JP6334428B2 - Method and apparatus for evaluating characteristics of lithium secondary battery - Google Patents

Description

  The present invention relates to a characteristic evaluation method and characteristic evaluation apparatus for a lithium secondary battery.

  Known examples of positive electrode active materials used in lithium secondary batteries include lithium iron phosphate and lithium manganese phosphate. These may be coated with a carbon material from the viewpoint of increasing conductivity. Moreover, the favorable charge / discharge characteristic of a lithium secondary battery is achieved by enlarging the BET specific surface area of the positive electrode active material coated with carbon (Patent Document 1).

JP2011-233438 (particularly paragraph 0027)

  This inventor examined the characteristic of the lithium secondary battery using the positive electrode active material coated with carbon. As a result, it was found that even when a positive electrode active material having a large BET specific surface area of a carbon-coated positive electrode active material was used, a lithium secondary battery having good charge / discharge capacity could not be obtained.

  The present invention has been made in view of such problems, and the problem to be solved by the present invention is that when a lithium secondary battery is produced using a carbon-coated positive electrode active material, the lithium secondary battery is produced. It is an object of the present invention to provide a lithium secondary battery characteristic evaluation method and a characteristic evaluation apparatus that can easily and reliably determine whether or not a battery has good charge / discharge characteristics.

The present inventor has intensively studied to solve the above problems. As a result, the following findings were found. That is, the gist of the present invention is that lithium secondary material using a carbon-coated positive electrode active material, which is a secondary fired product obtained by mixing and firing a primary fired product not coated with carbon and a carbon material. a method for evaluating the characteristics of the next cell, the secondary fired product and carbon material removal step of removing the carbon material is a cathode active material coated is, the secondary firing said carbon material has been removed a BET specific surface area measuring step for measuring the BET specific surface area for the positive electrode active material in which ones, and measured the BET specific surface area in the BET specific surface area measuring step, predetermined BET specific surface area and the relationship between the charge and discharge characteristics And a characteristic determining step for determining a charge / discharge characteristic of the lithium secondary battery based on the above, and a method for evaluating the characteristics of the lithium secondary battery.

At this time, in the carbon material removing step, it is preferable that the carbon material covering the positive electrode active material that is the secondary fired product is removed by firing in an atmosphere containing oxygen.

  Another aspect of the present invention is an apparatus for evaluating the characteristics of a lithium secondary battery using a carbon-coated positive electrode active material, the carbon material removing the carbon material covering the positive electrode active material A removing device, a BET specific surface area measuring device for measuring a BET specific surface area of the positive electrode active material from which the carbon material has been removed, a BET specific surface area measured by the BET specific surface area measuring device, and a predetermined BET specific surface area And a characteristic determining device that determines the charge / discharge characteristics of the lithium secondary battery based on the relationship between the charge / discharge characteristics and the charge / discharge characteristics.

  According to the present invention, when a lithium secondary battery is produced using a carbon-coated positive electrode active material, it is possible to easily and reliably determine whether or not the lithium secondary battery exhibits good charge / discharge characteristics. A characteristic evaluation method and characteristic evaluation apparatus for a secondary battery can be provided.

It is a block diagram which shows the characteristic evaluation apparatus of the lithium secondary battery of this embodiment. It is a figure which shows typically the shape of carbon coating lithium iron phosphate and the shape of only lithium iron phosphate which comprises it, (a) is an example of the shape whose medium BET specific surface area is medium, (B) is an example of a shape having a small overall BET specific surface area, and (c) is an example of a shape having a large overall BET specific surface area. It is a flowchart which shows the characteristic evaluation method performed with the characteristic evaluation apparatus of the lithium secondary battery of this embodiment. (A) is a graph plotting the relationship between the BET specific surface area and discharge capacity for lithium iron phosphate after carbon removal, and (b) is the BET specific surface area for lithium iron phosphate before carbon removal and It is the graph which plotted the relationship with discharge capacity.

  Hereinafter, a form for carrying out the present invention (this embodiment) will be described with reference to the drawings as appropriate. In the following description, “lithium iron phosphate” is used as an example of the positive electrode active material, but the positive electrode active material that can be used in the present embodiment is not limited to lithium iron phosphate. In addition to any positive electrode active material such as lithium manganese oxide and lithium cobaltate, the present invention can also be applied to a negative electrode active material such as lithium titanate.

  FIG. 1 is a block diagram showing a characteristic evaluation apparatus 5 for a lithium secondary battery according to this embodiment. The characteristic evaluation apparatus 5 is an apparatus for evaluating the characteristics of a lithium secondary battery using carbon-coated lithium iron phosphate. Specifically, the characteristic evaluation apparatus 5 evaluates the charge / discharge characteristics of a lithium secondary battery using the carbon-coated lithium iron phosphate by evaluating the physical properties of the carbon-coated lithium iron phosphate. It is.

  The characteristic evaluation device 5 includes a carbon material removing unit 1 (carbon material removing device), a BET specific surface area measuring unit 2 (BET specific surface area measuring device), a characteristic determining unit 3 (characteristic determining device), and a BET specific surface area database 4. And. In addition, the characteristic evaluation apparatus 5 includes a display unit (not shown, for example, a display) on which the evaluation result is displayed. In lithium secondary batteries, when lithium iron phosphate is used as the positive electrode active material, carbon-coated lithium iron phosphate is usually used from the viewpoint of compensating for the low conductivity of lithium iron phosphate. is there. Therefore, when the characteristic evaluation apparatus 5 evaluates the characteristics of the lithium secondary battery, first, the carbon covered with the lithium iron phosphate is removed by the carbon material removing unit 1.

  The carbon material removing unit 1 is, for example, a firing apparatus capable of firing in an atmosphere containing oxygen (for example, air). Firing can be performed, for example, at about 400 ° C. to 700 ° C. for about 3 hours to 24 hours. The carbon material removing unit 1 may be a device that peels off the carbon material on the surface by applying a mechanical impact to the carbon-coated lithium iron phosphate, such as a mill.

  The BET specific surface area measuring unit 2 measures the BET specific surface area of the lithium iron phosphate from which the carbon material has been removed by the carbon material removing unit 1. Although details will be described later, in this embodiment, charging / discharging of the lithium secondary battery is based on the BET specific surface area after removing the coated carbon material instead of the BET specific surface area of the carbon-coated lithium iron phosphate. Properties are being evaluated. By doing in this way, the charge / discharge characteristic of the lithium secondary battery using the lithium iron phosphate can be predicted more accurately than before.

  As the BET specific surface area measuring unit 2, for example, any BET specific surface area measuring device can be applied. That is, for example, an apparatus capable of measuring the BET specific surface area based on JIS Z 8830: 2013 (method for measuring the specific surface area of powder (solid) by gas adsorption) can be used.

  Based on the BET specific surface area measured by the BET specific surface area measuring unit 2, the characteristic determining unit 3 uses lithium iron phosphate before removing the carbon material (that is, lithium iron phosphate coated with carbon). The charge / discharge characteristics of the secondary battery are determined (predicted). When the characteristic determination unit 3 evaluates the charge / discharge characteristics, the characteristic determination unit 3 refers to the BET specific surface area database 4.

  The BET specific surface area database 4 records the correspondence between the BET specific surface area of lithium iron phosphate not coated with carbon and the charge / discharge characteristics (for example, discharge capacity) of a lithium secondary battery using the lithium iron phosphate. Has been. This correspondence is, for example, a mathematical formula, a table, a graph, or the like, and can be determined by a preliminary test or the like. Therefore, the characteristic determination unit 3 reads out the charge / discharge characteristics of the lithium secondary battery corresponding to the BET specific surface area of the lithium iron phosphate measured by the BET specific surface area measurement unit 2 from the BET specific surface area database 4. In the examples described later, the BET specific surface area database 4 records an approximate expression indicated by a broken line in FIG.

  The read charge / discharge characteristics are displayed on, for example, a display unit (not shown) so that the user can evaluate the charge / discharge characteristics.

  The characteristic determination unit 3 and the BET specific surface area database 4 are not shown, but a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and an HDD (Hard Disk Drive). And is configured. And the characteristic determination part 3 is embodied by the program (program which performs the flowchart shown in FIG. 3 mentioned later) recorded on ROM and HDD being performed by CPU.

  Here, the charge / discharge characteristics of the lithium secondary battery are evaluated based on the BET specific surface area of the lithium iron phosphate after removing the coated carbon material, not the BET specific surface area of the carbon-coated lithium iron phosphate. The reason for this will be described with reference to FIG.

  FIG. 2 is a diagram schematically showing the shape of carbon-coated lithium iron phosphate and the shape of only lithium iron phosphate constituting the carbon-coated lithium iron phosphate, and (a) shows a medium BET specific surface area. An example of the shape, (b) is an example of a shape having a small BET specific surface area as a whole, and (c) is an example of a shape having a large BET specific surface area as a whole. First, in lithium iron phosphate, the charge / discharge characteristics (for example, discharge capacity) of a lithium secondary battery become better as the area that can be contacted with lithium ions contained in the non-aqueous electrolyte is larger. Therefore, the larger the BET specific surface area of lithium iron phosphate, the better the charge / discharge characteristics.

  However, as shown in FIG. 2, there may be no correlation between the BET specific surface area of the carbon-coated lithium iron phosphate and the BET specific surface area of the lithium iron phosphate constituting it. For example, the BET specific surface area of the carbon-coated lithium iron phosphate 100A shown in FIG. 2A and the BET specific surface area of the lithium iron phosphate 10A after removing the carbon material 11A show the same tendency. (All are moderate).

  However, the BET specific surface area of the carbon-coated lithium iron phosphate 100B shown in FIG. 2B and the BET specific surface area of the lithium iron phosphate 10B constituting the carbon black lithium iron phosphate 100B are in a contradictory relationship. In this case, since the BET specific surface area of lithium iron phosphate 10B is large, originally good charge / discharge characteristics are exhibited. However, the BET specific surface area of the carbon material 11B that does not contribute to the charge / discharge characteristics is small. Therefore, if the BET specific surface area of the carbon-coated lithium iron phosphate 100B is simply measured, the BET specific surface area of the carbon material 11B is measured, so the measured value becomes small. As a result, according to the conventional evaluation method that has been evaluated based on the BET specific surface area of carbon-coated lithium iron phosphate 100B, it is evaluated that unsatisfactory charge / discharge characteristics are achieved. Become.

  Further, for example, in FIG. 2C, the BET specific surface area of the carbon material 11C is large. Therefore, if the BET specific surface area of the lithium iron phosphate 100C is simply measured, the measured value increases because the BET specific surface area of the carbon material 11C is measured. As a result, according to the conventional evaluation method, it is evaluated that the charge / discharge characteristics are good. However, since the BET specific surface area of lithium iron phosphate 10C after removing the carbon material is small, the charge / discharge characteristics are actually not good.

  In FIG. 2, for simplicity of explanation, the carbon material (the carbon material 11 </ b> A, etc., the same below) covers the entire surface of the lithium iron phosphate (the lithium iron phosphate 10 </ b> A, etc., the same below). ing. However, in reality, there may be a portion not covered with the carbon material on the surface of lithium iron phosphate. Therefore, simply measuring the BET specific surface area of carbon-coated lithium iron phosphate (carbon-coated lithium iron phosphate 100A, etc.), the BET specific surface area of the carbon material and the BET specific surface area of lithium iron phosphate And may be based on both.

  It depends on the lithium iron phosphate whether the lithium iron phosphate is completely carbon-coated, or if not, how much of the surface is carbon-coated. Therefore, simply measuring the BET specific surface area of carbon-coated lithium iron phosphate may fail to accurately measure the BET specific surface area of lithium iron phosphate.

  Therefore, in the present embodiment, not the BET specific surface area of the carbon-coated lithium iron phosphate (100A, 100B, 100C), but the lithium iron phosphate (10A, 10A, 11C) after removing the carbon material (11A, 11B, 11C). 10B, 10C), the charge / discharge characteristics of the lithium secondary battery are evaluated. In particular, by measuring the BET specific surface area of lithium iron phosphate after removing the carbon material from the carbon-coated lithium iron phosphate, not the BET specific surface area of lithium iron phosphate before being carbon-coated, More accurate charge / discharge characteristics can be evaluated. In other words, firing is usually performed to coat the carbon, but this firing may cause crystal growth of lithium iron phosphate and change the BET specific surface area. However, in this embodiment, since the BET specific surface area of the lithium iron phosphate after firing is measured, accurate evaluation becomes possible.

  FIG. 3 is a flowchart showing a characteristic evaluation method performed by the lithium secondary battery characteristic evaluation apparatus 5 (see FIG. 1) of the present embodiment. The operation of the characteristic evaluation apparatus 5 shown in FIG. 1 will be described with reference to FIG. In the flowchart shown in FIG. 3, for the sake of simplicity, the carbon material is removed by firing in an atmosphere containing oxygen, but the method for removing the carbon material is limited to this. is not.

  The sample (carbon-coated lithium iron phosphate) set in the characteristic evaluation apparatus 5 is baked in the atmosphere (in an atmosphere containing oxygen) by the carbon material removing unit 1 to remove the carbon material on the surface (step) S101, carbon material removing step). The carbon material reacts with oxygen in the atmosphere to change to carbon dioxide, and is discharged outside the characteristic evaluation device 5. The firing conditions at this time are not particularly limited as long as the carbon material can be oxidized and removed. For example, as described above, the firing condition may be about 400 ° C. to 700 ° C. and about 3 hours to 24 hours.

  After the carbon material is removed and the exposed lithium iron phosphate is sufficiently radiated, the BET specific surface area measuring unit 2 measures the BET specific surface area (step S102, BET specific surface area measuring step). The BET specific surface area can be measured, for example, using a measuring apparatus based on the above measuring method. And the characteristic determination part 3 reads the discharge capacity (charge / discharge characteristic) corresponding to the measured BET specific surface area from the BET specific surface area database 4 (step S103, characteristic determination step). Thereby, the discharge capacity (charge / discharge characteristics) of the lithium secondary battery using the sample (carbon-coated lithium iron phosphate) set in the characteristic evaluation apparatus 5 is determined.

  And finally, the characteristic determination part 5 displays the spilled discharge capacity on a display part (step S104). Thereby, the user can predict the discharge capacity of the lithium secondary battery when the lithium secondary battery is used using the sample.

  Next, a lithium secondary battery was fabricated by actually using carbon-coated lithium iron phosphate, and the relationship between the BET specific surface area and the discharge capacity was examined.

<Production of lithium secondary battery>
[Production Example 1]
Lithium carbonate (Li ₂ CO ₃ ), iron oxalate dihydrate (FeC ₂ O ₄ .2H ₂ O), and ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) were mixed. Next, the mixture was subjected to primary firing at 405 ° C. to obtain lithium iron phosphate not coated with carbon. The firing time was 4 hours.

300 g of the obtained lithium iron phosphate was pulverized for 2 hours in water using a bead mill without adding water-soluble carbon. Next, vacuum drying was performed at 120 ° C. overnight to obtain a dried product. And about the mixture which added coal pitch (MCP110C by JFE Chemical Co., Ltd.) so that it might become 3.5 mass% with respect to the obtained dried material, secondary baking was performed by heating at 720 degreeC for 4 hours. After secondary firing, cooling, crushing and classification (excluding those having a diameter of 45 μm or more by sieving) yielded carbon-coated lithium iron phosphate. The carbon-coated lithium iron phosphate was measured for BET specific surface area by using BELSORP-mini (manufactured by Nippon Bell Co., Ltd.) and found to be 6.01 m ² / g.

The obtained carbon-coated lithium iron phosphate was baked in the air at 500 ° C. for 6 hours to remove the carbon material on the surface. And when the BET specific surface area of the lithium iron phosphate exposed by removing the carbon material was measured, it was 0.05 m ² / g.

  In addition, the fired product after pulverization and classification (carbon-coated lithium iron phosphate), acetylene black (Denka Black (registered trademark), manufactured by Denki Kagaku Kogyo Co., Ltd., 75% press product), polyvinylidene fluoride ( Kureha Battery Materials Japan, # 9100) and polyvinylidene fluoride (Kureha Battery Materials Japan, # 7200) were mixed at a ratio of 91: 4: 2.5: 2.5 (mass ratio). did. Next, the obtained mixture was stirred and mixed in N-methylpyrrolidone to obtain a positive electrode mixture slurry (positive electrode material).

The obtained positive electrode mixture slurry was applied to an aluminum plate and then dried to produce a positive electrode. A lithium secondary battery was produced using the produced positive electrode, metallic lithium as the negative electrode, and a non-aqueous electrolyte. This non-aqueous electrolyte is a solution obtained by mixing LiPF ₆ so as to be 1 M in a solvent obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a ratio (volume ratio) of 3: 7. It is. About the produced lithium secondary battery, after performing constant current charge to 4.3V at 0.1C, constant current discharge was performed at 1C to 2.0V, and the discharge capacity was measured. As a result, the discharge capacity was 37 mAh / g.

[Production Example 2]
Primary firing was performed in the same manner as in Production Example 1 to obtain lithium iron phosphate not coated with carbon. 200 g of the obtained lithium iron phosphate and 6.6 g of polyvinyl alcohol powder (manufactured by Kuraray Co., Ltd., PVA-205) were mixed, heated to 720 ° C., and held at 720 ° C. for 6 hours (secondary firing) ). And about the baked product after secondary baking, it carried out similarly to the manufacture example 1, and the carbon-coated lithium iron phosphate was obtained. With respect to the obtained carbon-coated lithium iron phosphate, the BET specific surface area was measured in the same manner as in Production Example 1 and found to be 9.54 m ² / g.

Then, the carbon material on the surface of the obtained carbon-coated lithium iron phosphate was removed in the same manner as in Production Example 1. And when the BET specific surface area of the lithium iron phosphate exposed by removing the carbon material was measured, it was 1.64 m ² / g.

  Further, using the obtained carbon-coated lithium iron phosphate, a lithium secondary battery was produced in the same manner as in Production Example 1, and the discharge capacity was measured in the same manner as in Production Example 1. As a result, the discharge capacity was 113 mAh / g.

[Production Example 3]
At the time of secondary firing, “66 g of polyvinyl alcohol 10 mass% solution (manufactured by Kuraray Co., Ltd., RS-2117)” is used instead of “6.6 g of polyvinyl alcohol powder (manufactured by Kuraray Co., Ltd., PVA-205)”. A carbon-coated lithium iron phosphate was produced in the same manner as in Production Example 2 except that the above-described cases were observed. With respect to the obtained carbon-coated lithium iron phosphate, the BET specific surface area was measured in the same manner as in Production Example 1 and found to be 12.9 m ² / g.

Then, the carbon material on the surface of the obtained carbon-coated lithium iron phosphate was removed in the same manner as in Production Example 1. And when the BET specific surface area of the lithium iron phosphate exposed by removing the carbon material was measured, it was 2.03 m ² / g.

  Further, using the obtained carbon-coated lithium iron phosphate, a lithium secondary battery was produced in the same manner as in Production Example 1, and the discharge capacity was measured in the same manner as in Production Example 1. As a result, the discharge capacity was 125 mAh / g.

[Production Example 4]
At the time of the secondary firing, instead of “6.6 g of polyvinyl alcohol powder (PVA-205, manufactured by Kuraray Co., Ltd.)” A carbon-coated lithium iron phosphate was prepared in the same manner as in Production Example 2 except that “Mixed with 26.8 g of 50% by mass solution” manufactured by Chemical Co., Ltd. was used. With respect to the obtained carbon-coated lithium iron phosphate, the BET specific surface area was measured in the same manner as in Production Example 2. As a result, it was 8.76 m ² / g.

Then, the carbon material on the surface of the obtained carbon-coated lithium iron phosphate was removed in the same manner as in Production Example 1. And when the BET specific surface area of the lithium iron phosphate exposed by removing the carbon material was measured, it was 4.34 m ² / g.

  Further, using the obtained carbon-coated lithium iron phosphate, a lithium secondary battery was produced in the same manner as in Production Example 1, and the discharge capacity was measured in the same manner as in Production Example 1. As a result, the discharge capacity was 137 mAh / g.

[Production Example 5]
Lithium hydroxide (LiOH.H ₂ O), iron oxalate dihydrate (FeC ₂ O ₄ .2H ₂ O), and ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) in isopropyl alcohol after milling mixture having an average particle diameter D ₅₀ of a guide 2.5μm or less, by performing a primary firing at 405 ° C., to produce a lithium iron phosphate is not coated with carbon. The firing time was 4 hours.

  After primary firing, 3.2 kg of creosote oil (manufactured by JFE Chemical Co., HOB) as a carbon raw material was mixed with 80 kg of lithium iron phosphate. The mixture was heated to 680 ° C. and heated at 680 ° C. for 3 hours to perform secondary firing.

After the secondary firing, the carbon-coated lithium iron phosphate was obtained in the same manner as in Production Example 1. With respect to the obtained carbon-coated lithium iron phosphate, the BET specific surface area was measured in the same manner as in Production Example 1 and found to be 15.44 m ² / g.

Then, the carbon material on the surface of the obtained carbon-coated lithium iron phosphate was removed in the same manner as in Production Example 1. And when the BET specific surface area of the lithium iron phosphate exposed by removing the carbon material was measured, it was 10.82 m ² / g.

  Further, using the obtained carbon-coated lithium iron phosphate, a lithium secondary battery was produced in the same manner as in Production Example 1, and the discharge capacity was measured in the same manner as in Production Example 1. As a result, the discharge capacity was 149 mAh / g.

<Examination of characteristic evaluation method>
FIG. 4 (a) is a graph plotting the relationship between the BET specific surface area and discharge capacity for lithium iron phosphate after carbon removal, and FIG. 4 (b) is for lithium iron phosphate before carbon removal. It is the graph which plotted the relationship between a BET specific surface area and discharge capacity. In both Fig.4 (a) and FIG.4 (b), the BET specific surface area of the lithium iron phosphate used by each of manufacture examples 1-5 is plotted.

  As shown in FIG. 4 (a), between the BET specific surface area of lithium iron phosphate after removing the carbon material and the discharge capacity of the lithium secondary battery using the carbon-coated lithium iron phosphate. There was a correlation as shown by the broken line in the graph. Specifically, when the BET specific surface area is small to some extent, the discharge capacity increases rapidly, and when the BET specific surface area becomes large to some extent, the increase in discharge capacity becomes moderate.

  Moreover, although the method of coat | covering lithium iron phosphate with a carbon material is various in manufacture examples 1-5, even if it coat | covers with what kind of method, each manufacture example was plotted in the curve vicinity shown with a broken line. Therefore, it was found that if the discharge capacity is evaluated based on the BET specific surface area of the lithium iron phosphate after carbon removal, the discharge capacity can be accurately predicted. Note that a broken line (approximate expression) shown in FIG. 4A is recorded in the BET specific surface area database 4.

  On the other hand, as shown in FIG. 4B, no correlation was found when the relationship between the BET specific surface area and the discharge capacity was plotted for lithium iron phosphate before the carbon material was removed. Accordingly, in order to improve the discharge capacity of the lithium secondary battery, it is conceivable to increase the BET specific surface area of the carbon-coated lithium iron phosphate. However, this method does not necessarily increase the discharge capacity.

  That is, as described with reference to FIG. 2, even if the BET specific surface area of the carbon-coated lithium iron phosphate is large, lithium iron phosphate that contributes to charge / discharge (lithium iron phosphate after carbon removal) ) May not be large. Therefore, as in this embodiment, by removing the carbon material from the carbon-coated lithium iron phosphate and evaluating the charge / discharge characteristics based on the BET specific surface area of the lithium iron phosphate after the carbon removal, Predictions can be made more accurately and reliably than before.

DESCRIPTION OF SYMBOLS 1 Carbon material removal part 2 BET specific surface area measurement part 3 Characteristic determination part 4 BET specific surface area database 5 Characteristic evaluation apparatus 10A, 10B, 10C Lithium iron phosphate 11A, 11B, 11C Carbon material 100A, 100B, 100C Carbon-coated phosphorus Lithium iron oxide

Claims (3)

A method for evaluating characteristics of a lithium secondary battery using a carbon-coated positive electrode active material, which is a secondary fired product obtained by mixing and firing a primary fired product not coated with carbon and a carbon material Because
And a carbon material removal step of removing the carbon material covering the positive electrode active material is a secondary fired product,
A BET specific surface area measuring step for measuring the BET specific surface area for the positive electrode active material is the secondary fired product carbon material has been removed,
It said BET specific surface area measured in the BET specific surface area measuring step, predetermined BET specific surface area and the relationship between the charge and discharge characteristics, on the basis of, characterization to determine the charge and discharge characteristics of the lithium secondary battery And a step of evaluating the characteristics of the lithium secondary battery. In the carbon material removal step, the carbon material covering the positive electrode active material is a secondary fired product, and removing by firing in an atmosphere containing oxygen, according to claim 1 Method for evaluating characteristics of lithium secondary battery. An apparatus for evaluating the characteristics of a lithium secondary battery using a carbon-coated positive electrode active material,
A carbon material removing device that removes the carbon material covering the positive electrode active material;
A BET specific surface area measuring device for measuring a BET specific surface area of the positive electrode active material from which the carbon material has been removed;
A characteristic determining apparatus for determining charge / discharge characteristics of the lithium secondary battery based on a BET specific surface area measured by the BET specific surface area measuring apparatus and a predetermined relationship between the BET specific surface area and the charge / discharge characteristics. A device for evaluating characteristics of a lithium secondary battery, comprising:

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