JP5079219B2 - Graphite material for negative electrode of non-aqueous electrolyte secondary battery - Google Patents
Graphite material for negative electrode of non-aqueous electrolyte secondary battery Download PDFInfo
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- JP5079219B2 JP5079219B2 JP2005131603A JP2005131603A JP5079219B2 JP 5079219 B2 JP5079219 B2 JP 5079219B2 JP 2005131603 A JP2005131603 A JP 2005131603A JP 2005131603 A JP2005131603 A JP 2005131603A JP 5079219 B2 JP5079219 B2 JP 5079219B2
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- negative electrode
- secondary battery
- electrolyte secondary
- graphite
- graphite material
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- 239000007770 graphite material Substances 0.000 title claims description 47
- 239000011255 nonaqueous electrolyte Substances 0.000 title claims description 37
- 239000002245 particle Substances 0.000 claims description 85
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 59
- 229910002804 graphite Inorganic materials 0.000 claims description 46
- 239000010439 graphite Substances 0.000 claims description 46
- 229920000049 Carbon (fiber) Polymers 0.000 claims description 15
- 239000004917 carbon fiber Substances 0.000 claims description 15
- 239000002134 carbon nanofiber Substances 0.000 claims description 12
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 12
- 229910052799 carbon Inorganic materials 0.000 claims description 11
- 239000003575 carbonaceous material Substances 0.000 claims description 11
- 239000011230 binding agent Substances 0.000 claims description 10
- 239000000835 fiber Substances 0.000 claims description 7
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 7
- 239000012153 distilled water Substances 0.000 claims description 6
- 239000003792 electrolyte Substances 0.000 claims description 6
- 239000012298 atmosphere Substances 0.000 claims description 5
- 238000010438 heat treatment Methods 0.000 claims description 5
- 238000002441 X-ray diffraction Methods 0.000 claims description 4
- 239000002003 electrode paste Substances 0.000 claims description 4
- 238000007561 laser diffraction method Methods 0.000 claims description 3
- 230000001590 oxidative effect Effects 0.000 claims description 3
- 239000000470 constituent Substances 0.000 claims description 2
- 239000007864 aqueous solution Substances 0.000 claims 1
- 238000000034 method Methods 0.000 description 14
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 12
- 229910052744 lithium Inorganic materials 0.000 description 12
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 11
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- -1 lithium aluminum hydride Chemical compound 0.000 description 8
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- 229910052759 nickel Inorganic materials 0.000 description 7
- 229910052723 transition metal Inorganic materials 0.000 description 7
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- WYURNTSHIVDZCO-UHFFFAOYSA-N Tetrahydrofuran Chemical compound C1CCOC1 WYURNTSHIVDZCO-UHFFFAOYSA-N 0.000 description 6
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- 229910052748 manganese Inorganic materials 0.000 description 6
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- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 5
- 150000001875 compounds Chemical class 0.000 description 5
- 229910001416 lithium ion Inorganic materials 0.000 description 5
- 239000007774 positive electrode material Substances 0.000 description 5
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- 150000003624 transition metals Chemical class 0.000 description 5
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Classifications
-
- 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
Description
本発明は、充放電サイクル特性、大電流負荷特性に優れた非水電解質二次電池用の電極材料、それを用いた電極及び非水電解質二次電池に関する。 The present invention relates to an electrode material for a nonaqueous electrolyte secondary battery excellent in charge / discharge cycle characteristics and large current load characteristics, an electrode using the same, and a nonaqueous electrolyte secondary battery.
携帯機器の小型軽量化及び高性能化に伴い、高いエネルギー密度を有するリチウムイオン二次電池、すなわちリチウムイオン二次電池の高容量化が益々求められている。一方、リチウムイオン二次電池の低価格化も要求されており、低コスト高性能の負極用炭素材料の開発は急務となっている。 As portable devices become smaller and lighter and have higher performance, there is an increasing demand for higher capacity lithium ion secondary batteries having high energy density, that is, lithium ion secondary batteries. On the other hand, there is a demand for lower prices of lithium ion secondary batteries, and the development of low-cost and high-performance carbon materials for negative electrodes is an urgent task.
しかしながら、安価な天然黒鉛などはリン片状になりやすく、ペースト化して電極に塗布した場合、一方向に配向してしまう。従って、充電時に一方向に膨張してしまい、使用することが難しい。また、これを球状化する方法もあるが、電極作成時にプレスをかけると結局つぶれて配向してしまう。さらに表面がアクティブで初回充電時のガス発生が多く、初期効率が低い。さらに、サイクル特性もよくない。
メソカーボン小球体を黒鉛化した負極材は、容量こそ天然黒鉛に劣るが、配向性、初期効率、サイクル特性ともに抜群であり、広く使用されている。しかし、製造プロセスが複雑で低価格にすることが非常に難しい。
石油コークス、石炭コークス等から製造される代表的な人造黒鉛は比較的安価で強度も高く、つぶれにくいが、結晶性のよい針状コークスはリン片状になり配向してしまう。また、非針状コークスは形状が球形に近い粒子を得やすいが、放電容量が若干低めで初期効率も良くないものが多い。
However, inexpensive natural graphite or the like tends to be in the form of flakes, and when it is pasted and applied to an electrode, it is oriented in one direction. Therefore, it expands in one direction during charging and is difficult to use. There is also a method of spheroidizing this, but if it is pressed at the time of electrode preparation, it will eventually be crushed and oriented. In addition, the surface is active, gas is generated much during the first charge, and the initial efficiency is low. Furthermore, the cycle characteristics are not good.
A negative electrode material obtained by graphitizing mesocarbon spherules is inferior to natural graphite in capacity, but has excellent orientation, initial efficiency, and cycle characteristics, and is widely used. However, the manufacturing process is complicated and it is very difficult to reduce the price.
Typical artificial graphite produced from petroleum coke, coal coke, and the like is relatively inexpensive, high in strength, and is not easily crushed, but acicular coke with good crystallinity becomes flake shaped and oriented. Non-acicular coke tends to obtain particles having a nearly spherical shape, but many discharge capacities are slightly lower and initial efficiency is not good.
初期効率を向上させようとする試みは、数多く試みられている。
たとえば、文献１には、水酸基、アルデヒド基、カルボキシル基、キノン基等がリチウムと反応を起こして安定な化合物になると仮定して、二次電池に炭素材を組み込む前にあらかじめエーテル系、あるいはテトラヒドロフラン系有機溶媒中で水素化リチウムアルミニウム（LiAlH4）により還元処理して、アルキル化を行うことを提案している。また、文献２では、シランカップリング剤処理を行い、表面官能基を電気化学的に不活性な末端基に置換してしまうことが提案されている。しかしながら、これらの方法は、工程の増加が不可欠なことから、コスト的に大きな問題が発生し、実現するには現実的でない。
また、文献３では、適当なピッチコークスをバインダーと混練し、アチソン炉処理後、表面のｐＨを５〜６の弱酸性に調整することを提案しているが、結局含酸素官能基の影響で望ましい初期効率を得られていない。
For example, in Reference 1, it is assumed that a hydroxyl group, an aldehyde group, a carboxyl group, a quinone group, and the like react with lithium to become a stable compound, and an ether-based or tetrahydrofuran solution is incorporated in advance before incorporating a carbon material into a secondary battery. It has been proposed to perform alkylation by reducing with lithium aluminum hydride (LiAlH4) in organic solvents. Further, Document 2 proposes that a silane coupling agent treatment is performed to replace a surface functional group with an electrochemically inactive end group. However, these methods require an increase in the number of steps, so that a large problem arises in cost and is not practical to realize.
Reference 3 proposes kneading an appropriate pitch coke with a binder and adjusting the pH of the surface to a weak acidity of 5 to 6 after the treatment with the Atchison furnace. The desired initial efficiency is not obtained.
本発明は、従来よりも非常に高い初回充放電時の初期効率を有し、放電容量も高く、さらに、球状に近いリチウムイオン二次電池等の非水電解液二次電池負極用黒鉛材料を安価に提供することを目的とする。 The present invention provides a graphite material for a negative electrode of a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery having a very high initial efficiency at the time of first charge / discharge, a high discharge capacity, and a nearly spherical shape. The purpose is to provide it at low cost.
本発明者らは、上記課題を解決するために鋭意検討を重ねた結果、熱膨張係数を規定した特定の原料を粉砕後、一定条件の熱処理により黒鉛化し、その生成粒子を蒸留水中で懸濁させた際のｐＨを一定範囲に制御することにより、安価かつ容易に球状に近い粒子形状を得、かつ容量が高く、サイクル特性に優れ、不可逆容量が非常に小さくなることを見出し、本発明を完成した。
すなわち、本発明は以下の各発明からなる。
As a result of intensive studies to solve the above problems, the present inventors have pulverized a specific raw material having a specified thermal expansion coefficient, graphitized by heat treatment under a certain condition, and suspended the generated particles in distilled water. By controlling the pH at a certain range, a particle shape close to a spherical shape can be obtained inexpensively and easily, and the capacity is high, the cycle characteristics are excellent, and the irreversible capacity is very small. completed.
That is, the present invention comprises the following inventions.
（１）黒鉛質粒子４０質量部を蒸留水１００質量部中に懸濁分散した際の分散液のｐＨが7.0〜9.0である黒鉛質粒子を主成分とする非水電解液二次電池負極用黒鉛材料
（２）黒鉛質粒子が、その原料の炭素質材料を粉砕し、レーザー回折法により測定した平均粒子径が5〜40μmの炭素質粒子とし、該炭素質粒子を非酸化性雰囲気下で2５00℃以上の温度で熱処理した黒鉛質粒子であることを特徴とする上記（１）に記載の非水電解液二次電池負極用黒鉛材料。
（３）熱処理温度が、3000℃以上3300℃以下であり、得られた黒鉛質粒子のd002が0.3362nm〜0.3370nmである上記（２）に記載の非水電解液二次電池負極用黒鉛材料。
(1) For a non-aqueous electrolyte secondary battery negative electrode mainly composed of graphite particles having a pH of 7.0 to 9.0 when 40 parts by mass of graphite particles are suspended and dispersed in 100 parts by mass of distilled water Graphite material (2) Graphite particles are obtained by crushing the carbonaceous material as a raw material to obtain carbonaceous particles having an average particle diameter of 5 to 40 μm measured by a laser diffraction method, and the carbonaceous particles in a non-oxidizing atmosphere. The graphite material for a negative electrode of a non-aqueous electrolyte secondary battery as described in (1) above, wherein the graphite material is heat treated at a temperature of 2500 ° C. or higher.
(3) The non-aqueous electrolyte secondary battery negative electrode graphite material as described in (2) above, wherein the heat treatment temperature is 3000 ° C. or higher and 3300 ° C. or lower, and d002 of the obtained graphite particles is 0.3362 nm to 0.3370 nm. .
（４）黒鉛質粒子の30℃〜100℃のＣＴＥが4.7×10-6/℃以下であることを特徴とする上記（１）〜（３）のいずれかに記載の非水電解液二次電池負極用黒鉛材料。
（５）熱処理が、アチソン炉で行われる上記（１）〜（４）のいずれかに記載の非水電解液二次電池負極用黒鉛材料。
（６）黒鉛質粒子の、嵩密度が0.60g/cm3以上でかつ400回タッピングを行った際の嵩密度が1.0g/cm3以上である上記（１）〜（５）のいずれかに記載の非水電解液二次電池負極用黒鉛材料。
（７）黒鉛質粒子のＢＥＴ比表面積が3.0ｍ２／ｇ以下である上記（１）〜（６）のいずれかに記載の非水電解液二次電池負極用黒鉛材料。
（８）炭素質粒子が、石油系ピッチコークスからなる粒子、または石炭系ピッチコークスからなる粒子である上記（２）〜（７）のいずれかに記載の非水電解液二次電池負極用黒鉛材料。
(4) The non-aqueous electrolyte secondary solution according to any one of (1) to (3) above, wherein the graphite particles have a CTE of 30 ° C. to 100 ° C. of 4.7 × 10 −6 / ° C. or less. Graphite material for battery negative electrode.
(5) The graphite material for a non-aqueous electrolyte secondary battery negative electrode according to any one of (1) to (4), wherein the heat treatment is performed in an Atchison furnace.
(6) In any one of the above (1) to (5), the bulk density of the graphite particles is 0.60 g / cm 3 or more and the bulk density when tapping 400 times is 1.0 g / cm 3 or more. The graphite material for non-aqueous electrolyte secondary battery negative electrode of description.
(7) The graphite material for a nonaqueous electrolyte secondary battery negative electrode according to any one of the above (1) to (6), wherein the BET specific surface area of the graphite particles is 3.0 m 2 / g or less.
(8) The graphite for a nonaqueous electrolyte secondary battery negative electrode according to any one of (2) to (7), wherein the carbonaceous particles are particles made of petroleum pitch coke or particles made of coal pitch pitch coke. material.
（９）炭素質材料の30℃〜100℃のＣＴＥが4.8×10-6/℃以上6.0×10-6／℃以下であることを特徴とする上記（２）〜（８）のいずれかに記載の非水電解液二次電池負極用黒鉛材料。
（１０）炭素質粒子の平均粒子径が５〜４０μｍで、該粒子のアスペクト比が６以下である上記（２）〜（９）のいずれかに記載の非水電解液二次電池負極用黒鉛材料。
（１１）平均繊維径が２〜１０００ｎｍの炭素繊維を含む上記（１）〜（１０）のいずれかに記載の非水電解液二次電池負極用黒鉛材料。
（１２）黒鉛質粒子１００質量部に対して、炭素繊維を０.０１〜２０質量部含む上記（１１）に記載の非水電解液二次電池負極用黒鉛材料。
（１３）炭素繊維がアスペクト比１０〜１５０００の気相法炭素繊維である上記（１１）又は（１２）に記載の非水電解液二次電池負極用黒鉛材料。
(9) The carbonaceous material has a CTE of 30 ° C. to 100 ° C. of 4.8 × 10 −6 / ° C. or more and 6.0 × 10 −6 / ° C. or less. The graphite material for non-aqueous electrolyte secondary battery negative electrode of description.
(10) The graphite for non-aqueous electrolyte secondary battery negative electrode according to any one of (2) to (9), wherein the average particle diameter of the carbonaceous particles is 5 to 40 μm and the aspect ratio of the particles is 6 or less. material.
(11) The graphite material for a nonaqueous electrolyte secondary battery negative electrode according to any one of (1) to (10), comprising carbon fibers having an average fiber diameter of 2 to 1000 nm.
(12) The graphite material for a nonaqueous electrolyte secondary battery negative electrode as described in (11) above, containing 0.01 to 20 parts by mass of carbon fiber with respect to 100 parts by mass of the graphite particles.
(13) The graphite material for a negative electrode of a nonaqueous electrolyte secondary battery according to (11) or (12) above, wherein the carbon fiber is a vapor grown carbon fiber having an aspect ratio of 10 to 15000.
（１４）気相法炭素繊維が２０００℃以上で熱処理された黒鉛系炭素繊維である上記（１３）に記載の非水電解液二次電池負極用黒鉛材料。
（１５）気相法炭素繊維が、内部に中空構造を有するものである上記（１３）又は（１４）に記載の非水電解液二次電池負極用黒鉛材料。
（１６）気相法炭素繊維が、分岐状炭素繊維を含む上記（１３）〜（１５）のいずれかに記載の非水電解液二次電池負極用黒鉛材料。
（１７）気相法炭素繊維のＸ線回折法による（００２）面の平均面間隔ｄ００２が０.３４４ｎｍ以下である上記（１３）〜（１６）のいずれかに記載の非水電解液二次電池負極用黒鉛材料。
（１８）上記（１）〜（１７）のいずれかに記載の非水電解液二次電池負極用黒鉛材料とバインダーを含む電極ペースト。
（１９）上記（１８）に記載の電極ペーストを使用した電極。
（２０）上記（１９）に記載の電極を構成要素として含む二次電池。
（２１）30℃〜100℃のＣＴＥが4.8×10-6/℃以上6.0×10-6／℃以下である炭素質材料を粉砕し、得られた粉末をアチソン炉を用いて２５００℃以上の温度で黒鉛化することを特徴とする非水電解液二次電池負極用黒鉛質粒子の製造方法。
(14) The graphite material for a non-aqueous electrolyte secondary battery negative electrode according to (13) above, wherein the vapor grown carbon fiber is a graphite-based carbon fiber heat-treated at 2000 ° C. or higher.
(15) The graphite material for a non-aqueous electrolyte secondary battery negative electrode according to the above (13) or (14), wherein the vapor grown carbon fiber has a hollow structure therein.
(16) The graphite material for a nonaqueous electrolyte secondary battery negative electrode according to any one of (13) to (15), wherein the vapor grown carbon fiber includes a branched carbon fiber.
(17) vapor-phase process non-aqueous electrolyte according to any one of the average spacing d 002 of (002) plane measured by X-ray diffraction of the carbon fibers is less than 0.344 nm (13) ~ (16) two Graphite material for secondary battery negative electrode.
(18) An electrode paste comprising the graphite material for a nonaqueous electrolyte secondary battery negative electrode according to any one of (1) to (17) above and a binder.
(19) An electrode using the electrode paste according to (18) above.
(20) A secondary battery including the electrode according to (19) as a constituent element.
(21) A carbonaceous material having a CTE of 30 ° C. to 100 ° C. of 4.8 × 10 −6 / ° C. or higher and 6.0 × 10 −6 / ° C. or lower is pulverized, and the obtained powder is used at 2500 ° C. or higher using an Atchison furnace. A method for producing graphitic particles for a negative electrode of a non-aqueous electrolyte secondary battery, characterized by graphitizing at a temperature.
本発明による非水電解液二次電池負極用黒鉛材料を負極に使用した二次電池は
非常に高い初回充放電時の初期効率を有し、放電容量も高く、かつ１００サイクル後の容量保持率も高いものとなる。
The secondary battery using the graphite material for the negative electrode of the nonaqueous electrolyte secondary battery according to the present invention as the negative electrode has a very high initial efficiency at the first charge / discharge, a high discharge capacity, and a capacity retention after 100 cycles. Is also expensive.
以下本発明を詳しく説明する。
［負極黒鉛材料］
本発明の非水二次電池負極用黒鉛材料（負極黒鉛材料と略すこともある）は特定の黒鉛質粒子を主成分とするものである。この黒鉛質粒子は、この４０質量部を蒸留水１００質量部に懸濁分散した際のその懸濁液のｐＨが７．０〜９．０、好ましくは８〜９となる黒鉛質粒子である。懸濁液を上記の条件にしてｐＨを測定したのは測定が安定して出来るからである。
本発明の負極黒鉛材料はこの黒鉛質粒子を主成分、即ち黒鉛質粒子からなるもの、又は黒鉛質粒子に炭素繊維、他の黒鉛粒子等を好ましくは２０質量％以下で加えたものである。
The present invention will be described in detail below.
[Negative electrode graphite material]
The graphite material for a negative electrode of a non-aqueous secondary battery of the present invention (sometimes abbreviated as negative electrode graphite material) contains specific graphite particles as a main component. The graphite particles are graphite particles in which the suspension has a pH of 7.0 to 9.0, preferably 8 to 9 when 40 parts by mass is suspended and dispersed in 100 parts by mass of distilled water. . The reason why the pH was measured under the above-mentioned conditions is that the measurement can be performed stably.
The negative electrode graphite material of the present invention is composed of the graphite particles as a main component, that is, composed of graphite particles, or is obtained by adding carbon fibers, other graphite particles, and the like to the graphite particles at 20% by mass or less.
黒鉛質粒子のｐＨが７未満では電池の負極にした際の初回充放電時の不可逆容量が大きくなる。またｐＨが９を越えるものは得るのが難しい。黒鉛質粒子の水懸濁液は、一般には酸性のものが多いが、本発明のものは非酸性である。上記のｐＨの測定は例えば次のようにして行うことができる。
ねじ蓋つきサンプル瓶に黒鉛質粒子40gを入れ、蒸留水100gを加え、蓋をして超音波分散を40分実施する。その後室温にてｐＨを測定する。ｐＨ計はたとえば堀場製作所製のF-50型等で、ｐＨ標準液にて校正したものが使用できる。
If the pH of the graphite particles is less than 7, the irreversible capacity at the first charge / discharge when the negative electrode of the battery is made becomes large. Also, it is difficult to obtain a product having a pH exceeding 9. In general, water suspensions of graphite particles are mostly acidic, but those of the present invention are non-acidic. The above pH can be measured, for example, as follows.
Place 40g of graphite particles in a sample bottle with a screw cap, add 100g of distilled water, cover and perform ultrasonic dispersion for 40 minutes. The pH is then measured at room temperature. As the pH meter, for example, an F-50 type manufactured by HORIBA, Ltd., calibrated with a pH standard solution can be used.
本発明における黒鉛質粒子は、好ましくはその原料であるコークス等の炭素質原料を先ず粉砕し、レーザー回折法により測定した平均粒子径を５〜４０μｍ程度にする。次にこれを非酸化性雰囲気下で黒鉛化する。黒鉛化によって黒鉛質粒子の粒度はほぼ同じ５〜４０μｍとなる。粒度が５μｍより小さいのは表面積が大きくなるので避けた方がよい。また上限の４０μｍは負極の厚さからくる制限である。黒鉛化の温度は高い方がよく、例えば２５００℃以上、好ましくは２８００℃以上、さらに好ましくは３０００〜３３００℃である。黒鉛化処理の装置は、上記のような温度にできるものであり、かつ前記ｐＨが本発明の範囲に入るようになるものであれば制限なく使用可能であるが、一般に黒鉛化に使用されるアチソン炉が好ましい。
上記のように高温で黒鉛化して導電性をよくする。この黒鉛質粒子は結晶性のよい、ｄ００２が０．３３６２〜０．３３７０ｎｍのものが好ましい。ｄ００２が０．３３７０ｎｍを越えるものでは導電性が十分でなく、また０．３３６２未満のものは製造が難しい。
The graphitic particles in the present invention are preferably obtained by first pulverizing a carbonaceous raw material such as coke, which is the raw material, so that the average particle size measured by a laser diffraction method is about 5 to 40 μm. This is then graphitized under a non-oxidizing atmosphere. The particle size of the graphite particles becomes approximately the same 5 to 40 μm by graphitization. A particle size smaller than 5 μm should be avoided because it increases the surface area. Further, the upper limit of 40 μm is a limit resulting from the thickness of the negative electrode. The graphitization temperature should be higher, for example, 2500 ° C. or higher, preferably 2800 ° C. or higher, more preferably 3000 to 3300 ° C. The apparatus for graphitization treatment can be used without limitation as long as the temperature can be set as described above and the pH falls within the range of the present invention, but is generally used for graphitization. An Atchison furnace is preferred.
As described above, it is graphitized at high temperature to improve conductivity. The graphite particles preferably have good crystallinity and have a d002 of 0.3362 to 0.3370 nm. If d002 exceeds 0.3370 nm, the conductivity is insufficient, and if it is less than 0.3362, it is difficult to produce.
黒鉛結晶のｃ軸方向の結晶面間隔 d002は、既知の方法により粉末Ｘ線回折（ＸＲＤ）法を用いて測定することができる（野田稲吉、稲垣道夫，日本学術振興会，第117委員会試料，117-71-A-1(1963)、稲垣道夫他，日本学術振興会，第117委員会試料，117-121-C-5(1972)、稲垣道夫，「炭素」，1963，No.36，25-34頁参照。）。
また黒鉛質粒子の熱膨張係数（ＣＴＥ）は３０〜１００℃において４．７×１０−６／℃以下が好ましい。ＣＴＥがこの範囲を越えると電池の充放電における負極の膨張、収縮が大きくなり、種々の問題が起こり易くなる。ＣＴＥの下限は４．０×１０−６／℃程度まで可能である。
黒鉛質粒子のＣＴＥは黒鉛質粒子１００ｇにバインダー（軟化点７０℃）２５０ｇを加え、以下後述する原料のＣＴＥ測定と同様にして行う 。
The crystal plane distance d002 in the c-axis direction of the graphite crystal can be measured by a known method using a powder X-ray diffraction (XRD) method (Inadayoshi Noda, Michio Inagaki, Japan Society for the Promotion of Science, 117th Committee Sample) , 117-71-A-1 (1963), Michio Inagaki et al., Japan Society for the Promotion of Science, 117th Committee Sample, 117-121-C-5 (1972), Michio Inagaki, “Carbon”, 1963, No. 36 , Pages 25-34).
The coefficient of thermal expansion (CTE) of the graphite particles is preferably 4.7 × 10 −6 / ° C. or less at 30 to 100 ° C. When the CTE exceeds this range, the negative electrode expands and contracts during battery charging and discharging, and various problems are likely to occur. The lower limit of CTE can be up to about 4.0 × 10 −6 / ° C.
CTE of graphite particles is performed in the same manner as the CTE measurement of raw materials described later, after adding 250 g of binder (softening point 70 ° C.) to 100 g of graphite particles.
本発明における黒鉛質粒子の嵩密度（容器に充填しタピングしないときの密度）は、電極にした際の黒鉛質粒子の充填性をよくするため高い方がよく、０．６ｇ／ｃｍ３以上が好ましい。嵩密度を高くすることにより電極の単位体積当たりの充電容量が高くなる。またタッピング嵩密度は１．０ｇ／ｃｍ３以上が好ましく、その上限は１．３ｇ／ｃｍ３程度まで可能である。このタッピング嵩密度は黒鉛粒子を容器に充填し、４００回タッピングを行って測定したものである。これら二つの嵩密度の差は粒子の形状に関係し、その差が小さい程粒子は球状に近くなり、本発明における好ましい粒子となる。
また黒鉛質粒子のＢＥＴ比表面積は小さい方がよく、好ましくは３ｍ２／ｇ以下である。 比表面積が３ｍ２／ｇを超えると粒子の表面活性が高くなり、電解液の分解等によって、クーロン効率が低下する。さらに、電池の容量を高めるためには粒子の充填密度を上げることが重要である。そのためにもできるだけ球状に近いものが好ましい。この粒子の形状をアスペクト比（長軸の長さ／短軸の長さ）で表すとアスペクト比は６以下、好ましくは５以下である。
アスペクト比はＳＥＭ像より求められる。即ち、ＳＥＭ写真上の任意の３００個の粒子について最短部分Ａと、最長部分Ｂを計測し、Ａ／Ｂで求めることができる。計測は、ノギス等を使用して測定しても良いし、例えば、ＳＥＭ写真をコンピュータに取り込み、ニコレ性画像処理装置ＬＵＺＥＸ等を使用して計測することも可能である。
In the present invention, the bulk density of the graphite particles (the density when the container is filled and not tapped) is preferably high in order to improve the filling property of the graphite particles when used as an electrode, and is 0.6 g / cm 3 or more. preferable. Increasing the bulk density increases the charge capacity per unit volume of the electrode. The tapping bulk density is preferably 1.0 g / cm 3 or more, and the upper limit can be up to about 1.3 g / cm 3 . This tapping bulk density is measured by filling graphite particles into a container and tapping 400 times. The difference between these two bulk densities is related to the shape of the particles, and the smaller the difference, the closer the particles are to be spherical, and the preferred particles in the present invention.
Further, the BET specific surface area of the graphite particles should be small, preferably 3 m 2 / g or less. When the specific surface area exceeds 3 m 2 / g, the surface activity of the particles increases, and the Coulomb efficiency decreases due to decomposition of the electrolytic solution and the like. Furthermore, it is important to increase the packing density of the particles in order to increase the capacity of the battery. For that purpose, a spherical shape as close as possible is preferable. When the shape of the particles is expressed by an aspect ratio (long axis length / short axis length), the aspect ratio is 6 or less, preferably 5 or less.
The aspect ratio is obtained from the SEM image. That is, the shortest part A and the longest part B of any 300 particles on the SEM photograph can be measured and obtained by A / B. The measurement may be performed using a vernier caliper or the like. For example, an SEM photograph may be taken into a computer and measured using a smiley image processing apparatus LUZEX or the like.
本発明の黒鉛質粒子は炭素質材料から製造される。炭素質材料としては石油系ピッチコークス、石炭系ピッチコークスが好ましい。これらの中で特に、非針状コークスが好ましい。炭素質材料は30℃〜100℃の熱膨張係数（CTE）が4.8×10-6/℃以上6.0×10-6/℃以下であるものが好ましい。CTEがこの範囲より小さい場合は熱処理温度を上げても結晶性が思うように上がらず、放電容量が十分な範囲に入らない。また、CTEがこの範囲より大きいと、粉砕した場合に鱗片になりやすく、黒鉛化した後電池材料とした場合、一方向に配向して充放電時の電極の膨張が激しくなり好ましくない。さらに理由は定かでないが、前記懸濁液のｐＨが本発明の範囲に入るようにする場合、ＣＴＥがこの範囲の炭素質材料、特に非針状コークスを使用するとことが好ましい。 The graphite particles of the present invention are manufactured from a carbonaceous material. As the carbonaceous material, petroleum-based pitch coke and coal-based pitch coke are preferable. Among these, non-acicular coke is particularly preferable. The carbonaceous material preferably has a coefficient of thermal expansion (CTE) of 30 ° C. to 100 ° C. of 4.8 × 10 −6 / ° C. or more and 6.0 × 10 −6 / ° C. or less. When CTE is smaller than this range, the crystallinity does not increase as expected even if the heat treatment temperature is raised, and the discharge capacity does not fall within a sufficient range. On the other hand, if the CTE is larger than this range, it tends to be scaled when pulverized, and when it is used as a battery material after graphitization, it is not preferable because it is oriented in one direction and the electrode expands rapidly during charge and discharge. Although the reason is not clear, it is preferable to use a carbonaceous material having a CTE within this range, particularly non-acicular coke, when the pH of the suspension falls within the range of the present invention.
原料のCTEの測定は次の方法で行う。まず、試料500gを振動ミルで粉砕し、28メッシュの篩を用いて篩い分けし、その篩下を採る。それを60メッシュ、200メッシュの篩を用いて篩分けし、28〜60メッシュ60g、60〜200メッシュ32g、200メッシュ以下8gの割合で採取し、それを混合して全量を100gにする。この配合試料100gをステンレス容器に入れ、バインダーピッチ（軟化点７０℃）25gを加え、125℃のオイルバスで20分間加熱し均一に混合した後、１２５℃に加熱した加圧成型機に30g入れ、ゲージ圧450kg/cmで5分間加圧し、成型する。
成型品を磁性坩堝に入れ、焼成炉で室温から1000℃まで5時間で昇温後、1000℃で1時間保持して冷却する。この成型品を精密切断機で4.3×4.3×20.0mmに切断し、テストピースとする。本テストピースをTMA（熱機会分析装置）例えばセイコー電子製TMA/SS 350等で30〜100℃の膨張測定を行い、CTEを算出する。
原料は黒鉛化する前に粉砕する。原料の粉砕には公知のジェットミル、ハンマーミル、ローラーミル、ピンミル、振動ミル等が用いられる。粉末の粒度はレーザー回折式のCILUSで測定することが出来る。
The raw material CTE is measured by the following method. First, 500 g of a sample is pulverized with a vibration mill, sieved using a 28-mesh sieve, and the bottom of the sieve is taken. It is sieved using a 60 mesh or 200 mesh sieve and collected at a rate of 28-60 mesh 60 g, 60-200 mesh 32 g, 200 mesh or less 8 g, and mixed to make a total amount of 100 g. Put 100g of this blended sample in a stainless steel container, add 25g of binder pitch (softening point 70 ° C), heat in an oil bath at 125 ° C for 20 minutes, mix uniformly, and then put 30g in a pressure molding machine heated to 125 ° C. , Pressurize for 5 minutes at a gauge pressure of 450kg / cm and mold.
The molded product is put in a magnetic crucible, heated from room temperature to 1000 ° C. in 5 hours in a baking furnace, and then cooled by holding at 1000 ° C. for 1 hour. This molded product is cut into 4.3 x 4.3 x 20.0 mm with a precision cutting machine to make a test piece. The test piece is subjected to expansion measurement at 30 to 100 ° C. with a TMA (thermal opportunity analyzer) such as TMA / SS 350 manufactured by Seiko Electronics Co., Ltd., and CTE is calculated.
The raw material is pulverized before graphitization. A known jet mill, hammer mill, roller mill, pin mill, vibration mill or the like is used for pulverizing the raw material. The particle size of the powder can be measured with a laser diffraction type CILUS.
粉砕した炭素質粒子の平均粒子径は５〜４０μｍが適する。これを黒鉛化処理することによりほぼ５〜４０μｍの黒鉛粒子を得ることができる。この炭素質粒子のアスペクト比は黒鉛質粒子とほぼ同じ６以下、好ましくは５以下である。アスペクト比の求め方は前記黒鉛質粒子の場合と同様である。
得られた炭素粉末を前記した温度で黒鉛化する。黒鉛化は、炭素粉末が酸化しにくい雰囲気で行う。酸化してしまうと前記した懸濁液のｐＨが酸性側にシフトして電池の負極にした際の初期効率が低下する。このｐＨの値を本発明の範囲にするにはアチソン炉が好ましい。
The average particle size of the pulverized carbonaceous particles is suitably 5 to 40 μm. By graphitizing this, graphite particles of approximately 5 to 40 μm can be obtained. The aspect ratio of the carbonaceous particles is approximately 6 or less, preferably 5 or less, which is substantially the same as that of the graphite particles. The method for obtaining the aspect ratio is the same as in the case of the graphite particles.
The obtained carbon powder is graphitized at the aforementioned temperature. Graphitization is performed in an atmosphere in which the carbon powder is not easily oxidized. When oxidized, the pH of the suspension described above shifts to the acidic side, and the initial efficiency when the negative electrode of the battery is made decreases. In order to make this pH value within the range of the present invention, an Atchison furnace is preferred.
本発明における黒鉛質粒子の好ましい製造方法は、30℃〜100℃の熱膨張係数（CTE）が4.8×10-6/℃以上6.0×10-6/℃以下の炭素質材料（コークス）を粉砕し、その粉末をアチソン炉で２５００以上の温度で黒鉛化する方法である。このコークスは球状に近い非針状で、結晶性が高くない。前記懸濁液のｐＨは原料、黒鉛化方法などによって変わり、酸性のものも多く得られている。本発明において、懸濁液のｐＨが７〜９のものが得られる理由は定かでないが、コークスの結晶性、アチソン炉の雰囲気などが関与していることが考えられる。 A preferred method for producing graphite particles in the present invention is to pulverize a carbonaceous material (coke) having a coefficient of thermal expansion (CTE) of 30 ° C. to 100 ° C. of 4.8 × 10 −6 / ° C. to 6.0 × 10 −6 / ° C. Then, the powder is graphitized at a temperature of 2500 or more in an Atchison furnace. This coke has a non-needle shape close to a spherical shape and does not have high crystallinity. The pH of the suspension varies depending on the raw material, graphitization method, etc., and many acidic ones are obtained. In the present invention, the reason why the suspension having a pH of 7 to 9 is not clear, but it is considered that the coke crystallinity, the atmosphere of the Atchison furnace, etc. are involved.
本発明の負極黒鉛材料には前記黒鉛質粒子に炭素繊維を含めることができる。その含有量は、炭素繊維の高い導電性の効果を出すため、黒鉛質粒子１００質量部に対し、０．０１質量部以上が好ましい。また多すぎると黒鉛質粒子の特性による効果が下がるので、２０質量部以下が好ましい。炭素繊維としては気相法炭素繊維が好ましい。その平均繊維径が２〜１０００ｎｍのものを使用することができる。
気相法炭素繊維は、一般的には、有機遷移金属化合物を用いて有機化合物を熱分解することにより得ることができる。
気相法炭素繊維の原料となる有機化合物は、トルエン、ベンゼン、ナフタレン、エチレン、アセチレン、エタン、天然ガス、一酸化炭素等のガス及びそれらの混合物も可能である。中でもトルエン、ベンゼン等の芳香族炭化水素が好ましい。
有機遷移金属化合物は、触媒となる遷移金属を含むものである。遷移金属としては、周期律表第IVa、Ｖa、VIa、VIIa、VIII族の金属を含む有機化合物である。中でもフェロセン、ニッケロセン等の化合物が好ましい。
The negative electrode graphite material of the present invention may contain carbon fibers in the graphite particles. The content is preferably 0.01 parts by mass or more with respect to 100 parts by mass of the graphitic particles in order to obtain a high conductivity effect of the carbon fiber. Moreover, since the effect by the characteristic of a graphite particle will fall when there is too much, 20 mass parts or less are preferable. As the carbon fiber, vapor grown carbon fiber is preferable. Those having an average fiber diameter of 2 to 1000 nm can be used.
Vapor grown carbon fiber can be generally obtained by thermally decomposing an organic compound using an organic transition metal compound.
The organic compound used as a raw material for the vapor grown carbon fiber may be a gas such as toluene, benzene, naphthalene, ethylene, acetylene, ethane, natural gas, carbon monoxide, and a mixture thereof. Of these, aromatic hydrocarbons such as toluene and benzene are preferred.
The organic transition metal compound contains a transition metal serving as a catalyst. The transition metal is an organic compound containing metals of groups IVa, Va, VIa, VIIa, and VIII of the periodic table. Of these, compounds such as ferrocene and nickelocene are preferred.
また、気相法炭素繊維の好ましい形態として、分岐状繊維があるが、分岐部分はその部分を含めて繊維全体が互いに連通した中空構造を有している箇所があってもよい。そのため繊維の円筒部分を構成している炭素層が連続している。中空構造とは炭素層が円筒状に巻いている構造であって、完全な円筒でないもの、部分的な切断箇所を有するもの、積層した２層の炭素層が１層に結合したものなどを含む。また、円筒の断面は完全な円に限らず楕円や多角化のものを含む。なお、炭素層の結晶性について炭素層の面間隔ｄ００２は限定されない。因みに、好ましいものはＸ線回折法による平均面間隔ｄ００２が０.３４４ｎｍ以下、好ましくは、０.３３９ｎｍ以下、より好ましくは０.３３８ｎｍ以下であって、結晶のＣ軸方向の厚さＬｃが４０ｎｍ以下のものである。 Further, as a preferred form of vapor grown carbon fiber, there is a branched fiber, but the branched portion may have a hollow structure where the entire fiber including that portion is in communication with each other. Therefore, the carbon layer which comprises the cylindrical part of a fiber is continuing. A hollow structure is a structure in which a carbon layer is wound in a cylindrical shape, and includes a structure that is not a complete cylinder, a structure that has a partial cut portion, and a structure in which two stacked carbon layers are bonded to one layer. . Further, the cross section of the cylinder is not limited to a perfect circle, but includes an ellipse or a polygon. Note that the interplanar spacing d 002 of the carbon layer is not limited with respect to the crystallinity of the carbon layer. Incidentally, it is preferable that the average interplanar distance d 002 by the X-ray diffraction method is 0.344 nm or less, preferably 0.339 nm or less, more preferably 0.338 nm or less, and the thickness Lc in the C-axis direction of the crystal is 40 nm or less.
［負極及び二次電池］
本発明の負極用黒鉛材料を用いて公知の方法によりリチウム二次電池の電極（負極）を作製することができる。
電極は、通常のように結合材（バインダー）を溶媒で希釈して負極黒鉛材料と混練した負極材料をたとえば集電体（基材）に塗布することで作製できる。
バインダーについては、ポリフッ化ビニリデンやポリテトラフルオロエチレン等のフッ素系ポリマーや、ＳＢＲ（スチレンブタジエンラバー）等のゴム系等公知のものが使用できる。溶媒には、各々のバインダーに適した公知のもの、例えばフッ素系ポリマーならトルエン、Ｎ−メチルピロリドン等、ＳＢＲなら水等、公知のものが使用できる。
[Negative electrode and secondary battery]
An electrode (negative electrode) of a lithium secondary battery can be produced by a known method using the graphite material for negative electrode of the present invention.
The electrode can be produced by, for example, applying a negative electrode material obtained by diluting a binder (binder) with a solvent and kneading the negative electrode graphite material to a current collector (base material) as usual.
As the binder, known polymers such as a fluorine-based polymer such as polyvinylidene fluoride and polytetrafluoroethylene, and a rubber-based material such as SBR (styrene butadiene rubber) can be used. As the solvent, a known solvent suitable for each binder, for example, a fluorine-based polymer such as toluene and N-methylpyrrolidone, and a SBR that is known in water can be used.
バインダーの使用量は、負極黒鉛材料を１００質量部とした場合、１〜３０質量部が適当であるが、特に３〜２０質量部程度が好ましい。
負極黒鉛材料とバインダーとの混錬には、リボンミキサー、スクリュー型ニーダー、スパルタンリューザー、レディゲミキサー、プラネタリーミキサー、万能ミキサー等公知の装置が使用できる。
When the negative electrode graphite material is 100 parts by mass, the amount of the binder used is suitably 1 to 30 parts by mass, particularly preferably about 3 to 20 parts by mass.
For kneading the negative electrode graphite material and the binder, known devices such as a ribbon mixer, a screw type kneader, a Spartan rewinder, a redige mixer, a planetary mixer, and a universal mixer can be used.
混錬後の負極黒鉛材料の集電体への塗布は、公知の方法により実施できるが、例えばドクターブレードやバーコーターなどで塗布後、ロールプレス等で成形する方法等が挙げられる。
集電体としては、銅、アルミニウム、ステンレス、ニッケル及びそれらの合金など公知の材料が使用できる。
セパレーターは公知のものが使用できるが、特にポリエチレンやポリプロピレン性の不織布が好ましい。
Application of the kneaded negative electrode graphite material to the current collector can be carried out by a known method, and examples thereof include a method of applying with a doctor blade, a bar coater or the like and then molding with a roll press or the like.
As the current collector, known materials such as copper, aluminum, stainless steel, nickel, and alloys thereof can be used.
Although a well-known thing can be used for a separator, especially polyethylene and a polypropylene nonwoven fabric are preferable.
本発明におけるリチウム二次電池における電解液及び電解質は公知の有機電解液、無機固体電解質、高分子固体電解質が使用できる。好ましくは、電気伝導性の観点から有機電解液が好ましい。 As the electrolyte and electrolyte in the lithium secondary battery of the present invention, known organic electrolytes, inorganic solid electrolytes, and polymer solid electrolytes can be used. Preferably, an organic electrolyte is preferable from the viewpoint of electrical conductivity.
有機電解液としては、ジエチルエーテル、ジブチルエーテル、エチレングリコールモノメチルエーテル、エチレングリコールモノエチルエーテル、エチレングリコールモノブチルエーテル、ジエチレングリコールモノメチルエーテル、ジエチレングリコールモノエチルエーテル、ジエチレングリコールモノブチルエーテル、ジエチレングリコールジメチルエーテル、エチレングリコールフェニルエーテル等のエーテル；ホルムアミド、Ｎ−メチルホルムアミド、Ｎ，Ｎ−ジメチルホルムアミド、Ｎ−エチルホルムアミド、Ｎ，Ｎ−ジエチルホルムアミド、Ｎ−メチルアセトアミド、Ｎ，Ｎ−ジメチルアセトアミド、Ｎ−エチルアセトアミド、Ｎ，Ｎ−ジエチルアセトアミド、Ｎ，Ｎ−ジメチルプロピオンアミド、ヘキサメチルホスホリルアミド等のアミド；ジメチルスルホキシド、スルホラン等の含硫黄化合物；メチルエチルケトン、メチルイソブチルケトン等のジアルキルケトン；エチレンオキシド、プロピレンオキシド、テトラヒドロフラン、２−メトキシテトラヒドロフラン、１，２−ジメトキシエタン、１，３−ジオキソラン等の環状エーテル；エチレンカーボネート、プロピレンカーボネート等のカーボネート；γ−ブチロラクトン；Ｎ−メチルピロリドン；アセトニトリル、ニトロメタン等の有機溶媒の溶液が好ましい。 Examples of organic electrolytes include diethyl ether, dibutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, and ethylene glycol phenyl ether. Ether; formamide, N-methylformamide, N, N-dimethylformamide, N-ethylformamide, N, N-diethylformamide, N-methylacetamide, N, N-dimethylacetamide, N-ethylacetamide, N, N-diethyl Acetamide, N, N-dimethylpropionamide, hexamethylphosphorylamide Amides such as: Sulfur-containing compounds such as dimethyl sulfoxide and sulfolane; Dialkyl ketones such as methyl ethyl ketone and methyl isobutyl ketone; ethylene oxide, propylene oxide, tetrahydrofuran, 2-methoxytetrahydrofuran, 1,2-dimethoxyethane, 1,3-dioxolane, etc. Cyclic ethers; carbonates such as ethylene carbonate and propylene carbonate; γ-butyrolactone; N-methylpyrrolidone; solutions of organic solvents such as acetonitrile and nitromethane are preferred.
さらに、好ましくはエチレンカーボネート、ブチレンカーボネート、ジエチルカーボネート、ジメチルカーボネート、プロピレンカーボネート、ビニレンカーボネート、γ−ブチロラクトン等のエステル類、ジオキソラン、ジエチルエーテル、ジエトキシエタン等のエーテル類、ジメチルスルホキシド、アセトニトリル、テトラヒドロフラン等が挙げられ、特に好ましくはエチレンカーボネート、プロピレンカーボネート等のカーボネート系非水溶媒を用いることができる。これらの溶媒は、単独でまたは２種以上を混合して使用することができる。 Further preferably, esters such as ethylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, vinylene carbonate, γ-butyrolactone, ethers such as dioxolane, diethyl ether, diethoxyethane, dimethyl sulfoxide, acetonitrile, tetrahydrofuran, etc. Particularly preferred are carbonate-based non-aqueous solvents such as ethylene carbonate and propylene carbonate. These solvents can be used alone or in admixture of two or more.
これらの溶媒の溶質（電解質）には、リチウム塩が使用される。一般的に知られているリチウム塩にはＬｉＣｌＯ４、ＬｉＢＦ４、ＬｉＰＦ６、ＬｉＡｌＣｌ４、ＬｉＳｂＦ６、ＬｉＳＣＮ、ＬｉＣｌ、ＬｉＣＦ３ＳＯ３、ＬｉＣＦ３ＣＯ２、ＬｉＮ（ＣＦ３ＳＯ２）２等がある。 Lithium salts are used as solutes (electrolytes) for these solvents. Commonly known lithium salts include LiClO 4 , LiBF 4 , LiPF 6 , LiAlCl 4 , LiSbF 6 , LiSCN, LiCl, LiCF 3 SO 3 , LiCF 3 CO 2 , LiN (CF 3 SO 2 ) 2 and the like. is there.
本発明における負極黒鉛材料を使用したリチウム二次電池において、用いられる正極材料はリチウム含有遷移金属酸化物である。好ましくは、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｍｏ及びＷから選ばれる少なくとも１種の遷移金属元素とリチウムとを主として含有する酸化物であって、リチウムと遷移金属のモル比が0.3乃至2.2の化合物である。より好ましくは、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ及びＮｉから選ばれる少なくとも１種の遷移金属元素とリチウムとを主として含有する酸化物であって、リチウムと遷移金属のモル比が0.3乃至2.2の化合物である。なお、主として存在する遷移金属に対し３０モルパーセント未満の範囲でＡｌ、Ｇａ、Ｉｎ、Ｇｅ、Ｓｎ、Ｐｂ、Ｓｂ、Ｂｉ、Ｓｉ、Ｐ、Ｂなどを含有していても良い。上記の正極活物質の中で、一般式ＬｉｘＭＯ２（ＭはＣｏ、Ｎｉ、Ｆｅ、Ｍｎの少なくとも１種、ｘ＝０〜1.2。）、またはＬｉｙＮ２Ｏ４（Ｎは少なくともＭｎを含む。ｙ＝０〜２。）で表されるスピネル構造を有する材料の少なくとも１種を用いることが好ましい。 In the lithium secondary battery using the negative electrode graphite material in the present invention, the positive electrode material used is a lithium-containing transition metal oxide. Preferably, an oxide mainly containing at least one transition metal element selected from Ti, V, Cr, Mn, Fe, Co, Ni, Mo and W and lithium, wherein the molar ratio of lithium to the transition metal Is a compound of 0.3 to 2.2. More preferably, it is an oxide mainly containing at least one transition metal element selected from V, Cr, Mn, Fe, Co and Ni, and a molar ratio of lithium to transition metal of 0.3 to 2.2. A compound. In addition, Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, B, or the like may be contained in a range of less than 30 mole percent with respect to the transition metal present mainly. Among the above positive electrode active materials, the general formula Li x MO 2 (M is at least one of Co, Ni, Fe, and Mn, x = 0 to 1.2), or Li y N 2 O 4 (N is at least Mn It is preferable to use at least one material having a spinel structure represented by y = 0-2.
さらに、正極活物質はＬｉｙＭａＤ１-ａＯ２（ＭはＣｏ、Ｎｉ、Ｆｅ、Ｍｎの少なくとも１種、ＤはＣｏ、Ｎｉ、Ｆｅ、Ｍｎ、Ａｌ、Ｚｎ、Ｃｕ、Ｍｏ、Ａｇ、Ｗ、Ｇａ、Ｉｎ、Ｓｎ、Ｐｂ、Ｓｂ、Ｓｒ、Ｂ、Ｐの中のＭ以外の少なくとも１種、ｙ＝０〜1.2、ａ＝0.5〜１。）を含む材料、またはＬｉｚ（ＮｂＥ１-ｂ)２Ｏ４（ＮはＭｎ、ＥはＣｏ、Ｎｉ、Ｆｅ、Ｍｎ、Ａｌ、Ｚｎ、Ｃｕ、Ｍｏ、Ａｇ、Ｗ、Ｇａ、Ｉｎ、Ｓｎ、Ｐｂ、Ｓｂ、Ｓｒ、Ｂ、Ｐの少なくとも１種、ｂ＝１〜0.2ｚ＝０〜２。）で表されるスピネル構造を有する材料の少なくとも１種を用いることが特に好ましい。 Further, the positive electrode active material is Li y M a D 1-a O 2 (M is at least one of Co, Ni, Fe, Mn, D is Co, Ni, Fe, Mn, Al, Zn, Cu, Mo, Ag, Ag) , W, Ga, In, Sn, Pb, Sb, Sr, B, P, at least one material other than M, y = 0 to 1.2, a = 0.5 to 1), or Li z (N b E 1-b) 2 O 4 (N is Mn, E is Co, Ni, Fe, Mn, Al, Zn, Cu, Mo, Ag, W, Ga, in, Sn, Pb, Sb, Sr, B, It is particularly preferable to use at least one of materials having a spinel structure represented by at least one of P and b = 1 to 0.2z = 0 to 2.).
具体的には、ＬｉｘＣｏＯ２、ＬｉｘＮｉＯ２、ＬｉｘＭｎＯ２、ＬｉｘＣｏａＮｉ１-ａＯ２、ＬｉｘＣｏｂＶ１-ｂＯｚ、ＬｉｘＣｏｂＦｅ１-ｂＯ２、ＬｉｘＭｎ２Ｏ４、ＬｉｘＭｎｃＣｏ２-ｃＯ４、ＬｉｘＭｎｃＮｉ２-ｃＯ４、ＬｉｘＭｎｃＶ２-ｃＯ４、ＬｉｘＭｎｃＦｅ２-ｃＯ４（ここでｘ＝0.02〜1.2、ａ＝0.1〜0.9、ｂ＝0.8〜0.98、ｃ＝1.6〜1.96、ｚ＝2.01〜2.3。）が挙げられる。最も好ましいリチウム含有遷移金属酸化物としては、ＬｉｘＣｏＯ２、ＬｉｘＮｉＯ２、ＬｉｘＭｎＯ２、ＬｉｘＣｏａＮｉ１-ａＯ２、ＬｉｘＭｎ２Ｏ４、ＬｉｘＣｏｂＶ１-ｂＯｚ（ｘ＝0.02〜1.2、ａ＝0.1〜0.9、ｂ＝0.9〜0.98、ｚ＝2.01〜2.3。）が挙げられる。なお、ｘの値は充放電開始前の値であり、充放電により増減する。 Specifically, Li x CoO 2, Li x NiO 2, Li x MnO 2, Li x Co a Ni 1-a O 2, Li x Co b V 1-b O z, Li x Co b Fe 1-b O 2, Li x Mn 2 O 4, Li x Mn c Co 2-c O 4, Li x Mn c Ni 2-c O 4, Li x Mn c V 2-c O 4, Li x Mn c Fe 2- c O 4 (where x = 0.02 to 1.2, a = 0.1 to 0.9, b = 0.8 to 0.98, c = 1.6 to 1.96, z = 2.01 to 2.3). Most preferred lithium-containing transition metal oxides include Li x CoO 2 , Li x NiO 2 , Li x MnO 2 , Li x Co a Ni 1-a O 2 , Li x Mn 2 O 4 , and Li x Co b V 1. -b O z (x = 0.02~1.2, a = 0.1~0.9, b = 0.9~0.98, z = 2.01~2.3.) and the like. In addition, the value of x is a value before the start of charging / discharging, and increases / decreases by charging / discharging.
正極活物質の平均粒子サイズは特に限定されないが、0.1〜５０μｍが好ましい。0.5〜３０μｍの粒子の体積が９５％以上であることが好ましい。粒径３μｍ以下の粒子群の占める体積が全体積の１８％以下であり、かつ１５μｍ以上２５μｍ以下の粒子群の占める体積が、全体積の１８％以下であることが更に好ましい。比表面積は特に限定されないが、ＢＥＴ法で0.01〜５０ｍ２／ｇが好ましく、特に0.2ｍ２／ｇ〜１ｍ２／ｇが好ましい。また正極活物質５ｇを蒸留水１００ｍｌに溶かした時の上澄み液のｐＨとしては７以上１２以下が好ましい。 The average particle size of the positive electrode active material is not particularly limited, but is preferably 0.1 to 50 μm. The volume of particles of 0.5 to 30 μm is preferably 95% or more. More preferably, the volume occupied by a particle group having a particle size of 3 μm or less is 18% or less of the total volume, and the volume occupied by a particle group of 15 μm or more and 25 μm or less is 18% or less of the total volume. Although the specific surface area is not particularly limited, but is preferably 0.01 to 50 m 2 / g by the BET method, particularly preferably 0.2m 2 / g~1m 2 / g. The pH of the supernatant when 5 g of the positive electrode active material is dissolved in 100 ml of distilled water is preferably 7 or more and 12 or less.
以下に本発明について代表的な例を示し、さらに具体的に説明する。なお、これらは説明のための単なる例示であって、本発明はこれらに何等制限されるものではない。
下記例で用いた物性等は以下の方法により測定した。
［３］比表面積：
比表面積測定装置ＮＯＶＡ−１２００（ユアサアイオニクス（株）製）を用いて、窒素ガスを用いた一般的な比表面積の測定方法であるＢＥＴ法により測定した。
［４］電池評価方法：
（１）ペースト作成：
負極材料１質量部に呉羽化学社製ＫＦポリマーＬ１３２０（ポリビニリデンフルオライド（ＰＶＤＦ）を１２質量％含有したＮ−メチルピロリドン（ＮＭＰ）溶液品）０.１質量部を加え、プラネタリーミキサーにて混練し、主剤原液とした。
The present invention will be described in more detail below with typical examples. Note that these are merely illustrative examples, and the present invention is not limited thereto.
The physical properties used in the following examples were measured by the following methods.
[3] Specific surface area:
Using a specific surface area measuring apparatus NOVA-1200 (manufactured by Yuasa Ionics Co., Ltd.), measurement was performed by the BET method, which is a general method for measuring specific surface area using nitrogen gas.
[4] Battery evaluation method:
(1) Paste creation:
0.1 parts by mass of KF polymer L1320 (N-methylpyrrolidone (NMP) solution containing 12% by mass of polyvinylidene fluoride (PVDF)) made by Kureha Chemical Co., Ltd. was added to 1 part by mass of the negative electrode material, and a planetary mixer was used. The mixture was kneaded to obtain a base stock solution.
（２）電極作製：
主剤原液にＮＭＰを加え、粘度を調整した後、高純度銅箔上でドクターブレードを用いて２５０μｍ厚に塗布した。これを１２０℃、１時間真空乾燥し、１８ｍｍφに打ち抜いた。さらに、打ち抜いた電極を超鋼製プレス板で挟み、プレス圧が電極に対して約１×１０２〜３×１０２Ｎ／ｍｍ２（１×１０３〜３×１０３ｋｇ／ｃｍ２）となるようにプレスした。その後、真空乾燥器で１２０℃、１２時間乾燥後し、評価用電極とした。
(2) Electrode production:
NMP was added to the main agent stock solution to adjust the viscosity, and then applied onto a high purity copper foil to a thickness of 250 μm using a doctor blade. This was vacuum-dried at 120 ° C. for 1 hour and punched out to 18 mmφ. Further, the punched electrode is sandwiched between super steel press plates, and the press pressure is about 1 × 10 2 to 3 × 10 2 N / mm 2 (1 × 10 3 to 3 × 10 3 kg / cm 2 ) with respect to the electrode. It pressed so that it might become. Then, it dried at 120 degreeC and 12 hours with the vacuum dryer, and was set as the electrode for evaluation.
（３）電池作成：
下記のようにして３極セルを作製した。なお以下の操作は露点−８０℃以下の乾燥アルゴン雰囲気下で実施した。
ポリプロピレン製のねじ込み式フタ付きのセル（内径約１８ｍｍ）内において、上記（２）で作製した銅箔付き炭素電極（正極）と金属リチウム箔（負極）をセパレーター（ポリプロピレン製マイクロポ−ラスフィルム（セルガ−ド２４００））で挟み込んで積層した。さらにリファレンス用の金属リチウムを同様に積層した。これに電解液を加えて試験用セルとした。
（４）電解液：
ＥＣ（エチレンカーボネート）８質量部及びＤＥＣ（ジエチルカーボネート）１２質量部の混合品で、電解質としてＬｉＰＦ６を１モル／リットル溶解した。
(3) Battery creation:
A triode cell was produced as follows. The following operation was carried out in a dry argon atmosphere with a dew point of -80 ° C or lower.
In a cell (with an inner diameter of about 18 mm) with a screw-in type lid made of polypropylene, the carbon electrode with copper foil (positive electrode) and metal lithium foil (negative electrode) produced in (2) above were separated by a separator (polypropylene microporous film (Selga -2400)). Further, metallic lithium for reference was laminated in the same manner. An electrolytic solution was added thereto to obtain a test cell.
(4) Electrolyte:
In a mixed product of 8 parts by mass of EC (ethylene carbonate) and 12 parts by mass of DEC (diethyl carbonate), 1 mol / liter of LiPF 6 was dissolved as an electrolyte.
（５）充放電サイクル試験：
電流密度０.２ｍＡ／ｃｍ２（０.１Ｃ相当）で充放電試験を行った。
充電（炭素へのリチウムの挿入）はレストポテンシャルから０.００２Ｖまで０.２ｍＡ／ｃｍ２でＣＣ（コンスタントカレント：定電流）充電を行った。次に０.００２ＶでＣＶ（コンスタントボルト：定電圧）充電に切り替え、電流値が２５.４μＡに低下した時点で停止させた。その後３０分間の休止時間をとり放電に切り替えた。
放電（炭素からの放出）は０.２ｍＡ／ｃｍ２（０.１Ｃ相当）でＣＣ放電を行い、電圧１.５Ｖでカットオフした。その後３０分間の休止時間をとり、次の充電を行った。
サイクルは１００回行い、初回の放電容量に対する容量保持率を比較した。
(5) Charge / discharge cycle test:
A charge / discharge test was conducted at a current density of 0.2 mA / cm 2 (equivalent to 0.1 C).
Charging (insertion of lithium into carbon) was performed by CC (constant current: constant current) at 0.2 mA / cm 2 from the rest potential to 0.002V. Next, it switched to CV (constant volt: constant voltage) charging at 0.002 V, and stopped when the current value decreased to 25.4 μA. Thereafter, a 30-minute rest period was taken to switch to discharge.
As for discharge (release from carbon), CC discharge was performed at 0.2 mA / cm 2 (equivalent to 0.1 C), and cut off at a voltage of 1.5 V. Thereafter, a rest time of 30 minutes was taken, and the next charging was performed.
The cycle was performed 100 times, and the capacity retention with respect to the initial discharge capacity was compared.
実施例１
ＣＴＥが5.1×10-6/℃の石油系焼成コークス（非針状コークス）をハンマーミル（ホソカワミクロン製バンタムミル）で粉砕した。これを気流分級（日新エンジニアリング製ターボクラシファイアー）して平均粒子径14.8ミクロンの粒子を得た。これをネジふたつき黒鉛るつぼに充填し、アチソン炉にて３０００℃の熱処理を行った。得られた粒子の平均粒子径は15.2ミクロンであった。また。学振法にて測定したｄ002は、3.365オングストロームであった。電池評価では、初期効率、サイクル特性共に良好であった。（表１）
実施例２：ＣＴＥが5.8×10-6/℃の石油系焼成コークスを用いた他は実施例１と同様のテストを行った。結果を表１に示す。
実施例３：ＣＴＥが5.5×10-6/℃の石炭系焼成コークスを用いた他は実施例１と同様のテストを行った。結果を表１に示す。
Example 1
Petroleum-based calcined coke (non-needle coke) having a CTE of 5.1 × 10 −6 / ° C. was pulverized with a hammer mill (Hosokawa Micron Bantam Mill). This was air-flow classified (turbo classifier manufactured by Nissin Engineering Co., Ltd.) to obtain particles with an average particle size of 14.8 microns. This was filled in a graphite crucible with a screw lid, and heat-treated at 3000 ° C. in an Atchison furnace. The average particle diameter of the obtained particles was 15.2 microns. Also. D002 measured by the Gakushin method was 3.365 angstroms. In the battery evaluation, both initial efficiency and cycle characteristics were good. (Table 1)
Example 2 A test was performed in the same manner as in Example 1 except that petroleum-based fired coke having a CTE of 5.8 × 10 −6 / ° C. was used. The results are shown in Table 1.
Example 3 A test was performed in the same manner as in Example 1 except that coal-based calcined coke having a CTE of 5.5 × 10 −6 / ° C. was used. The results are shown in Table 1.
比較例１：ＣＴＥが7.2×10-6/℃の石油系焼成コークスを用いた他は実施例１と同様のテストを行った。結果を表１に示す。初期効率、サイクル特性は低い値となった。
比較例２：ＣＴＥが6.8×10-6/℃の石炭系焼成コークスを用いた他は実施例１と同様のテストを行った。結果を表１に示す。初期効率、サイクル特性は低い値となった。
比較例３：ＣＴＥが2.4×10-6/℃の焼成メソフェーズカーボン小球体を用いた他は実施例１と同様のテストを行った。結果を表１に示す。初期効率は良好だったが、サイクル特性は低い値となった。
Comparative Example 1: The same test as in Example 1 was performed except that petroleum-based calcined coke having a CTE of 7.2 × 10 −6 / ° C. was used. The results are shown in Table 1. Initial efficiency and cycle characteristics were low.
Comparative Example 2: The same test as in Example 1 was performed except that a coal-based fired coke having a CTE of 6.8 × 10 −6 / ° C. was used. The results are shown in Table 1. Initial efficiency and cycle characteristics were low.
Comparative Example 3 A test similar to that of Example 1 was performed except that calcined mesophase carbon microspheres having a CTE of 2.4 × 10 −6 / ° C. were used. The results are shown in Table 1. The initial efficiency was good, but the cycle characteristics were low.
本発明の負極黒鉛材料は、これを負極に用いた二次電池の充放電サイクル特性、充放電時の初期特性に優れており、リチウムイオン二次電池に好適に利用できる。 The negative electrode graphite material of the present invention is excellent in charge / discharge cycle characteristics and initial characteristics during charge / discharge of a secondary battery using the negative electrode graphite material as a negative electrode, and can be suitably used for a lithium ion secondary battery.
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