WO2012090728A1 - Non-aqueous electrolyte secondary cell - Google Patents
Non-aqueous electrolyte secondary cell Download PDFInfo
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- WO2012090728A1 WO2012090728A1 PCT/JP2011/079163 JP2011079163W WO2012090728A1 WO 2012090728 A1 WO2012090728 A1 WO 2012090728A1 JP 2011079163 W JP2011079163 W JP 2011079163W WO 2012090728 A1 WO2012090728 A1 WO 2012090728A1
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- electrolyte secondary
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- aqueous electrolyte
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- secondary battery
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
- H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Definitions
- the present invention relates to a non-aqueous electrolyte secondary battery using graphite coated with amorphous carbon as a negative electrode active material, and in particular, an initial efficiency which is the initial charge / discharge efficiency after battery assembly and a non-aqueous excellent in low-temperature characteristics.
- the present invention relates to an electrolyte secondary battery.
- non-aqueous electrolyte secondary batteries typified by lithium ion batteries that are lightweight and have high energy density have been widely used as power sources for mobile electronic devices such as mobile phones and notebook computers.
- non-aqueous electrolyte secondary batteries are being used as power sources for electric tools, electric vehicles (EV), and hybrid electric vehicles (HEV), and are required to have stable input / output characteristics even in a low temperature environment. Yes.
- a carbonaceous material is generally used because there is no generation of dendrites due to lithium deposition.
- a non-aqueous electrolyte secondary battery using graphite is a rechargeable battery. It is widely used because of its excellent flatness of potential during discharge, high safety, and high capacity.
- non-aqueous electrolyte secondary batteries that use graphite particles as the negative electrode active material have poor charge acceptance at low temperatures because the reaction sites that store and release lithium ions are limited to the edge surfaces of the graphite particles. Had problems.
- Patent Documents 1 and 2 describe a technique of providing a carbon layer on the surface of graphite particles.
- Patent Document 1 discloses a carbon negative electrode for a secondary battery in which a surface in contact with a carbon electrolyte solution serving as an active material is covered with amorphous carbon. According to the present invention, it is shown that the reduction in charge / discharge efficiency due to the decomposition of the electrolytic solution can be prevented.
- Patent Document 2 discloses a negative electrode material for a lithium ion secondary battery that includes a carbon layer having a lower crystallinity than the carbon particles on the surface of the carbon particles. According to this invention, it is shown that a negative electrode material for a lithium ion secondary battery excellent in charge / discharge efficiency, input / output characteristics, and life characteristics can be obtained.
- the surface of the graphite particles When the surface of the graphite particles is coated with amorphous carbon, the number of reaction points that can occlude and release lithium ions increases, so that the charge acceptability of the graphite particles improves. Since the surface of the highly crystalline graphite particles is highly active, it tends to cause a side reaction with the electrolytic solution. However, by coating with amorphous carbon, side reactions can be suppressed, and a decrease in irreversible capacity associated with the cycle can be suppressed.
- the present invention has been made in view of the above, and an object thereof is to provide a nonaqueous electrolyte secondary battery excellent in initial efficiency and low temperature characteristics.
- the inventors have found that the temperature variation between the graphite particles during firing for forming amorphous carbon on the surface of the graphite particles affects the initial efficiency and low temperature characteristics.
- the present invention has been completed based on such knowledge.
- the present invention provides a non-aqueous electrolyte secondary battery comprising a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous electrolyte having a non-aqueous solvent and an electrolyte salt,
- the substance includes graphite particles, and the graphite particles have at least a part of the surface coated with amorphous carbon, and the CO 2 adsorption amount is 0.24 to 0.36 cc / g. This is a non-aqueous electrolyte secondary battery.
- a method of mixing graphite particles and pitch as an amorphous carbon source and then firing at 800 to 1000 ° C. can be used.
- the amount of CO 2 adsorbed on the graphite particles can be measured using 3 hours of graphite particles dried in vacuum at 250 ° C. for 7 hours and then using an autosorb manufactured by Quantachrome.
- the CO 2 adsorption amount of the graphite particles can be controlled by changing the heat transfer path to the graphite particles in the firing furnace.
- a cubic or rectangular parallelepiped container having an open upper surface is used.
- the heat transfer path to the graphite particles can be changed, and the amount of CO 2 adsorption can be controlled. Is possible.
- the CO 2 adsorption amount of the graphite coated with amorphous graphite is less than 0.24 cc / g, the low temperature characteristics are not sufficient, and if it exceeds 0.36 cc / g, the initial efficiency is lowered. g or more and 0.36 cc / g or less is preferable.
- the CO2 adsorption amount of graphite is 0.30 cc / g or more, excellent low temperature characteristics can be obtained, and therefore, it is more preferably 0.30 cc / g or more and 0.36 cc / g or less.
- the amount of amorphous carbon covering the graphite particles is less than 0.01% by mass, the low temperature characteristics are not sufficient, and if it exceeds 2.0% by mass, the battery capacity decreases. It is preferable that it is 0.0 mass% or less.
- graphite used in the present invention either artificial graphite or natural graphite can be used, or both of them can be mixed and used.
- the positive electrode active material used in the present invention is not particularly limited as long as it is conventionally used as a positive electrode active material for a non-aqueous electrolyte secondary battery.
- a lithium cobalt composite oxide having a layered structure, a lithium nickel composite oxide, a lithium nickel manganese cobalt composite oxide, or a spinel type lithium manganese composite oxide or a mixture thereof may be used as a positive electrode active material. it can.
- non-aqueous solvent used in the non-aqueous electrolyte of the present invention it is preferable to use a non-aqueous solvent containing a cyclic carbonate and a chain carbonate.
- the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, and fluoroethylene carbonate.
- the chain carbonate include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, and methyl butyl carbonate. From the viewpoint of the viscosity of the solvent and the ionic conductivity, it is preferable to use a cyclic carbonate and a chain carbonate in a volume ratio of 5:95 to 40:60.
- electrolyte salt used for the said nonaqueous electrolyte what is generally used for the nonaqueous electrolyte secondary battery can be used. Specifically, LiPF 6 , LiBF 4 , LiAsF 6 , LiClO 4 , LiCF 3 SO 3 , Li (CF 3 SO 2 ) 2 , LiN (CF 3 SO 2 ) 2 , LiN (C 2 F 5 SO 2 ) 2 Etc. In particular, it is preferable that at least one of LiPF 6 or LiBF 4 is an electrolyte salt and the concentration thereof is 0.5 to 2 mol / L.
- the amorphous carbon present on the surface of the graphite particles acts to increase the reaction point of occlusion and release of lithium ions, and can improve the charge acceptability of the graphite particles.
- a non-aqueous electrolyte secondary battery is a graphite particle having at least a part of its surface coated with amorphous carbon and having a CO 2 adsorption amount in the range of 0.24 to 0.36 cc / g.
- Example 1 (Preparation of negative electrode) Graphite (artificial graphite) was used as the negative electrode active material. After mixing pitch with graphite so that the coating amount of amorphous carbon is 1% by mass, the pitch is fired and carbonized at 900 ° C. to form a coating layer made of amorphous carbon on the graphite particle surface. Formed. For firing, the inside of the container into which graphite was put was evenly partitioned with a plate made of carbon. The partitioning method was determined so that the correlation between the area of the portion partitioned by the partition plate and the CO 2 adsorption amount of graphite was obtained in advance, and the CO 2 adsorption amount was 0.32 cc / g.
- the positive electrode active material slurry was applied to both surfaces of a 15 ⁇ m thick aluminum current collector by a doctor blade method, dried, rolled with a roller press, and cut to obtain a positive electrode plate.
- the active material application amount of the negative electrode and the positive electrode was adjusted so that the charge capacity ratio (negative electrode charge capacity / positive electrode charge capacity) at a portion where the positive electrode and the negative electrode face each other was 1.1.
- the negative electrode plate and the positive electrode plate were wound through a separator made of a polyethylene microporous film, and a polypropylene tape was attached to the outermost periphery, and then pressed to obtain a flat spiral electrode body.
- a nonaqueous solvent was prepared by mixing so that the volume ratio (25 ° C.) of ethylene carbonate, propylene carbonate and ethyl methyl carbonate was 1: 1: 8. LiPF 6 as an electrolyte salt was dissolved in this non-aqueous solvent so as to be 1.0 mol / L to obtain a non-aqueous electrolyte.
- Example 2 A nonaqueous electrolyte secondary battery according to Example 2 was fabricated in the same manner as in Example 1 except that the CO 2 adsorption amount of graphite was 0.24 cc / g.
- Example 3 A nonaqueous electrolyte secondary battery according to Example 3 was fabricated in the same manner as in Example 1 except that the CO 2 adsorption amount of graphite was 0.30 cc / g.
- Example 4 A nonaqueous electrolyte secondary battery according to Example 4 was fabricated in the same manner as in Example 1 except that the amount of CO 2 adsorbed on graphite was 0.33 cc / g.
- Example 5 A nonaqueous electrolyte secondary battery according to Example 5 was produced in the same manner as in Example 1 except that the CO 2 adsorption amount of graphite was 0.36 cc / g.
- Comparative Example 1 A nonaqueous electrolyte secondary battery according to Comparative Example 1 was produced in the same manner as in Example 1 except that the CO 2 adsorption amount of graphite was 0.37 cc / g.
- Comparative Example 2 A non-aqueous electrolyte secondary battery according to Comparative Example 2 was fabricated in the same manner as in Example 1 except that the CO 2 adsorption amount of graphite was 0.41 cc / g.
- Comparative Example 4 A nonaqueous electrolyte secondary battery according to Comparative Example 4 was produced in the same manner as in Example 1 except that graphite that did not cover amorphous carbon was used as the negative electrode active material.
- Table 1 summarizes the physical properties, initial efficiency, and low temperature characteristics of the negative electrode active materials obtained by the above-described methods of Examples 1 to 5 and Comparative Examples 1 to 4. Further, FIG. 1 shows a correlation diagram between the CO 2 adsorption amount and the initial efficiency and low temperature characteristics, and FIG. 2 shows a correlation diagram between the BET specific surface area, the initial efficiency and low temperature characteristics.
- Table 1 shows that the amorphous carbon-coated graphite having a CO 2 adsorption amount in the range of 0.24 to 0.36 cc / g exhibits excellent initial efficiency and low temperature characteristics.
- a specific surface area has been used as a physical property value related to the initial efficiency and low temperature characteristics of the negative electrode active material of a nonaqueous electrolyte secondary battery.
- the correlation between the initial efficiency and the specific surface area of the low-temperature characteristics is broken depending on the amount of amorphous coated carbon. This is presumably because the electrochemical activity of the graphite surface changes when the graphite particles are coated with amorphous carbon.
- FIG. 1 shows that the amorphous carbon-coated graphite having a CO 2 adsorption amount in the range of 0.24 to 0.36 cc / g exhibits excellent initial efficiency and low temperature characteristics.
- a specific surface area has been used as a physical property value related to the initial efficiency and low temperature characteristics of the negative electrode active material of a nonaque
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Abstract
[Problem] The purpose of the present invention is to provide a non-aqueous electrolyte secondary cell exerting excellent low-temperature properties without reducing the initial efficiency even when the surface of graphite particles is covered with an amorphous carbon. [Solution] A non-aqueous electrolyte secondary cell provided with: a positive electrode having a positive active material; a negative electrode having a negative active material; and a non-aqueous electrolyte having a non-aqueous solvent and an electrolyte salt. The non-aqueous electrolyte secondary cell is characterized in that at least a portion of the surface of the negative active material is covered with an amorphous carbon and is characterized by containing graphite particles having a CO2 adsorption amount between 0.24 and 0.36cc/g.
Description
本発明は、非晶質炭素で被覆された黒鉛を負極活物質として用いる非水電解質二次電池に関し、特に電池組み立て後の初回の充放電効率である初期効率と、低温特性に優れた非水電解質二次電池に関する。
The present invention relates to a non-aqueous electrolyte secondary battery using graphite coated with amorphous carbon as a negative electrode active material, and in particular, an initial efficiency which is the initial charge / discharge efficiency after battery assembly and a non-aqueous excellent in low-temperature characteristics. The present invention relates to an electrolyte secondary battery.
近年、携帯電話、ノートパソコンといったモバイル電子機器の電源として、軽量で高エネルギー密度を有するリチウムイオン電池に代表される非水電解質二次電池が広く使用されている。さらに、非水電解質二次電池は電動工具や電気自動車（ＥＶ）、ハイブリッド電気自動車（ＨＥＶ）用の電源としても使用されつつあり、低温環境下でも安定した入出力特性を備えることが求められている。
In recent years, non-aqueous electrolyte secondary batteries typified by lithium ion batteries that are lightweight and have high energy density have been widely used as power sources for mobile electronic devices such as mobile phones and notebook computers. Furthermore, non-aqueous electrolyte secondary batteries are being used as power sources for electric tools, electric vehicles (EV), and hybrid electric vehicles (HEV), and are required to have stable input / output characteristics even in a low temperature environment. Yes.
非水電解質二次電池の負極活物質としては、リチウムの析出によるデンドライトの発生がないことから炭素質材料が一般的に使用されており、特に黒鉛を用いた非水電解質二次電池が、充放電時の電位の平坦性に優れており、安全性が高く、高容量であることから広く使用されている。
As a negative electrode active material for a non-aqueous electrolyte secondary battery, a carbonaceous material is generally used because there is no generation of dendrites due to lithium deposition. In particular, a non-aqueous electrolyte secondary battery using graphite is a rechargeable battery. It is widely used because of its excellent flatness of potential during discharge, high safety, and high capacity.
しかし、黒鉛粒子を負極活物質とする非水電解質二次電池は、リチウムイオンの吸蔵、放出を行う反応部位が黒鉛粒子のエッジ面に限定されるため、低温での充電受け入れ性が乏しいとの課題を有していた。
However, non-aqueous electrolyte secondary batteries that use graphite particles as the negative electrode active material have poor charge acceptance at low temperatures because the reaction sites that store and release lithium ions are limited to the edge surfaces of the graphite particles. Had problems.
黒鉛を負極活物質として用いる非水電解質二次電池の電池特性を改善する技術として、特許文献１及び２には、黒鉛粒子表面に炭素層を備える技術が記載されている。
As techniques for improving the battery characteristics of a non-aqueous electrolyte secondary battery using graphite as a negative electrode active material, Patent Documents 1 and 2 describe a technique of providing a carbon layer on the surface of graphite particles.
特許文献１には、活物質となる炭素の電解液と接する表面が非晶質炭素で覆われている二次電池用炭素負極が開示されている。この発明によれば、電解液の分解による充放電効率の低下を防ぐことができることが示されている。
Patent Document 1 discloses a carbon negative electrode for a secondary battery in which a surface in contact with a carbon electrolyte solution serving as an active material is covered with amorphous carbon. According to the present invention, it is shown that the reduction in charge / discharge efficiency due to the decomposition of the electrolytic solution can be prevented.
特許文献２には、炭素粒子の表面に、該炭素粒子よりも結晶性の低い炭素層を備えるリチウムイオン二次電池用負極材が開示されている。この発明によれば、充放電効率、入出力特性及び寿命特性に優れたリチウムイオン二次電池用負極材が得られることが示されている。
Patent Document 2 discloses a negative electrode material for a lithium ion secondary battery that includes a carbon layer having a lower crystallinity than the carbon particles on the surface of the carbon particles. According to this invention, it is shown that a negative electrode material for a lithium ion secondary battery excellent in charge / discharge efficiency, input / output characteristics, and life characteristics can be obtained.
黒鉛粒子の表面が非晶質炭素で被覆されると、リチウムイオンを吸蔵、放出しうる反応点が増加するため、黒鉛粒子の充電受け入れ性が向上する。結晶性の高い黒鉛粒子の表面は活性が高いため、電解液との副反応を起こしやすい。しかし、非晶質炭素で被覆することで、副反応の抑制が可能となり、サイクルに伴う不可逆容量の低下を抑制することができる。
When the surface of the graphite particles is coated with amorphous carbon, the number of reaction points that can occlude and release lithium ions increases, so that the charge acceptability of the graphite particles improves. Since the surface of the highly crystalline graphite particles is highly active, it tends to cause a side reaction with the electrolytic solution. However, by coating with amorphous carbon, side reactions can be suppressed, and a decrease in irreversible capacity associated with the cycle can be suppressed.
ところが、発明者らが確認した結果、黒鉛粒子に非晶質炭素を被覆すると、電池組み立て後の初回充放電時の不可逆容量が増大し、初期効率が低下してしまうとの課題が判明した。特に、黒鉛自体の初期効率の改善が求められるようになり、その課題が顕著なものとなっている。
However, as a result of confirmation by the inventors, it has been found that when graphite particles are coated with amorphous carbon, the irreversible capacity at the first charge / discharge after the battery assembly is increased and the initial efficiency is lowered. In particular, improvement in the initial efficiency of graphite itself has been demanded, and the problem has become remarkable.
本発明は、上記に鑑みなされたものであって、初期効率及び低温特性に優れた非水電解質二次電池を提供することを目的とする。
The present invention has been made in view of the above, and an object thereof is to provide a nonaqueous electrolyte secondary battery excellent in initial efficiency and low temperature characteristics.
発明者らは、黒鉛粒子の表面に非晶質炭素を形成させるための焼成時における黒鉛粒子間の温度バラツキが初期効率や低温特性に影響を与えることを見出した。本発明は、そのような知見に基づいて完成されたものである。
The inventors have found that the temperature variation between the graphite particles during firing for forming amorphous carbon on the surface of the graphite particles affects the initial efficiency and low temperature characteristics. The present invention has been completed based on such knowledge.
即ち、本発明は、正極活物質を有する正極と、負極活物質を有する負極と、非水溶媒と電解質塩を有する非水電解質と、を備える非水電解質二次電池であって、前記負極活物質は、黒鉛粒子を含み、前記黒鉛粒子は、表面の少なくとも一部が非晶質炭素で被覆されており、そのＣＯ２吸着量が０．２４～０．３６ｃｃ／ｇであることを特徴とする非水電解質二次電池である。
That is, the present invention provides a non-aqueous electrolyte secondary battery comprising a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous electrolyte having a non-aqueous solvent and an electrolyte salt, The substance includes graphite particles, and the graphite particles have at least a part of the surface coated with amorphous carbon, and the CO 2 adsorption amount is 0.24 to 0.36 cc / g. This is a non-aqueous electrolyte secondary battery.
黒鉛粒子に非晶質炭素を被覆するには、黒鉛粒子と非晶質炭素源としてのピッチを混合した後、８００～１０００℃で焼成する方法を用いることができる。黒鉛粒子のＣＯ２吸着量は、黒鉛粒子３ｇを真空、２５０℃で７ｈ乾燥させた後、Ｑｕａｎｔａｃｈｒｏｍｅ社製オートソーブを用いて測定することができる。
In order to coat the graphite particles with amorphous carbon, a method of mixing graphite particles and pitch as an amorphous carbon source and then firing at 800 to 1000 ° C. can be used. The amount of CO 2 adsorbed on the graphite particles can be measured using 3 hours of graphite particles dried in vacuum at 250 ° C. for 7 hours and then using an autosorb manufactured by Quantachrome.
黒鉛粒子のＣＯ２吸着量は、焼成炉内での黒鉛粒子への伝熱経路を変化させることで制御することができる。焼成炉へ黒鉛を投入する場合、上面が開放した立方体又は直方体の容器を用いる。このとき、伝熱性を有する板で容器内を小分けに仕切ることで、仕切り板からも黒鉛粒子に熱が伝わるため、黒鉛粒子への伝熱経路を変化させることができ、ＣＯ２吸着量の制御が可能となる。
The CO 2 adsorption amount of the graphite particles can be controlled by changing the heat transfer path to the graphite particles in the firing furnace. When introducing graphite into a firing furnace, a cubic or rectangular parallelepiped container having an open upper surface is used. At this time, since the heat is transferred from the partition plate to the graphite particles by dividing the inside of the container with a plate having heat transfer properties, the heat transfer path to the graphite particles can be changed, and the amount of CO 2 adsorption can be controlled. Is possible.
非晶質黒鉛で被覆された黒鉛のＣＯ２吸着量は、０．２４ｃｃ／ｇ未満だと低温特性が十分でなく、０．３６ｃｃ／ｇを超えると初期効率が低下するため、０．２４ｃｃ／ｇ以上０．３６ｃｃ／ｇ以下であることが好ましい。特に黒鉛のＣＯ２吸着量は０．３０ｃｃ／ｇ以上だと優れた低温特性が得られることから、０．３０ｃｃ／ｇ以上０．３６ｃｃ／ｇ以下であることがより好ましい。
If the CO 2 adsorption amount of the graphite coated with amorphous graphite is less than 0.24 cc / g, the low temperature characteristics are not sufficient, and if it exceeds 0.36 cc / g, the initial efficiency is lowered. g or more and 0.36 cc / g or less is preferable. In particular, when the CO2 adsorption amount of graphite is 0.30 cc / g or more, excellent low temperature characteristics can be obtained, and therefore, it is more preferably 0.30 cc / g or more and 0.36 cc / g or less.
黒鉛粒子を被覆する非晶質炭素量としては、０．０１質量％未満だと低温特性が十分でなく、２．０質量％を超えると電池容量が低下するため、０．０１質量％以上２．０質量％以下であることが好ましい。
If the amount of amorphous carbon covering the graphite particles is less than 0.01% by mass, the low temperature characteristics are not sufficient, and if it exceeds 2.0% by mass, the battery capacity decreases. It is preferable that it is 0.0 mass% or less.
本発明に使用する黒鉛としては、人造黒鉛又は天然黒鉛のいずれも使用することができ、その両者を混合して使用することもできる。
As the graphite used in the present invention, either artificial graphite or natural graphite can be used, or both of them can be mixed and used.
本発明に使用する正極活物質としては、従来から非水電解質二次電池用正極活物質として使用されているものなら、特に限定されない。例えば、層状構造を有するリチウムコバルト複合酸化物、リチウムニッケル複合酸化物、リチウムニッケルマンガンコバルト複合酸化物や、スピネル型リチウムマンガン複合酸化物を１種又はこれらの混合物を正極活物質として使用することができる。
The positive electrode active material used in the present invention is not particularly limited as long as it is conventionally used as a positive electrode active material for a non-aqueous electrolyte secondary battery. For example, a lithium cobalt composite oxide having a layered structure, a lithium nickel composite oxide, a lithium nickel manganese cobalt composite oxide, or a spinel type lithium manganese composite oxide or a mixture thereof may be used as a positive electrode active material. it can.
本発明の非水電解質に用いる非水溶媒としては、環状カーボネート、鎖状カーボネートを含む非水溶媒を使用することが好ましい。環状カーボネートとしては、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、フルオロエチレンカーボネートなどが挙げられ、鎖状カーボネートとしては、ジメチルカーボネート、メチルエチルカーボネート、ジエチルカーボネート、メチルプロピルカーボネート、メチルブチルカーボネートなどが挙げられる。溶媒の粘度、イオン伝導度の観点から、環状カーボネートと鎖状カーボネートを体積比５：９５～４０：６０の範囲で使用することが好ましい。
As the non-aqueous solvent used in the non-aqueous electrolyte of the present invention, it is preferable to use a non-aqueous solvent containing a cyclic carbonate and a chain carbonate. Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, and fluoroethylene carbonate. Examples of the chain carbonate include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, and methyl butyl carbonate. From the viewpoint of the viscosity of the solvent and the ionic conductivity, it is preferable to use a cyclic carbonate and a chain carbonate in a volume ratio of 5:95 to 40:60.
また、前記非水電解質に用いる電解質塩としては、非水電解質二次電池に一般的に使用されているものを使用することができる。具体的には、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＡｓＦ６、ＬｉＣｌＯ４、ＬｉＣＦ３ＳＯ３、Ｌｉ(ＣＦ３ＳＯ２)２、ＬｉＮ(ＣＦ３ＳＯ２)２、ＬｉＮ(Ｃ２Ｆ５ＳＯ２)２などが挙げられる。特にＬｉＰＦ６又はＬｉＢＦ４の少なくとも一方を電解質塩とし、その濃度が０．５～２ｍｏｌ／Ｌであることが好ましい。
Moreover, as electrolyte salt used for the said nonaqueous electrolyte, what is generally used for the nonaqueous electrolyte secondary battery can be used. Specifically, LiPF 6 , LiBF 4 , LiAsF 6 , LiClO 4 , LiCF 3 SO 3 , Li (CF 3 SO 2 ) 2 , LiN (CF 3 SO 2 ) 2 , LiN (C 2 F 5 SO 2 ) 2 Etc. In particular, it is preferable that at least one of LiPF 6 or LiBF 4 is an electrolyte salt and the concentration thereof is 0.5 to 2 mol / L.
黒鉛粒子表面に存在する非晶質炭素は、リチウムイオンの吸蔵、放出の反応点を増加するように作用し、黒鉛粒子の充電受け入れ性を向上させることができる。
The amorphous carbon present on the surface of the graphite particles acts to increase the reaction point of occlusion and release of lithium ions, and can improve the charge acceptability of the graphite particles.
そして、表面の少なくとも一部が非晶質炭素で被覆された黒鉛粒子であって、そのＣＯ２吸着量が０．２４～０．３６ｃｃ／ｇの範囲内にあるものを非水電解質二次電池用負極活物質として用いることで、充電受け入れ性に加えて、初期効率にも優れた非水電解質二次電池を得ることができる。
A non-aqueous electrolyte secondary battery is a graphite particle having at least a part of its surface coated with amorphous carbon and having a CO 2 adsorption amount in the range of 0.24 to 0.36 cc / g. By using as a negative electrode active material, a nonaqueous electrolyte secondary battery excellent in initial efficiency in addition to charge acceptability can be obtained.
以下、本発明を実施するための最良の形態を実施例及び比較例を用いて詳細に説明する。ただし、以下に示す実施例は、本発明の技術思想を具体化するための非水電解質二次電池の製造方法の一例を例示するものであって、本発明をこの実施例に特定することを意図するものではなく、本発明は特許請求の範囲に示した技術思想を逸脱することなく種々の変更を行ったものにも均しく適用し得るものである。
Hereinafter, the best mode for carrying out the present invention will be described in detail using examples and comparative examples. However, the following examples illustrate an example of a manufacturing method of a nonaqueous electrolyte secondary battery for embodying the technical idea of the present invention, and the present invention is specified as this example. The present invention is not intended, and the present invention can be equally applied to various modifications without departing from the technical idea shown in the claims.
（実施例１）
（負極の作製）
負極活物質として黒鉛（人造黒鉛）を使用した。黒鉛に対して、非晶質炭素の被覆量が１質量％となるようにピッチを混合した後、９００℃でピッチを焼成、炭化して、黒鉛粒子表面に非晶質炭素からなる被覆層を形成した。焼成は、黒鉛を投入する容器内を炭素からなる板で均等に仕切りを設けた。仕切り方法は、仕切り板で区画化された部分の面積と黒鉛のＣＯ２吸着量との相関を予め求めておき、ＣＯ２吸着量が０．３２ｃｃ／ｇとなるように決定した。 Example 1
(Preparation of negative electrode)
Graphite (artificial graphite) was used as the negative electrode active material. After mixing pitch with graphite so that the coating amount of amorphous carbon is 1% by mass, the pitch is fired and carbonized at 900 ° C. to form a coating layer made of amorphous carbon on the graphite particle surface. Formed. For firing, the inside of the container into which graphite was put was evenly partitioned with a plate made of carbon. The partitioning method was determined so that the correlation between the area of the portion partitioned by the partition plate and the CO 2 adsorption amount of graphite was obtained in advance, and the CO 2 adsorption amount was 0.32 cc / g.
（負極の作製）
負極活物質として黒鉛（人造黒鉛）を使用した。黒鉛に対して、非晶質炭素の被覆量が１質量％となるようにピッチを混合した後、９００℃でピッチを焼成、炭化して、黒鉛粒子表面に非晶質炭素からなる被覆層を形成した。焼成は、黒鉛を投入する容器内を炭素からなる板で均等に仕切りを設けた。仕切り方法は、仕切り板で区画化された部分の面積と黒鉛のＣＯ２吸着量との相関を予め求めておき、ＣＯ２吸着量が０．３２ｃｃ／ｇとなるように決定した。 Example 1
(Preparation of negative electrode)
Graphite (artificial graphite) was used as the negative electrode active material. After mixing pitch with graphite so that the coating amount of amorphous carbon is 1% by mass, the pitch is fired and carbonized at 900 ° C. to form a coating layer made of amorphous carbon on the graphite particle surface. Formed. For firing, the inside of the container into which graphite was put was evenly partitioned with a plate made of carbon. The partitioning method was determined so that the correlation between the area of the portion partitioned by the partition plate and the CO 2 adsorption amount of graphite was obtained in advance, and the CO 2 adsorption amount was 0.32 cc / g.
上述の非晶質炭素で被覆された黒鉛９８質量部と、増粘剤としてのカルボキシメチルセルロース１質量部と、結着剤としてのスチレンブタジエンゴム１質量部とを、分散媒としての水と混合して負極活物質スラリーとした。この負極活物質スラリーを厚さ１０μｍの銅製集電体の両面にドクターブレード法で塗布し、乾燥させた後、ローラープレス機により圧延し、切断して負極極板を得た。
98 parts by mass of graphite coated with the above amorphous carbon, 1 part by mass of carboxymethyl cellulose as a thickener, and 1 part by mass of styrene butadiene rubber as a binder are mixed with water as a dispersion medium. Thus, a negative electrode active material slurry was obtained. This negative electrode active material slurry was applied to both surfaces of a 10 μm thick copper current collector by the doctor blade method, dried, rolled with a roller press, and cut to obtain a negative electrode plate.
（正極の作製）
正極活物質としてのコバルト酸リチウム９０質量部と、導電剤としての黒鉛粉末５質量部と、結着剤としてのポリフッ化ビニリデン５質量部とを、分散媒としてのＮ－メチルピロリドンと混合して正極活物質スラリーとした。 (Preparation of positive electrode)
90 parts by mass of lithium cobaltate as a positive electrode active material, 5 parts by mass of graphite powder as a conductive agent, and 5 parts by mass of polyvinylidene fluoride as a binder are mixed with N-methylpyrrolidone as a dispersion medium. A positive electrode active material slurry was obtained.
正極活物質としてのコバルト酸リチウム９０質量部と、導電剤としての黒鉛粉末５質量部と、結着剤としてのポリフッ化ビニリデン５質量部とを、分散媒としてのＮ－メチルピロリドンと混合して正極活物質スラリーとした。 (Preparation of positive electrode)
90 parts by mass of lithium cobaltate as a positive electrode active material, 5 parts by mass of graphite powder as a conductive agent, and 5 parts by mass of polyvinylidene fluoride as a binder are mixed with N-methylpyrrolidone as a dispersion medium. A positive electrode active material slurry was obtained.
この正極活物質スラリーを厚さ１５μｍのアルミニウム製集電体の両面にドクターブレード法で塗布し、乾燥させた後、ローラープレス機により圧延し、切断して正極極板を得た。
The positive electrode active material slurry was applied to both surfaces of a 15 μm thick aluminum current collector by a doctor blade method, dried, rolled with a roller press, and cut to obtain a positive electrode plate.
なお、負極及び正極の活物質塗布量は、正極と負極が対向する部分での充電容量比（負極充電容量÷正極充電容量）が１．１となるように調整した。
In addition, the active material application amount of the negative electrode and the positive electrode was adjusted so that the charge capacity ratio (negative electrode charge capacity / positive electrode charge capacity) at a portion where the positive electrode and the negative electrode face each other was 1.1.
（電極体の作製）
上記負極極板及び正極極板をポリエチレン製微多孔膜からなるセパレータを介して巻回し、最外周にポリプロピレン製のテープを貼り付け、この後、プレスして、扁平渦巻電極体とした。 (Production of electrode body)
The negative electrode plate and the positive electrode plate were wound through a separator made of a polyethylene microporous film, and a polypropylene tape was attached to the outermost periphery, and then pressed to obtain a flat spiral electrode body.
上記負極極板及び正極極板をポリエチレン製微多孔膜からなるセパレータを介して巻回し、最外周にポリプロピレン製のテープを貼り付け、この後、プレスして、扁平渦巻電極体とした。 (Production of electrode body)
The negative electrode plate and the positive electrode plate were wound through a separator made of a polyethylene microporous film, and a polypropylene tape was attached to the outermost periphery, and then pressed to obtain a flat spiral electrode body.
（非水電解質の調製）
エチレンカーボネート、プロピレンカーボネート及びエチルメチルカーボネートの体積比（２５℃）が１：１：８となるように混合して、非水溶媒を調製した。この非水溶媒に電解質塩としてのＬｉＰＦ６を１．０ｍｏｌ／Ｌとなるように溶解させ、非水電解質とした。 (Preparation of non-aqueous electrolyte)
A nonaqueous solvent was prepared by mixing so that the volume ratio (25 ° C.) of ethylene carbonate, propylene carbonate and ethyl methyl carbonate was 1: 1: 8. LiPF 6 as an electrolyte salt was dissolved in this non-aqueous solvent so as to be 1.0 mol / L to obtain a non-aqueous electrolyte.
エチレンカーボネート、プロピレンカーボネート及びエチルメチルカーボネートの体積比（２５℃）が１：１：８となるように混合して、非水溶媒を調製した。この非水溶媒に電解質塩としてのＬｉＰＦ６を１．０ｍｏｌ／Ｌとなるように溶解させ、非水電解質とした。 (Preparation of non-aqueous electrolyte)
A nonaqueous solvent was prepared by mixing so that the volume ratio (25 ° C.) of ethylene carbonate, propylene carbonate and ethyl methyl carbonate was 1: 1: 8. LiPF 6 as an electrolyte salt was dissolved in this non-aqueous solvent so as to be 1.0 mol / L to obtain a non-aqueous electrolyte.
（電池の作製）
上記扁平渦巻電極体を、角形外装缶に挿入した後、注液孔を備える封口体により外装缶の開口部を封止し、注液孔を通じて上記の非水電解質を注液した。その後、注液孔を封止して、実施例１に係る厚み４．６ｍｍ×幅３４ｍｍ×高さ４３ｍｍの非水電解質二次電池を作製した。得られた非水電解質二次電池の設計容量は８００ｍＡｈである。 (Production of battery)
After the flat spiral electrode body was inserted into a rectangular outer can, the opening of the outer can was sealed with a sealing body having a liquid injection hole, and the nonaqueous electrolyte was injected through the liquid injection hole. Thereafter, the liquid injection hole was sealed, and a nonaqueous electrolyte secondary battery having a thickness of 4.6 mm, a width of 34 mm, and a height of 43 mm according to Example 1 was produced. The design capacity of the obtained nonaqueous electrolyte secondary battery is 800 mAh.
上記扁平渦巻電極体を、角形外装缶に挿入した後、注液孔を備える封口体により外装缶の開口部を封止し、注液孔を通じて上記の非水電解質を注液した。その後、注液孔を封止して、実施例１に係る厚み４．６ｍｍ×幅３４ｍｍ×高さ４３ｍｍの非水電解質二次電池を作製した。得られた非水電解質二次電池の設計容量は８００ｍＡｈである。 (Production of battery)
After the flat spiral electrode body was inserted into a rectangular outer can, the opening of the outer can was sealed with a sealing body having a liquid injection hole, and the nonaqueous electrolyte was injected through the liquid injection hole. Thereafter, the liquid injection hole was sealed, and a nonaqueous electrolyte secondary battery having a thickness of 4.6 mm, a width of 34 mm, and a height of 43 mm according to Example 1 was produced. The design capacity of the obtained nonaqueous electrolyte secondary battery is 800 mAh.
（実施例２）
黒鉛のＣＯ２吸着量を０．２４ｃｃ／ｇとしたこと以外は実施例１と同様にして、実施例２にかかる非水電解質二次電池を作製した。 (Example 2)
A nonaqueous electrolyte secondary battery according to Example 2 was fabricated in the same manner as in Example 1 except that the CO 2 adsorption amount of graphite was 0.24 cc / g.
黒鉛のＣＯ２吸着量を０．２４ｃｃ／ｇとしたこと以外は実施例１と同様にして、実施例２にかかる非水電解質二次電池を作製した。 (Example 2)
A nonaqueous electrolyte secondary battery according to Example 2 was fabricated in the same manner as in Example 1 except that the CO 2 adsorption amount of graphite was 0.24 cc / g.
（実施例３）
黒鉛のＣＯ２吸着量を０．３０ｃｃ／ｇとしたこと以外は実施例１と同様にして、実施例３にかかる非水電解質二次電池を作製した。 (Example 3)
A nonaqueous electrolyte secondary battery according to Example 3 was fabricated in the same manner as in Example 1 except that the CO 2 adsorption amount of graphite was 0.30 cc / g.
黒鉛のＣＯ２吸着量を０．３０ｃｃ／ｇとしたこと以外は実施例１と同様にして、実施例３にかかる非水電解質二次電池を作製した。 (Example 3)
A nonaqueous electrolyte secondary battery according to Example 3 was fabricated in the same manner as in Example 1 except that the CO 2 adsorption amount of graphite was 0.30 cc / g.
（実施例４）
黒鉛のＣＯ２吸着量を０．３３ｃｃ／ｇとしたこと以外は実施例１と同様にして、実施例４にかかる非水電解質二次電池を作製した。 Example 4
A nonaqueous electrolyte secondary battery according to Example 4 was fabricated in the same manner as in Example 1 except that the amount of CO 2 adsorbed on graphite was 0.33 cc / g.
黒鉛のＣＯ２吸着量を０．３３ｃｃ／ｇとしたこと以外は実施例１と同様にして、実施例４にかかる非水電解質二次電池を作製した。 Example 4
A nonaqueous electrolyte secondary battery according to Example 4 was fabricated in the same manner as in Example 1 except that the amount of CO 2 adsorbed on graphite was 0.33 cc / g.
（実施例５）
黒鉛のＣＯ２吸着量を０．３６ｃｃ／ｇとしたこと以外は実施例１と同様にして、実施例５にかかる非水電解質二次電池を作製した。 (Example 5)
A nonaqueous electrolyte secondary battery according to Example 5 was produced in the same manner as in Example 1 except that the CO 2 adsorption amount of graphite was 0.36 cc / g.
黒鉛のＣＯ２吸着量を０．３６ｃｃ／ｇとしたこと以外は実施例１と同様にして、実施例５にかかる非水電解質二次電池を作製した。 (Example 5)
A nonaqueous electrolyte secondary battery according to Example 5 was produced in the same manner as in Example 1 except that the CO 2 adsorption amount of graphite was 0.36 cc / g.
（比較例１）
黒鉛のＣＯ２吸着量を０．３７ｃｃ／ｇとしたこと以外は実施例１と同様にして、比較例１にかかる非水電解質二次電池を作製した。 (Comparative Example 1)
A nonaqueous electrolyte secondary battery according to Comparative Example 1 was produced in the same manner as in Example 1 except that the CO 2 adsorption amount of graphite was 0.37 cc / g.
黒鉛のＣＯ２吸着量を０．３７ｃｃ／ｇとしたこと以外は実施例１と同様にして、比較例１にかかる非水電解質二次電池を作製した。 (Comparative Example 1)
A nonaqueous electrolyte secondary battery according to Comparative Example 1 was produced in the same manner as in Example 1 except that the CO 2 adsorption amount of graphite was 0.37 cc / g.
（比較例２）
黒鉛のＣＯ２吸着量を０．４１ｃｃ／ｇとしたこと以外は実施例１と同様にして、比較例２にかかる非水電解質二次電池を作製した。 (Comparative Example 2)
A non-aqueous electrolyte secondary battery according to Comparative Example 2 was fabricated in the same manner as in Example 1 except that the CO 2 adsorption amount of graphite was 0.41 cc / g.
黒鉛のＣＯ２吸着量を０．４１ｃｃ／ｇとしたこと以外は実施例１と同様にして、比較例２にかかる非水電解質二次電池を作製した。 (Comparative Example 2)
A non-aqueous electrolyte secondary battery according to Comparative Example 2 was fabricated in the same manner as in Example 1 except that the CO 2 adsorption amount of graphite was 0.41 cc / g.
（比較例３）
黒鉛の非晶質炭素の被覆量を０．２５質量部とし、ＣＯ２吸着量を０．２２ｃｃ／ｇとしたこと以外は実施例１と同様にして、比較例３にかかる非水電解質二次電池を作製した。 (Comparative Example 3)
Nonaqueous electrolyte secondary according to Comparative Example 3 in the same manner as in Example 1 except that the amount of graphite covered with amorphous carbon was 0.25 parts by mass and the CO 2 adsorption amount was 0.22 cc / g. A battery was produced.
黒鉛の非晶質炭素の被覆量を０．２５質量部とし、ＣＯ２吸着量を０．２２ｃｃ／ｇとしたこと以外は実施例１と同様にして、比較例３にかかる非水電解質二次電池を作製した。 (Comparative Example 3)
Nonaqueous electrolyte secondary according to Comparative Example 3 in the same manner as in Example 1 except that the amount of graphite covered with amorphous carbon was 0.25 parts by mass and the CO 2 adsorption amount was 0.22 cc / g. A battery was produced.
（比較例４）
負極活物質として、非晶質炭素を被覆しない黒鉛を用いたこと以外は実施例１と同様にして、比較例４にかかる非水電解質二次電池を作製した。 (Comparative Example 4)
A nonaqueous electrolyte secondary battery according to Comparative Example 4 was produced in the same manner as in Example 1 except that graphite that did not cover amorphous carbon was used as the negative electrode active material.
負極活物質として、非晶質炭素を被覆しない黒鉛を用いたこと以外は実施例１と同様にして、比較例４にかかる非水電解質二次電池を作製した。 (Comparative Example 4)
A nonaqueous electrolyte secondary battery according to Comparative Example 4 was produced in the same manner as in Example 1 except that graphite that did not cover amorphous carbon was used as the negative electrode active material.
（物性値評価）
実施例１～５及び比較例１～３に係る非晶質炭素被覆黒鉛と、比較例４にかかる黒鉛のＣＯ２吸着量と比表面積を測定した。ＣＯ２吸着量は、Ｑｕａｎｔａｃｈｒｏｍｅ社製オートソーブを使用し、黒鉛３ｇを２５０℃、７ｈの真空乾燥の後、ＣＯ２吸着量を測定した。比表面積は、ＢＥＴ法により測定した。 (Property value evaluation)
The amount of CO 2 adsorbed and the specific surface area of the amorphous carbon-coated graphite according to Examples 1 to 5 and Comparative Examples 1 to 3 and the graphite according to Comparative Example 4 were measured. The amount of CO 2 adsorption was measured using an autosorb manufactured by Quantachrome, and 3 g of graphite was vacuum-dried at 250 ° C. for 7 hours, and then the amount of CO 2 adsorption was measured. The specific surface area was measured by the BET method.
実施例１～５及び比較例１～３に係る非晶質炭素被覆黒鉛と、比較例４にかかる黒鉛のＣＯ２吸着量と比表面積を測定した。ＣＯ２吸着量は、Ｑｕａｎｔａｃｈｒｏｍｅ社製オートソーブを使用し、黒鉛３ｇを２５０℃、７ｈの真空乾燥の後、ＣＯ２吸着量を測定した。比表面積は、ＢＥＴ法により測定した。 (Property value evaluation)
The amount of CO 2 adsorbed and the specific surface area of the amorphous carbon-coated graphite according to Examples 1 to 5 and Comparative Examples 1 to 3 and the graphite according to Comparative Example 4 were measured. The amount of CO 2 adsorption was measured using an autosorb manufactured by Quantachrome, and 3 g of graphite was vacuum-dried at 250 ° C. for 7 hours, and then the amount of CO 2 adsorption was measured. The specific surface area was measured by the BET method.
（初期効率測定）
実施例１～５及び比較例１～４の各電池について、２５℃で、０．２Ｉｔ（１６０ｍＡ）の定電流で充電し、電圧が４．２Ｖに達した後は、４．２Ｖの定電圧で電流が０．０２Ｉｔ（１６ｍＡ）になるまで充電した。その後、０．２Ｉｔ（１６０ｍＡ）の定電流で電圧が２．７５Ｖになるまで放電した。このとき測定した充電容量及び放電容量から以下の式に従い、初期効率を算出した。
初期効率（％）＝放電容量÷充電容量×１００ (Initial efficiency measurement)
The batteries of Examples 1 to 5 and Comparative Examples 1 to 4 were charged at 25 ° C. with a constant current of 0.2 It (160 mA), and after the voltage reached 4.2 V, the voltage was 4.2 V. The battery was charged until the current reached 0.02 It (16 mA). Thereafter, the battery was discharged at a constant current of 0.2 It (160 mA) until the voltage reached 2.75V. The initial efficiency was calculated according to the following formula from the measured charge capacity and discharge capacity.
Initial efficiency (%) = discharge capacity / charge capacity x 100
実施例１～５及び比較例１～４の各電池について、２５℃で、０．２Ｉｔ（１６０ｍＡ）の定電流で充電し、電圧が４．２Ｖに達した後は、４．２Ｖの定電圧で電流が０．０２Ｉｔ（１６ｍＡ）になるまで充電した。その後、０．２Ｉｔ（１６０ｍＡ）の定電流で電圧が２．７５Ｖになるまで放電した。このとき測定した充電容量及び放電容量から以下の式に従い、初期効率を算出した。
初期効率（％）＝放電容量÷充電容量×１００ (Initial efficiency measurement)
The batteries of Examples 1 to 5 and Comparative Examples 1 to 4 were charged at 25 ° C. with a constant current of 0.2 It (160 mA), and after the voltage reached 4.2 V, the voltage was 4.2 V. The battery was charged until the current reached 0.02 It (16 mA). Thereafter, the battery was discharged at a constant current of 0.2 It (160 mA) until the voltage reached 2.75V. The initial efficiency was calculated according to the following formula from the measured charge capacity and discharge capacity.
Initial efficiency (%) = discharge capacity / charge capacity x 100
（低温特性測定）
初期効率を測定した実施例１～５及び比較例１～４の各電池について、０℃で、０．２Ｉｔ(１６０ｍＡ)の定電流で充電し、電圧が４．２Ｖに達した後は、４．２Ｖの定電圧で電流が０．０２Ｉｔ（１６ｍＡ）になるまで充電した。その後、０．２Ｉｔ（１６０ｍＡ）の定電流で電圧２．７５Ｖになるまで放電した。このとき、電圧が４．２Ｖになるまで定電流で充電した容量を求め、「定電流充電容量（０℃）」とした。さらに、放電後の電池を室温（２５℃）で、０．２Ｉｔ（１６０ｍＡ）の定電流で充電し、電圧が４．２Ｖに達した後は、４．２Ｖの定電圧で電流が０．０２Ｉｔ（１６ｍＡ）になるまで充電した。このとき測定した充電終止に至までの充電容量を「充電容量（２５℃）」とし、以下の式に従い、低温特性を算出した。
低温特性（％）＝定電流充電容量（０℃）÷充電容量（２５℃）×１００ (Low temperature characteristic measurement)
The batteries of Examples 1 to 5 and Comparative Examples 1 to 4 whose initial efficiencies were measured were charged at 0 ° C. with a constant current of 0.2 It (160 mA), and after the voltage reached 4.2 V, thebatteries 4 The battery was charged at a constant voltage of 0.2 V until the current reached 0.02 It (16 mA). Thereafter, the battery was discharged at a constant current of 0.2 It (160 mA) until the voltage reached 2.75V. At this time, the capacity charged with a constant current until the voltage reached 4.2 V was obtained, and was defined as “constant current charging capacity (0 ° C.)”. Further, the discharged battery was charged at a constant current of 0.2 It (160 mA) at room temperature (25 ° C.), and after the voltage reached 4.2 V, the current was 0.02 It at a constant voltage of 4.2 V. The battery was charged until it reached (16 mA). The charge capacity up to the end of charge measured at this time was defined as “charge capacity (25 ° C.)”, and the low temperature characteristics were calculated according to the following formula.
Low temperature characteristics (%) = constant current charge capacity (0 ° C) ÷ charge capacity (25 ° C) x 100
初期効率を測定した実施例１～５及び比較例１～４の各電池について、０℃で、０．２Ｉｔ(１６０ｍＡ)の定電流で充電し、電圧が４．２Ｖに達した後は、４．２Ｖの定電圧で電流が０．０２Ｉｔ（１６ｍＡ）になるまで充電した。その後、０．２Ｉｔ（１６０ｍＡ）の定電流で電圧２．７５Ｖになるまで放電した。このとき、電圧が４．２Ｖになるまで定電流で充電した容量を求め、「定電流充電容量（０℃）」とした。さらに、放電後の電池を室温（２５℃）で、０．２Ｉｔ（１６０ｍＡ）の定電流で充電し、電圧が４．２Ｖに達した後は、４．２Ｖの定電圧で電流が０．０２Ｉｔ（１６ｍＡ）になるまで充電した。このとき測定した充電終止に至までの充電容量を「充電容量（２５℃）」とし、以下の式に従い、低温特性を算出した。
低温特性（％）＝定電流充電容量（０℃）÷充電容量（２５℃）×１００ (Low temperature characteristic measurement)
The batteries of Examples 1 to 5 and Comparative Examples 1 to 4 whose initial efficiencies were measured were charged at 0 ° C. with a constant current of 0.2 It (160 mA), and after the voltage reached 4.2 V, the
Low temperature characteristics (%) = constant current charge capacity (0 ° C) ÷ charge capacity (25 ° C) x 100
実施例１～５及び比較例１～４の上記の方法で得られた負極活物質の物性値、初期効率及び低温特性を表１にまとめた。また、ＣＯ２吸着量と初期効率及び低温特性との相関図を図１に、ＢＥＴ比表面積と初期効率及び低温特性との相関図を図２に示した。
Table 1 summarizes the physical properties, initial efficiency, and low temperature characteristics of the negative electrode active materials obtained by the above-described methods of Examples 1 to 5 and Comparative Examples 1 to 4. Further, FIG. 1 shows a correlation diagram between the CO 2 adsorption amount and the initial efficiency and low temperature characteristics, and FIG. 2 shows a correlation diagram between the BET specific surface area, the initial efficiency and low temperature characteristics.
表１から、ＣＯ２吸着量が０．２４～０．３６ｃｃ／ｇの範囲にある非晶質炭素被覆黒鉛は、初期効率及び低温特性ともに優れた特性を示すことがわかる。従来、非水電解質二次電池の負極活物質の初期効率や低温特性に関連する物性値として、比表面積が用いられていた。しかし、図２からわかるように、非晶質被覆炭素の多寡や有無により、初期効率や低温特性の比表面積との相関は崩れている。これは、黒鉛粒子に非晶質炭素被覆等を行うと、黒鉛表面の電気化学的な活性が変化してしまっているためと推察される。一方、図１によれば、初期効率及び低温特性とも、ＣＯ２吸着量に対して、高い相関を示していることがわかる。そのため、非晶質炭素を被覆した黒鉛については、その被覆量に関わらず、ＣＯ２吸着量を指標とすることで、初期効率と低温特性に優れた非水電解質二次電池を得ることができる。
Table 1 shows that the amorphous carbon-coated graphite having a CO 2 adsorption amount in the range of 0.24 to 0.36 cc / g exhibits excellent initial efficiency and low temperature characteristics. Conventionally, a specific surface area has been used as a physical property value related to the initial efficiency and low temperature characteristics of the negative electrode active material of a nonaqueous electrolyte secondary battery. However, as can be seen from FIG. 2, the correlation between the initial efficiency and the specific surface area of the low-temperature characteristics is broken depending on the amount of amorphous coated carbon. This is presumably because the electrochemical activity of the graphite surface changes when the graphite particles are coated with amorphous carbon. On the other hand, according to FIG. 1, it can be seen that both the initial efficiency and the low temperature characteristic show a high correlation with the CO 2 adsorption amount. Therefore, for graphite coated with amorphous carbon, a non-aqueous electrolyte secondary battery excellent in initial efficiency and low-temperature characteristics can be obtained by using the CO 2 adsorption amount as an index regardless of the coating amount. .
Claims (2)
- 正極活物質を有する正極と、負極活物質を有する負極と、非水溶媒と電解質塩を有する非水電解質と、を備える非水電解質二次電池であって、
前記負極活物質は黒鉛粒子を含み、前記黒鉛粒子は表面の少なくとも一部が非晶質炭素で被覆されており、当該黒鉛粒子のＣＯ２吸着量が０．２４～０．３６ｃｃ／ｇであることを特徴とする非水電解質二次電池。 A nonaqueous electrolyte secondary battery comprising a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a nonaqueous electrolyte having a nonaqueous solvent and an electrolyte salt,
The negative electrode active material includes graphite particles, and the graphite particles are at least partially covered with amorphous carbon, and the graphite particles have a CO 2 adsorption amount of 0.24 to 0.36 cc / g. A non-aqueous electrolyte secondary battery. - 前記非晶質炭素の被覆量が、前記黒鉛粒子に対して０．０１～２．０質量％である請求項１記載の非水電解質二次電池。 The non-aqueous electrolyte secondary battery according to claim 1, wherein a coating amount of the amorphous carbon is 0.01 to 2.0 mass% with respect to the graphite particles.
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