JP2011181486A - Evaluation method of electrolyte for secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an evaluation method of an electrolyte capable of appropriate evaluation when the electrolyte is applied to a secondary battery. <P>SOLUTION: The secondary battery having a secondary battery positive electrode having Li<SB>1-x</SB>FePO<SB>4</SB>as a positive electrode active material, a secondary battery negative electrode, and an electrolyte of evaluation object is assembled, and discharge characteristics after constant voltage charging of the secondary battery are measured, thereby, evaluation of the electrolyte for lithium ion battery is carried out. When the electrolyte for sodium ion battery is evaluated, evaluation is carried out using a secondary battery positive electrode having Na<SB>1-x</SB>FePO<SB>4</SB>as a positive electrode active material. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a method for evaluating an electrolytic solution for a secondary battery used in a lithium ion battery or a sodium ion battery, and electrolysis for a secondary battery at a high potential exceeding 5 V (vs Li / Li ⁺ ), which has been difficult in the past. It can be suitably used to evaluate the liquid.

  In order to meet the demand for higher energy density of lithium ion batteries and sodium ion batteries, a search for a positive electrode active material that is charged and discharged at a high potential is in progress. In a secondary battery using such a positive electrode active material, the electrolytic solution is also exposed to a high potential, and thus it is necessary to evaluate the withstand voltage characteristics of the secondary battery electrolytic solution.

  As a method for evaluating the withstand voltage characteristics of the electrolyte for secondary batteries, a stable electrode with a wide potential window, such as glassy carbon, platinum, or gold, is used, and an electrochemical method such as a potential-current curve or cyclic voltammogram is used. In addition, the oxidation-reduction current was observed in a wide potential range, and the stability as an electrolytic solution was evaluated based on the result (for example, Patent Document 1).

JP 2009-158240 A

  However, when the positive electrode active material is applied to an actual secondary battery, it is necessary for lithium ions and sodium ions to enter and exit between the electrolytic solution and the positive electrode active material during charging and discharging. In contrast, the above method of observing the oxidation-reduction current in a wide potential range using a stable electrode such as glassy carbon can measure the width of the potential window of the electrolytic solution, but the positive electrode at a high potential. It was not possible to judge whether lithium ions or sodium ions could enter or leave the active material. For this reason, when the electrolytic solution is applied to an actual secondary battery and charging / discharging is not performed smoothly, it cannot be determined whether the cause is the electrolytic solution or the positive electrode active material. Evaluation was not possible.

  The present invention has been made in view of the above-described conventional situation, and it is an issue to be solved to provide an electrolytic solution evaluation method capable of appropriate evaluation when the electrolytic solution is applied to a secondary battery. Yes.

The present inventors investigated the charge / discharge characteristics at a high potential that is not normally used for charging of various positive electrode active materials. As a result, it has been found that even when LiFePO ₄ is charged at an extremely high potential of 6 V (vs Li / Li ⁺ ), the amount of charge hardly decreases and lithium ions enter and exit smoothly. If the charge / discharge characteristics of the electrolytic solution are measured using a positive electrode using LiFePO ₄ as a positive electrode active material, the electrolytic solution can be accurately evaluated when the electrolytic solution is applied to an actual secondary battery. The present inventors have found that the present invention can be accomplished and have completed the present invention.

That is, the evaluation method of the secondary battery electrolyte of the first invention is Li _1-x FePO ₄ (wherein Fe is partly Co, Ni, Mn, Fe, Mg, Cu, Cr, V, Li, Nb , Ti may be substituted with one or more of Zr, and x represents a number of 0 or more and 1 or less), and a positive electrode for a secondary battery, a negative electrode for a secondary battery, and evaluation A secondary battery including a target electrolytic solution is assembled, and the electrolytic solution is evaluated by measuring discharge characteristics after constant voltage charging of the secondary battery.

In the method for evaluating an electrolyte for a secondary battery according to the first aspect of the invention, Li _1-x FePO ₄ (wherein part of Fe is Co, Ni, Mn, Fe, Mg, Cu, Cr, V, Li, Nb, Ti And Zr may be substituted with one or more of Zr, and x represents a number of 0 to 1 inclusive). This positive electrode active material is a positive electrode active material for a lithium ion battery that allows lithium ions to enter and exit from the electrolytic solution, and the evaluation of the electrolytic solution for a lithium ion battery can be performed. In the formula, x is a coefficient that varies in the range of 0 to 1 depending on the state of entering and exiting lithium ions.

Moreover, as a negative electrode of a secondary battery, if it is a material which can be used for a lithium ion battery, there will be no restriction | limiting in particular. For example, various carbon materials such as lithium metal, artificial graphite, natural graphite, and hard carbon, lithium titanate (Li ₄ Ti ₅ O ₁₂ ), H ₂ Ti ₁₂ O ₂₅ , H ₂ Ti ₆ O ₁₃ , Fe ₂ O _3, etc. Is mentioned. Moreover, the composite material which mixed these suitably can also be mentioned. Furthermore, there may be mentioned Si fine particles and Si thin films, and fine particles and thin films in which these Si are Si-based alloys such as Si—Ni, Si—Cu, Si—Nb, Si—Zn, Si—Sn. Further, SiO oxide, Si-SiO ₂ composite, Si-SiO ₂ - can be given complex, etc., such as carbon.

According to the test results of the inventors, Li _1-x FePO ₄ shows extremely excellent charge / discharge characteristics with little decrease in discharge capacity even when charged at an extremely high potential of 6 V (vs Li / Li ⁺ ). . For this reason, a positive electrode using this Li _1-x FePO ₄ as a positive electrode active material and a negative electrode for a secondary battery are brought into contact with an electrolytic solution for a lithium ion battery to be evaluated to form a secondary battery. If the charge / discharge characteristics are measured, lithium ions can enter and exit smoothly at the positive electrode, so that the electrolyte can be evaluated accurately.
Therefore, according to the method for evaluating an electrolytic solution for a secondary battery of the first invention, it is possible to accurately evaluate the electrolytic solution when the electrolytic solution is applied to an actual lithium ion battery.

A part of Fe in Li _1-x FePO ₄ may be substituted with one or more of Co, Ni, Mn, Fe, Mg, Cu, Cr, V, Li, Nb, Ti, and Zr. . This is because even in the case of a positive electrode active material obtained by substituting Fe with the above-mentioned other elements, there is almost no decrease in the amount of charge due to high potential charging, and the positive electrode active material exhibits extremely excellent charge / discharge characteristics.

The secondary battery electrolyte evaluation method of the second invention is Na _1-x FePO ₄ (wherein part of Fe is Co, Ni, Mn, Fe, Mg, Cu, Cr, V, Li, Nb, Ti And Zr may be substituted with one or more of Zr, and x represents a number of 0 or more and less than 1, and a positive electrode for a secondary battery having a positive electrode active material, a negative electrode for a secondary battery, A secondary battery provided with an electrolytic solution is assembled, and the electrolytic solution is evaluated by measuring discharge characteristics after constant voltage charging of the secondary battery.

In the method for evaluating an electrolytic solution for a secondary battery according to the second aspect of the invention, Na _1-x FePO ₄ (wherein part of Fe is Co, Ni, Mn, Fe, Mg, Cu, Cr, V, Li, Nb, Ti and A positive electrode for a secondary battery using a positive electrode active material, which may be substituted with one or more of Zr, and x represents a number of 0 or more and less than 1, is used. This positive electrode active material is a positive electrode active material for a sodium ion battery that allows sodium ions to enter and exit from the electrolytic solution, and can be used to evaluate the electrolytic solution for a sodium ion battery. In the formula, x is a coefficient that varies in the range of 0 to 1 depending on the state of entering and exiting lithium ions.

The negative electrode of the secondary battery is not particularly limited as long as it is a material that can be used for a sodium ion battery. Examples thereof include various carbon materials such as sodium metal, artificial graphite, natural graphite, and hard carbon, and lithium titanate (Li ₄ Ti ₅ O ₁₂ ). Moreover, the composite material which mixed these suitably can also be mentioned.

Na _1-x FePO ₄ shows very good charge / discharge characteristics with little decrease in charge even when charged at a high potential. For this reason, a positive electrode using this Na _1-x FePO ₄ as a positive electrode active material and a negative electrode for a secondary battery are brought into contact with an electrolyte to be evaluated to form a secondary battery, and the charge / discharge characteristics of the secondary battery are measured. Then, since sodium ions can smoothly enter and exit from the positive electrode, the electrolyte solution can be evaluated accurately.
Therefore, according to the method for evaluating an electrolytic solution for a secondary battery of the second invention, it is possible to accurately evaluate the electrolytic solution when the electrolytic solution is applied to an actual sodium ion battery.

A part of Fe in Na _1-x FePO ₄ may be substituted with one or more of Co, Ni, Mn, Fe, Mg, Cu, Cr, V, Li, Nb, Ti, and Zr. . This is because even in the case of a positive electrode active material obtained by substituting Fe with the above-mentioned other elements, there is almost no decrease in the amount of charge due to high potential charging, and the positive electrode active material exhibits extremely excellent charge / discharge characteristics.

  By including a conductive additive in the positive electrode for secondary battery used in the method for evaluating an electrolytic solution of the present invention, an electron conduction path between the current collector and the positive electrode active material can be secured. Although carbon black and graphite can be used as the conductive assistant, it is preferable to use glassy carbon and / or conductive diamond-like carbon. Glassy carbon and conductive diamond-like carbon have a much wider potential window than carbon black and graphite, and are stable even at high potentials. For this reason, when an electrolytic solution is evaluated under a high potential, a current resulting from oxidation / reduction of the conductive additive itself hardly flows, so that it does not interfere with the evaluation of the electrolytic solution.

  Furthermore, it is preferable that the positive electrode active material contained in the positive electrode for secondary batteries used in the method for evaluating an electrolytic solution of the present invention is surrounded by glassy carbon and / or conductive diamond-like carbon. In this case, an electron conduction path between the current collector and the positive electrode active material can be further ensured.

  Further, in the method for evaluating an electrolytic solution of the present invention, the voltage of constant voltage charging performed before measuring discharge characteristics is not particularly limited, but in order to perform evaluation at a high potential, 5 V (vs Li / Li +) It is preferable that the voltage be 6 V (vs Li / Li +) or higher for evaluation at a higher potential.

<Example>
The charging characteristics of the electrolytic solution 1 and the electrolytic solution 2 for lithium ion batteries prepared as follows were evaluated.

(Electrolytic solution 1)
Using a solvent in which ethylene carbonate (EC), dimethyl carbonate (DMC), and sebaconitrile (SB) were mixed in a volume ratio of 25:25:50, LiBF ₄ as a lithium salt was 1 mol / L. Dissolved.

(Electrolytic solution 2)
The lithium salt was LiPF ₆ (1 mol / L), and the other components were the same as in the electrolytic solution 1.

(Electrolytic solution 3)
Using a solvent in which ethylene carbonate (EC), dimethyl carbonate (DMC), and glutaronitrile were mixed at a volume ratio of 25:25:50, LiBF4 as a lithium salt was dissolved to 1 mol / L. It was.

<Production of lithium ion battery>
In order to evaluate the electrolytic solution 1 to the electrolytic solution 3, lithium ion batteries were prepared using these electrolytic solutions, and charge / discharge characteristics were measured. Details are shown below.

Preparation of positive electrode LiFePO ₄ powder, glassy carbon powder and polytetrafluoroethylene (PTFE) powder in a weight ratio of 70: 25: 5 were mixed in an agate mortar and cold rolled to form a sheet-like electrode. Obtained. This was punched out to a diameter of 8 mm to obtain a positive electrode pellet.

Assembling the Lithium Ion Battery As shown in FIG. 1, a bottomed cylindrical SUS316L positive electrode can 11 and a bottomed cylindrical flat SUS316L negative electrode cap 12 are prepared. Next, as shown in FIG. 2, a spacer 13 made of SUS316L, a positive electrode pellet 14, and a separator 15 are filled in the positive electrode can 11. On the other hand, the SUS316L wave washer 16, the SUS316L spacer 17 and the lithium negative electrode 18 are filled in the negative electrode cap 12. And after putting electrolyte solution in the positive electrode can 11, the negative electrode cap 12 was mounted and crimped | sealed through the insulating gasket 19, and it was set as the lithium ion battery.

-Evaluation of electrolyte-
<Example 1>
About the lithium ion battery using the electrolyte solution 1 and the electrolyte solution 2 comprised as mentioned above, charging / discharging was repeated and the battery characteristic was measured. Charging was performed at a constant voltage of 5.5 V up to 175 mAh / g (active material amount). However, in the lithium ion battery using the electrolytic solution 2, charging was performed with constant current control at the start of charging, and charging was performed at a constant voltage of 5.5 V from when the voltage between the electrodes reached 5.5V . On the other hand, the discharge was performed at a constant current of a discharge rate of 0.05C, and the discharge was stopped when the voltage reached 2.5V.

As a result, in the lithium ion battery using the electrolytic solution 1 to which LiBF ₄ was added as the electrolyte, as shown in FIG. 3, the discharge capacity hardly changed even after 10 charge / discharge cycles. From this result, it was found that even when LiFePO ₄ was charged at a high potential of 5.5 V, lithium ions smoothly entered and exited during charge and discharge and functioned normally as a positive electrode active material. Moreover, it turned out that the electrolyte solution 1 has the outstanding charging / discharging characteristic with a little fall of charge capacity.

On the other hand, in the lithium ion battery using the electrolytic solution 2 using LiPF ₆ as the electrolyte, as shown in FIG. 4, the charging current decreases every time charging / discharging is repeated, and several cycles of charging / discharging are repeated. As a result, it was found that the discharge amount rapidly decreased. Since this rapid decrease in the amount of discharge was not observed in the electrolytic solution 1, it was not caused by the positive electrode active material LiFePO ₄ but by the electrolytic solution 2, and the electrolytic solution 2 was decomposed. And the formation of a passive film based on polymerization.

In addition, for lithium ion batteries using the electrolyte 1, normal charging with a charge rate of 0.05 C, and charge rate of 10 C at the start of charging, and after reaching 6 V (vs Li / Li +), constant potential charging It was measured. As a result, as shown in FIG. 5, it was found that the discharge capacities were almost the same in both charging methods and the potential window was wide, so that even high-voltage charging at 6V could sufficiently withstand practical use. In addition, since LiFePO ₄ is normally charged even at a high voltage of 6 V and is extremely excellent in voltage resistance, it has been found that LiFePO ₄ is suitable as a positive electrode active material when an electrolytic solution is evaluated.

<Comparative Example 1>
About the said electrolyte solution 1 and the electrolyte solution 2, the glassy carbon board was made into the working electrode, the platinum wire was used for the counter electrode, and the electrolyte solution was evaluated by the measurement of a potential-current curve. The sweep speed was 5 mV / second.

  As a result, it was shown that both of the electrolytic solution 1 (FIG. 6) and the electrolytic solution 2 (see FIG. 7) have a wide potential window in the same range. In the above example in which a lithium ion battery was prepared for the same electrolytic solution and the charge / discharge characteristics were measured, the behaviors of the electrolytic solution 1 and the electrolytic solution 2 are clearly different as shown in FIGS. Such a difference could not be found by measuring the potential-current curve.

<Example 2>
About the lithium ion battery using the electrolyte solution 1 and the electrolyte solution 3 comprised as mentioned above, charging / discharging was repeated and the battery characteristic was measured. The charge / discharge characteristics were performed under the following conditions.
Charging CC-CV charging 6V cutoff 150mAh / g
Discharge CC discharge 0.01C Cutoff 2.5V

  As a result, in the lithium ion battery using the electrolytic solution 1 to which sebaconitrile was added as a dinitrile, the discharge capacity that was almost the same as the first time could be secured as shown in FIG. On the other hand, in the electrolytic solution 3 in which glutaronitrile was added as a dinitrile, the discharge capacity was as low as 116 mAh / g from the first discharge, and after the second forced charge, the discharge capacity was further reduced to 92 mAh / g. Since this rapid decrease in the amount of discharge was not observed in the electrolytic solution 1, it was not attributed to the positive electrode active material LiFePO4 but to the electrolytic solution 3. The formation of a passive film based on polymerization was suggested.

<Comparative example 2>
About the said electrolyte solution 1 and the electrolyte solution 3, the glassy carbon plate was made into the working electrode, the platinum wire was used for the counter electrode, and the electrolyte solution was evaluated by the measurement of a potential-current curve. The sweep speed was 5 mV / second.

  As a result, as shown in FIG. 9, it was shown that both of the electrolytic solution 1 and the electrolytic solution 3 have a wide potential window in the same range. In Example 2 in which a lithium ion battery was manufactured for the same electrolytic solution and the charge / discharge characteristics were measured, the behaviors of the electrolytic solution 1 and the electrolytic solution 3 were clearly different as shown in FIG. Such a difference could not be found by measuring the potential-current curve.

In the evaluation of the electrolytic solution 1 to the electrolytic solution 3, LiFePO ₄ was used as the positive electrode active material. However, it is obvious that sodium ions can smoothly enter and exit if NaFePO ₄ is used instead. The liquid can be evaluated. Even if a part of Fe of LiFePO ₄ or NaFePO ₄ is replaced with one or more of Co, Ni, Mn, Fe, Mg, Cu, Cr, V, Li, Nb, Ti, and Zr, a high potential is obtained. It is clear that lithium ions and sodium ions can smoothly enter and exit, and the electrolyte can be evaluated using these as positive electrode active materials.
As described above, when LiFePO4 is used as the positive electrode active material, the battery is forcibly charged at a desired high voltage and the discharge capacity is confirmed, the electrolyte is actually used as a secondary battery. It is possible to appropriately evaluate whether or not it is possible.

  In addition, the electrolytic solution evaluation method of the present invention includes not only an electrolytic solution combining an organic solvent and a lithium or sodium electrolyte, but also a polyethylene oxide-based or polyacrylonitrile-based polymer electrolyte, a NASICON-type solid electrolyte, a Li2S- It can also be applied to P2S5 solid electrolytes.

(Current collector for positive electrode)
When the electrolytic solution evaluation method of the present invention is performed at a high potential, the molding material for the positive electrode current collector is required to be stable during charging. In particular, when using a phosphate-based and olivine fluoride-based positive electrode active material having an olivine-type crystal structure with a high redox potential, it is preferable to use a material excellent in corrosion resistance.

For example, when LiPF ₆ or LiBF ₄ is used as the electrolyte, austenitic stainless steel, Ni, Al, Ti, or the like can be used, but it is preferable to select them appropriately in consideration of the operating potential of the positive electrode active material to be used. For example, when LiPF ₆ is used as the electrolyte, it can be used even at 6 V with respect to the Li / Li ⁺ electrode. However, when LiBF ₄ is used as the electrolyte, SUS304 is 5.8 V or less with respect to the Li / Li ⁺ electrode. It can be used only when charge / discharge is possible. More preferable are SUS316, SUS316L and SUS317 to which molybdenum is added for improving corrosion resistance. Further, when LiTFSI is used as the electrolyte, it is preferable that LiPF ₆ coexists in order to form a corrosion-resistant film on the surface of the positive electrode current collector. LiBETI and LiTFS are the same as in LiTFSI.

In addition, a conductive corrosion-resistant film made of one or more of conductive DLC (diamond-like carbon), glassy carbon, gold, and platinum is formed on a conductive metal material such as Al, Ni, titanium, and austenitic stainless steel. Can also be used as a current collector. When the electrolyte is a lithium salt such as LiBF ₄ or LiPF ₆ that easily forms a fluoride film, a thick fluoride film is formed on the aluminum and the corrosion resistance is improved, but the electronic conductivity is lowered, and consequently The increase in output accompanying the increase in ohmic overvoltage is impeded. If the conductive metal material such as Al is coated with the conductive DLC, the fluoride film is generated only in a very small area of the defective portion of the conductive DLC.

Here, the conductive diamond-like carbon is carbon having an amorphous structure in which both diamond bonds (SP ₃ hybrid orbital bonds between carbons) and graphite bonds (SP ₂ hybrid orbital bonds between carbons) are mixed. Among them, the one whose conductivity is 1000 Ωcm or less. However, in addition to the amorphous structure, those having a phase composed of a crystal structure partially composed of a graphite structure (that is, a hexagonal crystal structure composed of SP ₂ hybrid orbital bonds) and thereby exhibiting conductivity are also included. . Diamond-like carbon having properties intermediate between graphite and diamond adjusts the conductivity by adjusting the ratio of SP ₂ hybrid orbital bonds and SP ₃ hybrid orbital bonds of the carbon atoms constituting diamond-like carbon during film formation. be able to.
Of course, you may coat | cover the said corrosion-resistant electroconductive metal material with electroconductive DLC.
The shape and structure of the current collector can be arbitrarily designed according to the structure of the positive electrode active material and the battery.

(Current collector for negative electrode)
The current collector for the negative electrode can be formed of a general-purpose conductive metal material, Cu, Al, Ni, Ti, austenitic stainless steel, or the like.
However, when a nitrile compound is used for the electrolytic solution (including combined use with other organic solvents), it is necessary to select appropriately according to the Li salt in the electrolytic solution. That is, when LiPF ₆ or LiBF ₄ is used as the electrolyte, austenitic stainless steel, Ni, Al, Ti, or the like can be used. However, it is necessary to select appropriately according to the operating potential of the negative electrode active material to be used. In the case of using carbon or Si as the negative electrode active material, when LiBF ₄ is used as the electrolyte, a current collector made of Al, Ni, Ti, austenitic stainless or the like other than Cu can be used. In the case where lithium titanate or a Fe ₂ O ₃ based compound is used as the negative electrode active material, all of the above materials containing Cu are applicable. On the other hand, when LiPF _{6 is} used as the electrolyte, Al, Ni and Ti are preferable, and austenitic stainless steel and Cu are not preferable. In addition, when LiTFSI, LiBETI, or LiTFS is used as the electrolyte, any of Ni, Ti, Al, Cu, and austenitic stainless steel can be used.

(Electroconductive member for positive electrode)
Some positive electrode active materials have low electrical conductivity. Therefore, it is preferable to provide a sufficient electron conduction path between the positive electrode active material and the current collector by interposing a conductive electron conduction member.

  Here, the form of the electron conducting member is not particularly limited as long as an electron conducting path can be formed between the positive electrode active material and the current collector. For example, carbon black such as acetylene black, graphite powder, diamond-like carbon, glassy Conductive powder (conductive aid) such as carbon can be used. Diamond-like carbon and glassy carbon have a much wider potential window than carbon black and graphite, and are excellent in corrosion resistance when a high potential is applied, and therefore can be suitably used. Moreover, it is also preferable that metal fine particles are supported on these conductive assistants. Examples of the metal fine particles include Pt, Au, Ni and the like. These may be used alone or an alloy thereof.

  Further, conductive diamond-like carbon may be attached to the particles made of the positive electrode active material by a dry plating method. In this case, the conductive diamond-like carbon plays the role of a conductive auxiliary agent, and the electron conductivity that is a characteristic necessary for the positive electrode for the secondary battery is imparted. Furthermore, since conductive diamond-like carbon has a wide potential window and is excellent in durability against a high potential, a positive electrode active material having a high energy density in which a charging reaction is performed at a high potential can be effectively used.

As the electron conductive material, a conductive film (such as a DLC film) covering the positive electrode active material or a conductive thin film (such as a gold thin film) in which the positive electrode active material is embedded can be used.
In particular, since the Li ₂ NiPO ₄ F-based positive electrode active material has low conductivity of its own and / or its surface coating, it does not function as a positive electrode of a lithium ion battery if it is simply supported on a current collector. There is a case. In order to evaluate the performance of the Li ₂ NiPO ₄ F-based positive electrode active material, it can be physically driven into a conductive thin film such as gold with a hammer or the like to form the positive electrode of the battery.
Here, the Li ₂ NiPO ₄ F-based positive electrode active material refers to Li ₂ NiPO ₄ F and a material appropriately doped with dopant.

(Electroconductive member for negative electrode)
The thing similar to the electron conductive member for positive electrodes can be used.

  The present invention is not limited to the description of the embodiment of the invention. Various modifications may be included in the present invention as long as those skilled in the art can easily conceive without departing from the description of the scope of claims.

It is sectional drawing of the battery case used for the lithium ion battery. It is sectional drawing of a lithium ion battery. 2 is a graph showing charge / discharge characteristics of a lithium ion battery using an electrolytic solution 1. 4 is a graph showing charge / discharge characteristics of a lithium ion battery using an electrolytic solution 2. 2 is a graph showing charge / discharge characteristics of a lithium ion battery using an electrolytic solution 1. It is the electric potential-current curve of the electrolyte solution 1 (working electrode: glassy carbon electrode). It is the electric potential-current curve of the electrolyte solution 2 (working electrode: glassy carbon electrode). It is a graph which shows the charging / discharging characteristic of the lithium ion battery using the electrolyte solution 1 and the electrolyte solution 3. FIG. It is the electric potential-current curve of the electrolyte solution 1 and the electrolyte solution 3 (working electrode: glassy carbon electrode).

Claims (4)

Li _1-x FePO ₄ (However, part of Fe may be substituted with one or more of Co, Ni, Mn, Fe, Mg, Cu, Cr, V, Li, Nb, Ti, and Zr. , X represents a number of 0 or more and 1 or less), and a secondary battery including a positive electrode for a secondary battery having a positive electrode active material, a negative electrode for a secondary battery, and an electrolyte to be evaluated,
An evaluation method of an electrolytic solution, wherein the electrolytic solution is evaluated by measuring discharge characteristics after constant voltage charging of the secondary battery. Na _1-x FePO ₄ (However, part of Fe may be substituted with one or more of Co, Ni, Mn, Fe, Mg, Cu, Cr, V, Li, Nb, Ti, and Zr. , X represents a number from 0 to less than 1), and a secondary battery comprising a positive electrode for a secondary battery having a positive electrode active material, a negative electrode for a secondary battery, and an electrolyte to be evaluated,
An evaluation method of an electrolytic solution, wherein the electrolytic solution is evaluated by measuring discharge characteristics after constant voltage charging of the secondary battery.   The method for evaluating an electrolytic solution according to claim 1, wherein the positive electrode for a secondary battery contains glassy carbon and / or conductive diamond-like carbon as a conductive auxiliary agent.   4. The method for evaluating an electrolyte solution for a secondary battery according to claim 1, wherein the positive electrode active material is surrounded by glassy carbon and / or conductive diamond-like carbon. 5.

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