invention.
First, a command to start discharging of the lithium ion secondary battery is transmitted from the battery controller 26 to the lithium ion secondary battery module 21 to be charged / discharged to start the cycle (step 301).

  The lithium ion secondary battery module 21 that has received the signal, for example, after the start of discharge, the voltage measurement unit 22, the current measurement unit 23, the temperature measurement unit 24, and the time measurement unit 25 perform a discharge current Id, a discharge time (from the start of discharge). ) Td, battery voltage V and battery temperature T are measured and transmitted to the battery controller 26.

  The internal resistance calculation means in the battery controller 26 calculates the internal resistance D of the battery from these four parameters (V, I, T, t) (step 302).

  The lithium ion secondary battery module 21 measures the internal resistance D at any time during charging and discharging, and compares the internal resistance threshold value Ds1 with the internal resistance D (step 303). Here, when the internal resistance D is larger than the internal resistance threshold Ds1, that is, when it is detected by the internal resistance increase detection means that the internal resistance D exceeds the internal resistance threshold Ds1, the charge / discharge current value is determined by the deterioration determination means. Is limited to a predetermined current value or less (step 304). That is, the charge / discharge current value is made smaller than the charge / discharge current value before the internal resistance of the lithium ion secondary battery exceeds the internal resistance threshold value Ds1. When the internal resistance D is equal to or less than the internal resistance threshold value Ds1, the charge / discharge cycle before determination is continued.

  Furthermore, the lithium ion secondary battery module 21 measures the internal resistance D at any time during charging and discharging, and compares the internal resistance threshold value Ds2 with the internal resistance D (step 305). Here, when the internal resistance D is equal to or greater than the internal resistance threshold Ds2, the limit of the charge / discharge current value is maintained (step 304). When the internal resistance D is smaller than the internal resistance threshold Ds2, a charge / discharge cycle with an initial charge / discharge current is started (step 306).

  The internal resistance threshold value Ds1 and the internal resistance threshold value Ds2 can be set from FIG. The left vertical axis indicates the internal resistance, and the right vertical axis indicates the lower limit voltage on the discharge side during the cycle. The relationship between the internal resistance and the cycle discharge lower limit voltage varies depending on the electrode, electrolyte solution, or the like that is a constituent member of the lithium ion secondary battery. There is a correlation between the internal resistance and the cycle lower limit voltage, and if the internal resistance threshold value Ds1 and the internal resistance threshold value Ds2 that are internal resistances are determined, the discharge-side lower limit voltage during the cycle can be predicted. Since the voltage changes only within the discharge-side lower limit voltage range, the charge / discharge cycle can be continued.

  Moreover, as shown in FIG. 5, the tendency of the increase rate of the internal resistance with respect to the charge / discharge cycle varies greatly depending on the environmental temperature. Therefore, it is preferable that the limit value, which is the threshold value of the internal resistance, is appropriately set according to the temperature change by the internal resistance threshold value setting means.

Next, Embodiment 2 of the present invention will be described with reference to the drawings.
The lithium ion secondary battery of Embodiment 2 uses the same battery as that of Embodiment 1, and uses the secondary battery system shown in FIG.

Next, a charge / discharge control method of the battery controller 26 will be described.
FIG. 6 is a flowchart of the secondary battery system according to the second embodiment of the present invention.
First, a command to start discharging of the lithium ion secondary battery is transmitted from the battery controller 26 to the lithium ion secondary battery module 21 that charges and discharges to start the cycle (step 401).

  The lithium ion secondary battery module 21 that has received the signal, for example, after the start of discharge, the voltage measurement unit 22, the current measurement unit 23, the temperature measurement unit 24, and the time measurement unit 25 perform a discharge current Id and a discharge time (discharge start). Elapsed time) td, battery voltage V, and battery temperature T are measured and transmitted to the battery controller 26.

  The battery controller 26 calculates the internal resistance D of the battery from these four parameters (V, I, T, t) (step 402).

  The lithium ion secondary battery module 21 measures the internal resistance D at any time during charging and discharging, and compares the internal resistance threshold value Ds1 with the internal resistance D (step 403). Here, when the internal resistance D is larger than the internal resistance threshold value Ds1, charging / discharging is stopped by the deterioration determining means (step 404). That is, the charge / discharge current value is made smaller than the charge / discharge current value before the internal resistance of the lithium ion secondary battery exceeds the internal resistance threshold value Ds1. When the internal resistance D is equal to or less than the internal resistance threshold value Ds1, the initial charge / discharge cycle is continued.

  Further, the lithium ion secondary battery module 21 measures the internal resistance D at any time while charging / discharging is stopped, and compares the internal resistance threshold Ds2 with the internal resistance D (step 405). Here, when the internal resistance D is equal to or greater than the internal resistance threshold Ds2, the charge / discharge stop is maintained (step 404). When the internal resistance D is smaller than the internal resistance threshold Ds2, the initial charge / discharge cycle is restarted (step 406).

In the charging / discharging stop period, the internal resistance threshold value Ds2 can be set from the relationship between the internal resistance and the cycle discharge lower limit voltage in FIG. 4 or a value calculated from an expression given in advance. D (t) is an internal resistance corresponding to the pause time, Da is a coefficient, Dc is a constant, and τa is a time constant.
D (t) = Da · exp (τa / t) + Dc
D (t) is an expression representing the relaxation state of the internal resistance with respect to the pause time. As shown in FIG. 7, the change in the internal resistance and the fitting result substantially match the pause time. Therefore, by using this equation, it is possible to estimate the change in the internal resistance with respect to the pause time, and the value of the internal resistance can be set as the internal resistance threshold value Ds2.

  When the internal resistance threshold value Ds2 is not set, if the charge / discharge cycle is continued as it is, the battery reaches a lower limit voltage at which it can be safely used, and the charge / discharge cycle is stopped. In that case, the internal resistance gradually decreases by leaving the unloaded state for a certain period. Therefore, it is possible to start the charge / discharge cycle after a certain period of time, but the coating on the positive and negative electrode surfaces generated by the decomposition components in the electrolyte is compared with the case where the charge / discharge cycle by the limit value is stopped. Thus, a large amount remains on the surfaces of the positive electrode and the negative electrode, and the internal resistance inevitably increases from the initial value, and the number of cycles that can be charged / discharged decreases.

  As described above, according to the present embodiment, the lithium ion secondary battery module 21 includes the battery controller 26, and the battery controller 26 detects the internal resistance of the lithium ion secondary battery 21, and the lithium ion secondary battery By controlling the charge / discharge current according to the state of the battery, the rise in the internal resistance of the lithium ion secondary battery is suppressed, the internal resistance of the battery is within an appropriate range, and a long-life secondary having good cycle characteristics. A battery system can be provided.

  Next, an experimental result verifying the effect of the present invention in a simulated manner will be described.

  A lithium ion battery was used for the effect verification test of Embodiment 1 of the present invention. A wound lithium ion battery as shown in FIG. 1 was produced as follows. In the verification test, a cylindrical battery (hereinafter referred to as 18650 type battery) having a battery size diameter of 18 mm and a length of 65 mm was used.

First, LiMn _1/3 Ni _1/3 Co _1/3 O ₂ is used as the positive electrode active material, carbon black (CB1) and graphite (GF1) are used as the conductive material, and polyvinylidene fluoride (PVDF) is used as the binder. The solid content weight at the time of drying was set to NMP (N-- as a solvent so that the ratio was LiMn _1/3 Ni _1/3 Co _1/3 O ₂ : CB1: GF1: PVDF = 86: 9: 2: 3. A positive electrode material paste was prepared using methylpyrrolidone). This positive electrode material paste is applied to the aluminum foil used as the positive electrode current collector 1, dried at 80 ° C., pressed with a pressure roller, and dried at 120 ° C. to form the positive electrode layer 2 on the positive electrode current collector 1. Formed.

  Next, pseudo-anisotropic carbon, which is amorphous carbon, is used as the negative electrode active material, carbon black (CB2) is used as the conductive material, and PVDF is used as the binder. A negative electrode material paste was prepared using NMP as a solvent so as to have a ratio of carbon: CB2: PVDF = 88: 5: 7. This negative electrode material paste is applied to the copper foil used as the negative electrode current collector 4, dried at 80 ° C., pressed with a pressure roller, and dried at 120 ° C. to form the negative electrode layer 5 on the negative electrode current collector 4. Formed.

A separator 7 was sandwiched between the produced electrodes to form a wound electrode group, which was inserted into the negative electrode battery can 13. Further, an electrolytic solution was injected, and the open end portion of the negative electrode battery can 13 was caulked to produce a wound lithium ion battery. In the electrolytic solution, 1 mol / l of lithium salt LiPF ₆ as an electrolyte is dissolved in a mixed solvent mixed at a volume composition ratio of EC: DMC: EMC = 20: 40: 40, and a solution comprising the mixed solvent and the lithium salt is further dissolved. Based on the total weight, 0.8% by weight of VC was added.

  FIG. 8 shows the relationship between the internal resistance implemented to verify the effect of the present invention and the charge / discharge pattern of the test. When the internal resistance threshold value Ds1 which is the threshold value of the internal resistance is reached, the charge / discharge current value is limited from the prior charge / discharge current. The cycle is continued by limiting the charge / discharge current value until the threshold value of the internal resistance reaches the internal resistance threshold value Ds2. When the threshold value of the internal resistance becomes 2 or less, the charge / discharge cycle with the initial charge / discharge current value is resumed. The internal resistance threshold value Ds1 and the internal resistance threshold value Ds2 are set from FIG. There is a correlation between the internal resistance and the cycle lower limit voltage. When the internal resistance threshold value Ds1 and the internal resistance threshold value Ds2 that are internal resistances are determined, the discharge-side lower limit voltage of the cycle is inevitably determined. Since the voltage changes only within the discharge-side lower limit voltage range, the charge / discharge cycle can be continued. The secondary battery system proposed in the present invention suppresses an increase in internal resistance and can continue the charge / discharge cycle. Therefore, it is considered that there is an effect of obtaining good charge / discharge cycle characteristics.

  In the effect verification test of Embodiment 2, the same 18650 type battery as that of Example 1 was used. FIG. 9 shows the relationship between the internal resistance implemented to verify the effect of the invention and the charge / discharge pattern of the test. When the limit value 3, which is the threshold value of the internal resistance, is reached, the charge / discharge current is stopped. When the threshold value of the internal resistance becomes the limit value 4 or less, the charge / discharge cycle is restarted. The limit value 3 and the limit value 4 can be determined in the same manner as in the first embodiment.

  Further, the charge / discharge stop period t3 to t4 can also be determined by the equation D (t). The internal resistance of FIG. 4, the cycle lower limit voltage, and the internal resistance obtained by D (t) are compared to determine the charge / discharge stop period. When the limit values 3 and 4 that are internal resistances are determined, the discharge-side lower limit voltage of the cycle is inevitably determined, and the voltage changes only within the discharge-side lower limit voltage range, so that the charge / discharge cycle can be continued.

  The secondary battery system proposed in the present invention suppresses an increase in internal resistance and can continue the charge / discharge cycle. Therefore, it is considered that there is an effect of obtaining good charge / discharge cycle characteristics.

  The present invention is not limited to the above-described embodiment, and can be appropriately modified and applied without departing from the gist thereof.

  For example, although the battery is a wound type lithium ion secondary battery, the present invention is applied to a stacked type lithium ion secondary battery in which a plurality of positive plates and a plurality of negative plates are alternately stacked via separators. May be.

DESCRIPTION OF SYMBOLS 1 Positive electrode collector 2 Positive electrode layer 3 Positive electrode 4 Negative electrode collector 5 Negative electrode layer 6 Negative electrode 7 Separator 8 Positive electrode lead 9 Negative electrode lead 10 Positive electrode insulating material 11 Negative electrode insulating material 12 Positive electrode battery lid 13 Negative electrode battery can 14 Gasket 21 Lithium Ion secondary battery module 22 Voltage measurement unit 23 Current measurement unit 24 Temperature measurement unit 25 Time measurement unit 26 Battery controller 27 Electric load 100 Lithium ion secondary battery

Claims (6)

A positive electrode containing a positive electrode active material capable of inserting and extracting lithium ions;
A negative electrode containing amorphous carbon capable of inserting and extracting lithium ions;
A separator disposed between the positive electrode and the negative electrode;
A secondary battery system comprising a lithium ion secondary battery, the organic electrolyte solution comprising:
The maximum current value at the time of charge and discharge in the lithium ion secondary battery is a time rate of 5C or more,
Charge / discharge control means for controlling charge / discharge of the lithium ion secondary battery;
Internal resistance calculating means for calculating the internal resistance of the lithium ion secondary battery;
Internal resistance increase detection means for detecting that the internal resistance of the lithium ion secondary battery calculated by the internal resistance calculation means exceeds the internal resistance threshold value Ds1,
When the internal resistance of the lithium ion secondary battery calculated by the internal resistance calculation means is larger than the internal resistance threshold Ds1 when the battery surface temperature of the lithium ion secondary battery is 25 ° C. or less, the charging / discharging is performed. A secondary battery system comprising: a deterioration determination unit configured to make a charge / discharge current value of the lithium ion secondary battery smaller than a charge / discharge current value before the internal resistance of the lithium ion secondary battery exceeds the internal resistance threshold value Ds1. In claim 1,
Battery state detecting means for detecting a battery surface temperature of the lithium ion secondary battery;
A secondary battery system comprising: an internal resistance threshold value setting unit that sets the internal resistance threshold value Ds1 according to a battery surface temperature detected by the battery state detection unit. In claim 1 or 2,
When the internal resistance of the lithium ion secondary battery calculated by the internal resistance calculation unit is larger than the internal resistance threshold value Ds1, the deterioration determination unit calculates the charge / discharge current value of the lithium ion secondary battery being charged / discharged. A secondary battery system that is controlled below a predetermined current value. In any one of Claims 1 thru | or 3,
When the internal resistance of the lithium ion secondary battery calculated by the internal resistance calculation means becomes larger than the internal resistance threshold value Ds1, the deterioration determination means stops charging / discharging of the lithium ion secondary battery being charged / discharged. Secondary battery system. In claim 1 or 2,
The secondary battery system has a lithium ion secondary battery module that combines a plurality of the lithium ion secondary batteries in series, parallel, or series-parallel,
After the deterioration determination means makes the charge / discharge current value of the lithium ion secondary battery being charged / discharged smaller than the charge / discharge current value before the internal resistance of the lithium ion secondary battery exceeds the internal resistance threshold Ds1,
When the internal resistance of the lithium ion secondary battery is smaller than the internal resistance threshold value Ds2 preset by the internal resistance calculating means, the charge / discharge current value of the lithium ion secondary battery module being charged / discharged is determined by the deterioration determining means. The secondary battery system which controls to the charging / discharging electric current value before the internal resistance of the said lithium ion secondary battery exceeds the said internal resistance threshold value Ds1. A positive electrode containing a positive electrode active material capable of inserting and extracting lithium ions;
A negative electrode containing amorphous carbon capable of inserting and extracting lithium ions;
A separator disposed between the positive electrode and the negative electrode;
A method for controlling a secondary battery system including a lithium ion secondary battery, comprising:
The maximum current value at the time of charge and discharge in the lithium ion secondary battery is a time rate of 5C or more,
Charge / discharge control means for controlling charge / discharge of the lithium ion secondary battery;
Internal resistance calculating means for calculating the internal resistance of the lithium ion secondary battery;
Internal resistance increase detection means for detecting that the internal resistance of the lithium ion secondary battery calculated by the internal resistance calculation means exceeds the internal resistance threshold value Ds1,
When the internal resistance of the lithium ion secondary battery calculated by the internal resistance calculation means is larger than the internal resistance threshold Ds1 when the battery surface temperature of the lithium ion secondary battery is 25 ° C. or less, the charging / discharging is performed. A deterioration determination means for reducing a charge / discharge current value of the lithium ion secondary battery to a charge / discharge current value before the internal resistance of the lithium ion secondary battery exceeds the internal resistance threshold value Ds1. Control method.