JP2015053249A - Degradation analysis method of battery and carbon material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a degradation analysis method of battery performing degradation analysis of an electrode active material itself quantitatively.SOLUTION: A degradation analysis method of battery determines whether or not the degradation cause of battery is derived from the electrode active material, by performing differential scanning calorimetry (DSC) of a fully charged electrode, and measuring the activation energy of the electrode active material. Preferably, differential scanning calorimetry (DSC) is performed by changing the rate of temperature rise, and the activation energy is determined from the inclination obtained by measuring the endothermic and exothermic peak temperature T(K) when the rate of temperature rise is a(°C/min), and plotting the ln(a/Tm) on the axis of ordinate and the 1/Ton the axis of abscissa.

Description

  The present invention relates to a battery deterioration analysis method.

  Lithium ion batteries are expected to be widely used as automobiles and storage batteries in the future because of their high energy density and relatively good output characteristics.

  As the battery is repeatedly charged and discharged, the capacity and output characteristics decrease. However, elucidating the cause and removing the cause leads to improvement of the battery characteristics.

  Conventionally, battery deterioration analysis has been performed by analyzing changes in the crystal structure of the electrode active material by, for example, electrical resistance measurement or XRD (X-ray diffraction measurement).

JP 2003-317810 A JP 2007-134049 A

Journal of The Electrochemical Society, 152 (1) (2005) A73-79.

However, it is not possible to determine whether the deterioration of the battery is derived from the electrode active material or the influence of the peeling between the electrode layer and the current collector only by measuring the electric resistance. In addition, in XRD, changes in the crystal structure of the electrode active material can be seen, but it is impossible to quantitatively analyze how much the electrode active material has deteriorated.
This invention is made | formed in view of the said situation, Comprising: It aims at providing the deterioration analysis method of the battery which determines quantitatively whether deterioration of a battery originates in an electrode active material.

In order to solve the above problems, the following configuration is adopted.
(1) By performing differential scanning calorimetry (DSC) of a fully charged electrode, the activation energy of the electrode active material is measured, and it is determined whether or not the cause of battery deterioration is derived from the electrode active material Degradation analysis method.
(2) Differential scanning calorimetry (DSC) is performed by changing the heating rate, and the endothermic peak temperature T _m (K) is measured when the heating rate is a (° C./min). a / T _m ² ), and the slope obtained by plotting 1 / T _m on the horizontal axis is defined as the activation energy, and the battery deterioration analysis method according to (1).
(3) via the use of an activation energy E _a electrode active material deterioration degree of the activation energy E ₀ and full charge when the electrode active material after the battery deterioration test of the electrode active material during fully charged when the battery deterioration test start The battery degradation analysis method according to (1) or (2), defined by E _a / E ₀ .
(4) The battery deterioration analysis method according to (3), wherein if E _a / E ₀ is 1.10 or more, it is determined that the cause of battery deterioration is derived from the electrode active material.
(5) A solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a volume ratio of 2: 3, an electrolytic solution containing 1 mol / L LiPF ₆ as an electrolyte, a fully charged carbon material, Was adjusted to a mass ratio of 0.6: 1 to 1: 1, sealed in a 27 μL chrome steel nickel sealed container with a total mass of 7 mg to 14 mg, and a heating rate of 1 ° C./min. . , 2 ° C./min. , 5 ° C./min. The carbon material whose activation energy of the endothermic peak observed between 250 ° C. and 300 ° C. is 130 kJ / mol or more when DSC measurement is performed at these three levels.

  According to the present invention, by quantitatively analyzing the deterioration of the electrode active material itself, it is possible to determine whether the deterioration of the battery is derived from the electrode active material and to perform the deterioration analysis of the battery.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an external view and a cross-sectional view illustrating a schematic configuration of a laminated lithium ion secondary battery including a positive electrode plate and a negative electrode plate to which a battery deterioration analysis method according to an embodiment of the present invention is applied. It is an example of the measurement result of DSC.

  Hereinafter, a battery deterioration analysis method according to an embodiment of the present invention will be described with reference to the drawings.

In the battery degradation analysis method according to a preferred embodiment of the present embodiment, the battery is composed of a positive electrode, a negative electrode, and an electrolytic solution. The form of the battery may be any of coin, cylinder, laminate type and the like. After the battery is fully charged, the battery is disassembled in an atmosphere having a low concentration of O ₂ and H ₂ O, and the electrolyte and the electrolytic solution are washed and dried to obtain an electrode for DSC measurement. The electrode for DSC measurement is placed in a sealed container having pressure resistance and corrosion resistance. DSC measurement is performed using this sealed container. The DSC measurement is performed at a temperature increase rate of at least three levels. With respect to each endothermic exothermic peak temperature T _m (K) obtained when the temperature rising rate is changed and the temperature rising rate a (° C./min) at that time, the vertical axis is ln (a / T _m ² ), and the horizontal axis is 1 / _Tm is plotted, and the slope obtained is the activation energy. The degree of active material degradation is defined as E _a / E ₀ using the activation energy E ₀ of the active material at the time of full charge at the start of the degradation test, which is obtained from DSC, and the activation energy E _a of the active material after the degradation test. .

  You may put electrolyte solution in an airtight container at the time of DSC measurement. In this case, it is necessary to keep the active material / electrolyte (mass ratio) constant when determining the activation energy at each temperature increase rate.

  In the present invention, it is possible to quantitatively analyze the deterioration of the battery by measuring the activation energy of the active material using the endothermic peak derived from the thermal structure change of the active material.

(Measurement of activation energy)
A solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a volume ratio of 2: 3, an electrolytic solution containing 1 mol / L LiPF ₆ as an electrolyte, and a fully charged carbon material, The ratio was adjusted to 0.6: 1 to 1: 1, and the mixture was sealed in a 27 μL chromium steel nickel sealed container with a total mass of 7 mg to 14 mg, and the heating rate was 1 ° C./min. , 2 ° C./min. , 5 ° C./min. DSC measurement is performed at a temperature range of 50 to 400 ° C.
A graphite material having an activation energy of an endothermic peak observed between 250 ° C. and 300 ° C. is preferably 130 kJ / mol or more, more preferably 132 kJ / mol or more, further preferably 135 kJ / mol or more and 140 kJ / mol or less. It is. Carbon materials with an activation energy of 130 kJ / mol or more are unlikely to delaminate between graphite layers, making it difficult to lose activity as a battery.

  The details of the battery deterioration analysis method when a lithium ion battery is used will be described below.

(Positive electrode)
A substance containing Li and capable of releasing Li by charging can be used as the electrode active material. For example, lithium metal phosphate or lithium-containing metal oxide can be used.

(Negative electrode)
A substance capable of storing Li by charging can be used as the electrode active material. A carbon material such as artificial graphite or natural graphite may be used alone, or a simple substance such as Si, Sn, Ge, Al, In or a compound, a mixture, a eutectic or the like containing at least one of the elements. A composite of particles containing a solid solution and a carbon material may be used.

  An electrode active material (sometimes referred to simply as an active material) can be made into a mixture by mixing a conductive additive and a binder, and the mixture can be applied to a current collector to form a sheet-like electrode. .

  The binder can be selected arbitrarily, but polyethylene, polypropylene, ethylene propylene copolymer, ethylene propylene terpolymer, butadiene rubber, styrene butadiene rubber, butyl rubber, polytetrafluoroethylene, poly (meth) acrylate, polyvinylidene fluoride, polyethylene oxide , Polypropylene oxide, polyepichlorohydrin, polyphasphazene, polyacrylonitrile, and the like.

  The conductive aid can be arbitrarily selected, but conductive metal powder such as silver powder; conductive carbon powder such as furnace black, ketjen black, and acetylene black; carbon nanotube, carbon nanofiber, vapor grown carbon fiber, etc. It is done. As the conductive aid, vapor grown carbon fiber is preferable. The vapor grown carbon fiber preferably has a fiber diameter of 5 nm to 0.2 μm. The fiber length / fiber diameter ratio is preferably 5 to 1000. The content of the vapor grown carbon fiber is preferably 0.1 to 10% by mass with respect to the electrode active material.

(Electrolyte)
A non-aqueous electrolyte in which a lithium salt is dissolved in an aprotic solvent can be exemplified.

The aprotic solvent is arbitrarily selected, but at least one or two selected from the group consisting of ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, and vinylene carbonate The above mixed solvent is preferable.
Examples of the lithium salt include LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSO ₃ CF ₃ , CH ₃ SO ₃ Li, and CF ₃ SO ₃ Li.

A so-called solid electrolyte or gel electrolyte can also be used as the nonaqueous electrolyte. Examples of the solid electrolyte or the gel electrolyte include a polymer electrolyte such as a sulfonated styrene-olefin copolymer, a polymer electrolyte using polyethylene oxide and MgClO ₄ , and a polymer electrolyte having a trimethylene oxide structure. The non-aqueous solvent used for the polymer electrolyte is preferably at least one selected from the group consisting of ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, and vinylene carbonate.

  Furthermore, the lithium secondary battery in a preferred embodiment of the present embodiment is not limited to the positive electrode, the negative electrode, and the non-aqueous electrolyte, and may include other members as necessary. For example, a separator that separates the positive electrode and the negative electrode may be provided. The separator is essential when the non-aqueous electrolyte is not a polymer electrolyte. For example, a nonwoven fabric, a woven fabric, a microporous film, a combination thereof, and the like can be given. More specifically, a porous polypropylene film, a porous polyethylene film, or the like can be used as appropriate.

  The positive electrode current collector can be arbitrarily selected, and examples thereof include a conductive metal foil, a conductive metal net, and a conductive metal punching metal. As the conductive metal, aluminum or an aluminum alloy is preferable. A carbon film may be formed on the positive electrode current collector to improve conductivity with the positive electrode mixture. Examples of the negative electrode current collector include a conductive metal foil, a conductive metal net, and a conductive metal punching metal. As the conductive metal, copper or a copper alloy is preferable.

(Battery form)
As the form of the battery, any form such as a coin type, a cylindrical type, and a laminate type can be used.

(Definition of full charge)
When charging the battery, the battery is charged within the decomposition potential of the electrolytic solution, and when the current value reaches 0.01 C, the battery is fully charged. For example, charging is performed by CC (constant current: constant current) charging at a current of 0.2 C from the rest potential, then switching to CV (constant voltage: constant voltage) charging at 2 mV, and when the current value drops to 0.01 C To stop charging.

(Battery disassembly)
It is desirable to disassemble so as not to cause a short circuit, and to carry out in a state not exposed to O ₂ and H ₂ O. Specifically, it is desirable that O ₂ is 500 ppm or less and H ₂ O is dew point of −50 ° C. or less.

(Electrode cleaning solution)
For cleaning the electrode, a cleaning liquid that is highly volatile and capable of removing the electrolyte and the electrolytic solution is used. For example, when the electrolytic solution contains ethylene carbonate, ethyl methyl carbonate is desirable.

(Electrode cleaning)
In a state where the electrode is not exposed to O ₂ and H ₂ O, the electrode is placed in a container and a cleaning solution is added until the electrode is immersed. It is desirable to immerse for at least 10 seconds or more. Thereafter, the electrolytic solution is taken out and the same operation is performed with a new cleaning solution. The washing is preferably performed 3 to 5 times.

(Dry electrode)
It is desirable to carry out for 5 minutes or more under vacuum conditions.

(Enclosed in a sealed container)
After washing and drying the electrode in a state not exposed to O ₂ and H ₂ O, only the active material is scraped off and the mass is measured, and the active material is packed into a sealed container having pressure resistance and corrosion resistance and the lid is covered. SUS can be used as the material of the container. At this time, an electrolytic solution can also be added.

(DSC measurement)
A temperature range can be performed in arbitrary ranges. Preferably it is 50-400 degreeC. A plurality of sealed containers prepared under the same conditions are prepared, and DSC measurement is performed for each sealed container at a different heating rate. It is desirable that each heating rate be separated by 2 times or more. Moreover, it is desirable that the kind of temperature increase rate is 3 levels or more.

(Calculation of activation energy)
With respect to each endothermic exothermic peak temperature T _m (K) obtained when the temperature rising rate is changed and the temperature rising rate a (° C./min) at that time, the vertical axis is ln (a / Tm ² ), and the horizontal axis is 1 / The slope obtained when _Tm is plotted is defined as the activation energy (kJ / mol).

(Calculation of active material degradation)
The active material activation energy E ₀ at the time of full charge at the start of the test obtained from DSC and the activation energy E _a of the active material after the battery test are defined as E _a / E _0. To do. However, the degree of electrode active material deterioration is calculated using the endothermic peak based on the thermal structure change of the active material. If E _a / E ₀ is 1.10 or more, it can be determined that the cause of battery deterioration is derived from the electrode active material.

  As described above, according to the battery deterioration analysis method of the present invention, it can be quantitatively determined whether or not the battery deterioration is derived from the active material.

  Hereinafter, the present invention will be described in more detail with reference to examples. Note that these are merely illustrative examples, and the present invention is not limited by these.

Example 1
1. 1 is a schematic diagram of a laminated lithium ion secondary battery including a positive electrode plate 1 and a negative electrode plate 2 to which a battery deterioration analysis method according to an embodiment of the present invention is applied. FIG. The positive electrode plate 1 and the negative electrode plate 2 form a laminate via a separator 3 and are housed in an exterior material made of a laminate film 4 together with a non-aqueous solvent electrolyte containing a lithium salt. The positive electrode terminal 5 is electrically connected to the positive electrode current collector 7, and the negative electrode terminal 6 is electrically connected to the negative electrode current collector 9 inside the laminate film 4.

Specific conditions of the manufactured laminate battery are as follows.
・ Battery capacity (when not used): 30 mAh
・ Positive electrode active material: lithium iron phosphate (90% by mass)
-Positive electrode conductive assistant: carbon black (3 mass%), vapor grown carbon fiber (2 mass%)
・ Positive electrode binder: Polyvinylidene fluoride (5% by mass)
・ Negative electrode active material: Graphite A (natural graphite made in China) (97% by mass)
Negative electrode binder: styrene butadiene rubber (1.5% by mass), carboxymethyl cellulose (1.5% by mass)
-Separator: made of polypropylene-Electrolyte: lithium hexafluorophosphate (1 mol / L)
・ Electrolyte: Mixed liquid of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate

2. Charging Step An unused battery was made 100% SOC (State of Charge) using a charging / discharging machine ACD-01 (manufactured by Asuka Electronics). The initial potential at this time was 3.7 V, and the current value was 0.03 mA.

3. Disassembly cleaning process The fully charged battery was disassembled under the conditions of O ₂ 0.3 ppm and dew point of −70 ° C., and the taken-out negative electrode was taken out after being immersed in ethyl methyl carbonate (EMC) for 10 seconds. In the same manner, the immersion was repeated three times with a fresh EMC, and then dried under vacuum for 5 minutes to obtain a measurement electrode.

4). Sample Encapsulation in Sealed Container From the washed and dried measurement electrode, only the active material was scraped using a spatula, and 5.0 mg of the scraped active material was placed in a 27 μL chromium steel nickel sealed container (made by Netch). Thereafter, 6.0 mg of electrolyte solution (1M LiPF6, EC / EMC = 2/3 (v / v)) was added, and the cap was quickly capped. Similarly, a total of three samples for DSC measurement were prepared.

5. DSC measurement DSC3200SA (made by Netch) was used. An empty sealed container was used on the reference side. The heating rate is 1 ° C./min. , 2 ° C./min. , 5 ° C./min. This was done at three levels. The measurement was performed in a temperature range of 50 ° C to 400 ° C. Temperature rising rate 5 ° C./min. FIG. 2 shows the result of measurement performed in FIG.

6). Calculation of activation energy One endothermic peak was observed between two large peaks in DSC measurement. The endothermic peak because it is said to be derived from the peeling energy graphite layers was calculated activation energy E _1. When there is structural disturbance due to deterioration, the activation energy is considered to increase.

(Example 2)
DSC measurement was performed under the same conditions as in Example 1 except that the battery electrode after 500 cycles of charge / discharge was used, and capacity retention rates C ₂ and E ₂ were obtained.

(Example 3)
DSC measurement was performed under the same conditions as in Example 1 except that the electrode of a battery that was left at 60 ° C. for 4 weeks in a fully charged state was used to obtain capacity retention ratios C ₃ and E ₃ .

Example 4
Except for using graphite B (manufactured by Nippon artificial graphite) in the negative electrode subjected to DSC measurement under the same conditions as in Example 1 to obtain E _4.

(Example 5)
Except for using 500 cycles cell electrodes after the charging and discharging of the carried out DSC measurement under the same conditions as in Example 4, to obtain the capacity retention ratio C ₅ and E _5.

(Example 6)
DSC measurement was performed under the same conditions as in Example 4 except that the electrode of a battery left at 60 ° C. for 4 weeks in a fully charged state was used, and capacity retention ratios C ₆ and E ₆ were obtained.

  As shown in Table 1, it was found that both graphite A and B had different degrees of deterioration after 500 cycles of charge / discharge and after a storage test. This indicates that deterioration due to changes between the graphite layers occurs due to repeated charge and discharge cycles, but in the storage test, other factors cause deterioration of the battery. Further, when graphite A and B are compared, the degree of deterioration after 500 cycles is different. This indicates that graphite B has better charge / discharge cycle characteristics as an electrode active material than graphite A.

(Example 7)
Performs DSC measurement under the same conditions as in Example 1 except for using was prepared by the following steps graphite was determined the activation energy E ₇ of an endothermic peak between calculated and two large exothermic peak deterioration degree. Further, the capacity retention ratio was obtained C ₇ when the battery produced was subjected to a charge and discharge of 2000 cycles. Thereafter, DSC measurement was performed under the same conditions as in Example 1, and the degree of deterioration was calculated.

(Production of raw coke and graphite)
A fragrance having a structure in which four benzene rings are bonded to each other when volatile components that come out when heated at 200 ° C. to 800 ° C. in 100 g of coke are trapped with liquid nitrogen and the volatile components are measured by GS-MS. The ratio of aromatic hydrocarbons (pyrene, tetracene, triphenylene, chrysene, tetraphen as a skeleton) is 0 when the ratio of aromatic hydrocarbons having a structure in which 1 to 5 benzene rings are bonded is 1. The coke which becomes 4 or more and less than 0.5 was used as a raw material. This is pulverized with a bantam mill manufactured by Hosokawa Micron. Next, air classification is performed with a turbo classifier TC-15N manufactured by Nissin Engineering, and a carbon material having a D50 = 13.5 μm substantially free of particles having a particle size of 0.5 μm or less is obtained. This pulverized carbon material and 10% by mass of Mn (manufactured by High Purity Chemical Laboratory: about 10 μm) are mixed in an inert atmosphere (N ₂ ), filled in a graphite crucible, and graphitized furnace (SCC-U-30). / 300 (manufactured by Kurata Giken) at 3100 ° C. to obtain a graphite material.

(Example 8)
Graphite was produced under the same conditions as in Example 7 except that the amount of Mn added during graphitization was 5% by mass. Carried out DSC measurement under the same conditions as in Example 1 using the prepared graphite was determined the activation energy E ₈ of the endothermic peak between two major exothermic peak. Further, the capacity retention ratio was obtained C ₈ when performing the charging and discharging of 2000 cycles. Further, the deterioration degree was calculated.

Example 9
Graphite was produced under the same conditions as in Example 7 except that the amount of Mn added during graphitization was 15% by mass. Carried out DSC measurement under the same conditions as in Example 1 using the prepared graphite was determined the activation energy E ₉ endothermic peak between two major exothermic peak. Further, the capacity retention ratio was obtained C ₉ when performing the charging and discharging of 2000 cycles. Further, the deterioration degree was calculated.

(Comparative Example 1)
Graphite was produced under the same conditions as in Example 7 except that the carbon material and Mn were mixed in air. Carried out DSC measurement under the same conditions as in Example 1 using the prepared graphite was determined endothermic peak activation energy E ₁₀ of between two major exothermic peak. Further, the capacity retention ratio was obtained _{C 10} when performing the charging and discharging of 2000 cycles. Further, the deterioration degree was calculated.

(Comparative Example 2)
Except that Mn was not used during graphitization, graphite was prepared using the same raw material as in Example 7. Carried out DSC measurement under the same conditions as in Example 1 using the prepared graphite was determined the activation energy E ₁₁ of the endothermic peak between two major exothermic peak. Further, the capacity retention ratio was obtained _{C 11} when performing the charging and discharging of 2000 cycles. Further, the deterioration degree was calculated.

(Comparative Example 3)
A fragrance having a structure in which four benzene rings are bonded to each other when volatile components that come out when heated at 200 ° C. to 800 ° C. in 100 g of coke are trapped with liquid nitrogen and the volatile components are measured by GS-MS. The ratio of aromatic hydrocarbons (pyrene, tetracene, triphenylene, chrysene, tetraphen as a skeleton) is 0 when the ratio of aromatic hydrocarbons having a structure in which 1 to 5 benzene rings are bonded is 1. The graphite was produced under the same conditions as in Example 7 except that coke having a value of 2 or more and less than 0.3 was used as a raw material. Carried out DSC measurement under the same conditions as in Example 1 using the prepared graphite was determined the activation energy E ₁₂ of the endothermic peak between two major exothermic peak. Further, the capacity retention ratio was obtained _{C 12} when performing the charging and discharging of 2000 cycles. Further, the deterioration degree was calculated.

(Comparative Example 4)
Except that Mn was not used during graphitization, graphite was prepared using the same raw material as in Comparative Example 3. Carried out DSC measurement under the same conditions as in Example 1 using the prepared graphite was determined the activation energy E ₁₃ of the endothermic peak between two major exothermic peak. Further, the capacity retention ratio was obtained _{C 13} when performing the charging and discharging of 2000 cycles. Further, the deterioration degree was calculated.

(Comparative Example 5)
A fragrance having a structure in which four benzene rings are bonded to each other when volatile components that come out when heated at 200 ° C. to 800 ° C. in 100 g of coke are trapped with liquid nitrogen and the volatile components are measured by GS-MS. The ratio of aromatic hydrocarbons (pyrene, tetracene, triphenylene, chrysene, tetraphen as a skeleton) is 0 when the ratio of aromatic hydrocarbons having a structure in which 1 to 5 benzene rings are bonded is 1. The graphite was produced under the same conditions as in Example 7 except that coke having a value of 1 to less than 0.2 was used as a raw material. Carried out DSC measurement under the same conditions as in Example 1 using the prepared graphite was determined the activation energy E ₁₄ of the endothermic peak between two major exothermic peak. Further, the capacity retention ratio was obtained _{C 14} when performing the charging and discharging of 2000 cycles. Further, the deterioration degree was calculated.

(Comparative Example 6)
Except not using Mn at the time of graphitization, graphite was produced using the same raw material as Comparative Example 5. Carried out DSC measurement under the same conditions as in Example 1 using the prepared graphite was determined endothermic peak activation energy E ₁₅ of between two major exothermic peak. Further, the capacity retention ratio was obtained _{C 15} when performing the charging and discharging of 2000 cycles. Further, the deterioration degree was calculated.

(Comparative Example 7)
A fragrance having a structure in which four benzene rings are bonded to each other when volatile components that come out when heated at 200 ° C. to 800 ° C. in 100 g of coke are trapped with liquid nitrogen and the volatile components are measured by GS-MS. The ratio of aromatic hydrocarbons (pyrene, tetracene, triphenylene, chrysene, tetraphen as a skeleton) is 0 when the ratio of aromatic hydrocarbons having a structure in which 1 to 5 benzene rings are bonded is 1. A graphite was produced under the same conditions as in Example 7 except that coke having a value of 5 or more and less than 0.6 was used as a raw material. Using the prepared graphite subjected to DSC measurement under the same conditions as in Example 1 to obtain the activation energy E ₁₆ of the endothermic peak between two major exothermic peak. Further, the capacity retention ratio was obtained _{C 16} when performing the charging and discharging of 2000 cycles. Further, the deterioration degree was calculated.

(Comparative Example 8)
Except that Mn was not used during graphitization, graphite was prepared using the same raw material as in Comparative Example 6. Carried out DSC measurement under the same conditions as in Example 1 using the prepared graphite was determined the activation energy E ₁₇ of the endothermic peak between two major exothermic peak. Further, the capacity retention ratio was obtained _{C 17} when performing the charging and discharging of 2000 cycles. Further, the deterioration degree was calculated.

  As shown in Table 2, in Example 7, the degree of deterioration was close to 1, the negative electrode itself did not lose its activity as a battery, and it can be said that the decrease in capacity was due to the influence of electrode peeling and the like. On the other hand, in Comparative Examples 1 to 7, the capacity retention rate is close to that of Example 7, but the degree of deterioration is larger than 1.10. That is, the electrode itself has lost its activity as a battery. These are related to the activation energy E. Since the activation energy E is based on the delamination energy between the graphite layers at the time of DSC measurement, it can be said that the larger this value, the less the delamination between the graphite layers occurs, and the less the activity of the battery is lost. In Comparative Example 1, Mn was oxidized, and the catalytic effect at the time of graphitization became small. Therefore, the activation energy is considered to be different from Example 7. From Example 7 and Comparative Example 2, it can be said that the activation energy changes due to the catalytic effect during graphitization with Mn, and it is considered that a more uniform graphite structure is formed. From Comparative Examples 3 and 8, it can be said that selection of raw material coke is also important. This is also due to the fact that if the graphite structure is too large, the expansion and contraction is large, and changes between the graphite layers are likely to occur. In addition, if the graphite structure is too small, it is difficult to form a uniform structure, and a change between the graphite layers is likely to occur due to the mixed state of the amorphous and graphite structures.

  The battery deterioration analysis method according to the present invention makes it possible to quantitatively determine whether or not the battery deterioration is derived from the electrode active material. The battery deterioration analysis method of the present invention can be used in battery deterioration analysis used in various fields. For example, personal computers, tablet computers, notebook computers, mobile phones, wireless devices, electronic notebooks, electronic dictionaries, PDAs (Personal Digital Assistants), electronic meters, electronic keys, electronic tags, power storage devices, electric tools, toys, Electric and electronic devices such as digital cameras, digital video, AV equipment and vacuum cleaners; electric vehicles, hybrid vehicles, electric bikes, hybrid bikes, electric bicycles, electric assist bicycles, railway engines, aircraft, ships and other transportation systems; sunlight It can be used for batteries used in power generation systems such as power generation systems, wind power generation systems, tidal power generation systems, geothermal power generation systems, heat difference power generation systems, and vibration power generation systems.

Claims (5)

  A battery deterioration analysis method for measuring activation energy of an electrode active material by performing differential scanning calorimetry (DSC) of a fully charged electrode and determining whether or not the cause of battery deterioration is derived from the electrode active material . Differential scanning calorimetry (DSC) is performed while changing the temperature rise rate, and the endothermic peak temperature T _m (K) is measured when the temperature rise rate is a (° C./min), and the vertical axis is ln (a / T The battery degradation analysis method according to claim 1, wherein an activation energy is a slope obtained when _m ² ) and 1 / T _m is plotted on the horizontal axis. Using the activation energy E ₀ of the electrode active material at the time of full charge at the start of the battery deterioration test and the activation energy E _a of the electrode active material at the time of full charge after the battery deterioration test, the degree of electrode active material deterioration is expressed as E _a / degradation analysis method of a battery according to claim 1 or claim 2, defined by E _0. The battery deterioration analysis method according to claim 3, wherein if E _a / E ₀ is 1.10 or more, it is determined that the cause of battery deterioration is derived from the electrode active material. A solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a volume ratio of 2: 3, an electrolytic solution containing 1 mol / L LiPF ₆ as an electrolyte, and a fully charged carbon material, Ratio was adjusted to 0.6: 1 to 1: 1, and sealed in a sealed container of 27 μL chromium steel nickel with a total mass of 7 mg to 14 mg. , 2 ° C./min. , 5 ° C./min. The carbon material whose activation energy of the endothermic peak observed between 250 ° C. and 300 ° C. is 130 kJ / mol or more when DSC measurement is performed at these three levels.