JP5603590B2 - Negative electrode active material for lithium secondary battery and in-vehicle lithium secondary battery using the same - Google Patents

Description

  The present invention relates to a negative electrode active material for a lithium secondary battery and an in-vehicle lithium secondary battery using the same.

  Lithium rechargeable batteries have higher energy density than other rechargeable batteries, so they can be reduced in size and weight, so mobile phones, personal computers, personal digital assistants (PDAs) and It is widely used as a power source for mobile electronic devices such as handy video cameras, and its demand is expected to increase in the future.

  In addition, hybrid electric vehicles (HEVs) that combine a gasoline engine with an electric vehicle or a motor driven by a nickel metal hydride battery have been developed to increase energy and environmental issues, and the number of such vehicles has increased. . In these automobiles, there is a demand for higher performance of batteries used, and lithium secondary batteries are attracting attention as a means of meeting this demand.

  In a lithium secondary battery, a carbon material that is excellent in terms of safety and life is generally used as a negative electrode material (negative electrode active material). Among the carbon materials, the graphite material is an excellent material having a high energy density, which is obtained at a high temperature of at least about 2,000 ° C., usually about 2,600 to 3,000 ° C., but has high input / output characteristics. And has problems with cycle characteristics. For this reason, for example, for high input / output applications such as power storage and electric vehicles, the use of a low-crystalline carbon material that is fired at a temperature lower than that of the graphite material and has a low degree of graphitization is mainly studied.

  In recent years, from the viewpoint of further improving the performance of hybrid electric vehicles, further improvement in performance has been demanded for lithium secondary batteries, and there is an urgent need to improve the performance. In particular, the characteristics of the lithium secondary battery are required to sufficiently reduce the potential on the negative electrode side to improve the actual battery voltage and exhibit sufficiently high output characteristics.

  In addition, the discharge capacity of the lithium secondary battery can be raised as an important characteristic so that a current that is an energy source of the hybrid electric vehicle can be sufficiently supplied. In addition, the ratio of the charge capacity to the discharge capacity, that is, the initial efficiency is required to be high so that the discharge current amount is sufficiently higher than the charge current amount.

  Furthermore, in order to enable charging in a short time, the lithium secondary battery preferably maintains a high charge capacity up to a high current density, and is also required to have a high capacity maintenance rate. That is, it is required to improve such characteristics as output characteristics, discharge capacity, initial efficiency, capacity maintenance ratio and the like in a balanced manner.

  For the purpose of such a lithium secondary battery, many carbon materials such as coke and graphite have been studied as a negative electrode material. However, although the discharge capacity described above can be increased, the initial efficiency is not sufficient. In addition, the actual battery voltage is insufficient, the high output characteristics in recent years cannot be satisfied, and the capacity maintenance factor requirement cannot be satisfied.

  For example, Patent Document 1 discloses a carbonaceous material that defines a specific specific surface area, an X-ray diffraction crystal thickness, and the like obtained by pyrolysis or calcining carbonization of an organic compound as a negative electrode material using intercalation or doping. However, it is still insufficient for in-vehicle applications such as HEV.

  Patent Document 2 discloses the use of a carbonaceous material obtained by heat-treating a specific coating layer on a carbonaceous material having a graphite-like structure as a negative electrode material, and Patent Document 3 discloses a low-temperature material as a negative electrode material. Carbon materials having a relatively high discharge capacity have been disclosed by removing impurities to a higher degree by heat-treating in an inert atmosphere using coke heat-treated as a raw material. It did not have sufficient battery characteristics for in-vehicle applications.

  Patent Document 4 discloses that a lithium secondary battery having a large charge / discharge capacity can be supplied by using heat-treated coke obtained by heat-treating raw coke of petroleum or coal at 500 to 850 ° C. as a negative electrode material. However, it was not sufficient in terms of output characteristics in in-vehicle applications such as for HEV.

  Most of the researches on negative electrode materials for lithium secondary batteries using low-crystal carbon materials made from coke as described above are aimed at improving the characteristics of the negative electrode materials for secondary batteries as power sources for small portable devices. In fact, a negative electrode material having sufficient characteristics suitable for a high current input / output lithium secondary battery represented by a secondary battery for HEV has not been developed.

  On the other hand, adding various compounds to an organic material or a carbonaceous material to improve battery characteristics has also been studied. For example, Patent Document 5 discloses a negative electrode material obtained by carbonizing an organic material or a carbonaceous material by adding a phosphorus compound, and Patent Document 6 discloses a carbon material containing boron and silicon as graphite. Although the negative electrode material obtained by making it into a device is disclosed, as in the above, it is still not sufficient for practical use in terms of output characteristics or the like in an in-vehicle application such as for HEV.

JP 62-90863 A JP-A-6-5287 JP-A-8-102324 JP-A-9-320602 JP-A-3-137010 Japanese Patent Laid-Open No. 11-40158

  The present invention can sufficiently improve the output characteristics of a lithium secondary battery, and has novel characteristics that are practically required for in-vehicle applications such as for HEV including discharge capacity, initial efficiency, and capacity maintenance ratio. It aims at obtaining a negative electrode active material.

The inventors of the present invention have intensively studied to achieve the above object. As a result, with respect to 100 parts by weight of coal-based and / or petroleum-based (hereinafter referred to as coal-based) raw coke, the phosphorus compound and the boron compound are each 0.1 parts by weight to 6.0 parts by weight in terms of phosphorus and boron. The negative electrode active material for a lithium secondary battery, which is obtained by calcining a coke material added at a ratio of 800 parts at a temperature of 800 ° C. to 1400 ° C. , sufficiently reduces the potential of the negative electrode of the lithium secondary battery As a result, it was found that the actual battery voltage can be improved and that the battery has practical characteristics required for in-vehicle use such as output characteristics, discharge capacity, initial efficiency and capacity retention rate, and the present invention has been completed.

  The “coal-based coke” in the present invention is a petroleum-based and / or coal-based heavy oil, for example, using a coking facility such as a delayed coker, and the maximum temperature reached at a temperature of about 400 ° C. to 700 ° C. It means the one obtained by carrying out thermal decomposition and polycondensation reaction for about hours.

  According to the present invention, the output characteristics of a lithium secondary battery can be sufficiently improved, and have practical characteristics required for in-vehicle applications such as for HEV including discharge capacity, initial efficiency, and capacity maintenance ratio, and performance. A negative electrode active material excellent in balance can be provided.

  Hereinafter, the present invention will be described in more detail based on an embodiment of a negative electrode active material for a lithium secondary battery.

  The negative electrode active material for a lithium secondary battery of the present invention is first prepared by using a coal-based heavy oil, for example, a coking facility such as a delayed coker, and the maximum temperature reached about 400 ° C. to 700 ° C. for about 24 hours. Coal coke is obtained by advancing thermal decomposition and polycondensation reaction. Thereafter, the obtained coal-based raw coke mass is pulverized to a predetermined size. An industrially used pulverizer can be used for the pulverization. Specific examples include an atomizer, a Raymond mill, an impeller mill, a ball mill, a cutter mill, a jet mill, and a hybridizer, but are not particularly limited thereto.

  The heavy coal oil used here may be either a heavy petroleum oil or a heavy coal oil, but the heavy heavy oil is richer in aromaticity. , S, V, Fe, etc. are less impurities and less volatile matter, so it is preferable to use heavy coal oil.

In addition, although the size of the coal-based raw coke powder after pulverization and the calcined coke powder such as coal-based calcined coke powder is not particularly limited, the average particle size required as the median diameter is more preferably 5 to 15 μm, At this time, the BET specific surface area is more preferably 5 m ² / g or less. When the average particle diameter is less than 5 μm, the specific surface area increases excessively, and the initial efficiency of the obtained lithium secondary battery may be reduced. On the other hand, when the average particle diameter exceeds 15 μm, the charge / discharge characteristics of the lithium secondary battery may be deteriorated. If the BET specific surface area exceeds 5 m ² / g, as described above, the specific surface area may increase excessively and the initial efficiency of the lithium secondary battery may be reduced. The BET specific surface area is desirably about 2 m ² / g or more from the viewpoint of forming fine pores.

  A phosphorus compound and a boron compound are added to the above-mentioned coke powder. The addition is performed by blending the above-mentioned coal-based raw coke powder with the following amounts of phosphorus compound and boron compound and putting them in a predetermined mold (first addition method).

  The addition of the phosphorus compound and the boron compound can be performed at the time of obtaining a lump of coal-based raw coke instead of after obtaining the coal-based raw coke powder (second addition method). In this case, by putting the lump of coal-based raw coke into a pulverizer and simultaneously putting the above-described phosphorus compound and boron compound into the pulverizer and pulverizing the lump, the phosphorus compound and the boron compound Coal-based raw coke powder obtained by adding can be obtained.

  Therefore, since the phosphorus compound and boron compound can be added simultaneously with the pulverization of the coal-based raw coke mass, the operation of adding the phosphorus compound or the like separately at the time of firing can be omitted. For lithium secondary batteries The whole manufacturing process of a negative electrode active material can be simplified.

  However, both of the first addition method and the second addition method differ only in the manufacturing process of the lithium secondary battery negative electrode active material due to the difference in the specific method of addition, and the lithium secondary battery There is almost no change in the output characteristics, discharge capacity, initial efficiency, and capacity retention rate of the negative electrode active material itself.

  The amount of the phosphorus compound added is preferably 0.1 to 6.0 parts by weight, more preferably 0.5 to 5.0 parts by weight, in terms of phosphorus, with respect to 100 parts by weight of coal-based raw coke. It is preferable. If the addition amount is less than the lower limit, the effect of adding the phosphorus compound may not be sufficiently obtained. On the other hand, if the addition amount exceeds the upper limit, the crystallization of the coke surface may progress and the output characteristics may deteriorate. is there.

  Moreover, it is preferable that the addition amount of the said boron compound is 0.1-6.0 weight part in conversion of boron with respect to 100 weight part of coal-type raw cokes, Furthermore, 0.5-5.0 weight part is preferable. It is preferable that If the addition amount is less than the lower limit, the effect of adding the boron compound may not be sufficiently obtained. On the other hand, if the addition amount exceeds the upper limit, carbonization of coke is excessively promoted, and unreacted boron may remain. There is a risk that the output characteristics, discharge capacity, initial efficiency, and capacity retention rate of the negative electrode active material for lithium secondary batteries will deteriorate.

  As the phosphorus compound described above, phosphoric acids are preferable from the viewpoints of easily preparing an aqueous solution and having high safety. Phosphoric acid (orthophosphoric acid) is more preferably used as the phosphoric acid, but is not limited thereto, and can be appropriately selected from linear polyphosphoric acid, cyclic polyphosphoric acid, various phosphoric ester compounds, and the like. Any one of these phosphoric acids may be used alone, or two or more thereof may be used in combination.

Moreover, it is preferable to use boron carbide (B ₄ C) as the boron compound described above. This is because even if boron carbide decomposes during firing, the resulting components are only boron for achieving the object of the present invention, and carbon which is a constituent element of coke which is a base material of the negative electrode active material. And since other components are not included, it is because the bad influence to the negative electrode active material by this component can be suppressed.

  Such coke is fired. The firing temperature is preferably 800 ° C. or higher and 1400 ° C. or lower at the highest temperature reached. Preferably it is 900 to 1200 degreeC, More preferably, it is the range of 900 to 1100 degreeC. If the firing temperature exceeds the upper limit, the crystal growth of the coke material is excessively promoted, and the output characteristics, discharge capacity, initial efficiency, capacity retention rate of the negative electrode active material for lithium secondary batteries may be deteriorated, and From the viewpoint of mass productivity, it is not preferable. On the other hand, if the firing temperature is lower than the lower limit, not only the sufficient crystal growth is not possible, but also the addition effect of phosphorus compound and boron compound is not sufficient in the carbonization process of coke, and similarly, the negative electrode active material for lithium secondary battery Output characteristics, discharge capacity, initial efficiency, and capacity retention rate may be deteriorated.

  The holding time at the highest temperature is not particularly limited but is preferably 30 minutes or longer. The firing atmosphere is not particularly limited, but may be an inert gas atmosphere such as argon or nitrogen, a non-oxidizing atmosphere in a non-sealed state such as a rotary kiln, or a non-oxidizing atmosphere in a sealed state such as a lead hammer furnace. An oxidizing atmosphere may be used.

When a lithium secondary battery is formed using such a negative electrode active material of the present invention as a negative electrode material, a lithium-containing transition metal oxide LiM (1) _X O ₂ (wherein x is 0 ≦ x ≦ 1 in the range, wherein M (1) represents a transition metal and consists of at least one of Co, Ni, Mn, Ti, Cr, V, Fe, Zn, Al, Sn, In) Or LiM (1) _y M (2) _2-y O ₄ (wherein y is a numerical value in the range of 0 ≦ y ≦ 1 and M (1) and M (2) represent transition metals) , Co, Ni, Mn, Ti, Cr, V, Fe, Zn, Al, Sn, In), transition metal chalcogenides (Ti, S ₂ , NbSe, etc.), vanadium oxide (V ₂ O _5, V ₆ O ₁₃ , V ₂ O _4, V ₃ O _6, etc.) and lithium compounds, general formula M _x Mo ₆ Ch _6-y (where x is 0 ≦ x ≦ 4, y is a numerical value in the range of 0 ≦ y ≦ 1, where M is a metal including a transition metal and Ch is a chalcogen metal) or activated carbon, activated carbon A positive electrode active material such as carbon fiber can be used.

Further, Examples of the electrolyte filling the space between the positive electrode and the negative electrode, and any known ones can be used, for example _{LiClO 4, LiBF 4, LiPF 6} , LiAsF 6, LiB (C 6 H 5), LiCl LiBr, Li ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, Li (CF ₃ SO ₂ ) ₃ C, Li) CF ₃ CH ₂ OSO ₂ ) ₂ N, Li (CF ₃ CF ₂ CH ₂ OSO ₂ ) ₂ N, Li (HCF ₂ CF ₂ CH ₂ OSO ₂ ) ₂ N, Li ((CF ₃ ) ₂ CHOSO ₂ ) ₂ N, LiB [C ₆ H ₃ (CF ₃ ) ₂ ] ₄ Mention may be made of mixtures of more than one species.

  Examples of the non-aqueous electrolyte include propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 1,1-dimethoxyethane, 1,2-dimethoxyethane, 1,2 -Diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, anisole, diethyl ether, sulfolane, methylsulfolane, acetonitrile, chloronitrile, propionitrile , Trimethyl borate, tetramethyl silicate, nitromethane, dimethylformamide, N-methylpyrrolidone, ethyl acetate, trimethylorthoformate, nitrobenzene Benzoyl chloride, benzoyl bromide, tetrahydrothiophene, dimethyl sulfoxide, 3-methyl-2-oxazolidone, ethylene glycol, sulfite, a single solvent or a mixture of two or more solvents such as dimethyl sulfite may be used.

  In general, when the negative electrode is formed using the negative electrode active material, fluorine resin powder such as polyvinylidene fluoride (PVDF) or polyimide (PI) resin, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC) ) And the like, and the binder and the negative electrode active material are mixed using a solvent such as N-methylpyrrolidone (NMP), dimethylformamide, water, alcohol or the like. A slurry is prepared, applied onto a current collector, and dried.

   The present invention will be specifically described below based on examples. However, the content of this invention is not restrict | limited by these Examples.

Example 1
Using a refined pitch from which heavy quinoline insolubles have been removed from heavy coal-based oil, a bulk coke produced by heat treatment at a temperature of 500 ° C. for 24 hours by a delayed coking method (raw coke) is obtained. The raw coke powder having an average particle size of 9.9 μm was obtained.

  Phosphoric acid ester (14% by mass active phosphorus solid resin: trade name HCA manufactured by Sanko Co., Ltd., chemical name: 9,10-dihydro-9-oxa-10) with respect to 100 parts by weight of raw coke powder obtained as described above. -Osfaphenanthrene-10-oxide) 25.0 parts by weight (phosphorus conversion: 3.5 parts by weight) and boron carbide 1.9 parts by weight (boron conversion: 1.5 parts by weight) were added.

  Next, the coke material formed by adding the phosphate ester and boron carbide is heated from room temperature at a rate of 600 ° C./hour, and after reaching 900 ° C. (maximum temperature reached), the carbon is kept for another 2 hours for carbonization. Treatment (firing) was performed to obtain a negative electrode active material for a lithium secondary battery.

  Next, 5% by mass of polyvinylidene fluoride (PVDF, manufactured by Kureha Co., Ltd.) as a binder is added to the negative electrode active material for a lithium secondary battery, and a slurry is prepared by kneading N-methylpyrrolidone (NMP) as a solvent. Was applied to a copper foil having a thickness of 18 μm uniformly to obtain a negative electrode foil, which was dried and pressed to a predetermined electrode density to prepare an electrode sheet, from which a diameter of 15 mmΦ In order to evaluate the electrode characteristics of the single electrode of the negative electrode, metallic lithium cut into about 15.5 mmΦ was used as the counter electrode.

In addition, a coin cell was prepared by using LiPF ₆ dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio 1: 1 mixture) as the electrolyte solution at a concentration of 1 mol / l, and using a porous membrane of propylene as the separator. The lithium secondary battery was manufactured. The discharge characteristics when a constant current discharge of 5 mA / cm ² was performed in a voltage range in which the terminal voltage was 0 V and the discharge upper limit voltage was 1.5 V at a constant temperature of 25 ° C. were examined. The results are shown in Table 1.

(Examples 2-3)
In Example 1, the amount of phosphate ester added and the amount of boron carbide were changed from 3.5 parts by weight in terms of phosphorus and 1.5 parts by weight in terms of boron to 2.5 parts by weight in terms of phosphorus and 2 in terms of boron. Except for changing to 5 parts by weight (Example 2), 1.5 parts by weight in terms of phosphorus, and 3.5 parts by weight (Example 3) in terms of boron, the same operation as in Example 1 was performed, and lithium was A secondary battery was obtained. Further, the discharge characteristics were examined in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 1)
Using a coke material of 100 parts by weight of raw coke powder and without adding phosphate ester and boron carbide, the same operation as in Example 1 was performed to obtain a lithium secondary battery. Further, the discharge characteristics were examined in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 2)
A lithium secondary battery was obtained in the same manner as in Example 1 except that 100 parts by weight of raw coke powder was used and 5.0 parts by weight of phosphoric acid ester alone was added. Further, the discharge characteristics were examined in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 3)
A lithium secondary battery was obtained in the same manner as in Example 1 except that 100 parts by weight of raw coke powder was used and 5.0 parts by weight of boron carbide was added in terms of boron. Further, the discharge characteristics were examined in the same manner as in Example 1. The results are shown in Table 1.

(Examples 4 to 6)
In Examples 1 to 3, a lithium secondary battery was obtained by performing the same operations as in Examples 1 to 3 except that the firing temperature (maximum temperature reached) of the coke material was changed from 900 ° C to 1000 ° C. Further, the discharge characteristics were examined in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Examples 4-6)
In Comparative Examples 1 to 3, operations similar to those of Comparative Examples 1 to 3 were performed, respectively, except that the firing temperature (maximum temperature reached) of the coke material was changed from 900 ° C. to 1000 ° C. to obtain lithium secondary batteries. Further, the discharge characteristics were examined in the same manner as in Example 1. The results are shown in Table 1.

(Examples 7 to 9)
In Examples 1 to 3, a lithium secondary battery was obtained by performing the same operations as in Examples 1 to 3 except that the firing temperature (maximum temperature reached) of the coke material was changed from 900 ° C to 1100 ° C. Further, the discharge characteristics were examined in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Examples 7-9)
In Comparative Examples 1 to 3, operations similar to those in Comparative Examples 1 to 3 were performed, respectively, except that the firing temperature (maximum temperature reached) of the coke material was changed from 900 ° C. to 1100 ° C., to obtain lithium secondary batteries. Further, the discharge characteristics were examined in the same manner as in Example 1. The results are shown in Table 1.

(Examples 10 to 12)
In Examples 1 to 3, a lithium secondary battery was obtained by performing the same operations as in Examples 1 to 3 except that the firing temperature (maximum temperature reached) of the coke material was changed from 900 ° C to 1200 ° C. Further, the discharge characteristics were examined in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Examples 10-12)
In Comparative Examples 1 to 3, the same operation as in Comparative Examples 1 to 3 was performed except that the coke material firing temperature (maximum temperature reached) was changed from 900 ° C. to 1200 ° C. to obtain lithium secondary batteries. Further, the discharge characteristics were examined in the same manner as in Example 1. The results are shown in Table 1.

(Examples 13 to 20)
In Example 5, the amount of phosphate ester added and the amount of boron carbide were changed from 2.5 parts by weight in terms of phosphorus and boron to 0.5 parts by weight in terms of phosphorus and 0.5 parts by weight in terms of boron ( Example 13), 0.5 parts by weight in terms of phosphorus, 2.5 parts by weight in terms of boron (Example 14), 0.5 parts by weight in terms of phosphorus, 5.0 parts by weight in terms of boron (Example 15) 2.5 parts by weight in terms of phosphorus, 0.5 parts by weight in terms of boron (Example 16), 2.5 parts by weight in terms of phosphorus, 5.0 parts by weight in terms of boron (Example 17), in terms of phosphorus 5.0 parts by weight, 0.5 parts by weight in terms of boron (Example 18), 5.0 parts by weight in terms of phosphorus, 2.5 parts by weight in terms of boron (Example 19), 5.0 parts by weight in terms of phosphorus Parts, and 5.0 parts by weight in terms of boron (Example 20). To obtain a lithium secondary battery. Further, the discharge characteristics were examined in the same manner as in Example 1. The results are shown in Table 2.

  As apparent from Table 1 and Table 2, in the negative electrode active material for lithium secondary batteries according to Examples, obtained by firing a coke material in which phosphate ester and boron carbide were added to raw coke powder according to the present invention. It can be seen that the performance balance of output characteristics, discharge capacity, initial efficiency and capacity maintenance ratio is good. In particular, by adding the addition amount at a ratio of 0.5 parts by weight to 5.0 parts by weight in terms of phosphorus and boron with respect to 100 parts by weight of raw coke powder, the output characteristic (W) was 10 W or more. The discharge capacity (mAh / g) is 280 (mAh / g) or higher, the initial efficiency (%) is 75 (%) or higher, and the capacity retention rate (%) is 68 (%) or higher. It can be seen that a carbon material for a negative electrode material of a lithium secondary battery (a negative electrode active material for a lithium secondary battery) is obtained.

  In addition, Comparative Examples 1, 4, 7 and 10 are cases in which a coke material composed only of raw coke powder is used, but the capacity retention rate is higher at each firing temperature than in the examples according to the present invention. It can be seen that the characteristics are inferior. In particular, when the firing temperature is 1000 ° C. or less, the discharge capacity (mAh / g) is 280 (mAh / g) or more, but the output characteristic (W) is lower than that of the embodiment according to the present invention. It can be seen that the balance of the characteristics as the carbon material for the negative electrode material of the lithium secondary battery is inferior. When the firing temperature is 1200 ° C., the output characteristic (W) is 10 (W) or more, but the discharge capacity (mAh / g) is less than 280 (mAh / g), and the negative electrode of the lithium secondary battery It turns out that the balance of the characteristic as a carbon material for materials is inferior.

  Further, Comparative Examples 2, 5, 8 and 11 are cases where only a phosphorus compound is added to raw coke powder, but the capacity retention ratio is higher than that of the example according to the present invention at each firing temperature. It turns out that it is inferior. In particular, when the firing temperature is 1100 ° C. or lower, the output characteristic (W) is less than 11 (W), and it can be seen that the balance of the characteristic is inferior compared to the example according to the present invention.

  Further, Comparative Examples 3, 6, 9 and 12 are cases where only a boron compound was added to raw coke powder, but the capacity retention rate was higher than that of the example according to the present invention at each firing temperature. It turns out that it is inferior. In particular, when the firing temperature is 1100 ° C. or lower, the discharge capacity (mAh / g) is 280 (mAh / g) or higher, but the output characteristics (W) are lower than in the embodiment according to the present invention. It can be seen that the balance of the characteristics as the carbon material for the negative electrode material of the lithium secondary battery is inferior.

(Example 21)
A lithium secondary battery was produced in the same manner as in Example 2 except that the binder used in producing the negative electrode foil was changed from polyvinylidene fluoride to a polyimide resin (manufactured by Ube Industries). Further, the discharge characteristics were examined in the same manner as in Example 1. The results are shown in Table 3. For comparison, the results relating to Example 2 are also shown in Table 2.

(Example 22)
A lithium secondary battery was produced in the same manner as in Example 5 except that the binder used for producing the negative electrode foil was changed from polyvinylidene fluoride to a polyimide resin (manufactured by Ube Industries). Further, the discharge characteristics were examined in the same manner as in Example 1. The results are shown in Table 3. For comparison, the results regarding Example 5 are also shown in Table 2.

(Example 23)
A lithium secondary battery was produced in the same manner as in Example 8, except that the binder used in producing the negative electrode foil was changed from polyvinylidene fluoride to polyimide resin (manufactured by Ube Industries). Further, the discharge characteristics were examined in the same manner as in Example 1. The results are shown in Table 3. For comparison, the results regarding Example 8 are also shown in Table 2.

  As is clear from Table 3, DOD (Depth of Discharge) even when the binder used for producing the negative electrode from the negative electrode active material for lithium secondary batteries is changed from polyvinylidene fluoride to polyimide. : 50 is sufficiently small, and the output characteristics are increased. That is, it can be seen that the substantial potential of the negative electrode made of the carbon material for the negative electrode material decreases, and the actual battery voltage of the secondary battery increases, thereby increasing the output characteristics.

  Further, the output characteristic (W) is 11 W or more, the discharge capacity (mAh / g) is 350 (mAh / g) or more, the initial efficiency (%) is 77 (%) or more, and the capacity retention rate (%) It can be seen that a carbon material for a negative electrode material of a lithium secondary battery (a negative electrode active material for a lithium secondary battery) exhibiting good discharge characteristics of 76% or more can be obtained.

  On the other hand, as is apparent from Table 3, when the negative electrode of the lithium secondary battery is made of polyimide, the DOD (depth of discharge: Depth) is lower than that of the case where polyvinylidene fluoride is used as the binder. of Discharge): 50 is decreased, and it can be seen that the output characteristic (W) is improved. It can also be seen that the capacity retention rate (%) is also improved. Note that the cause of the change in the discharge characteristics of the secondary battery due to the change of the binder type in this way has not been clarified at present.

  While the present invention has been described in detail based on the above specific examples, the present invention is not limited to the above specific examples, and various modifications and changes can be made without departing from the scope of the present invention.

Claims (5)

With respect to 100 parts by weight of coal-based and / or petroleum-based (hereinafter referred to as coal-based) raw coke, the phosphorus compound and boron compound are each in a ratio of 0.1 parts by weight to 6.0 parts by weight in terms of phosphorus and boron. A negative active material for a lithium secondary battery, which is obtained by firing the added coke material at a temperature of 800 ° C to 1400 ° C.   The negative active material for a lithium secondary battery according to claim 1, wherein the raw coke is in the form of a pulverized powder.   With respect to 100 parts by weight of the total amount of raw coke, the phosphorous compound is 0.5 to 5.0 parts by weight in terms of phosphorus, and the boron compound is 0.5 to 5.0 parts by weight in terms of boron. The lithium secondary battery negative electrode active material according to claim 1, wherein the negative electrode active material is added at a ratio of A vehicle-mounted lithium secondary battery using the lithium secondary battery negative electrode active material according to any one of claims 1 to 3. The in-vehicle lithium secondary battery according to claim 4, which is used for a hybrid vehicle and an electric vehicle.