JP2005149793A - Calculation method of charging/discharging upper limit temperature of lithium secondary battery, charging/discharging method of lithium secondary battery, and battery system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a calculation method of charging/discharging upper limit temperature and a charging/discharging method of lithium secondary battery capable of restraining the deterioration of a cycle property of lithium manganate. <P>SOLUTION: The calculation method of upper limit temperature is characterized by determining an activation energy of a main side reaction causing the deterioration of the battery, depending on the temperature of the lithium secondary battery at use and the lowering of capacity at the above temperature, and applying the charging/discharging temperature when an activation energy is changed as an upper limit temperature. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for calculating a charge / discharge upper limit temperature of a lithium secondary battery, a charge / discharge method for a lithium secondary battery, and a battery system including the lithium secondary battery.

With the recent rise in energy and environmental problems, development of high-performance lithium secondary batteries is urgently needed. Among various lithium secondary batteries, a lithium secondary battery using a metal oxide as a positive electrode active material is most promising in that it has a high energy density.
Conventionally, batteries using lithium cobalt oxide (LiCoO ₂ ) as a metal oxide have been commercially available. However, since cobalt is a rare resource and expensive, manganese has recently been replaced with lithium cobalt oxide, which is cheaper. The use of lithium acid (LiMn ₂ O ₄ ) has been studied.

By the way, while lithium manganate is cheaper than lithium cobaltate, side reactions such as manganese ions eluting into the organic electrolyte occur when stored in an organic electrolyte at a high temperature, compared to batteries using lithium cobaltate, There is a problem that the capacity reduction of the lithium secondary battery under high temperature becomes large. Incidentally, regarding the relationship between the lithium secondary battery and the temperature, various problems are pointed out in Patent Document 1 and Patent Document 2 below.
JP-A-8-37736 JP 2002-51478 A

  Although lithium manganate has the above-mentioned drawbacks, it is desirable to use an inexpensive material from the viewpoint of cost reduction. Therefore, lithium manganate is most promising from this viewpoint. Therefore, it is required to solve the above-described reduction in capacity of a battery using lithium manganate at a high temperature from the viewpoint of charge / discharge temperature.

  As described above, side reactions such as elution reaction of manganese ions tend to occur as the temperature during charge and discharge increases, so if charging and discharging are performed at a temperature lower than the temperature at which this side reaction increases, cycle characteristics are improved. Is possible. For this reason, development of the means which can measure the temperature range which a side reaction increases is desired.

  This invention is made in view of the said situation, Comprising: The calculation method of the charging / discharging upper limit temperature which can suppress the capacity | capacitance fall of a lithium secondary battery, and the charging / discharging method of a lithium secondary battery are provided. For the purpose.

In order to achieve the above object, the present invention employs the following configuration.
The calculation method of the charge / discharge upper limit temperature of the lithium secondary battery of the present invention is a calculation method of the upper limit temperature when charging and discharging the lithium secondary battery,
The activation energy of the main side reaction that causes battery deterioration is determined from the operating temperature of the lithium secondary battery and the capacity decrease at that temperature, and the charge / discharge temperature when the activation energy changes is defined as the upper limit temperature of charge / discharge. It is characterized by doing.
That is, by repeatedly charging and discharging the lithium secondary battery, the deterioration rate (k) per cycle of the discharge capacity is determined according to the charge / discharge temperature, and the Arrhenius equation shown in the following [Equation 1] together with the charge / discharge temperature (T) The activation energy (Ea) of a major side reaction that causes a decrease in battery capacity is obtained by applying to the above, and the charge / discharge temperature when the activation energy changes is defined as the upper limit temperature of charge / discharge.

  The above calculation method is preferably applied to a lithium secondary battery using lithium manganate as a positive electrode active material. However, if the activation energy can be calculated for the capacity reduction of the battery, lithium manganate is used. The present invention can also be applied to a battery other than a lithium secondary battery used as a positive electrode active material.

  According to the method for calculating the upper limit of charge / discharge temperature of a lithium secondary battery, the temperature at which the activation energy changes is defined as the upper limit temperature of charge / discharge. Therefore, even when the size or shape of the battery changes, An optimum upper limit temperature can be obtained, which can be useful for suppressing a decrease in battery capacity.

The reason why the temperature at which the activation energy changes is defined as the upper limit temperature of charge / discharge is as follows.
In a temperature range higher than the upper limit temperature, the capacity of the battery is greatly reduced, and a change can also be confirmed in the activation energy required from the capacity reduction of the battery. Thereby, it is considered that some side reaction that greatly reduces the battery capacity occurs particularly in the temperature range exceeding the upper limit temperature. For this reason, if charging / discharging is performed in a temperature range in which the capacity decrease of the battery is small, that is, the upper limit temperature or less, side reactions can be suppressed and the cycle characteristics of the lithium secondary battery can be improved.

Next, the method for charging and discharging the lithium secondary battery according to the present invention obtains the activation energy of the main side reaction that causes battery deterioration from the operating temperature of the lithium secondary battery and the capacity decrease at that temperature in advance. When the temperature at which the activation energy changes is defined as the upper limit temperature of charge / discharge, charge / discharge is performed at the upper limit temperature or less.
The above calculation method is preferably applied to a lithium secondary battery using lithium manganate as a positive electrode active material. However, if the activation energy for reducing the battery capacity can be calculated, lithium manganate is used as the positive electrode. It can be applied to other than the lithium secondary battery as the active material.

  According to such a charging / discharging method of the lithium secondary battery, the temperature at which the activation energy changes is set as the upper limit temperature of charging / discharging, and charging / discharging is performed below this upper limit temperature. The cycle characteristics of the battery can be improved.

In addition, the battery system of the present invention obtains the activation energy of the main side reaction that causes battery deterioration from the operating temperature of the lithium secondary battery and the capacity decrease at the temperature in advance, and when the activation energy changes When the temperature is the upper limit temperature of charge / discharge, charge / discharge is performed at the upper limit temperature or less.
The upper limit temperature is preferably 60 ° C. or lower, and more preferably 18 ° C. or lower.

  According to the battery system described above, the temperature at which the activation energy changes is set as the upper limit temperature of charge / discharge, and the lithium secondary battery is charged / discharged below this upper limit temperature. The cycle characteristics of the battery can be improved.

  According to the method for calculating the charge / discharge upper limit temperature of the lithium secondary battery of the present invention, the temperature at which the activation energy changes is defined as the charge / discharge upper limit temperature, so even if the size or shape of the battery changes, The optimum upper limit temperature for the battery can be determined, which can be useful for suppressing cycle deterioration.

  Moreover, according to the charging / discharging method of the lithium secondary battery of the present invention, the temperature when the activation energy is changed is set as the upper limit temperature of charging / discharging, and charging / discharging is performed at or below this upper limit temperature, thereby suppressing side reactions. It becomes possible to improve the cycle characteristics of the lithium secondary battery.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The lithium secondary battery applicable to the method for calculating the charge / discharge upper limit temperature and the charge / discharge method of the present invention preferably has the following configuration.

  FIG. 1 shows an example of a lithium secondary battery applicable to the present invention. The lithium secondary battery 1 is a so-called square shape, and includes a plurality of positive electrodes (positive electrodes) 2, a plurality of negative electrodes (negative electrodes) 3, and a space between the positive electrode 2 and the negative electrode 3. The separator 4... Arranged and a non-aqueous electrolyte (non-aqueous electrolyte) are mainly used.

  The positive electrode 2..., The negative electrode 3... And the separator 4... And the non-aqueous electrolyte are housed in a battery case 5 made of stainless steel or the like. A sealing plate 6 is attached to the upper part of the battery case 5. A safety valve 9 for preventing an increase in the internal pressure of the battery is provided almost at the center of the sealing plate 6. The separator 4 is made of a porous polymer material film such as polyethylene or polypropylene, a glass fiber, a nonwoven fabric made of various polymer fibers, or the like.

  A positive electrode tab 12 is formed at one end of the positive electrodes 2... And a positive electrode lead 12 b connecting the positive electrode tabs 12 a is attached to the upper part of the positive electrode tabs 12 a. A positive electrode terminal 7 penetrating the sealing plate 6 is attached to the positive electrode lead 12b. Similarly, negative electrode tabs 13a are formed at one end of the negative electrodes 3 ..., and negative electrode leads 13b for connecting the negative electrode tabs 13a are attached to the upper portions of the negative electrode tabs 13a. A negative electrode terminal 8 that penetrates the sealing plate 6 is attached to the negative electrode lead 13b. With the above configuration, current can be taken out from the positive terminal 7 and the negative terminal 8.

  Next, as shown in FIG. 2, the negative electrode 3 is composed of a negative electrode current collector 3a made of Cu foil or the like, and a negative electrode film 3b formed on the negative electrode current collector 3a. The negative electrode tab 13a is formed at one end of the negative electrode current collector 3a. The negative electrode film 3b is formed, for example, by mixing a negative electrode active material powder such as graphite for electrochemically desorbing lithium and a binder such as polyvinylidene fluoride. In some cases, a conductive additive powder such as carbon black is added to the negative electrode film 3b.

  As the negative electrode active material, in addition to graphite, various carbon materials such as coke, pyrolytic carbon, glassy carbon, amorphous carbon, graphitized carbon fiber, fired bodies of various polymer materials, mesocarbon micro beads, activated carbon and the like Can be used. Alternatively, an alloy such as Si, Sn, or In that can be charged / discharged at a relatively low potential, or a metal oxide / nitride may be used. As the binder for the negative electrode 3, polyimide or the like can be used in addition to polyvinylidene fluoride.

  The positive electrode 2 includes a positive electrode current collector (current collector) 2a made of, for example, an Al foil, and a positive electrode film (electrode film) 2b formed on the positive electrode current collector 2a. The positive electrode tab 12a is protruded from one end of the positive electrode current collector 2a. The positive electrode film 2b is formed into a film shape by mixing a positive electrode active material powder, a conductive additive powder, and a binder.

As the positive electrode active material powder, those capable of electrochemically removing and inserting lithium are preferable. For example, any one of lithium manganate, lithium cobaltate, lithium nickelate, lithium ferrate, vanadium oxide, lithium vanadate, etc. , Or two or more. In addition, as the conductive additive powder, for example, a carbonaceous material such as carbon black, acetylene black, graphite, or carbon fiber can be used. Further, as the binder, for example, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, styrene butadiene rubber or the like can be used.
Furthermore, a conductive polymer material such as polyaniline, polypyrrole, polythiophene, or polyimidazole may be added to the positive electrode film 2b. Since these conductive polymer materials are electrochemically stable and excellent in electron conductivity, there is an effect of reducing the internal resistance of the positive electrode film 2b.
As the positive electrode current collector 2a, a metal foil, a metal net, an expanded metal, or the like can be used, and these materials may be Ti, stainless steel, etc. in addition to Al.

  As shown in FIG. 2, the positive electrode layer 2 b and the negative electrode layer 3 b are opposed to each other with the separator 4 interposed therebetween. In FIG. 2, for simplicity of explanation, the electrode films 2b and 3b are formed on one side of the current collectors 2a and 3a. However, the electrode films 2b and 3b are shown in FIG. Of course, the film may be formed on both surfaces of the electric conductors 2a and 3a.

  Next, the non-aqueous electrolyte (non-aqueous electrolyte) includes either or both of a cyclic carbonate ester and a chain carbonate ester, and further includes a solute. In particular, it is preferable that a solute is dissolved in a mixture of both a cyclic carbonate and a chain carbonate.

Examples of the cyclic carbonate include propylene carbonate, ethylene carbonate, butylene carbonate and the like. Examples of the chain carbonate include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl butyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate, and acetate.
The cyclic carbonates and chain carbonates are not limited to those listed above, and any one can be used as long as it can dissociate the solute and the quaternary ammonium salt.
Furthermore, ethers such as 1,2-dimethoxyethane, 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran and diethyl ether may be used.

The solutes include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiN (RfSO ₂ ) ₂ , LiC (RfSO ₂ ) ₃ , LiC _n F Examples of the lithium salt include _{2n + 1} SO ₃ (n ≧ 2) and LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group].

  Furthermore, it can replace with said non-aqueous electrolyte and can also use a solid electrolyte (non-aqueous electrolyte). Examples of the solid electrolyte include a gel electrolyte obtained by impregnating the non-aqueous electrolyte into a polymer matrix such as polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, and polyacrylonitrile. Further, when a solid electrolyte is used, the separator 4 may be omitted.

Next, a method for calculating the charge / discharge upper limit temperature of the lithium secondary battery of the present invention will be described.
First, charging / discharging of the lithium secondary battery is repeated at least twice within a predetermined temperature range, and the deterioration rate per cycle of the discharge capacity for each charging / discharging temperature is obtained.
The charge / discharge temperature is preferably in the temperature range in which the battery can operate, for example, in the range of −30 ° C. to 80 ° C. When the temperature is −30 ° C. or lower, the deterioration is extremely small, and thus it takes time for evaluation, which is not preferable. Moreover, since electrolyte solution freezes and it may not function as a battery, it is not preferable. Moreover, when it exceeds 80 degreeC, since deterioration of the constituent material of a battery will become large and charging / discharging capacity will fall extremely, it is unpreferable.
The charge / discharge temperature is preferably set in increments of 2 ° C to 10 ° C within a range of -30 ° C to 80 ° C. If the temperature increment is set to 2 ° C or less, the number of measurement points increases remarkably, and it takes a long time to calculate the upper limit temperature. This is not preferable, and if the temperature increment exceeds 10 ° C, the accuracy of the upper limit temperature calculation is increased. Since it falls, it is not preferable.

The charging is preferably performed by, for example, a constant current / constant voltage method. That is, charging is performed at a constant current until the battery voltage reaches the charging upper limit voltage (constant current charging), and after reaching the charging upper limit voltage, a current is supplied for a predetermined charging time while maintaining the upper limit voltage (constant voltage charging). . The charging upper limit voltage during constant current / constant voltage charging is preferably in the range of 4.1 V to 4.2 V, although it depends on the configuration of the positive and negative electrodes of the battery. The charging current during constant current charging is preferably in the range of 0.1C to 5C, although it depends on the battery size. Furthermore, the charging time during constant voltage charging is preferably within 10 hours, although it depends on the battery size.
The discharge is preferably performed by constant current discharge. That is, the battery is discharged at a constant current until the battery voltage reaches the discharge lower limit voltage (constant current discharge). The discharge lower limit voltage is preferably in the range of 2.5 V to 3.5 V, although it depends on the configuration of the positive and negative electrodes of the battery. The discharge current is preferably in the range of 0.1C to 5C, although it depends on the battery size.

Next, the deterioration rate D (%) per cycle of the discharge capacity is, for example, when the discharge capacity at the first cycle is Q ₁ (Ah) and the discharge capacity at the 100th cycle is Q ₁₀₀ (Ah),
_{D (%) = (Q 1} -Q 100) / Q 1/100 ( cycles) × 100
It is calculated by the following formula.
The retention rate of discharge capacity E (%) is, for example, the discharge capacity at the first cycle and _{Q 1,} when the discharge capacity of the 100th cycle was _{Q 100,}
E (%) = Q ₁₀₀ / Q ₁ × 100
It is calculated by the following formula.

  Next, the lithium secondary battery is repeatedly charged and discharged to determine the deterioration rate (k) per cycle of the discharge capacity according to the charge / discharge temperature, and the Arrhenius shown in the above [Formula 1] together with the charge / discharge temperature (T). The activation energy (Ea) of the main side reaction that causes a decrease in battery capacity is obtained by applying to the above equation, and the charge / discharge temperature when the activation energy changes is defined as the upper limit temperature of charge / discharge. To do.

Specifically, a graph is created with the charge / discharge temperature as the horizontal axis and the deterioration rate of the discharge capacity as the vertical axis. The deterioration rate is displayed in logarithm, and the charge / discharge temperature is displayed in reciprocal. When the plots on the graph are connected by a straight line, the slope of the straight line is defined as the activation energy of a major side reaction that causes the capacity of the battery to decrease.
FIG. 3 shows an example of the graph. In the graph shown in FIG. 3, three straight lines (i) to (iii) are shown. In this case, the slopes of the straight lines (i) to (iii) are activation energies of main side reactions that cause a decrease in battery capacity. _Further, the relationship of _{T 1 <T 2 <T 3} .
As shown in FIG. 3, the straight line (i) is in the range from the reciprocal temperature 1 / T ₁ to 1 / T ₂ , and the slope of the straight line (i) is activated in the range T _{1 to} T ₂ . Energy. Similarly, the slope of the straight line of (ii) is the activation energy in the range of T ₂ through T _3, the activation energy in the range linear slope of T ₁ through T ₄ of (iii).
Thus, in FIG. 3, the slope of the straight line changes at temperatures T ₂ and T ₃ .

And in this invention, charging / discharging temperature when activation energy changes is made into upper limit temperature of charging / discharging. The charge / discharge temperature when the activation energy changes is not limited to one, and a plurality of charge / discharge temperatures may exist. For example, in the case of FIG. 3, the temperature at which the activation energy changes is two, T ₂ and T ₃ . In such a case, in the present invention, it is preferable to select the lowest temperature as the upper limit temperature. That it is preferable that the T ₂ are the case of FIG.

The reason why the temperature at which the activation energy changes is defined as the upper limit temperature of charge / discharge is as follows.
As shown in FIG. 3, the slope of the straight line changes as the charging / discharging temperature increases. This is considered to be caused by some side reaction that greatly reduces the battery capacity particularly in the temperature range exceeding the upper limit temperature. . Thus in FIG. 3, it is less reduced capacity of the battery in a low temperature region to a temperature T ₃ on the boundary, toward the low temperature region is less reduction capacity of the battery was further the temperature T ₂ in the boundary.
Therefore, if charging / discharging is performed in a temperature range where the capacity decrease of the battery is small, that is, not more than the upper limit temperature defined in the present invention, it is possible to suppress the side reaction and improve the cycle characteristics of the lithium secondary battery. Become.

  In addition, as a side reaction occurring at the time of charging / discharging of the lithium secondary battery, for example, a solvent or an electrolyte in the electrolytic solution is decomposed to form a surface film on the negative electrode, or a gas such as hydrofluoric acid is generated. Reaction is considered.

Next, the charging / discharging method of the lithium secondary battery of this invention is demonstrated. In this charging method, charging / discharging is performed at a temperature lower than the upper limit temperature obtained by the above calculation method. That is, the charge / discharge of the lithium secondary battery is repeatedly performed in advance for each temperature, and the deterioration rate of the discharge capacity at each charge / discharge temperature is obtained. And let the rate of change of the deterioration rate with respect to charging / discharging temperature be the activation energy of charging / discharging reaction, and let temperature when the said activation energy change be upper limit temperature of charging / discharging. The lithium secondary battery is charged and discharged at a temperature lower than the upper limit temperature thus determined. In the above example, charging and discharging at a temperature T ₂ below.

  According to such a charging / discharging method, since charging / discharging is performed below the upper limit temperature of charging / discharging, it becomes possible to suppress the side reaction and improve the cycle characteristics of the lithium secondary battery.

  Moreover, as a battery system of this invention, what installed said lithium secondary battery in the environment where temperature control is possible, such as the inside of a thermostat, can be illustrated. By performing charging / discharging in a state where the ambient temperature of the lithium secondary battery is set to the above upper limit temperature or less, side reactions can be suppressed and the cycle characteristics of the lithium secondary battery can be improved. In particular, in order to reduce the ambient temperature of the lithium secondary battery to 60 ° C. or less, it can be sufficiently handled by avoiding direct sunlight and improving ventilation. As an example, a battery can be installed in a structure similar to a hundred-leaf box. In addition, to reduce the ambient temperature of lithium secondary batteries to 18 ° C or less, avoid direct sunlight and improve ventilation, depending on the environment in which the battery is installed, it may be forced to blow air to cool it, Water cooling or the like may be performed. Moreover, although a battery may be cooled with a cooler, a semiconductor, etc., it is not restricted to this form.

(Experimental example 1)
90% by weight of lithium manganate as a positive electrode active material, 5% by weight of graphite as a conductive material, 5% by weight of polyvinylidene fluoride (PVdF) as a binder, and 50% solid content in N-methylpyrrolidone (NMP) as a solvent It mixed so that it might become a slurry. While continuously applying this to an aluminum foil serving as a current collector, it was dried at 80 ° C. to form a coating film. Next, the coating film on the current collector was pressure-molded with a roller press so that the film density was 2.4 g / cm ³ to produce a positive electrode. Next, this positive electrode was dried by heating at 110 ° C. for 9 hours while reducing the pressure to 100 Pa or less.
Further, 90% by weight of graphite as a negative electrode active material, 10% by weight of a binder and PVdF were mixed with NMP as a solvent so as to have a solid content of 50% to obtain a slurry. Subsequently, it dried at 80 degreeC, applying this continuously to copper foil, and formed the coating film. Next, the coating film on the copper foil was pressure-molded by a roll press so that the film density was 1.4 g / cm ³ , thereby producing a negative electrode. Next, this negative electrode was dried by heating at 130 ° C. for 72 hours while reducing the pressure to 100 Pa or less.

Next, cut the positive electrode and the negative electrode so that the area is a circle of 2 cm ² , combine these positive and negative electrodes, manufacture a coin-type battery with a separator between both electrodes, and charge / discharge test Went. As the non-aqueous electrolyte for the coin-type battery, EC and DMC are mixed so that the mixing ratio EC: DMC is 1: 2, and LiPF ₆ is added to this mixed solvent at a concentration of 1 (mol / L). What was melt | dissolved so that it might become was used.
Next, charging / discharging of the coin-type battery was performed at 25 ° C., and the capacity retention rate after 100 cycles when the discharge capacity at the first cycle was 100% was determined. Further, the deterioration rate per cycle from 1 to 100 cycles was determined. The results are shown in Table 1, FIG. 4 and FIG.

  The charging was performed under the condition that a current of 1/3 C was supplied until the battery voltage reached 4.15 V, and then the charging was performed until the current value became 5% or less of the set value. The discharge was performed under the condition of discharging at 1/3 C until the battery voltage reached 3.1V.

(Experimental Examples 2 to 12)
Next, a coin-type battery was prepared and charged / discharged in the same manner as in Experimental Example 1 except that the temperature at which charging / discharging was performed was changed as shown in Table 1. And the capacity | capacitance maintenance factor and degradation rate after 100 cycles were calculated | required for each temperature. The results are shown in Table 1, FIG. 4 and FIG.

  FIG. 4 is a graph showing the relationship between the capacity retention rate (%) and the charge / discharge temperature. The vertical axis in FIG. 4 is the deterioration rate, and the horizontal axis is the charge / discharge temperature. FIG. 5 is a graph showing the relationship between the deterioration rate (%) and the charge / discharge temperature. The vertical axis in FIG. 4 is a logarithmic display of the deterioration rate, and the horizontal axis is a reciprocal display of the charge / discharge temperature. The temperature in parentheses is the charge / discharge temperature.

As shown in Table 1, FIG. 4 and FIG. 5, the deterioration of the lithium secondary battery increases as the charging / discharging temperature rises. In particular, as shown in FIG. 4, when the charging / discharging temperature exceeds 60 ° C., 100 cycles. It was confirmed that the capacity retention rate later decreased to 90% or less.
Moreover, as shown in FIG. 5, when the logarithm of the deterioration rate and the reciprocal of the temperature were plotted, three straight lines could be drawn with a specific temperature (18 ° C., 60 ° C.) as a boundary. As a result, it was confirmed that the battery deterioration was progressed mainly by three reactions having different activation energies. In particular, it is presumed that causes of battery deterioration such as electrolytic solution decomposition and manganese elution change depending on a specific temperature. It was confirmed that the capacity retention rate after 100 cycles was 98% or more at 18 ° C. or less where the slope of the straight line was small and the activation energy was considered to be small. Therefore, in this experiment example, it is estimated that 18 degreeC is the upper limit temperature of charging / discharging.

It is a perspective view which shows an example of the nonaqueous electrolyte secondary battery which is embodiment of this invention. It is a perspective view which shows the principal part of the nonaqueous electrolyte secondary battery shown in FIG. The graph for demonstrating the calculation method of the charging / discharging upper limit temperature of the lithium secondary battery which is embodiment of this invention. The graph which shows the relationship between a capacity | capacitance maintenance factor (%) and charging / discharging temperature. It is a graph which shows the relationship between the deterioration rate (%) of discharge capacity, and charging / discharging temperature, Comprising: A vertical axis | shaft is a logarithm display of a deterioration rate and a horizontal axis is a reciprocal display of charging / discharging temperature.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Lithium secondary battery, 2 ... Positive electrode (positive electrode), 2a ... Positive electrode collector, 2b ... Positive electrode film, 3 ... Negative electrode (negative electrode), 3a ... Negative electrode collector, 3b ... Negative electrode film, 4 ... Separator, 5 ... Battery case, 6 ... Sealing plate

Claims (5)

It is a calculation method of the upper limit temperature when charging and discharging a lithium secondary battery,
The activation energy of the main side reaction that causes battery deterioration is determined from the operating temperature of the lithium secondary battery and the capacity decrease at that temperature, and the charge / discharge temperature when the activation energy changes is defined as the upper limit temperature of charge / discharge. A method for calculating a charging / discharging upper limit temperature of a lithium secondary battery. A method of charging and discharging a lithium secondary battery,
The activation energy of the main side reaction that causes the battery deterioration is obtained in advance from the operating temperature of the lithium secondary battery and the capacity decrease at that temperature, and the temperature when the activation energy changes is defined as the upper limit temperature of charge / discharge. When
Charging / discharging of a lithium secondary battery characterized by performing charging / discharging below the said upper limit temperature. The activation energy of the main side reaction that causes the battery deterioration is obtained in advance from the operating temperature of the lithium secondary battery and the capacity decrease at that temperature, and the temperature when the activation energy changes is defined as the upper limit temperature of charge / discharge. When
A battery system for charging and discharging a lithium secondary battery at a temperature equal to or lower than the upper limit temperature.   The battery system according to claim 3, wherein the upper limit temperature is 60 ° C. or less. The battery system according to claim 3, wherein the upper limit temperature is 18 ° C or lower.

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